Eubalaena glacialis Right whale
The Report of the Right Whale Workshop (IWC SC/35/Rep2, 1983) suggests that this species was formerly distributed throughout this region. Berzin and Doroshenko (1982) cite Berzin and Yablakov (1978) in stating that the population is currently severely depleted, with probably only a few hundred animals left in the entire North Pacific. No interactions with fisheries are recorded.
Balaena mysticetus Bowhead whale
The population in the North Pacific is divided into two stocks. One moves from the Beaufort Sea to the Bering Sea and therefore partly into area 61, in winter; the other is confined to the Sea of Okhotsk (NCC 1980). The population of the former has been estimated at around 4 000 animals at present, and that of the latter 200–400 (Braham 1982). Interactions with fisheries would seem unlikely, although the possibility of net entanglement should not be ignored for this species or the previous one, as even a few mortalities could affect the population.
Eschrichtius robustus Grey whale
The Korean stock of this species may now be extinct, although the South Koreans are thought to have killed at least 67 between 1948 and 1966 (Wolman and Rice 1979). Feeding occurs, for both east and west Pacific stocks, in area 18 and food consists largely of amphipods (Blokhin and Pavlyuchkov 1983). No interactions with fisheries are likely at present, with the reservation that net entanglements are always possible.
Balaenoptera physalus Fin whale
Tomilin (1967) states that this species is found in the Sea of Japan and Sea of Okhotsk, and as far south as Taiwan. Tomilin lists a great number of food species, and notes that whereas one North Pacific sample yielded stomach contents data indicating the diet was mostly crustacea, another sample taken during a ‘herring run’ contained mostly herring. Fish species listed in the diet include Clupea harengus, Mallotus villosus, Ammodytes personatus, Boreogadus saida, Theragra chalcogramma and a number of other species including cod and salmon. Despite the diet, there do not seem to be any records of interactions with fisheries. The population for the whole North Pacific has been estimated at between 14 and 19 000.
Balaenoptera musculus Blue whale
Wintering in the waters around Japan, Korea and Taiwan, the blue whale spends the summer around the Kurils, Kamchatka and Chukotka. The diet consists entirely of pelagic crustacea especially Thysanoessa inermis and Nematoscelis megalops (Tomilin 1967). The population size in the North Pacific has been estimated at between 1400 and 1900 (Berzin and Vladimirov 1981). There appear to be no recorded interactions with fisheries.
Balaenoptera acutorostrata Minke whale
The IWC recognises 2 stocks in area 61, the Sea of Japan - Yellow Sea - East China Sea stock, and the Okhotsk Sea - West Pacific stock. Block quotas for the periods 1980–1984 have been set by the IWC for catches of this species which total 5 312 for both stocks (IWC Annexe E 1983). The population size is not known, but may number in the tens of thousands. According to Tomilin (1967) this species eats walleye pollock, saffron cod, herring, capelin, sandlance and pelagic crustacea in the North Pacific. Clearly the diet indicates that there is some interaction with fisheries for food fish species. A few individuals have been reported in drift nets (2 in 1980) and fixed nets (1 in 1980) in Japan (IWC 1982: Prog. Rep. Japan).
Balaenoptera borealis Sei whale
Tomilin (1967) states that this whale is less well adapted to eating fish than minke or fin whales, and that although some fish are consumed, squid and crustaceans, especially Calanus are more important in the diet in the North Pacific. The population size has been estimated for the whole North Pacific at between 8 600 and 2 100 (Berzin and Vladimirov 1981). No interactions with fisheries are apparent, although if commercial species are included in the diet, then there may be an interaction to some extent.
Balaenoptera edeni Bryde's whale
Miyashita and Kasamatsu (1983) have presented a population estimate of the northwestern Pacific stock of this species to the IWC. They estimate a total population size of 4400; this estimate was not discussed at the 1983 IWC meeting due to lack of time. Omura (1966) has studied the diet of this species in the northwest Pacific, and concludes that this is mostly euphausiids. The distribution of the Bryde's whale extends as far as about 43°N, and although no interactions with the fisheries have been reported, this species is also known to eat fish (Best 1967).
Megaptera novaeangliae Humpback whale
Tomilin (1967) states that this species migrates from Kamchatka and the Sea of Okhotsk to southern Japan, Bonin Island and the Mariana and Marshall Islands. There are insufficient data to estimate the population size, but only a few sightings from the northwest Pacific have been reported to the IWC in the last few years, so the population may number in the hundreds, and is clearly in a critical state. The diet of this species in the Soviet Far East has been described by Tomilin (1967) as partly similar to the fin whale, including herring, capelin, cod, salmon, sand eels, greenling, euphausiids and a variety of other shoaling crustacea. Although no recent interactions with fisheries have been recorded, probably due to the low population level, Tomilin describes an account by S K Klumov of 2 humpbacks causing trouble to fishermen by pursuing pink salmon off the Kuril Islands. A whaling boat was summoned, which killed one of the whales. Clearly the potential for conflict exists if the population ever increases again.
Berarduis bairdii Baird's beaked whale
Confined to the North Pacific (McCann 1975), 39 Baird's beaked whales were taken in the 1981/82 season by Japanese boats (IWC 1983: Prog Rep Japan). This species is known to feed on deep sea fish and squids including Gonatus fabricii and Onychoteuthis (Mitchell 1975); the status of the population is not known. There are no records in the Japanese Progress Reports to the IWC of incidental captures of this species, and its diet would seem to preclude any other interactions with fisheries at present unless there is any competition for squid.
Mesoplodon densirostris Blainville's beaked whale
Watson (1981) records this species from Formosa, which may be the limit of its northerly distribution. There are no more detailed data, and interactions with fisheries seem unlikely.
Mesoplodon stejnegeri Stejneger's beaked whale
Only known from about 12 specimens, this species is thought to range from Honshu to the Bering Sea (Hershkovitz 1966). No interactions with fisheries are likely.
Mesoplodon bowdoini Andrew's beaked whale
The only record in this area of this otherwise southerly species is given by Nishiwaki (1962) from the Sea of Japan (Akita beach), interactions with fisheries seem unlikely on this basis alone.
Mesoplodon ginkgodens Ginko-toothed beaked whale
Recorded from Japan and Taiwan (Leatherwood and Reeves 1983), Watson (1981) also reports this species in at least 2 further, unconfirmed occasions on Japanese longlines near Taiwan. These seem to be the only records of Mesoplodon species interacting with fisheries. The implications are unclear, but it is possible that the captured animals may have taken the bait from the longline, if the bait was squid.
Mesoplodon carlhubbsi Hubb's beaked whale
Apparently restricted to waters off northwest Honshu (Leatherwood and Reeves 1983). There do not seem to be any interactions with fisheries.
Ziphius cavirostris Cuvier's beaked whale
This species has been caught in Japanese small whale fisheries in small numbers (Mitchell 1975) although there do not appear to be any records of such catches in recent years. Stomach contents analysed from the fishery indicate a diet of deepwater fish and of squid. There are no indications of the size of the population in area 61, and no apparent records of by-catches. Interactions with fisheries seem unlikely.
Physeter macrocephalus Sperm whale
Distributed throughout the area, chiefly south of 40°N, males may venture as far as the ice (Tomilin 1967). This species is still currently hunted by the Japanese in the North Pacific, with a catch quota of 890. There are no reliable estimates for the total population size in area 61, but this could be in the hundreds of thousands. Berzin (1972) summarises information on the diet of the sperm whale in this area, suggesting that the major part of this is squid. The type of squid eaten varies from author to author, but Gonatidae, Histioteutidae and Ommastrephidae all appear to be important families of squid in the sperm whale diet. Tomilin (1967) suggests that when fish do occur in the diet, these are chiefly elasmobranchs (see introductory section also). Interactions with fisheries would seem unlikely, except that Ommastrephid squids are an important part of the Japanese squid catches. The implications of this are unclear.
Kogia breviceps Pygmy sperm whale
Mitchell (1975a) states that this species is taken by chance with hand harpoons at the rate of 3 to 6 a year in southern Japan. Tomilin (1967) records this species from the Kuril Islands. The only records of interactions with fisheries seem to be Miyazaki's (1983) assertion that this species is taken sporadically in set nets or by other fisheries.
Kogia simus Dwarf sperm whale
Miyazaki (1983) suggests that this species is taken sporadically in some fisheries, but provides no data on this. The diet is probably mainly squid (Fitch and Brownell 1968).
Monodon monoceros Narwhal The occurrence of this species in the Bering Sea is described as exceptional by Leatherwood and Reeves (1983). Tomilin (1967) states that the diet is mostly cephalopods, but includes some fish such as skate, flounder, halibut, cod, salmon and herring, which presumably makes conflicts with fisheries possible, although there do not appear to be any records of such.
Delphinapterus leucas White whale
Tomilin (1967) describes this species as widespread in the coastal zone of cold waters, occurring as far south as the Sea of Japan. Gurevich (1980) has reviewed the diet. Interactions with fisheries do not seem to have been reported, although clearly a diet which includes salmon and other commercial species could lead to some conflict.
Steno bredanensis Rough-toothed dolphin
There is little data on this species in this area, except that Miyazaki (1983) records the capture of 23 of this species in a drive fishery for small cetaceans. There are no indications of interactions with fisheries, and Mitchell (1975a) describes it as rare in Japanese coastal waters.
Sousa chinensis Indo-pacific hump-backed dolphin
Leatherwood and Reeves (1983) describe this species as occurring up to the Canton River in southern China. There do not appear to be any interactions with fisheries recorded, but this is a coastal species which one might expect to be prone to net entanglement.
Peponocephala electra Melon-headed whale
Recorded in Japanese catch statistics of small whales infrequently, 140 were taken in a drive fishery in 1979 (Miyazaki 1983). There are no other indications of the abundance of this species, and no other obvious records of interactions with fisheries.
Feresa attenuata Pygmy killer whale
Rarely recorded worldwide, Nishiwaki et al (1965) reported 14 individuals captured in the Izu drive fishery. Almost nothing is known of this species' habits, but Nishiwaki et al report that the captured specimens ate sardines. Interactions with fisheries are therefore conjectural.
Pseudorca crassidens False killer whale
This species does not appear to be particularly uncommon, and Mitchell (1975a) states that it is commonly seen at sea. Mitchell also cites a number of Japanese authors in stating that it causes much damage to the tuna longline fishery. This species is not infrequently taken incidentally to other fisheries; Miyazaki (1983) records 32 in set nets between 1972 and 1981. Large numbers are also taken in drive fisheries, as well as by harpoon. Miyazaki (1983) records 1374 individuals taken in this way by drive and harpoon fisheries. Perhaps the best known of these fisheries occurs at Iki Island, where this species is one of those culled, largely for the reason that they are reported to damage the line fishery for yellowtail (Seriola quinqueradiata) in that area. Kasuya (1984 in press) has described the situation in detail. Between April 1976 and January 1982 953 false killer whales were killed in driving operations. This and other species are said to interfere with fishing operations on an offshore fishing ground, and at the same time as dolphin presence on the fishing ground was increasing, yellowtail availability was decreasing. Kasuya has investigated the diets of the four species involved, and concludes that Pseudorca is the only species “that interferes significantly and directly with the fishery for the share of yellowtail”. The data, however, were too scanty to determine the extent of this competition.
Orcinus orca Killer whale
Occasionally taken by the small whale fishery in Japan, Miyazaki (1983) records a total of 12 taken in a 6 year period, by driving and by “small type whaling”. Mitchell (1975a) cites Ohsumi (1972) in stating that this species is common mainly in northern waters. The report of the Killer Whale Workshop (IWC 1982) cites Nishiwaki and Handa (1958) in reporting the diet of this species in the northwest Pacific to include cod, flatfish, sardines, salmon, tuna, mackerel, atka mackerel, bonito, cephalopods and a wide variety of marine mammals. Clearly there is scope for a number of interactions with fisheries, although none seem to have been reported as yet.
Globicephala macrorhynchus Short-finned pilot whale
This species is commonly recorded amongst the incidental and commercial catch in Japanese waters. Miyazaki (1983) reports 2 563 caught in the commercial fishery, and 133 caught in gill nets, seine nets and, mostly (119) in set nets. It is evidently not uncommon. The diet is thought to consist of squid, so competitive interactions with the squid fishery are quite possible.
Lagenorhynchus obliquidens Pacific white-sided dolphin
The diet and population numbers are summarized in the species accounts. This species is taken in drive and harpoon fisheries, and is also very frequently caught incidentally. Miyazaki (1983) reports a total of 241 caught in seine nets (55), gill nets (70), and set nets (16), over a 6 year period. This species is another which has been involved in the Iki Island controversy (see Pseudorca crassidens, above). A total of 466 were taken between 1976 and 1982 (Kasuya 1984 in press). Kasuya suggested that this species was not in competition with the yellowtail fishery.
Lagenodelphis hosei Fraser's dolphin
Fraser's dolphin was once thought to be very rare; Hammond and Leatherwood (1983) described them as the most conspicuous cetacean in one area of the Philippines. Miyazaki (1983) reports that this species is taken sporadically in set nets, strandings and other fisheries around Japan, so that its status and the extent of possible interaction with fisheries are not clear.
Tursiops truncatus Bottlenose dolphin
Tomilin (1967) suggests that Japan represents the northernmost limit of the distribution of this species. It appears to be fairly common, as Miyazaki (1983) reports a commercial catch of over 6 500 animals in a 6 year period, during which time 263 were also taken incidentally in set nets (254) and gill nets (9). Another of the Iki Island species, 4147 animals were taken between 1976 and 1982, but Kasuya (1984 in press) adds that yellowtail were not found in any of the stomachs examined. This species is also taken in unknown numbers in a drive fishery in Taiwan reportedly, in part at least, for “predation control” (Hammond and Leatherwood 1983).
Grampus griseus Risso's dolphin
Miyazaki's (1983) catch statistics record 723 of this species in the commercial catch between 1976 and 1981, and a further 75 caught incidentally in set nets. This is the fourth species involved in the Iki Island conflict, 525 having been taken between 1976 and 1981; Kasuya (1984 in press) goes on to state that this species lives exclusively on squid. The amount of competition between this, and other squid eating marine mammals, and local fisheries is unknown.
Stenella longirostris Spinner dolphin
This species does not occur often in the incidental or commercial catch statistics of Miyazaki (1983), who states that it is only taken sporadically, which suggests that it is not common in the northwest Pacific; there do not appear to be any readily available analyses on the abundance, or diet, of this species in this area.
Stenella coeruleoalba Striped dolphin
Nishiwaki (1975) describes this species around Japan. There is an extensive commercial fishery for this species, catches of which reached 20 000 per year, but which have subsequently declined (Nishiwaki 1975). In 1981, 4813 were taken (Miyazaki 1983). Nishiwaki states that the current population size around Japan is 0.4 - 0.6 million animals, whose main food is squid; squid fishermen catch this species occasionally, which is said not to bother them. Miyazaki's statistics indicate that Japanese incidental catches of this species are mostly in gill nets (750 in a 6 year period) with less caught in fixed nets (22 in the same period). Competitive interactions with squid fishery may be likely, but little seems to have been published on this problem, in English at least.
Stenella attenuata Spotted dolphins Spotted dolphins are taken in drive fisheries in Japan - 7 505 having been taken between 1976 and 1981 (Miyazaki 1983), and also as incidental captures in set nets, 20 having been recorded over the same period. There are no obvious population estimates, but the above figures would suggest that, around Japan at least, spotted dolphins are not as common as striped dolphins.
Delphinus delphis Common dolphin
Commonly caught in gill nets and set nets, 128 and 171 animals were taken in each of these types of nets respectively, between 1976 and 1981 (Miyazaki 1983). Although there are no readily available analyses of the diet of this species in area 61, the diet seems very likely to include some commercial species, so that a certain amount of competitive interaction is also likely.
Lissodelphis borealis Northern right whale dolphin
This species is apparently caught in Japanese waters, although Miyazaki (1983) does not record the numbers involved, or the type of fishery. As squid have been recorded in some stomachs, competitive interactions with the squid fishery are always possible.
Phocoenoides dalli Dall's porpoise
There is an extensive fishery for this species in the waters around Japan, described by Miyazaki (1983), the mean annual catch exceeds 8 000. There are further mortalities through gill net and set net entanglements (544 and 102 respectively over 6 years : Miyazaki (1983). The North Pacific salmon gill net fishery also imposes a very high mortality on this species, which Jones (1983) has suggested may be as high as 40 000 animals per year for the whole North Pacific. The effect of all of these mortalities on the population is unknown at present, but Bouchet's (1983) total North Pacific and Bering Sea population estimate of 790 - 1 783 000 animals suggests that the estimated numbers of animals caught in fishing gear may be having a significant effect on the population. Wilke and Nicholson's (1958) data suggests a diet of squid and myctophids. The extent of any competition with fisheries for squid is not clear.
Neophocaena phocaenoides Finless porpoise
Marcuzzi and Pilleri (1971) state that this species is found in coastal waters as far north as Japan. Hammond and Leatherwood (1983) state that they are sufficiently common in the waters around Hong Kong that they can be found at least 1 day in 4 “usually in murky coastal waters”. Further north, in Japan, Miyazaki (1983) records 5 finless porpoises being harpooned between 1976 and 1981, and a further 19 captured in set nets, and 2 in gill nets during the same period. If catch rates are an indication of abundance, this species cannot be among the more common ones in Japanese coastal waters. The extent of competitive interactions with fisheries are not clear, but the inclusion of prawns and shrimps in the diet would suggest some competition is possible.
Lipotes vexillifer Beiji
The size of the population of this species is unknown, but presumed small. Pei-Xun (1981) describes the situation suggestion that the decrease in numbers of this species may be due to fewer fish, and “the ruining of appropriate biotopes for Lipotes due to harnessing the river and increased navigation”. The main threat, however, is said to be the hook fishery. About 50% of nearly 100 animals found dead between 1950 and 1980 had died from having eaten hooks.
Eumatopias jubatus Steller sea lion
At least 20 000 northern sea lions are thought to breed in the Kuril Islands and the Sea of Okhotsk (Mate 1982a). Mate states that in January sea lions appear off northern Hokkaido and then depart northward around May. Schusterman (1981) states that relatively little study has been made of the diet of this species, but that flatfish, rockfish, cod, pollock, smelt, greenling and some salmon have all been found. Invertebrates are also found to be important, especially bivalve and cephalopod molluscs. Mate (1982a) states that “competition with man for food may also be present though the trophic relations of the northern sea lion, other pinnipeds and man are poorly understood”. He also states that 4 000 of these animals are captured incidental to fishing operations, though presumably many of these are in area 67.
Zalophus californianus Californian sea lion
Mate (1982) states that the population of this species which bred in the Sea of Japan is at best rare, and may be extinct.
Callorhinus ursinus Northern fur seal
The bulk of the population of this species is found in area 67, but there are breeding populations in area 61 on Robben Island, the Kuril and the Commander Islands which amount to about 360 000 animals (Lander and Kajimura 1982). Feeding has been described in detail by Kajimura (1984) and by Perez and Bigg (1981), and is said to occur offshore, at areas of upwelling or over the continental slope (Gentry 1981). Food species include a wide range of commercial fish and squid. Herring, anchovy, salmon, capelin, saury, hake, pollock, rockfish, atka mackerel, sand lance and squids including Loligo opalescens are all listed by Lander and Kajimura (1982). They continue that “the competion between man, the fur seal and other forms of marine life, for certain stocks of fish, is a problem in resource allocation”. Another of the points that Lander and Kajimura make is that survival rates in the population have been in decline; the recovery of the stock, after the cessation of female harvesting in 1968, did not occur as was predicted. Swartzman and Haar (1984) tested the hypothesis that this decline in survival rate might be due to a reduction in carrying capacity by commercial fishing operations. They conclude that this is not the case, and that in the 1970's fur seal consumption of one important fish, the pollock, actually increased. The competition between fur seals and fisheries is therefore still very unclear.
There is also a certain amount of incidental mortality to fur seals associated with fishing activities. Fukuhara (1974 cited in Lander and Kajimura 1982) estimates that between 3 150 and 3 750 northern fur seals are killed incidentally each year in the Japanese mothership fishery for salmon in area 61.
Odobenus rosmarus Walrus
Fay (1981) gives the southern limit of the distribution of this species as the Kamchatka Peninsular, though a few have reached Honshu. It is not clear how many of the estimated 140 000 (Brenton 1979) Pacific walruses move into area 61. There are no obvious records of interactions with fisheries, and apart from occasional net entanglements these would seem unlikely unless the benthic invertebrate fauna of the western Bering Sea becomes exploited.
Phoca vitulina Harbour seal
Occurring from north eastern Hokkaido, through the Kuril Islands to southern and eastern Kamchatka and the Commander Islands, with a population of perhaps 5 – 8 000, (Bigg 1981). Although the diet of this species often includes commercial species (Bonner 1979c) there appear to be few records of interactions with fisheries, possibly due to the relatively small population size and northerly distribution in this area. Naito (1976) reports some harbour seals being caught in salmon set nets and other nets, but no figures are available.
Phoca largha Largha seal
Distributed around the coast of area 61 from the Yellow Sea and the Po Hai Sea to Kamchatka and the Bering Sea (Bigg 1981). Bigg cites Tikhomirov (1966) in stating that this is the only seal harmful to commercial fish in the Sea of Okhotsk, but gives no further details. The population size is estimated at around 135 to 200 000 in the Sea of Okhotsk, 133 to 250 000 in the Bering Sea, and has not been estimated in the Po Hai Sea (Bonner 1979b). Naito (1976) states that this species is occasionally caught in nets, without giving any other details. Competitive interactions with fisheries are unclear.
Phoca hispida Ringed seal
There is one population of this species in the Sea of Okhotsk and around the Kurils (Stirling and Calvert 1979). Individuals are occasionally seen as far as Honshu, Japan, where they sometimes get trapped in salmon set nets and other nets (Naito 1976). A population size of 800 000 to 1 million is given by Frost and Lowry (1981), who also state that fish of the cod family and pelagic crustacea make up the bulk of the diet. Naito (1976) reports this species as being caught in nets occasionally, without giving details. The competitive interaction with fisheries is not clear.
Phoca fasciata Ribbon seal
Burns (1981) gives the southern limit of the distribution of this species as Hokkaido, and citing Shustov (1972) suggests a population in the Sea of Okhotsk of 140 000 animals. He also states that the diet is poorly known, but may include fish and crustacea. Interactions with fisheries do not appear to have been studied, but Naito (1976) refers to 3 ribbon seals caught in offshore gill nets around Japan.
Erignathus barbatus Bearded seal
The distribution of this species is very similar to the previous one in area 61, according to Burns (1981), though it does not extend as far south into the Sea of Japan. Naito (1976) states that bearded seals are seen rarely in Honshu, however, Stirling and Archibald (1979) give a population estimate for Soviet stocks, including area 18, as around 450 000; it is not clear what proportion of these are found in area 61. Feeding is on bottom dwelling invertebrates (Stirling and Archibald 1979), so competitive interactions with fisheries are unlikely; Naito (1976) states that this species is also occasionally taken in fishing nets.
This area together with area 67 is characterized by a large number of marine mammals, species and individuals, and intensive fisheries. Area 61 is also the most productive region of all. The high productivity, intensive fisheries and large number of marine mammals however, also means that many of the marine mammal species must be competing to some extent with fisheries.
Of the 50 species listed above, only walruses, bearded seals and 4 species of baleen whale are unlikely to consume commercial species. About 16 other species are known to feed on squid, which in this area is fairly heavily fished; it would seem that in contrast to most other areas of the world, where often only tens of thousands of tonnes of squid are caught, there is a possibility here that some squid eating marine mammals may compete directly with fisheries.
Of the remaining 28 species, most are thought to eat some commercial fish at least.
DEMERSAL FISH RESOURCES
Reported catches of demersal species in 1981 totalled around 9 million tonnes, to which should be added a proportion of the million tonnes of fish reported merely as ‘marine fishes’. Most stocks are probably heavily fished Gulland (1983).
Gulland (1983) contrasts the northern areas of this region, the Sea of Okhotsk and Japanese coastal waters, which have relatively little shelf area, and in which demersal species are not so important, with the wide shelf areas of the Yellow Sea and East China Sea, where demersal species become more important.
GADIDAE
As in the North Atlantic waters, this family is the dominant one in the fisheries of the region.
Theragra chalcogramma Alaska pollock
This species is fished in what is the largest single species fishery in the world. Catches in area 61 are currently in excess of 3 million tonnes, and appear to be relatively stable over the past few years (FAO 1981). The species is widespread throughout northern parts of the area, and is thought to be fully exploited (FAO 1981). Alaska pollock are known to be an important food species of northern fur seals Callorhinus ursinus in the Sea of Japan and Sea of Okhotsk (Lander and Kajimura 1982), and are also eaten by a number of other species including fin and minke whales (Tomilin 1967). The effects of the fishery on these predators, or vice versa, is not known. Swartzman and Haar (1984) found that over a period of fishery expansion on this species, northern fur seal diets included progressively more pollock, though the size of fish eaten dropped.
They suggest this may be due to the fact that the fishery takes the larger fish, and as this species is cannibalistic, fewer large fish enable more smaller fish to survive. Clearly the dynamics of competition are not simple.
PLEURONECTIFORMES
The majority of the catch of flatfish (202 000 tonnes) is not broken down into species in the fishery statistics. Clearly this is an important fishery, but relatively few marine mammal species are known to include flatfish in their diets, these include killer whales, white whales, sea lions and possibly other pinnipeds.
Further south, the species composition changes and a number of more tropical species become important in the landings. There is some suggestion that stocks of demersal fish in the East China Sea may be overexploited (FAO 1981a).
SCIAENIDAE
As in other warm waters drums and croakers are amongst the most important commercial species. Yellow croakers (Pseudosciaena spp) are particularly important species, with catches exceeding 100 000 tonnes, but are reported to have fallen considerably (FAO 1981a), possibly as a result of over-exploitation.
Other important demersal stocks in area 61 include atka mackerel, Pleurogrammus azonus, which yielded 123 000 tonnes in 1981, a drop from 296 000 tonnes in 1976, and which is known to be included in the diet of killer whales in this region. Sandlance, Ammodytes personatus, have yielded catches of between 224 000 tonnes and 103 000 tonnes since 1976 (FAO 1983), and are known to be eaten by fin whales, minke whales, humpback whales and probably other species too.
PELAGIC FISH RESOURCES
The total pelagic catch in 1981 exceeded 7 million tonnes (FAO 1983). As with the demersal stocks, all stocks are said to be heavily fished (FAO 1981a). Gulland (1983) suggests that the pelagic species are more important than demersal ones in northerly areas around Japan and the Sea of Okhotsk. Many of these stocks have fluctuated in abundance widely (Nagasaki 1973).
CLUPEIDAE
Sardinops melanosticta Japanese pilchard
The largest fishery in the area is for this species which in 1981 yielded 3.6 million tonnes. The stocks have recovered dramatically from very low catches in the early 1960's (FAO 1981a). Distributed mainly in the coastal waters of Japan (FAO 1981) this species might be expected to provide food for a number of marine mammal species, although the only obvious references to this are for killer whales and pygmy killer whales (see above). Other coastal small cetaceans would seem likely to prey on such an apparently abundant fish, of which the common dolphin, which is known to feed on sardines extensively elsewhere (see area 37), springs to mind most readily.
Clupea pallasi Herring
Predominant in northerly waters around Sakhalin Island, the Sea of Okhotsk and the western corners of the Bering Sea, this species yielded 130 000 tonnes in 1981 (FAO 1983), down from 405 000 tonnes in 1973 (FAO 1978). Herring have been found in fin whales, minke whales, humpback whales, narwhals, white whales and fur seals, but this list is unlikely to be exhaustive.
Oncorhynchus spp. Salmon
Salmon are amongst the most important commercial species in this area. Six species are caught, and of these chum salmon are the most important in terms of weight, with over 100 000 tonnes taken in 1981; catches over all species totalled 150 000 tonnes (FAO 1983). The main spawning sites are in Kamchatka, but there are extensive gill net fisheries throughout much of the open sea in area 61, and in some coastal waters. Salmon are very frequently reported in the diets of marine mammals, as a cursory inspection of those species listed above should verify. Being an economically valuable fish, any predator on salmon is likely to generate a certain amount of conflict with fishermen. The case of the grey seal in Scottish waters, however, should caution against assuming in all reported cases of salmon in marine mammal stomachs that this is an important, or even a regular diet item.
Other pelagic species which are important include mackerel and, as in other areas tuna. Various jacks and small clupeids, as well as the Pacific saury and some scads Decapterus spp.
INVERTEBRATE RESOURCES
CRUSTACEA
As elsewhere in Far Eastern waters, shrimps and prawns feature prominently as economically important resources particularly in the Yellow Sea. Over 300 000 tonnes were taken in 1981. Further north, crabs become more important, tanner crabs (Chionectes spp) are particularly important in Japanese coastal waters, and king crab (Paralithodes) is important in the Sea of Okhotsk (FAO 1981). The importance of such relatively large crustacea in the diets of marine mammals is not clear. One or two species, notably the finless porpoise in southerly waters, could be competing for some of these species.
CEPHALOPODS
Over 600 000 tonnes of cephalopods were reported in the catch statistics for area 61 in 1981 (FAO 1983). Japanese fisheries for cephalopods are described by Okutani (1977). At least some stocks of squid appear to be overfished at present. Okutani suggests that the jigging fishery for Todarodes pacificus may have had a significant impact on the stocks. Octopuses are also said to be fully exploited around Japan. Okutani, however, also points out the potential for the exploitation of oceanic squids of the family Ommastrephidae. The interaction between the squid fishery and marine mammals is a subject which has been very little studied. In view of the number of species which feed in whole or in part on squid, there is clearly scope for a great deal more study into this problem, particularly in an area such as this, where some squid stocks have already been heavily exploited, and where there also seems to be the scope for an increase in the fishery.
Gulland (1983) summarizes the fisheries of the region. In the north, Soviet vessels are principally medium to large vessels, mainly trawling for Alaska pollock. Japanese vessels are both small coastal vessels using a great variety of gears, and offshore vessels using seines and trawls. Distant water boats also trawl and gill net salmon. Zhu De-Shan (1980) describes the Chinese fisheries. Small motorized fishing vessels dominate, with some 1600 larger vessels. The main methods of fishing in the South China Sea are said to be trawling and also purse-seining, for scad, mackerel, round herrings and sardines. In the East China Sea, Yellow Sea and Po Hai Sea, gill netting and line-fishing supplement trawling and seining. According to Gulland (1983), Korean fisheries have developed in much the same way as the Chinese, but that very little is known of North Korean fishing activities. The fishery from the Chinese island of Taiwan is also one in which small to medium sized vessels are important, using a variety of gear in the coastal zone, and mostly trawls and purse seines offshore. The Korean purse seine fishery is known to take some small cetaceans as a by-catch (IWC 1982).
In the most productive fishery area in the world, where almost all the fished stocks appear to be either heavily fished or overexploited, and one where a great variety of marine mammal species are recorded, conflict would seem inevitable. Gear conflicts are commonplace in Japanese waters, and seem to be fairly extensively documented in Reports to the International Whaling Commission. Interactions in other areas, however, appear to have received very little attention, or else are not readily available.
Operational interactions
The paper by Miyazaki (1983) summarizes all reported incidental captures of 14 species of small cetaceans over a six year period. Most commonly caught were striped dolphins, followed by Dall's porpoise, bottlenose and pacific white sided dolphins.
A significant by-catch for Dall's porpoise exists in northern Pacific waters in the salmon gill net fishery, which extend from area 61 into area 67. Total mortalities could be as high as 20 000 animals a year (Jones 1983).
Naito (1976) records 4 species of seal, ringed, harbour, largha and bearded which are occasionally taken in nets.
False killer whales are said to harass tuna longliners in this, and other, areas (Mitchell 1975a).
Humpbacks are once reported (Tomilin 1967) annoying salmon fishermen in Soviet waters.
Watson (1981) has recorded two unconfirmed captures of Ginkgo-toothed beaked whales on tuna longlines.
4 species of dolphin have been culled at Iki Island due to interference with the yellowtail fishery there, though this may also be seen as an expression of an assumed biological interaction.
The 1982 Small Oetacean Sub-Committee Report to the IWC indicated that some small cetaceans were taken incidentally in the Korean mackerel/purse seine fishery.
Biological interactions
A great number of biological interactions might be assumed to occur in this area. The squid fishery, in particular, may have brought a number of otherwise peripheral species into competition with fisheries. Despite some detailed work, there appear to be no obvious examples of such competition being proved to affect either marine mammals or fisheries. Clearly, considerably more analysis is required before the extent of these interactions will be even partly understood.
Eubalaena glacialis Right whale
The report of the Right Whale Workshop (IWC 1983 SC/35/Rep2) indicates that no population estimates are available for this species in the northeast Pacific, but a maximum one day count of 8 animals is recorded. Berzin and Vladimirov (1981) suggest a population size of around 2–500 for the whole North Pacific. Townsend's (1975) charts indicate that it was formerly an abundant species in these waters. Omura et al (1969) indicate that the diet in the North Pacific is confined to pelagic crustacea. There are no reports of interactions with fisheries.
Balaena mysticetus Bowhead whale
Migrations occur from the Beaufort and Chuckchi Seas in area 18, to the Bering Sea in winter. This stock was decimated in the last century (Tomilin 1967). The size of the stock has been estimated to be between 3390 and 4325 (Braham 1982). Fish are not consumed by this whale (Marquette et al 1982) and there is no indication of any interaction with fisheries.
Eschrichtius robustus Grey whale
Migrating from the Chuckchi and Bering Seas to California and Mexico to breed, Watson (1981) states that these animals cross the Gulf of Alaska at speeds of around 185 km per day. Wolman and Rice (1979) suggest the population may number around 11 000. The food does not include fish, and no interactions with fisheries seem likely in this area at present.
Balaenoptera physalus Fin whale
The size of the population in area 67 is unknown, but Berzin and Vladimirov (1981) suggest between 14 and 19 000 individuals in the North Pacific. Tomilin (1967) describes feeding in the western North Pacific, which includes numerous fish species, mostly small shoaling ones such as capelin, herring, pollock and sand eels, as well as a variety of pelagic crustacea, and even some squid. Despite the presumed inclusion of fish in the diet, there appear to be no reported conflicts with fisheries.
Balaenoptera musculus Blue whale
Berzin and Vladimirov (1981) suggest a population of between 1 400 and 1 900 in the North Pacific. Fish are not eaten (Tomilin 1967) and no interactions seem likely.
Balaenoptera acutorostrata Minke whale
The population size in the eastern North Pacific is unknown, but a figure in the region of 100 000 animals might not seem too unreasonable. The diet in the North Pacific is said by Tomilin (1967) to include pollock, saffron, cod, herring, capelin, sand lance and pelagic crustacea. There do not appear to be any reports of interactions with fisheries, although clearly the diet may overlap with some commercial catches.
Balaenoptera borealis Sei whale
The population size in this area is unknown, but as Berzin and Vladimirov (1981) suggest between 8 600 and 21 000, for the whole North Pacific, a figure of less than or near to 10 000 animals might be reasonable for area 67. The food consists mostly of pelagic crustacea although squid and small amounts of fish may be taken too, according to Tomilin (1967). Rice (1977) however reports that off California at least, anchovies (Engraulis mordax) are the dominant food, and also states that they feed on saury (Cololabis saira) and jack mackerel (Trachurus symmetricus). Despite this, there are no reported conflicts between this species and fisheries.
Megaptera novaeangliae Humpback whale
Berzin and Vladimirov (1981) have suggested a population size of between 1200 and 1600 for the whole North Pacific; part of the North Pacific population migrates from the Chuckchee Sea to California and Mexico. The diet is said to include fish, and Rice (1977) found 60% of the diet was northern anchovy (Engraulis mordax) and 40% was krill (Euphausia pacifica). There appear to be no reported conflicts with fisheries, but with such a small population any entanglements could affect the population.
Berardius bairdii Baird's beaked whale
The population size is unknown, Laevastu et al (1980) have suggested about 10 000 for the North Pacific. The diet is thought to consist mostly of squid, and no interactions with fisheries have been reported.
Mesoplodon stejnegeri Stejneger's beaked whale
Recorded as far south as Monterey in California this species is said to strand fairly commonly in the Aleutians (Leatherwood and Reeves 1983) where it may be most common. The diet is presumably squid; there are no reported interactions with fisheries.
Mesoplodon carlhubbsi Hubb's beaked whale
Leatherwood and Reeves (1983) suggest a distribution from about 50° to about 30°N, this species is known from only a few standings. The diet is presumably squid, and no interactions with fisheries are recorded.
Ziphius cavirostris Cuvier's beaked whale
Known from as far north as the Bering Sea (Mitchell 1975), there are not enough data to estimate a population size. The diet is presumably mostly squid. There do not appear to be any interactions with fisheries.
Physeter macrocephalus Sperm whale
The population size in area 67 is not known, but could be in the tens of thousands. The diet includes squid and some fish, of which deepwater species including grenadiers, rockfish, sculpins and cods are most important (Berzin 1972). Authorities differ as to the importance of fish in sperm whale diets in this area. There are no apparent conflicts with fisheries in area 67.
Monodon monoceros Narwhal Mitchell (1975) and Tomilin (1967) state that this species is confined to the Arctic Ocean, but Leatherwood and Reeves (1983) suggest the range may extend into the Bering Sea. The diet is known to include commercial fish (Tomilin 1957), but this species is presumably not very frequently found in area 67, and conflicts seem unlikely.
Delphinapterus leucas White whale
Mitchell (1975) states this species is found in the subarctic, in shallow water. The population size in area 67 is unknown, but Gurevich's (1980) review suggests a population in the thousands. The diet in this region is reported to include salmonids, herring, navaja, flatfish and smelt (Gurevich 1980). Lowry and Frost (1984 in press) noted that this whale has already been perceived as a threat by salmon fishermen in Bristol Bay, where during the 1950's white whales were scared away from salmon runs with reportedly improved recovery of sockeye stocks. These authors, whilst noting the lack of adequate data on feeding and trophic relationships in the area, suggest that there may be potential for interaction between white whales and fisheries, although “their mobility may reduce the probability of significant interactions with fisheries”. Mate (1980) reports that white whales damage gill nets in Alaska but do not remove fish; they feed seasonally on smelt and salmon, and have been excluded successfully from the Kvichak river estuary where they consume salmon smolts, by recorded killer whale sounds (Fish and Vania 1971).
Orcinus orca Killer whale
The population size in area 67 is unknown. McAlister (1981) has suggested a figure of around 1 000 in the Bering Sea alone, in summer. The population for the whole of area 67 might be as many as 10 000 as a very rough estimate. The diet has not been studied in detail in this region, but Braham and Dalheim (1982) suggest that fish are eaten when locally abundant, but marine mammals are eaten when fish are scarce. Tomilin (1967) included herring, cod, skates, smelt, capelin, halibut, sharks and salmonids amongst the fish eaten by this species. Matkin and Fay (1984) state that killer whales are associated with salmon fisheries, but have not been considered as major contributors to any conflicts. Mate (1980) states that killer whales are said to frighten salmon in British Columbia, making them difficult to catch.
Globicephala macrorhynchus Short-finned pilot whale
There are no population estimates for area 67, but this species only occurs as far north as the Gulf of Alaska (Mitchell 1975). Feeding is presumably mostly on squid, and there appear to be no records of interactions with fisheries, although squid fishermen have been annoyed by this species in California (see area 77).
Lagenorhynchus obliquidens Pacific white-sided dolphin
Leatherwood and Reeves (1983) state that this species ranges as far north as the Bering Sea. The population size is unknown, but seems likely to number in the tens of thousands. The diet is thought to include hake (Merluccius productus), anchovies (Engraulis mordax), and squids, so that some competition with fisheries may occur for prey species. There do not appear to be any records of conflicts however.
Grampus griseus Risso's dolphin
This species is recorded as far north as British Columbia (Mitchell 1975), but there are no estimates of its abundance in area 67. The diet is generally presumed to consist mostly of squid, and there are no obvious records of any interactions with fisheries in this area.
Stenella coeruleoalba Striped dolphin
Marcuzzi and Pilleri (1971) both record this species as far north as the southern Bering Sea, around the Aleutian Islands. Data on abundance are lacking in this area but a population in the hundreds of thousands might be expected. The diet is elsewhere known to consist of small mesopelagic fish. There do not appear to be any records of interactions with fisheries in this area.
Lissodelphis borealis Northern right whale dolphin
Rice and Scheffer (1968) record this species as far north as British Columbia. The population size in the North Pacific has been estimated at around 40 000 by Laevastu et al (1980). The diet has been found to include squids and lantern fish, and there are no apparent interactions with fisheries in this area.
Phocoena phocoena Harbour porpoise
This species is said to occur as far north as Point Barrow in Alaska. The population in the North Pacific has been estimated at around 20 000, 5 000 of which may occur in the eastern Bering Sea, Gulf of Alaska and west coast of America (Laevastu et al 1980). McAlister (1981) states that the diet of this species consists mostly of bottom fish such as cod, herring, fry, flounder, and only rarely any invertebrates. Lowry and Frost (1984 in press) suggest that this species has a reasonably high potential for interaction with fisheries in the Bering Sea as it forages extensively on commercial species, although its mobility may reduce the probability of significant interactions. Matkin and Fay (1984) also list this species as one which is of minor importance in interactions with salmon fisheries in southeast Alaska, and estimate that around 50 may die in salmon net entanglements per year in one particular fishery.
Phocoenoides dalli Dall's porpoise
The population in the North Pacific and Bering Sea may number around 1 million animals (Bouchet 1983). The diet consists of mostly of lantern fish but also includes squid, saury, hake, herring, jack mackerel, bathypelagic and deepwater benthic fish (Crawford, cited in McAlister 1981). Lowry and Frost (1984) do not rate this species particularly highly as a potential competitor with fisheries, though this is due in part to the fact that they suggest the population of this species may currently be depleted as a result of incidental captures and mortalities. Mortalities in high seas drift net fisheries for salmon are high, and may number as many as 20 000 in the whole of the North Pacific. Matkin and Fay (1984) found this species to be of minor importance in operational interactions with salmon gill net fisheries in southeast Alaska.
Eumatopias jubatus Steller sea lion Distributed throughout the continental shelf waters from the Bering Sea south to California, breeding occurs from the Pribilof Islands southward to California. The population breeding in area 67 has been estimated at slightly less than 200 000 (Mate 1982a). The diet is known to include a number of commercial species and includes pollock, flatfish, rockfish, capelin, sandlance, sculpins and salmon. In their study of biological interactions between marine mammals and commercial fisheries in the Bering Sea, Lowry and Frost (1984 in press) find this to be one of the 3 species for which there is greatest potential for interactions with fisheries, based on their feeding habits and demography. Operational interactions are reported by Matkin and Fay (1984) in southeast Alaskan salmon gill net fisheries, where marine mammals do an estimated $350 000 damage per year to gear and catch. Most of this damage is attributed to sea lions and harbour seals. About 400 sea lions are thought to be killed in this fishery. Everitt et al (1981) also report damage to salmon gill net fishery catch and gear in Washington, some of which is attributed to steller sea lions. Loughlin and DeLong (1983) report steller sea lions becoming trapped in trawl nets in the US-South Korean joint venture fishery for walleye pollack in the Shelikof Strait, Alaska. In 1982, 1 393 sea lions are estimated to have been killed in trawl nets, and a further 222 in 1983, the difference being possibly due to differences in location and dates of the fishery in the two years. Mate (1980) reports that this species is also responsible for removing halibut and sablefish from longlines in Alaska waters; it is claimed that up to 50% of the sablefish in a Japanese longline fishery south of the Pribilofs may be damaged in this way. It seems likely that incidental kills occur throughout the range of this species, but detailed data have been collected from only a few sites. Conflict with fishermen would also appear to be widespread.
Zalophus californianus Californian sea lion Odell (1981) considers the range of this species to extend as far north as British Columbia. The population size is unclear, but in area 67 probably numbers in the tens of thousands (total population 75 – 100 000 Mate 1982). The diet is not well known either, but may include hake, northern anchovy and cephalopods amongst the other species. Operational interactions between this species and fisheries are widespread. Everitt et al (1981) report this problem in Washington State coastal waters, where, in one salmon drift net fishery, up to 30% of the catch may be damaged by marine mammals, including sea lions. Competitive interactions would seem to be possible, although no detailed analysis of this problem has been yet made. This species has been blamed however, for a decline in the salmon catches of sport fishermen in Washington and Oregon (Mate 1980).
Callorhinus ursinus Northern fur seal
Gentry (1981) describes the distribution of this species in the eastern Pacific from around the Pribilof Islands in the Bering Sea, around the shelf area of North America as far as California. This part of the population he estimates at around 1.3 million animals. The feeding habits of this species in area 67 are discussed exhaustively by Perez and Bigg (1981) and by Kajimura (1984 in press). The diet is varied and includes more than 50 species, the principle ones being walleye pollock (Theragra chalcogramma), capelin (Mallotus villosus), atka mackerel (Pleurogrammus monopterygius), herring (Clupea harengus), northern anchovy (Engraulis mordax), Pacific whiting (hake) (Merluccius productus), Pacific saury (Cololabis saira), rockfish (Scorpaenidae) and in some areas salmon. This diet and the abundance of fur seals in the Bering Sea lead Lowry and Frost (1984 in press) to conclude that this species is one of the most likely to compete with fisheries in that area. Swartzmann and Haar (1984 in press) have examined the hypothesis that the increased fishing effort on, and catches of, walleye pollock, one of the fur seals' major foods, might be responsible for a decrease in fur seal survival rates in the Bering Sea, and for the current decline in the fur seals abundance. Their analysis did not support this hypothesis, suggesting that fur seals' consumption of pollock had increased after the fishery started. This study, which was based on extensive feeding data, is one of the few to have attempted to link a marine mammal's population dynamics with the activities of a fishery, and yet despite Lowry and Frost's finding that this species is very likely to compete with fisheries, no such effect on the population dynamics or feeding behaviour was found.
Operational interactions between fur seals and fisheries are widespread, and in particular, there is increasing concern that floating fishnet scraps, especially from the salmon drift net fishery may be having some serious effect on the population. Fowler (1982) examined the relationship between fur seals and fisheries and also concluded that competition was not the cause of reduction in fur seal numbers. He suggests that entanglement may be responsible for a large part of the observed decline, with 5% or more of the population dying this way, as more than 50 000 seals per year.
Odobenus rosmarus Walrus
Confined to the Bering Sea, in area 67, the population in the Bering-Chuckchi region is thought to number around 200 000 animals (Fay 1981). The walrus diet consists mainly of benthic invertebrates. Lowry and Frost (1984 in press), and Harwood (1981), have pointed out the potential for competitive interactions between this species and fisheries. Walruses are said to show little feeding plasticity, specializing in sedentary organisms, for which at present there is no commercial interest. Should a fishery for such prey items ever develop, some conflict would seem probable.
Phoca vitulina Harbour seal
This species is said to be littoral in distribution and non-migratory, the population in area 67 extending from the Bering Sea to California (Bigg 1981). The population the area is not known, but may number more than 250 000 (Laevastu et al 1980). Feeding is said to be opportunistic and includes a wide variety of fish (Bigg 1981). Lowry and Frost (1984 in press) found this to be one of the most likely species to compete for food with fisheries in the Bering Sea, especially for pollock, herring and salmon.
Operational interactions are widespread with regard to this species. Mate (1980) reports that harbour seals are a particular nuisance in the Copper River Delta and Bristol Bay Salmon gill net fisheries. Matkin and Fay (1984) found that this was one of the 2 principle species involved in damage to catch and gear of 2 salmon gill net fisheries in southeast Alaska, which amounted to a loss of about $350 000 per year. In addition, around 500 harbour seals are thought to die in salmon gill nets in the region, although this is said to have little effect on the population dynamics of this stock. In Washington State, harbour seals are implicated as the main cause of significant damage and loss to the catch of further salmon gill net fisheries (Everitt et al 1981). Mate (1980) states that up to 30% of the catch in the Columbia river salmon fishery may be damaged, mostly by harbour seals, and that this species has also been blamed for a decline in catches by sport fishermen.
Phoca largha Largha seal
This species is closely related to the preceding one, but breeds on ice, and not on land; the distribution is therefore confined to the Bering Sea, where up to 250 000 animals may breed (Bigg 1981). As this species feeds more extensively in northern waters of the Bering Sea, Lowry and Frost (1984 in press) suggest that it may not be as likely to compete with fisheries as the harbour seal. Operational interactions are likewise limited by this species' habitat.
Phoca hispida Ringed seal
This is another of the so called ‘ice seals’, confined in area 67 to the northern Bering Sea (Frost and Lowry 1981). Up to 200 000 ringed seals may occur in the eastern Bering Sea for parts of the year (Laevastu et al 1980). The diet is said to consist largely of arctic cod (Boreogadus saida) and a large zooplankton. For this reason, and because of its remote habitat, interactions with fisheries seem unlikely.
Phoca fasciata Ribbon seal
Confined to the Bering Sea, up to 100 000 animals may be present for part of the year in the eastern part (Laevastu et al 1980). The diet is poorly known, but may include crustaceans and fish (Burns 1981). Interactions with fisheries seem unlikely.
Erignathus barbatus Bearded seal
The population of bearded seals in the eastern Bering Sea may reach 250 000 for part of the year (Laevastu et al 1980). The diet consists mostly of benthic organisms, but some schooling demersal fish are also taken (Burns 1981). The diet and remote habitat would seem to make interactions with fisheries unlikely at present.
Mirounga angustirostris Northern elephant seal
This species ranges up the western American coast as far as British Columbia, although the breeding sites are all in area 77. The proportion of the estimated 50 000 individuals in the population which feed in area 67 is not known. The diet consists mostly of deepwater fish, competition seems unlikely. There appear to be no records of gear conflicts in area 67, although occasional entanglements might be expected.
The diets and population sizes of marine mammals in this area are possibly better known than in any other statistical area. In recent years much attention has been given to the problem of marine mammal interactions with fisheries in this area, possibly because of the valuable salmon fishery, which is often perceived to compete with marine mammals and possibly because, in the Bering Sea at least, the density of marine mammal biomass appears to be quite high. The area is also well supplied with suitable fishery centres for the study of this problem, notably the Northwest and Alaska Fisheries Center.
Of the 33 species listed above, at least 15 are known to consume some commercial fish, notably anchovy, herring, pollock and salmon.
7 other species appear to be largely squid eating, although of these sperm whales and pilot whales also consume fish, in uncertain quantities. Of the remaining species, 3 are baleen whales which do not consume fish, grey whales and walruses eat invertebrate benthos and other non commercial species, striped dolphins and northern right whale dolphins appear to feed on non commercial fish such as myctophids, whilst elephant seals consume mainly deepwater fish species. Finally 3 ice seals are both remote and unlikely to compete with fisheries anyway.
DEMERSAL FISH RESOURCES
Demersal fish resources are fished on the shelf area of the Bering Sea, in the Gulf of Alaska and to a lesser extent down the narrow shelf of the North American coast. The fisheries in this area are said to be closely controlled by the coastal states (FAO 1981a), so that many of the stocks appear fairly healthy. The catch in 1981 was around 1.6 million tonnes for all demersal finfish (FAO 1983).
GADIDAE
Theragra chalcogramma Alaska pollack This is the largest single species fishery in the area, with catches in 1981 exceeding 1 million tonnes (FAO 1983). Gulland (1983) states that this species is pretty close to being fully exploited, and that not much of an increase in sustained yield can be expected. This fishery appears to be pursued largely by foreign vessels in area 67, and especially in the Bering Sea. Pollack are important food for a number of marine mammal species, as already noted. The fishery on this species seems to have had unpredictable effects on the feeding of some marine mammals at least. Swartzman and Haar (1984 in press) found that over the period of the fishery small pollack increased in the diet of fur seals. They suggest this may be due to an increase in smaller fish as the fishery removes larger, cannibalistic fish.
Gadus macrocephalus Pacific cod are found over much the same area as pollack, in the southern Bering Sea and along the Aleutian ridge. The catch in 1981 was 100 000 tonnes, which is about what the estimated potential is (90 000 tonnes : FAO 1981), but there are suggestions (FAO 1981b) that this species may be increasing in abundance.
Merluccius productus North Pacific hake or whiting have an estimated potential of 150 000 tonnes (FAO 1981), slightly more than the reported catch of 120 000 tonnes in 1981 (FAO 1981a). The distribution is along the north west American coast, as far north as British Columbia. This is an important diet item of a number of species, especially the sea lions and fur seal.
PLEURONECTIFORMES
Limanda aspera Yellowfin sole have been heavily fished in the past, but may now be increasing in abundance (FAO 1981a). The main area of concentration of this species is in the southern Bering Sea. In 1981 the catch was only 77 000 tonnes (FAO 1983). Few marine mammal species, other than bottom feeders, might be expected to feed on this species but it is not an unimportant commercial stock.
Other important demersal stocks include halibut (Hippoglosus stenolepis) which is fished all along the shelf edge, with a total catch in 1981 of over 15 000 tonnes. The stock was heavily fished by the local longline fishery, but has recovered under management (Chapman et al 1962), but trawl fisheries for other species may be affecting catches of halibut through a significant by-catch of young halibut. There is reported to be some depredation of halibut caught on longlines by steller sea lions, although this may not be as widespread as in previous decades when the fishery was larger (Mate 1980).
PELAGIC FISH RESOURCES
Gulland (1983) states that in general pelagic resources are not abundant enough to attract foreign vessels, and do not fetch high enough prices to attract local vessels. The exception to this is salmon. The total potential for the area has been estimated at 1.2 million tonnes, but catches totalled less than half a million tonnes in 1981 (FAO 1983).
Clupea pallasi Herring is one of the very few pelagic species fished for in this area at present. The catch in 1981 was 83 000 tonnes (FAO 1983), and except locally, e.g. around Vancouver Island, the stocks are lightly fished. Herring are known to be eaten by a number of marine mammal species, but with such light fishing, competition with fisheries may not be important.
Oncorhynchus spp. Salmon The catches in 1981 totalled 364 000 tonnes, and are taken by purse seines, gill nets and by trolling. The fleet size is grossly in excess of what is needed to take this volume of catch, and the maintenance of an adequate spawning is only assured by very strict control on the type, location, and timing of commercial fishing. There are also important native American and sport fisheries. Salmon, by virtue of their market value, are always an important fish to consider in the interaction of marine mammals and fisheries. This is especially true in this area where salmon and marine mammals are both so abundant. Almost all the fish eating marine mammals in this area are known to include at least some salmon in their diets. More importantly perhaps, one of the main fishing methods, gill netting, seems particularly prone to depredation and damage by pinnipeds. Conflict in this area would seem to be quite unavoidable at present given the abundance of marine mammals, the value of the catch, and the methods of fishing.
INVERTEBRATE RESOURCES
CRUSTACEANS
Although several marine mammal species are known to feed on crustaceans, these are mostly pelagic, and there is little conflict with fisheries. The main crustacean fisheries are for king crabs (Paralithodes spp) and snow crabs (Chionectes spp), although some shrimps are also taken.
CEPHALOPODS
Reported catches of cephalopods in area 67 in 1981 were trivial, amounting to less than 5000 tonnes (FAO 1983). Voss (1973) has suggested a total potential of more than 600 000 tonnes. Fiscus (1982) has studied the predation of squid by marine mammals in this area, but in the absence of squid fisheries, interactions are not significant.
The catches in this area show an interesting split between local and foreign fleets. Japan takes the largest catch (900 000 tonnes in 1981), but most of this is made up from Alaska pollack, with smaller amounts of flatfish, Pacific cod and hake. These stocks are fished by Japanese trawlers. In contrast to this, U.S. and Canadian catches amounted to just over 950 000 tonnes, more than a third of which was salmon. The exploitation of other commercially valuable species such as crabs is also confined to the coastal states (FAO 1983, Gulland 1983).
In an area where marine mammals are said to consume more fish than the total catch by fishermen (Laevastu and Favorite 1977), interactions between the two are certain to take on great significance. In an area where salmon is also the most important catch, and where efficient gear is explicitly banned, conflict between fishermen and pinnipeds in particular, would seem inevitable.
Operational interactions
The limited number of fisheries in this area limits the number of potential gear conflicts; the salmon gill net fishery appears to be the main area of conflict, though no doubt other, less well reported cases exist in the other fisheries, especially the Canadian and U.S. coastal fisheries.
Salmon gill nets have been reported as major areas of conflict. There is often severe depredation of fish, and also damage to the gear. The marine mammals involved appear to be mainly pinnipeds, especially harbour seals and sea lions. Some incidental mortalities to marine mammals are also reported for these conflicts. Mate (1980) also reports harbour seals and sea lions affecting salmon troll fisheries in British Columbia.
Drifting scraps of monofilament net, which does not decompose are trapping and often killing what may be very large numbers of marine mammals, most notably the Northern fur seal. There are few data on this at present.
Halibut and sablefish longline fisheries are affected by sea lions taking caught fish.
Killer whales are said to frighten salmon, making them difficult to catch (Mate 1980).
Biological interactions
The problem of biological interaction between marine mammals and fisheries in this area has received considerable scientific attention, particularly from the Northwest and Alaska Fisheries Center, at Seattle. Laevastu and Favorite (1977) have estimated the amount of finfish consumed by marine mammals in the Bering Sea, which they put at around 2.4 million tonnes. Such quantities of fish consumed might help to argue strongly that competition between marine mammals and fisheries in the area is intense.
Although it has generally been agreed that the consumption of commercial fish by marine mammals represents a very large tonnage of fish, the mechanics of the competition between the two ‘predator’ groups has proved more difficult to assess. One of the few such analyses was unable to find any causal connection between an increase in fishing effort and catch by the pollack and herring fishery, and a decrease in the survival rate of one of their major predators, the Northern fur seal. Contrary to expectation, the predation on pollack was thought to have increased during the period of increased fishing.
In this area as elsewhere, competition between marine mammals and fisheries has proved difficult to demonstrate, even if it is generally accepted by fishermen and fisheries scientists alike, to be important.
Balaenoptera physalus Fin whale
Known to occur in “all seas”(Hershkovitz 1966), like most baleen whales, this species has rarely been recorded in the tropics. Soegiarto and Polunin (1982) confirm the presence of this species in the Java Sea, listing it as one of the cetacean species occurring in Indonesian waters. There are no abundance estimates, nor any information on feeding in this area. There are no apparent records of interactions with fisheries either.
Balaenoptera musculus Blue whale
Tomilin (1967) states that this species is virtually cosmopolitan, preferring the open sea, and shunning the tropics. Soegiarto and Polunin (1982) record it as present in Indonesian waters, with records from South Java and the Savu Sea. There are no estimates of abundance, nor any information pertaining to feeding. The population would seem unlikely to exceed a few hundred at most at any time of the year. Interactions with fisheries are not recorded and would seem unlikely.
Balaenoptera acutorostrata Minke whale
Recorded by Soegiarto and Polunin (1982) from the Straits of Malacca, North Sumatra, South Java and the Savu Sea. There are no obvious indications of any population estimate, feeding data or records of interactions with fisheries. The population would seem unlikely to exceed a few tens of thousands at most, at any time of the year.
Balaenoptera borealis Sei whale
Recorded by Soegiarto and Polunin (1982) from Kalimantan, Java and the Savu Sea. There are no obvious population estimates nor information on feeding for area 71 and no records of interactions with fisheries. A population estimate of many more than a few thousand might not be considered reasonable.
Balaenoptera edeni Bryde's whale
Recorded from the Straits of Malacca and the Savu Sea by Soegiarto and Polunin (1982). Once again there do not appear to be any detailed data on this species in this area. The population may presumably be less transient than other baleen whales in the area, and by comparison with other areas some fish might be eaten.
Megaptera novaeangliae Humpback whale
Townsend's (1935) charts record catches in the Marianas and in the Coral Sea. Soegiarto and Polunin (1982) also provide a sighting record for eastern Indonesia. Once again there are no detailed data on this species in this area. The population in the area would be unlikely to exceed a very few hundred at present.
Mesoplodon pacificus Longman's beaked whale
The first of only two specimens of this species was recorded from Queensland Rice and Sheffer 1968). There are no other relevant data on this species, which must be considered very rare at present.
Mesoplodon densirostris Blainville's beaked whale
Soegiarto and Polunin (1982) record this species from eastern Papua New Guinea. There appear to be no other records in this area but it is generally presumed to inhabit waters throughout area 71 (Leatherwood and Reeves 1983). There are no detailed data on this species in this area, but like all Mesoplodon species, it does not appear to be common.
Mesoplodon layardii Straptoothed whale
Watson (1981) records this species from northern Queensland. It is not known from any other parts of area 71; the population must be considered small.
(Mesoplodon bowdoini Andrew's beaked whale
If Nishiwaki's (1962) record of this species in Japan indicates a population there, then the distribution may extend through area 71 to New Zealand where it is recorded by Leatherwood and Reeves (1983))
(Mesoplodon ginkgodens Ginkgo-toothed whale
This species has been recorded in Japan and Ceylon, and so may presumably inhabit area 71 also, but as yet there are no records).
Ziphius cavirostris Cuvier's beaked whale
Known from all seas, Soegiarto and Polunin (1982) record this species from the Java Sea and the Savu Sea. There are no detailed data from area 71.
Physeter macrocephalus Sperm whale
Townsend's (1935) maps show a scattering of catches in the east, around New Guinea and on the equator (On The Line). More recently catches of this species have been made from 2 whaling villages on the Island of Lomblen, Nusu Tenggara, in eastern Indonesia. There do not appear to be any estimates of population abundance in this area, and no interactions with fisheries are reported. A population of more than a few hundred thousand may be unlikely.
Kogia breviceps Pygmy sperm whale
Generally assumed to live in tropical warm seas (Mitchell 1975 e.g.). Soegiarto and Polunin (1982) provide sightings records of this species from Kalimantan and Nusu Tenggara in Indonesia. Whilst Mitchell (1975), citing Weber (1923), states that this species was hunted, and may still be hunted by villagers in Nusu Tenggara. There are no data on abundance or feeding, but this does not appear to be a common species anywhere. Interactions with fisheries seem unlikely at present.
Kogia simus Dwarf sperm whale
Another uncommon species, Soegiarto and Polunin (1982) record this whale from the Savu Sea. There do not seem to be any detailed data from this area, and interactions with fisheries would seem unlikely.
Steno bredanensis Rough-toothed dolphin
Tas'an and Leatherwood (1983) refer to the occurrence of this species off northern Java. There do not appear to be any more detailed data than this for area 71; it is a rarely seen oceanic species, and may be considered unlikely to interact with fisheries.
Sousa chinensis Indo-Pacific hump-backed dolphin
Soegiarto and Polunin (1982) state that this species is found in all coastal, generally muddy, waters in Indonesia. Leatherwood and Reeves (1983) state that its range extends up towards Japan. Bannister (1977) records the incidental capture of this species in shark nets in Queensland, but says only that 13 small cetaceans have been recorded in nets in one area in one year. It would seem likely that this species is caught quite frequently in nets along most of the coasts of this area, but data are lacking.
Orcaella brevirostris Irrawaddy dolphin
Recorded by Soegiarto and Polunin (1982) in all coastal muddy waters of Indonesia, and in the river Mahakam in Kalimantan. Watson (1981) states that they are still fairly common throughout their range. Bannister (1977) records them in shark nets off Queensland, but it is not clear how many. Tas'an and Leatherwood (1983) describe a population in Semayang Lake, Kalimantan, which feed on carp (Cyprinidae), 14 of which were captured and transported alive to Jakarta. This species is another which seems likely to be involved in incidental captures throughout the area, but for which data are lacking.
Peponocephala electra Melon-headed whale
Recorded by Soegiarto and Polunin (1982) in the Savu Sea, Hammond and Leatherwood (1983) describe this species as common around the Phillippines. There are no obvious data on feeding for this species with fisheries. The fact that they are described as common, around the Phillippines at least, suggests that some incidental capture is most likely.
Feresa attenuata Pygmy killer whale
The range is presumed to include area 71, though the only obvious record is given in Soegiarto and Polunin (1982) as a possible sighting in eastern Nusu Tenggara. There are no data on feeding or interactions with fisheries in this area; interactions would seem unlikely at present.
Psuedorca crassidens False killer whale
Soegiarto and Polunin (1982) give a number of records of this species from throughout Indonesia. Marcuzzi and Pilleri (1971) suggest that it is pelagic and oceanic. Bannister (1977) records an unknown number which are caught in shark nets off Queensland. Harwood et al (1983) found one amongst 46 identified small cetaceans caught in the Taiwanese gill net fishery for tuna, mackerel and sharks, off Northern Australia. It is not clear if this was in area 57 or 71, but such catches are presumably likely in both areas. These incidental captures of this species in Australian waters suggest that other captures may occur in other waters of area 71, but so far have not been reported. The status of the population is unclear. Mitchell's (1975a) suggestion that it causes damage to tuna longlining fisheries may be relevant to this area.
Orcinus orca Killer whale
Soegiarto and Polunin (1982) record this species from Kalimantan and the Savu Sea. There seem to be few other records of this species in this area, although Sivasubramanian (1964) states that it damages tuna longlining fisheries throughout this area as well as the Indian Ocean. There are no abundance estimates, nor feeding data for this area, and apart from damaging tuna longlines and catch, no other records of interactions.
Globicephala macrorhynchus Short-finned pilot whale
Recorded by Soegiarto and Polunin (1982) from Java, Sumatra and the Savu Sea. Leatherwood and Reeves (1983) states that its distribution in the southern hemisphere is poorly known. No interactions with fisheries are recorded.
Lagenodelphis hosei Fraser's dolphin
Hammond and Leatherwood (1983) state that in a 100 mile radius around Cebu City, the Philippines, this was the most conspicuous species, frequently encountered, usually in large herds. They are thought to inhabit the entire area (Perrin et al 1973a). Not yet recorded in any interactions with fisheries in this area, these would seem likely in seine or gill nets, if they are as common in the rest of area 71 as they appear to be around Cebu City.
Tursiops truncatus Bottlenose dolphin
Apparently common throughout the area, it is reported in a number of gear conflicts. Tas'an and Leatherwood (1983) record the incidental capture of one individual, “accidentally netted by fishermen near Manago, northeast Sulawesi”. Harwood et al (1983) report that 36 out of 46 identified small cetaceans caught in Taiwanese gill nets off Northern Australia were bottlenose dolphins. They estimate that more than 2 000 small cetaceans are killed this way every year, a high proportion of which are presumably this species. This may have a significant effect on any local population, but there are no data published on such effects.
Grampus griseus Risso's dolphin
Reported by Soegiarto and Polunin (1982) in the South China Sea, Leatherwood et al (1983) were also informed that this species inhabits the waters around Penang. There are no indications of abundance in area 71, apart from general comments that they are ‘relatively common’ (Watson 1981). No interactions with fisheries are apparent in this area.
Stenella longirostris Spinner dolphin
Known to occur throughout the area, Tas'an and Leatherwood (1983) report the incidental capture of 9 in the Java Sea, adding that they are generally found away from shallow coastal waters. Harwood et al (1983) report the presence of 6 of this species out of 46 identified cetaceans in gill nets off the north Australian coast. They estimate that more than 2 000 small cetaceans are caught in this way every year. Bannister (1977) states that at that time no purse seining on dolphin associated tuna was carried out in Australian waters.
There are no other apparent cases of this species interacting with fisheries in this area, but as inshore fisheries are known to include it as a by-catch in India (Jones 1976), such incidents cannot be ruled out in this area, which also has extensive inshore fisheries.
Stenella coeruleoalba Striped dolphin
Although recorded by Soegiarto and Polunin (1982) in the Java and Savu Seas, there do not appear to be any reported interactions with fisheries in this area, nor any indication of population abundance.
Stenella attenuata Spotted dolphin
Hammond and Leatherwood (1983) report sightings, on half a dozen occasions, groups of 2 – 800 spotted dolphins off Cebu in the Philippines. This species has been reported in small numbers (3 out of 46 identified cetaceans) in the gill net fishery off North Australia. There are no indications of abundance, but this is generally a common species. There are no other obvious recorded interactions with fisheries in this area.
Delphinus delphis Common dolphin
Seen in the Straits of Malacca by Leatherwood et al (1983), this species does not appear to have been recorded in any incidental captures in this area, although this might seem likely. There are no indications of abundance, but elsewhere this seems to be a common species. There are no indications of diet in this area either.
Neophocaena phocaenoides Finless porpoise
Leatherwood and Reeves (1983) state that this species is distributed in coastal waters throughout Indonesia, and northwards to Japan. Tas'an and Leatherwood (1983) record 2 individuals caught accidentally in gill nets off northern Java. For such a coastal species it would be surprising if more such interactions were not recorded. Leatherwood and Reeves (1983) state that the diet consists of small squid, prawns and shrimps, as well as small fish.
Dugong dugon Dugong
Known to occur throughout most of this region (Bertram and Bertram 1973), the Dugong
population has been seriously affected by accidental mortalities in gill nets. Soegiarto and Polunin (1982) state that “Indonesia remains an important refuge for the dugong in southern Asia. There is little information on its populations, for as everywhere it is an elusive and sensitive animal”. About 1 000 animals are taken per year around the island of Aru in eastern Indonesia (Compost 1980). Heinsohn (1972) states that after the introduction of shark nets around a number of bathing bays in Queensland, 158 dugongs were caught between 1964 and 1971. The Magnetic Island population was almost completely destroyed in one year. This exemplifies the effect which gill nets can have on this species throughout its range. Marsh et al (1984) estimate more than 1 000 dugongs may be taken accidentally in inshore and estuarine gill net fisheries for barramundi and threadfin bream in northern Australian waters.
There is almost no information on the feeding habits of species of marine mammal in this area, and so it is difficult to relate marine mammal feeding to fisheries in this area.
There are six species of baleen whale known to occur in this area, but almost nothing is known of baleen whale feeding in the tropics, if indeed there is any; Bryde's whale is the possible exception. Leatherwood et al (1983) report seeing one individual eating mackerel near Sri Lanka, and presumably fish may be eaten in this area also.
Of the 24 other marine mammals listed above, 6 are beaked whales which are generally presumed to feed on squid, as are pilot whales and sperm whales. Dugongs consume sea grasses, and the finless porpoise is said to eat shrimps and prawns as well as small squid and fish (Leatherwood and Reeves 1983). Leatherwood et al (1983) suggest that Irrawaddy dolphins eat catfish.
The diets of the remaining 14 species are conjectural.
DEMERSAL FISH RESOURCES
The total recorded demersal catch was just over 0.5 million tonnes, but as Gulland (1983) points out, catches may be under-reported especially in scattered rural communities fishing in the coastal zone. The coastal and shallow water stocks are probably heavily fished, especially off densely inhabited coasts, but many deepwater stocks are probably still only lightly fished. The total catch is made up of a very great number of species, most of which are grouped by genus or family in any fishery statistics. Most fishing in the area is small-scale with a few trawlers, notably in the Gulf of Thailand (Gulland 1983).
Gulland (1983) states that there is a broad similarity in the species composition of the catch throughout the area. In the Gulf of Thailand this consists of 200–300 or more species (Tiews 1973). The demersal community consists of a number of small species, ‘trash fish’, a variety of intermediate sized species, and larger predatory fish, which fetch higher prices. Gulland (1983) amongst others has noted the change in species composition which results when such communities are heavily fished.
LEIOGNATHIDAE
Slipmouths and ponyfish, these are amongst the smallest of the commercially caught non trash fish. They feed on small bottom dwelling invertebrates in shallow water. Reported catches have been relatively stable at around 100 000 tonnes for at least six years throughout area 71. In the Gulf of Thailand, however, the introduction of a trawl fishery in the 1960's lead to a shift in species composition, in which the total catch of these species declined dramatically (Ritragsa 1974).
Other medium sized fish include the threadfin breams Nemipteridae, monocle bream Scolopsis, and red mullets Mullidae, all of which feed mostly on bottom dwelling invertebrates and are prey for larger fish. Reported catches of these 3 groups totalled about 90 000 tonnes in 1981 (FAO 1983).
The larger, predatory, fish include snappers and groupers which fetch higher prices than the smaller fish, and may be caught by selective means, such as hand lines (Gulland et al 1974).
Many of the stocks of demersal fish may be over exploited at present (Gulland 1983) but there are considerable difficulties associated with assessment, notably the problems arising from catches with hundreds of species. Gulland suggests that some of the deeper water stocks are under-exploited, but are out of reach of inshore fishermen. The use of trawlers is not always possible in such situations, when competition with small scale fishermen arises. For this reason Indonesia has banned trawling in her waters (Keppres No. 3/1980 and Inpres 11/1982 : Indonesia Times 14.8.1982).
The effects of exploitation of demersal fish stocks, especially the effects of species changes, are difficult enough to assess. The problem of trying to assess the extent of interactions between marine mammals and fisheries would seem intractible in this region at present, not least because of the lack of data on marine mammal feeding.
PELAGIC FISH RESOURCES
The catch in 1981 of all pelagic species is recorded as just under 2.5 million tonnes. Once again, there is a problem of species identification. Some stocks may already be heavily fished, whilst others could sustain substantially greater catches.
Sardinellas, Decapterus species and Indian mackerels (Rastrelliger spp.) are all important components of the pelagic catch, each group yielding more than 200 000 tonnes in 1981.
Other important species include tunas which, taken together, yield catches in excess of 500 000 tonnes in this region.
Again, there are difficulties involved in trying to assess potential interactions between marine mammals and fish stocks when the diets of marine mammals are unknown, and when stock assessments are also problematic. Gulland (1983) suggests that some of the mackerel stocks are over-exploited, whilst many of the scad (Decapterus spp.) stocks may yield greater catches.
INVERTEBRATE RESOURCES
CRUSTACEA
Shrimps and prawns play a large role in the fishing economics of most nations in this area. In Indonesia banana prawns (Penaeus merguiensis) accounted for 54 000 million rupiahs in 1979, more than twice the value of any other species (Indonesia, Fishery Statistics 1981).
The fisheries for crustacea are conducted both by trawl and by a variety of other artisanal gears. The state of the stocks is not clear, but in general they may be fully exploited already (Gulland et al 1974). The implications of this for marine mammals such as Neophocaena are also unclear.
CEPHALOPODS
The total cephalopod catches in 1981 were about 150 000 tonnes in 1981 (FAO 1983), but there does not appear to be any published estimate of the cephalopod potential of this area.
According to Gulland (1983) these are chiefly artisanal, with the notable exception of the Gulf of Thailand trawl fishery. Artisanal gear includes a variety of local seine nets, as well as the more usual hand lines, beach seines, shrimp nets, lift nets and a variety of traps.
Artisanal fisheries are chiefly confined to a narrow coastal strip, upto 12 miles from land. This area is also the zone of highest fish density, and where larger vessels occur, they too tend to fish close in to the shore, where stocks are densest. This leaves a very uneven distribution of effort, implying an uneven pattern of exploitation.
For offshore marine mammals this uneven distribution of fishing effort may be advantageous, with less interaction, operational or biological, than might be expected if the fishing effort were more evenly spread out. Inshore, coastal or neritic species of marine mammal however, would seem to be more likely to conflict with fisheries. Not only would a zone of heavy fishing, mostly with artisanal gear, imply a large number of by-catches of marine mammals, but the local depletion of fish stocks mentioned by Gulland (1983) could also bring such coastal species into a situation of ‘biological conflict’, through reduced prey biomass.
All the fishery interactions reported in this area are operational in nature, which is perhaps not surprising in an area which is one of the 4 most productive fishery areas in the world (Gulland 1983), where almost all fishing is performed by small scale coastal fisheries.
Operational interactions
A long-range gill net fishery off northern Australia, catching mackerel, sharks and tuna is known to take a by-catch of small cetaceans of 46 identified individuals. 36 were Tursiops truncatus, 6 were Stenella longirostris, 3 were S. attenuata and l was Pseudorca crassidens. The total number of small cetaceans taken in this fishery is estimated at more than 2 000 per year. (Harwood et al 1983).
Sivasubramanian (1964) has claimed that killer whales damage tuna longlines and catch throughout the area.
Shark nets in Queensland take a number of species including dugongs, bottlenose dolphins, Irrawaddy dolphins, humpback dolphins and at least one false killer whale
(Bannister 1977).
Gill nets in northern Java are known to take some finless porpoises (Tas'an and Leatherwood 1983).
One bottlenose dolphin has been reported netted accidentally in Sulawesi.
Biological interactions
None are reported, although in the coastal zone, where many fish stocks are heavily exploited, some degree of overlap in prey species might be expected.
