Animal ecology is the significant area of study for scientists. It is a study of animals and how they associate to each other and how they relate to the environment. There are different forms of animal ecology. With animal ecology, there are several factors, most of which are human caused, which is presently threatening them.
Ecology of some terrestrial and aquatic Animals:
Ecology and Biology of Fish Species:
Many clupeid species are marine, but few are anadromous (shads) and Ethmalosa fimbriata (bonga) are adopted to resist low salinities mainly in rainy season.
a) Bonga (Ethmalosa fimbriata): Bonga is the most significant clupeid species in coastal inshore waters of Nigeria. This species hardly ever goes below 20 m. It is more euryhaline than flat sardinella and it is found in estuaries, the sea, lagoons and also in places which are responsible to have great variations in salinity. Ethmalosa tends to be more abundant in Nigerian estuaries during period October-April.
b. Shad (Ilisha africana): Shad is the anadromous clupeid inhabiting inshore waters, sand beaches and estuaries (in approximately all fresh waters). Ilisha africana has maximum length (L∞) of approx 22 cm and it has good preference for crustacea and small fishes (juveniles). It may be caught at surface or near bottom down to approx 25 m. Therefore it can be target species for beach seine, gillnet, purse seine and inshore trawl fisheries.
c) Sardine (Sardinella spp.): Flat sardinella is found from Mauritania to Angola. It is coastal fish, more euryhaline, most frequently found to be abundant near outlet of water courses. It prefers warmer waters with temperature above 24°C and appears to avoid waters which are not clear. It is not very plentiful in areas without upwelling where the warm and low saline superficial layer is permanently present as in Baight of Biafra and large portion of Nigerian shelf.
Following carangid species are fairly abundant in Nigerian waters: Caranx spp., Chloroscombrus chrysurus, Decapterus rhonchus and Trachurus spp. There are generally schooling species distributed on continental shelf but some happen in brackish waters particularly when young.
a. Various jacks (Caranx spp.): Caranx spp. has wide distribution along West African coast from Senegal to Angola. Few species inhabit inshore waters and estuaries and others are located in deeper waters (more than 100-m depth). Therefore, this fish group can be susceptible to both artisanal and industrial fleets. Caranx spp. feed mostly on fish but also on shrimps, some crabs and invertebrates.
b. Atlantic pumber (Chloroscombrus chrysurus): Chloroscombrus chrysurus occurs along West African coast from Mauritania to Angola. This schooling pelagic species inhabits Nigerian continental shelf at depths of 10-50 m. It also occurs in estuaries and mangrove fringed lagoons and brackishwater areas. Its juveniles are at times located offshore in association with jellyfish.
c. False scad ("Decapterus rhonchus" = Caranx rhonchus): This is a schooling carangid species inhabiting near bottom waters, mostly between 30 m and 50 m but can be located in waters over 200 m depth. It feeds on small fish and invertebrates. This species is mostly exploited by industrial fleets using trawls, but it can also be fished by artisanal motorized canoes using gillnets.
a. Lesser African threadfin (Galeoides decadactylus): Galeoides decadactylus doesn't appear to penetrate below thermolcline. It founds in inshore waters adjacent to sandy beaches. Species is known to grow female gonads by passage through nonfunctional hermaphroditic stage arising from normal male. Understanding its reproductive and recruitment strategy appear to be essential in managing of fish species. Galeoides prefers silty and sand-silty bottoms.
b. Royal threadfin (Pentanemus quinquarius): Pentanemus quinquarius has the normal reproductive cycle. It founds on sandy bottoms down to the depth of 50 m. It is caught by artisanal gillnet fishery on nearshore sandy bottoms but species is also harvested offshore by industrial fleet using trawls.
c. Giant African threadfin (Polydactylus quadrifilis): Giant African threadfin (Polydactylus quadrifilis) can grow up to lengths 150-200 cm. Species inhabits inshore and offshore sandy bottoms up to the depth of 50 m. It also founds in estuaries and lagoons fringed by mangrove.
Croakers and drums are significant sciaenid species in Nigeria. This fish species group is mainly marine but also founds seasonally in brackishwater areas. Most of the species inhabit sandy and muddy bottoms in coastal areas with large river flows.
a. Bobo croaker (Pseudotolithus elongatus): Pseudotolithus elongatus prefers surroundings which are less saline. Actually, commercial concentrations correspond to great estuaries in gulf of guinea where species can be caught in large quantities in certain seasons. They inhabit mud bottoms in coastal waters up to 50-m depth but also enter estuaries and coastal lagoons. This species, with maximum length of approx 45 cm, moves further offshore to spawn during rainy season. P. elongatus is equally harvested by artisanal and industrial fleets. It can be caught with bottom trawls, setnets, beach seines and longlines.
b. Longneck croaker (Pseudotolithus typus): Pseudotolithus types grows to the larger size than P. elongatus. It gets the maximum length (L∞) of 100 cm and fish of 50-cm length are common in catch. Main fishing ground for this species is from Gulf of Guinea to Congo. It is the most significant commercial sciaenid species in Nigeria.
It inhabits mud and sandy bottoms up to the depth of 150 m but it is more abundant in waters of less than 60 m and temperature above 18°C. It also founds in estuaries. Therefore, it is fished by artisanal and industrial fleets using bottom trawls, bottom setnets and longlines.
c. Boe drum (Pteroscion peli): Pteroscion peli found along west coast of Africa, from Senegal to Angola. It inhabits mud and sandy-mud bottoms in coastal waters extending to 200-m depth. But it is most common in waters of less than 50-m depth.
Seabreams found in fairly deep waters of continental shelf and off slope. Small young individuals do found in shallow waters but mostly at the depth greater than 15 m, forming aggregations. Adult seabreams are more solitary. At times majority of individuals are male at first maturity and females appear later (protandric hermaphroditisms). As protogynic hermaphroditism is related with efficient use of good resources and parental care, it seems to be better strategy for exploited sparid species.
a. Angola dentex (Dentex angolensis): Dentex angolensis occurs along West African coast from Morocco 33°N to Angola. It inhabits different bottoms on continental shelf and slope from approx 15 m to about 300-m depth. It is protogynic hermaphrodite with most individuals beginning as females and changing to males at length 18-23 cm.
b. Red pandora (Pagellus bellottii): The geographical distribution of P. bellottii extends from the straits of Gibraltar to Angola and also around the Canary Islands. It is a protogynic hermaphrodite (the majority of individual are first females), then become males. Red pandora is omnivorous with a predominantly carnivorous diet consisting of crustacea, cephalopods, small fish and worms.
This is one of the most abundant sparid species in the CECAF area but it is not a target species of artisanal fisheries in Nigeria. It is possibly caught by the trawl fishery but separate catch data are not reported.
Other fish species:
Information concerning biology and ecology of other exploited fish (like, Ariidae, Bagridae, Cynoglossidae, Pomadasyidae, Serranidae, etc.) plus species groups treated above also reveals interaction between brackishwater and open-sea fisheries and possible competition between different sectors of any of fisheries on certain species.
Three commercially significant penaeid shrimps found in Nigerian waters. Penaeus notialis (pink shrimp) is by far the most dominant species. It founds in estuaries, lagoons, creeks and open sea. Parapenaeopsis atlantica (Guinea shrimp) is also quite abundant in open sea depth 10-16 m. Estuarine white shrimp (Palaemon hastatus) occurring in brackish waters and open sea is mostly exploited by artisanal fishermen.
As the kinds of exploitation (and operational zones of different gears) are very diversified, there are in fact numerous successive recruitment phases:
i) When shrimps leave nursery edges and become accessible to artisanal fisheries;
ii) When they reach large bays where they are accessible to small trawlers;
iii) During migration, when they are caught by fixed nets;
iv) When they reach sea and are caught by industrial trawlers.
Entry process in different fisheries is related with development stage of shrimps. If recruitment is stated as probability of shrimp of given size to be found in fishing area this probability can be stated for shrimps of each size as percentage of shrimps at that size, in total population which is present in that area. If percentages are plotted against size the recruitment curve will be obtained.
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