Available data indicate that the distribution of a number of species is limited by the depth of the thermocline and is influenced by the type of bottom deposits (sand and silts) and also the depths of the continental shelf, the slope of which is variable. There are discreet ecological fish communities each of which is fairly homogenous. However, there is also ecological and microgeographical heterogenity of fish communities. Migration of cohort species from the estuaries and creeks to the open shelf areas and vice versa also occurs. The distribution patterns of species assemblages or communities on the continental shelf of Liberia are shown in Figures 7a, 7b and 7c.
The following fish communities are exploited by the various fishing units:
the coastal suprathermoclinal sciaenid community (on soft deposits). This community presents a particular “estuarine” facies very close inshore and in the creeks;
the coastal suprathermoclinal sparid community (on sandy and harder substrates);
the eurybathic fish species;
the deep shelf community and continental slope community.
The sciaenid community inhabiting the estuaries and creeks consists of Pseudotolithus elongatus, Polydactylus quadrifilis, Pomadasys jubelini, Drepane africana, Arius spp., Cynoglossus spp., Ilisha africana, Ethmalosa fimbriata, Penaeus duorarum notialis, Parapenaeopsis atlantica, Trichiurus lepturus and Sphyraena spp.
The dominant elements of this fish community are: Pseudotolithus senegalensis and P. typus (Sciaenidae); Galeoides decadactylus and Pentanemus quinquarius (Polynemidae); Pomadasys jubelini (Pomadasyidae); Drepane africana (Drepanidae); Arius spp. (Ariidae); Cynoglossus spp. (Cynoglossidae); Ilisha africana, Ethmalosa fimbriata (Clupeidae) and Parapenaeus atlantica.
The dominant species are Sparus caeruleostictus), Pagrus ehrenbergi, Pagellus belottii, Decapterus punctatus, Dentex spp. and Epinephelus are common on the sand and rocky bottoms in the inshore suprathermocline areas.
According to Villegas and Garcia (1983) the coastal reefs and shallow Holocene coral banks (above the thermocline are occupied by this community dominated by Lutjanus spp. They pointed out, however, that this community which is of particular interest to artisanal fisheries has never been well sampled and described by preceeding studies based on trawl surveys.
The deep - water sparid community which occurs on both sandy and muddy bottoms below the thermocline, down to the edge of the continental shelf includes: Dentex angolensis ( = Dentex polli), Priacanthus arenatus, Pagellus bellottii, Boops boops, Epinephelus aeneus and Arioma ledanoisi (particularly abundant in Liberia) and Balistes capriscus. This community occupies probably also the Holocene fossil coral banks which line the continental shelf; and towards the edge of the shelf Epinephelus aeneus is more abundant (Villegas and Garcia, 1983).
The fish species with a large depth distribution range on the continental shelf of Liberia are: Cynoglossus, Vomer setapinnis, Brachydeuterus auritus, Trichiurus lepturus, Raja spp., Penaeus notialis, etc. It should be noted that this eurybathic fish species group is harvested both by the artisanal fishermen and the industrial fleet. But there is no proper documentation on migration patterns of species constituting this fish group.
There is a somewhat diverse pelagic fishery resource (Okera, 1976; Longhurst, 1983). the coastal pelagic fish species include Caranx, Sphyraena, Cybium, Trichiurus, Sardinella, Ethmalosa, Chloroscombrus, Vomer, Ilisha africana, etc.
The species are:
| (a) Deep shelf community | Illex coindetii, |
| Squalus fernandinus | |
| and Squatina oculata; | |
| (b) Continental slope community | Hypoclidonia bella, |
| Chlorophtalmus atlanticus, | |
| Synagrops microlepsis, | |
| Merluccius polli ( = M. | |
| cadenati) and Paracubiceps multisquamis |
This fish community is not exploited by national fisheries because of its low level of profitability.
Most clupeid species are marine but some anadromous shads (Ilisha) and bonga (Ethmalosa) are adapted to withstand low salinities, particularly in the rainy season.
(a) Ethmalosa fimbriata ( = Ethmalosa dorsalis) (bonga)
Ethmalosa (bonga) is an important clupeid species in the inshore waters of Liberia. Bonga is more euryhaline than the flat sardine and it occurs in estuaries and on the continental shelf as well as in lagoons. This species prefers warm turbid waters. It is dominant in inshore areas without upwelling but with strong surface desalination. Its migrations seem small in extent and limited to estuaries and adjacent coastal areas (Longhurst, 1960).
Ethmalosa is a non-selective filter feeder subsisting mainly on large diatoms and phytoplankton. Salzen (1958) gives detailed information on the biology of bonga.
Migration of bonga into and out of the estuaries is associated with seasonal changes in salinity as well as with abundance of plankton in the estuary during the dry season. For example, Ethmalosa is most abundant in the Liberian rivers during the period November-April. As the dry season progresses, the species move further up the river and then during the wet season (May-October) again moves down the estuary toward the sea. The migration is probably due to environmental factors and is linked with spawning and feeding needs.
(b) Sardinella aurita (round sardine)
Sardinella aurita occurs almost throughout the CECAF area. It is a coldwater species extending to the shoreline. The species schools near the surface during upwelling and retreats below the thermocline up to a depth of 300 m during the hot season (ATLANTNIRO, 1980). Sardinella aurita occurs on the continental shelf of Liberia. However, there is no dense concentration of round sardine in the Liberian sector because of the absence of coldwater upwelling.
(c) Sarinella eba (flat sardine)
Sardinella eba prefers warm waters with a temperature above 24°C and appears to avoid turbid waters. Spawning is more or less continuous throughout the year but there is a period of maximum reproduction which should be during the hot season in Liberia and Côte d'Ivoire.
The young fish are concentrated in the coastal waters from where they gradually move off as they grow older; but the stratification toward the open sea with age is never so clearcut as it is for the Sardinella aurita (Boely, 1979), and the great majority of the adults remain confined over the shallow half of the continental shelf.
(d) Ilisha africana (shad)
Shad is an anadromous clupeid species inhabiting inshore waters, sandy beaches and estuaries (in almost fresh waters). The species feeds mostly on crustaceans and small juvenile fish.
It may be caught at the surface or near the bottom down to about 25 m. Hence it can be a target species for beach-seine, gillnet, purse-seine and inshore trawl fisheries. It is common in the CECAF coastal areas between Sierra Leone/Liberia and Congo.
The following carangids occur in the waters of Liberia: jacks, crevalles, scads, bumper, pompanos and blue runners. There are mostly schooling species distributed on the continental shelf but some occur in brackish waters especially when young.
(a) Caranx spp. (various jacks)
Caranx spp. have wide distribution along the West African coast from Senegal to Angola. Some species inhabit inshore waters and estuaries and others are located in deeper waters (over 100 m depth). Hence, this fish group can be vulnerable to both artisanal and industrial fishing fleets. Caranx spp. feed mainly on small fish, shrimps, some crabs and other invertebrates. This fish species group is caught by pelagic and bottom trawls, seines, set gillnets, ring-nets and sometimes on line gear.
(b) Chloroscombrus chrysurus (Atlantic bumper)
Chloroscombrus chrysurus (Atlantic bumper) occurs along the West African coast from Mauritania to Angola. This schooling pelagic species inhabits the Liberian continental shelf at depths of 10–15 m. It also occurs in estuaries and mangrove-fringed lagoons and brackish water areas. Atlantic bumper can be a target species for the canoe fleets using set gillnets and seines as well as for the industrial fleets using trawls. Fishing grounds for this species are located on the continental shelf at depths of 10–50 m.
(c) Decapterus rhonchus (-Caranx rhonchus) (false scad)
Decepterus rhonchs (false scad) is a schooling carangid inhabiting near-bottom waters mostly between 30 and 50 m but can also be located in waters over 200 m depth. This species makes seasonal migrations. Results of the joint USSR-Liberia fishery investigations conducted in 1982 indicate denser aggregations of Decapterus from September to March and in areas with water temperature 15°–22°C. Incidentally, during the same period massive spawning occurs at depths of 10–30 m.
The croakers, drums and meagres are the most important sciaenid species in Liberia. This fish species group is primarily marine but also occurs seasonally in brackish water areas. Most of the species inhabit sandy and muddy bottoms in coastal areas with large river flows.
(a) Pseudotolithus (Pseudotolithus) senegalensis (Cassava croaker)
Pseudotolithus (Pseudotolithus) senegalensis occurs along the West African coast between Morocco and Angola, but is rare north of Senegal. It inhabits mud, sandy and rocky bottoms from the shoreline to 70 m depth; the smaller and younger ones prefer shallow waters and move to midwaters when bottom temperature falls below 18°C. Pseudotolithus, senegalensis occurs in similar habitats as Pseudotolithus (Fonticulus) elongatus. The two species are jointly harvested by artisanal and industrial fisheries, using set gillnets, beach-seines, longlines and bottom trawls.
(b) Pteroscion peli (Boe drum)
Pteroscion peli occurs only along the West Coast of Africa from Senegal to Angola, where it is found in midwaters as well as on mud and sandy mud bottoms. Its depth distribution extends from the shoreline to 200 m but the species prefers waters of less than 50 m. Pteroscion is more abundant in the northern sector of Liberia than in the south. This species is an important element of trawl catches.
(a) Galeoides decadactylus (lesser African threadfin)
Galeoides decadactylus does not appear to penetrate below the thermocline. It occurs in inshore waters adjacent to sandy beaches. The species is known to develop female gonads by passage through a nonfunctional hermaphroditic stage arising from a normal male (Longhurst, 1965). Hence understanding its reproductive and recruitment strategy is important in order to forecast the effect of fishing on the reproductive potential of stocks whose females could be reduced below critical level by fishing.
Galeoides prefers silty and sand-silty bottoms. It is a semi-diadromous fish with spawning migration into estuaries and lower reaches of rivers. There are two spawning seasons:
the dry season with a smaller spawning stock (March-June) when salinity is high; and
the rainy season with a greater spawning stock (June-December) when temperatures and salinities are lower.
Galeoides decadactylus feeds on benthic organisms such as Crustacea and Polychaetes. Although the species is not abundant in Liberia, it is still a target species for the artisanal fishery using gillnets and beach-seines as well as the industrial fleets employing trawls in the inshore areas.
(b) Pentanemus quinquarius (royal threadfin)
Pentanemus quinquarius has a normal reproductive cycle. It occurs on sandy bottoms down to a depth of 50 m. It is caught by the artisanal gillnet fishery on near shore sandy bottoms; but the species is also harvested offshore by the industrial fleet using trawls. Additionally, Pentanemus can be caught with beachseines.
(c) Polydactylus quadrifilis (giant African threadfin)
The giant African threadfin (Polydactylus quadrifilis) can grow up to lengths from 150 cm to 200 cm. The species inhabits inshore and offshore sandy bottoms up to a depth of 50 m. It also occurs in estuaries and lagoons fringed by mangrove.
This fish species is jointly harvested by the arti sanal and industrial fleets. Its attractive marketable size makes it extremely vulnerable to the gillnet and beach-seine fisheries.
The adult seabreams mostly occur in fairly deep waters of the continental shelf and off the slope. The small young individuals do occur in shallow waters but mostly at a depth greater than 15 m, forming aggregations. The adult seabreams are more solitary. The most common species are Dentex angolensis and Pagellus bellottii. The seabreams are mainly caught by industrial trawler fleets operating in Liberia. Many species are hermophroditic (having both male and female gametes). Sometimes the majority of individuals are male at first maturity and the females appear later (protandric hermophroditism). In Dentex angolensis, the females are more numerous at first maturity and the males appear later (protogynic hermophroditism). Since protogynic hermophroditism is associated with efficient utilization of food resources and parental care, it could possibly enhance the resilience of exploited sparids species such as Dentex angolensis.
(a) Dentex angolensis (Angola dentex)
Dentex angolensis occurs along the West African coast from Morocco 33°N to Angola. It inhabits various bottoms on the continental shelf and the slope from about 15 m to about 300 m depth. It is a protogynic hermophrodite with most individuals beginning as females and changing to males at a length of 18–23 cm. This particular reproductive behaviour should give the stock a better resilience to fishing.
Dentex angolensis is known to occur on the Liberian shelf but the species is not an important element of the artisanal fisheries. It is caught by the trawl fishery but separate statistics are not yet available. Angola dentex is carnivorous and feeds on crustaceans, small fish, molluscs and other invertebrates. It can be caught in bottom trawls, bottom setnets and longlines.
(b) Pagellus bellottii (red pandora)
Pagellus bellottii occurs in the CECAF sector extending from the Straits of Gibraltar to Angola and also around the Canary Islands. P. bellotti inhabits hard and sandy bottoms and is mostly caught in bottom trawls, traps and hooks on line.
(c) Sparus caeruleostictus (- Pagrus ehrenbergii) (bluespotted seabream)
Sparus caeruleostictus inhabits hard bottoms with rocks and rubble up to 150 m depth. The bigger and older individuals prefer the deeper waters whereas the younger fish live much more inshore. The species attains sexual maturity at about 2 years. The species makes spawning migrations parallel to the coastline.
The bluespotted seabream is carnivorous and feeds on bivalves, crustaceans and fish. In Liberia and Sierra Leone the species has been observed in association with flying gurnards (Dactylopterus) and the driftfish (Arioma) (ATLANTNIRO, 1983). The bluespotted seabream can be caught with bottom trawls, seines and traps.
The grey triggerfish (Balistes capriscus) is not abundant in Liberian waters. It occurs in two big concentrations in the sectors Guinea-Sierra Leone and Côte d'Ivoire-Togo respectively. The two populations seem to be separated by the Liberian sector.
In summer during the rainy season, aggregation of the Guinea stock of Balistes capriscus mostly occurs north of Sherbro Island (Sierra Leone). In the dry season (winter) the species migrates southward and forms some structure of individual schools in northern Liberia near the border with Sierra Leone.
Balistes capriscus can attain a maximum length LMAX of 45 cm, but it is reported that the size at first capture (lc) in some trawls catches is less than 14 cm. Sexual maturity is attained at an average length (Lm) of 20–21 cm. Spawning occurs in the dry season (November-February). Balistes capriscus is a benthophage, feeding mostly on crustaceans, molluscs, echinoderms, Polychaetes and corals but in open waters it can also feed on macroplankton and fish larvae.
Fishing grounds are located throughout its depth range on the continental shelf. Triggerfish is rapidly gaining commercial importance in West Africa. It can be fished with bottom trawls, traps, beach-seines and handlines. But there is no grey triggerfish fishery in Liberia.
Three commercially important penaeid shrimps occur in Liberian waters, namely, Penaeus notialis, Penaeus kerathurus in the coastal zone and Parapenaeus longirostris in deeper water. The pink shrimp (P. notialis is by far the most dominant and inhabits the same areas as the Caramote prawn (P. kerathurus). Parapenaeus longirostris is less abundant and occurs in deeper waters which are presently not fished by the artisanal fleets. An industrial fishery for P. longirostris has not yet been developed. Information from resource surveys and commercial fishing show that the coastal penaeid shrimps are more abundant in the northern sector of Liberia bordering with Sierra Leone. The littoral species Parapenaeopsis atlantica is also present in Liberia but its potential is not known.
The coastal penaeid shrimps have interesting recruitment features, details of which are given by Garcia and Le Reste (1981). The first phase in the life of coastal penaeid shrimps takes place at sea between three weeks and one month, and thereafter in the coastal zones, in bays, estuaries, in mangrove swamps which are rich in food, or in submerged vegetation (during the juvenile and sub-adult stage for about 3 months). As their development progresses the shrimps migrate toward greater and greater depths. When the areas of distribution of juveniles and adults are clearly separated geographically, a true migration seaward occurs at an age of about 3 months after which spawning takes place.
(a) Penaeus (Farfantepenaeus) notialis (southern pink shrimp)
The southern pink shrimp is known to exist from Mauritania (Cape Blanc 21°N) to Angola. It inhabits and or muddy sand bottoms between 10 m and 100 m depth. It prefers waters with temperature of 18–24°C.
Data on the life cycle, growth rate and natural mortality of Panaeus notialis are given by Garcia (1977) and Garcia and Lhomme (1980).
The pink shrimp fishery is more intensive in the northern sector of Liberia and Sierra Leone. Penaeus notialis can be caught in lagoons with traps, stow-nets, conical nets, beach seines, trawls towed by two persons and double-rigged bottom trawls. The best season for shrimping is between April and September (rainy season).
(b) Penaeus kerathurus (Caramote prawn)
Penaeus kerathurus prefers more sandy bottoms with detritus and seagrass beds, between depths of 5–50 m. It spawns during the period May-November and its post-larvae are found around river mouths and in lagoon areas. The species appears to be more abundant in Sierra Leone than in Liberia. It is much less abundant than P. notialis and it is mostly caught in bottom trawls.
(c) Parapenaeus longirostris (deepwater rose shrimp)
This species inhabits sandy mud bottoms between 100 m and 400 m in waters with temperatures of 8–15°C and can migrate into coastal areas during upwelling seasons. It is more abundant off the coastal sector between Morocco and Senegal. It is less abundant on the shelf of Sierra Leone and Liberia. A deepwater industrial shrimp fishery is not yet developed in Liberia and might be uneconomical.
