5. POTENTIAL FISHERY RESOURCES AND PRESENT STATE OF EXPLOITED STOCKS

5.1 NOMINAL CATCH DATA

The present system of collecting fishery statistical data was initiated in 1978. The Bureau of Fisheries (Monrovia) has since then tried to improve on the system. The major constraints to establishing a viable data base have been:

1. availability of adequate financial means; and

2. lack of trained manpower to be deployed in various fish production centres.

Fishery data of long-time series are not readily available. The exact catch magnitudes of both the artisanal and industrial sectors are not known because of inadequate sampling of the marine landings along the Liberian coast. The present total annual marine catch estimate is put at less than 12 000 t (FAO, 1986).

The artisanal fishery uses purse-seines, beach-seines, gillnets, lines and hooks to catch 1 000–2 000 t fish of which about 60% are coastal pelagics (with about 50% of Sardinella). Tuna, billfish and bonito account for about 10% of the artisanal catch. The other major fish species groups exploited by artisanal fishermen are barracuda (5%), soles (5%), croakers (5%), and sharks and rays (4.5%). The magnitude of artisanal catch and the species composition are illustrated in Table 9.

The industrial fishery mostly exploits demersal fish and shrimp. The major finfish species groups caught by the industrial fleet are soles, seabreams, croakers, threadfins and African sicklefish (Drepane) as shown in Table 10. This species composition indicates that the main community exploited is the coastal sciaenid community.

Available data indicate that shrimp catches dominated the industrial fisheries in the early 1970s. whereas finfish dominated the catches in the late 1970s. The estimated catch and importance of various species harvested by artisanal and industrial fishing fleets are given in Table 11. Mesurado Fishing Company landed substantial magnitudes of imported finfish during 1970–1980 as illustrated in Table 12. Historical trends in mean annual catch of shrimp in Liberian waters are given in Table 13.

Available catch data indicate that fish production of the industrial sector is almost twice that of the artisanal fishery. It is estimated that the 200 registered canoes catch about 1 000 t of fish. Thus the catch rate of a canoe is about 5 t/year. Assuming each canoe fishes for at least 200 days a year, the average catch per canoe per day would be 25 kg. Marchal (personal communication) gives much higher estimates of artisanal and industrial marine catch statistics (metric tons) for Liberia for the period 1981/1983, viz.

Dioury (1983) gives the following estimated marine catch magnitudes:

1. coastal artisanal fishery 2 140 t;

2. Liberian industrial fishery 5 500 t; and,

3. foreign industrial fishery 2 330 t.

The total reported annual marine catch for the years 1983, 1984 and 1985 was 11 277 t, 10 650 t and 7 478 t respectively (FAO, 1987).

5.2 CATCH PER UNIT EFFORT (CPUE) DATA

Information of fishing effort expended by artisanal fishermen to obtain a certain quantity of fish is scanty. In most instances only total weight of catch and the value of fish are recorded. Information on number of gillnets, castnets, hooks, beach-seines, etc., used is still inadequate. Additionally, there are no data in Liberia, on catch rates and discards from shrimp trawlers or other major gears operated by the industrial fleets, but the discards are likely to be considerable. Reliable data on separate catch and effort magnitudes in the creeks, estuaries, coastal lagoons and inshore waters are still lacking.

Fishing effort data of the Liberian industrial fleet can be derived from the list of trawlers and shrimpers licensed to fish, but there are no long-time historical data on the actual number of vessels which have fished in a particular period. Neither is there reliable information on the extent of fishing. Inferences on the evolution of fishing effort for the finfish trawl fishery can be made from Table 14; whereas trends in catch, effort and catch per unit effort of the industrial shrimp fishery are shown in Table 15. Additionally catches and catch rates of the industrial finfish trawl fishery are illustrated in Table 16. The variation in monthly catches and catch rates of the industrial finfish trawl fishery is given in Table 17.

5.3 BIOMASS AND POTENTIAL ESTIMATES OF FINFISH SPECIES

The estimates presented are based on the results of several acoustic and exploratory fishing surveys which have been conducted in Liberian waters. Acoustic surveys have enabled the study of bottom types, distribution of species by depth and determination of biomass by species groups. Exploratory fishing has facilitated determination of species composition, total catch magnitudes, vital biological factors of available species, rates and catchability. Finally, the exploratory surveys have provided information observations on temperature, salinity, dissolved oxygen levels and turbidity, all of which affect the distribution of fish. A summary of information concerning various surveys conducted on the continental shelf of Liberia is given by Van der Knaap (1985) and shown in Table 18. The source of information to all scientific expeditions listed in the same table are shown in the bibliographic references of this report.

Williams (1968) gives details of the major regional fishing survey (the Guinean Trawling Survey). This survey covered the West African region from Dakar (Senegal), to the Angolan border using standard fishing methods. Prior to this, the Centre de Recherches Océanographiques (Abidjan) conducted a modest trawl survey of Liberian waters during 1964 and 1965. The West Africa Fisheries Research Institute at Freetown did some trawl surveying with the CAPE ST. MARY in northern Liberian waters, and the Polish fisheries research trawler BIRKUT is also known to have conducted a few trawl stations in Liberian waters (Williams, 1968).

The Guinean Trawling Survey used 600 HP side trawlers. The results of the survey are given in Table 19 and 20. Maximum catch rates of commercially desirable species were found in depths of 30 to 40 m, which coincide with depths of maximum shrimp catches. At greater depths, catches of 0.5 t/h were obtained in the northern region in depths of 70 to 100 m, but the fish caught (mainly Brachydeuterus) are of minor commercial value.

In the inshore waters (less than 50 m) catch rates in the north were higher than those in the south; similarly in offshore waters (greater than 70 m), catch rates in the north were higher than those for the south (Williams, 1968).

After the Guinean Trawling Survey, an exploratory fishing survey was undertaken (Anon. 1978) by a Romanian vessel of the Polish B-22 class (88 m, 2 500 HP) belonging to the Interprindeua de Pescuit Oceanic of Tulcea. This vessel was supposed to fish in deeper waters and deliver its landings to Mesurado in Monrovia. But there are no reported accounts on the performance of this vessel.

During January and February of 1981 a trawl survey was undertaken by the USSR using the research trawler BELOGORSK, a partly-converted vessel of the Tropik class (80 m, 1 340 HP). This survey lasted 19 days. Trawls were made down to a depth of 300 m. Catch rates were quite variable: from 10 to 10 000 kg/h tow, with an average of about 840 kg/h tow. It is estimated that in the depth range 20–100 m, average catch rates ranged from 398 to 726 kg/h. It is reported that catch rates were high near the shelf edge (200 m). The Soviet report gives the following biomass estimates of some demersal species (ATLANTNIRO, 1981):

This list shows that the traditional fishing grounds for coastal sciaenid community were not sampled and the biomass estimates cannot be compared to the landings to estimate fishing pressure. In addition the calculations usually assume that the trawl catches all the fish present in its path. This is not entirely true and the biomasses given should be considered as minimum estimates.

Acoustic surveys, the conventional method for estimating stock sizes of small pelagic fishes, were conducted as part of the USSR/Liberia BELOGORSK programme and the Norwegian DR. FRIDTJOF NANSEN regional programmes but the species whose biomasses were estimated by ATLANTNIRO (1981) do not include the coastal sciaenids. The estimates are for deepwater demersal species only.

The BELOGORSK survey (ATLANTNIRO, 1981) reported sonifying dense schools, 40 m in vertical extent, in the area off Blo at a depth of about 60 m. Catch rates from these schools of 3 t/30 min of Sardinella aùrita were obtained. Similar smaller schools off Vedabo consisted of small scombrids, cuttlefish, S. aurita, and Decapterus spp. ATLANTNIRO (1981) reports the following biomass estimates:

Biomass estimates based on the 1981 DR. FRIDTJOF NANSEN survey in Liberian waters (FAO, 1984) are given below:

The mean density for the surveyed area of the continental shelf is 24 t/n.mi².

The estimated biomass for Liberia is less than that of neighbouring Sierra Leone and Côte d'Ivoire, viz.

The duration of the acoustic surveys conducted by the Soviet and Norwegian expeditions was short, being 3 days for the entire Liberian coast in each expedition. This raises a quesion on the variability of the estimates. Seasonal variability is expected for these pelagic species. It is therefore not easy to determine accurately future fish yields from such short surveys.

5.4 POTENTIAL OF DEMERSAL FISH SPECIES

The results of various trawl surveys indicate scarcity of demersal fish in Liberian waters. Domain in Troadec and Garcia (1980), using biomass estimates based on the Guinean Trawling Survey (GTS), derived a maximum potential yield of 9 000 t excluding Brachydeuterus. FAO (1978) gives an estimated potential of 14 000 t/year based on the work of scientists in Liberia. Dioury (1981) using comparative figures of Sierra Leone and Côte d'Ivoire put the potential of Liberian demersal fish at 15 000 t. The total annual catch of demersal fish species is about 6 400 t.

It is difficult to determine the expected potential increase of the Liberian demersal fishery as data are lacking on fish by-catch of shrimpers and demersal catch taken by other countries fishing on the Liberian continental shelf.

5.5 POTENTIAL OF COASTAL PELAGIC FISH SPECIES

The estimated standing stock of the coastal pelagic fish in Liberian waters is put at 43 600 t (ATLANTNIRO, 1981) and at about 94 200 t (Stromme et al., 1982; FAO, 1984). The present annual catch of pelagic species is about 3 600 t (according to records available to FAO and CECAF). It should also be noted that the estimated biomass of coastal pelagic fish consists of Clupeidae, Engraulidae and Carangidae.

An unbiased estimate of maximum sustained yield (MSY) is given by Garcia, Sparre and Csirke (in preparation),

where M = natural mortality, B = estimated biomass, and Y = catch.

There are no good estimates of M for various carangids and clupeids in Liberian waters but considering estimates of M for these two species groups in adjacent tropical waters, the average natural mortality for coastal pelagic fish should be about 0.85 (Burgess et al.). According to Caddy (personal communication), the small clupeids have a natural mortality rate of about 1.0 whereas for the medium-sized carangids M is approximately 0.7.

Using the ATLANTNIRO (1981) biomass estimate of 43 600 t and a catch of 3 600 t, it can be shown with equation (1), that the MSY of coastal pelagic fish is 19 000–20 000 t.

Using the pelagic fish biomass of 94 200 t determined by Strømme et al. (1982), and a catch of 3 600 t, then the MSY is about 41 000 t.

Considering that MSY is of the order of 19 000–41 000 t and that the present-day catch of pelagic fish (Y) is less than 3 600 t, there are still good prospects for developing both artisanal and industrial pelagic fisheries in Liberia.

In the situation of Liberia, where the present-day annual catch of pelagic fish is still a small portion of the biomass (B), the Gulland (1971) equation, MSY = 0.5MB, leads to similar estimates of the MSY.

5.6 POTENTIAL OF THE COASTAL PENAEID SHRIMP FISHERY

Data on fishing effort of shrimpers is very scanty. In most cases only numbers of vessels fishing are recorded. There are few data on fishing trips, steaming time, searching time and duration of tows. Estimates of annual catch rates, only based on number of vessels operating at a given season, leads to biased estimates of effort and its evolution with time.

The time spent trawling is the ideal measure of fishing effort. If the vessel switches from one fishing ground to another, the time spent at sea increases and the catch per day at sea drops. But the catch per haul per hour may still be high.

The fishing power of a trawler is assumed to be linearly related to the vessel's engine power. Vessels which have mostly operated in Liberian waters have had two power ratings: the 335 HP (251 kW) and the 365 HP (274 kW). One can assume that the 335 HP vessel is 0.92 of the 365 hp vessel in fishing power. The characteristics, particularly engine power of some vessels which have operated in Liberian waters, are given in Table 21.

On the basis of vessel power rating given in Table 21, Burgess Management Associates (1984) estimated the number of 365 HP vessels which have operated in Liberian waters during the period 1971–1981 and shown in Table 22.

Everett (1976) states that in 1970 Mesurado had three chartered Swedish vessels and bought five 343 HP vessels; in 1971 they operated seven vessels. Continental Seafoods took delivery of six (Bassi-class) trawlers in early 1971, which Everett reported as having 343 HP (D343 Caterpillar) engines. Everett notes that these boats made initial fishing trips and caught perhaps 30 t each per year. Further, other Bassi-class trawlers operated by Continental Seafoods elsewhere (e.g., NEWEBE IV) were rated at 385 HP (at 1 250 rpm), so some uncertainty as to their exact power exists. Pease (1972) described the Liberian shrimp fleet as consisting of 12 Mesurado vessels, 15 Greek - owned vessels, and 10 US vessels, that is a total of 37 vessels.

During 1979 and prior to the April 1980 civil disturbances, Continental Seafoods operated 12 shrimpers and Mesurado operated 12 vessels. In December 1980 Continental Seafoods sold their Liberian fleet to Sierra Fishing Company of Freetown. After April 1980, the policy of the Liberian Government emphasized more the supply of finfish to the Liberian people and Mesurado switched to finfish trawling. By 1981 shrimping in Liberian waters was negligible. The decline in shrimp catch is illustrated in Tables 13 and 22.

The logistic (surplus production) model has been used by FAO (1977), Garcia (1977) and Garcia and Lhomme (1980) to estimate maximum sustainable yields (MSY) of shrimp for various sectors of the CECAF region. The reliability of surplus production model is affected by unstable shrimp stock structure and varying environmental factors affecting recruitment.

Assuming that Liberian shrimp stock is independent of that of Sierra Leone, Shotton (1982, 1983) and Burgess et al. (1984) give estimates of maximum economic yield (MEY) of the Liberian shrimp fishery. According to Shotton (1983), maximum economic rent for the Liberian shrimp fishery would be generated with a fleet size of fourteen 365 HP trawlers. This fishing effort would result in an MEY) of 800 t with a landed value of US$ 5.7 million and an MSY of 1 200–1 600 t for Liberian waters. Assuming, on the contrary, that Liberian and Sierra Leone stocks are mixed, FAO (1977) gives an MSY of 1 870 t with a catch rate of 13.9 kg/h for the whole area. Considering the 1983 total catches of shrimp by Sierra Leone and Liberia of about 2 300 t, this estimate is somewhat low. There is a need for more CPUE data to verify these estimates. The analysis is even made more difficult by the interaction of the Liberian shrimpers fleet with shrimpers from Côte d'Ivoire and Sierra Leone as the origin of the shrimps landed is not always easy to ascertain. Côte d'Ivoire catches at least 500 t of marine shrimp per year. Hence, the combined catch of shrimp by Sierra Leone, Liberia and Côte d'Ivoire in 1983 was about 3 000 t.