A Study of the Fish Fauna of Tagwai Lake Minna, Nigeria, in Relation to Gear Selectivity
The fish fauna of Tagwai Lake Minna, Nigeria, was studied from July to September, 2010. Sampling was carried out during the day using different gears. A total of 1,669 specimens were sampled made up of 8 species in 7 genera and 6 families. Variation in the mesh size used greatly influenced catch in the lake. Cash net recorded the highest amount of catch (1,435) and gill net recorded the highest amount of fish species (6). Two Cichlids species, Tilapia zilli and Sarotherodon galilaeus were the most abundant in the catch, amounting to 33.01 and 26.06%, respectively. The families of Cichlidae and Mormyridae were the most abundant constituting 59.18 and 29.95% of the total catch respectively. Fish abundance showed low catches during the raining season (33.01%) and daytime.
Received: January 10, 2013;
Accepted: March 05, 2013;
Published: April 04, 2013
Nigeria is blessed with abundant natural aquatic resources in marine, estuarine
and fresh water environment. The fresh water bodies of Nigeria, with over 270
fish species, are the richest in fish diversity in West Africa (Tobor,
1992). Niger State is blessed with vast wetland resources totaling over
72,234 hectares of water surface area (Ita et al.,
1985). Among the people of this state, fish constitutes a major percentage
of their protein intake. Besides, fishing activities have become a source of
employment for the teeming populace (Ibiwoye et al.,
However, fishing in this state is practiced on a very low scale, mainly for
subsistence (Gabriel, 2000). Thus, over the years, the
demand for fish has continuously outweighed supply as in most parts of Nigeria
(Meye and Ikomi, 2008). Fishing activities in these
water bodies are intense all year round with fishermen using all types of fishing
gears and sometimes explosives (though illegal) to increase their catches (Idodo-Umeh,
2003). In most cases, their fishing efforts are not commensurate with their
catches. Therefore, if an inventory of the commercially important species including
the seasonal diurnal variations in abundance, as well as the gear selectivity
of these species are studied and results made known to the fishermen then they
can target their fishing efforts at particular seasons, with the appropriate
gear, to achieve better fish catches. Knowledge of fish biology and species
composition of different water bodies is necessary to enhance the management
of water resources (Meye and Ikomi, 2008).
Hitherto, published information on the fishes and fisheries of Niger state
have mainly been on the Kainji reservoir basin at the expense of the numerous
lakes and rivulets in the area (Ita et al., 1985).
This present study, therefore, was carried out to elucidate the fish fauna species
composition and relative abundance in relation to the influence of gear selectivity
in Tagwai Lake, Minna, Nigeria.
MATERIALS AND METHODS
Study area: This study was conducted in Minna, located within Latitude
6°33' E and Longitude 9°3' N, covering a land area of 88km2.
The area has a tropical climate with mean annual temperature of 30.2°C,
relative humidity of 61% and annual rainfall of 1,344 mm. The vegetative cover
reflects that of savanna zone, dominated by grass but with scattered trees species.
The area is characterized by two distinct seasons, i.e. a rainy season between
April and October and dry season between November and March (The
Nigerian Congress, 2007).
Tagwai Lake is about 10 km away from Minna, located at Latitude 6°39' to
6°44' East and Longitude 9°34' to 9°37' North to South West of Minna-Suleja
The lake was constructed by the impoundment of Tagwai Lake in 1978 for the
purpose of domestic water supply to Minna metropolis. The dam has a catchment
area of about 27,000 km2. The average rainfall of the area was estimated
to be about 60 inches per annum (Ibiwoye et al.,
2006). The vegetation is varied; the river bank emanates from rocky base
of hills forming a valley and is characterized by sparse growth of trees, shrubs
and dense grasses. The surrounding environment shows savanna woodland vegetation
interrupted in many places by cultivated areas (Alkali, 1994).
Fishing in the area is dominated by artisanal fishermen that use manually operated
wooden (dug-out) canoes, using mostly cast net, gill nets, driftnet and traps
Fish sampling, preservation and identification: Fresh samples were collected
from the lake bi-weekly between the months of July and September, 2010. A uniform
fishing effort of two fishermen for seven hours duration per day (00:00-07:00
h) was maintained throughout the study period. The gears and methods used were
in accordance with the recommendations of Gullard (1980),
that reliable sampling should involve a combination of two or more gears. The
gears used are cast nets (10-15 mm mesh size) and gill nets (2 mm) mesh size.
The fish specimens were collected into an iced box and transported to the laboratory
immediately, where they were preserved in 10% for further examination (Meye
and Ikomi, 2008).
Fish identification was done as far as possible using available keys of Olaosebikan
and Raji (1998), Teugels et al. (1992) and
Determination of fish species relative abundance: The Relative abundance
of the fish species was estimated using the formula:
||Relative abundance of each species (%)
||Total Abundance for all species
The abundance of the fish species was categorized according to the criteria
of Meye and Ikomi (2008):
||≥10% = Dominant
||1-9% = Subdominant
||<1% (but caught more than once) = Occasional
||<1% (and caught only once) = rare
Statistical analysis: All fish species collected were counted to determine
species abundance. The abundance score of the species was estimated by calculating
the relative abundance (%) of each species as given above as adopted from Benech
et al. (1983).
Ichthyo fauna: The fish fauna encountered in Tagwai Lake during the
study period are presented on Table 1. A total of seven species,
belonging to seven (7) genera and six (6) families were recorded in this study.
The highest number of species (59.18%) was observed in the family Cichlidae;
followed by Mormyridae (29.95%), Mochokidae (8.98%), Bagridae
(1.01%) while Clariidae and Alestidae each constituted less
than 1% of the total catch.
The three most dominant species of fish encountered in this study were T.
zilli, M. rume and S. galilaeus having a relative abundance
of 33.01, 29.95 and 26.06% respectively. The sub-dominant species included Synodontis
nigritis with 8.98%, while the occasional and rare species were A. occidentals
with 1.01%, C. gariepinus with 0.05% and A. leciscus with
Gear selectivity: Table 2 shows the species composition
of fishes harvested with the different gears used. The cast net recorded the
highest number of individuals (1,435) with three species and distantly followed
by gill net with 234 individuals made up of 6 species.
||A check list of fish fauna in Tagwai Lake showing abundance
and relative abundance (%) during the rainy season
|| Gear selectivity of fish species in Tagwai Lake (July-September)
Drift net, local trap and hook and line yielded no catch during the study
period. T. zilli, M. rume and S. galilaeus were vulnerable
only to cast net, while T. zilli, Synodontis nigritis, A.
occidentals, C. gariepinus, A. leciscus and Hemichromis fasciatus
were vulnerable to gill net and interestingly, T. zilli is the only
fish species that was vulnerable to both cast and gill nets respectively. During
this study period, the fish species encountered or caught were not vulnerable
to drift net, local trap and hook and line.
The primary objective of a sampling survey of this nature is to attempt to
find out what fish species exist in the lake and, perhaps, elucidate the factors
governing abundance. However, according to Benech et al.
(1983) fish community studies are not generally equivalent to Ichthyocoenosis
because the description of any fish community is a biased image arising from
the sampling of a group of fishes in a particular environment at a given time.
Gear selectivity and sampling strategies are usual sources of these biases as
documented by Meye and Ikomi (2008). Despite these
obstacles, attempts will be made to compare data obtained in this study with
that from related works.
The Ichthyofauna of Tagwai Lake during the rainy season encountered 8 species
from 6 families appear to be lower than that of most water bodies in the state.
Ninteen species from 9 families were encountered in Shiroro dam (Ikomi
and Sikoki, 1998). It is also low when compared with other water bodies
in the country. Elechi Creek in Rivers state had 35 species from 20 families
(Allison et al., 1997) and 23 species from 17
families in the mangrove habitat of the Lagos Lagoon (Nwadukwe,
1995). The present study is also lower than that of Urie Creek in Igbide,
Niger Delta with 45 species from 24 families (Meye and
Reasons for the low fish species occurrence in the lake during the study period
were ascribed to the large volume of water during the wet season, available
fish were now dispersed over a wider area and fishing became more difficult.
Also, during the wet season, the high level of water and subsequent flood favoured
reproductive activities, hence fishes show restricted movement making them less
vulnerable to catch (Offem et al., 2011).
Gear selectivity was observed in the fish catch from Tagwai Lake, the variation
in mesh size and gear used may have greatly influenced species composition and
abundance in this study as reported by Meye and Ikomi,
2008. To support the above submission, Ufodike et
al. (1989) opined that gill net technology and catch period or techniques
are essential in maximizing fish catches. Both cast and gill nets constituted
more than 50% of the catch in this study, which were dominated mainly by the
Cichlids and the Mocholcids. These results agree with those of
Meye and Ikomi (2008), Ockiya (1996)
and Udolisa (1982) in the Lagos Lagoon. The gill nets
high selectivity may be connected with the morphometric projections on the body
of most species such as Mocholcids (S. nigirita) and the presence
of scales on most other species such as Cichlids (T. zilli). These
projections make such fishes susceptible to gill net (Meye
and Ikomi, 2008). In the case of cast net, its very high selectivity may
be connected with the heterogeneous mesh size of different panels used which
made it possible to catch fishes of different sizes.
The low selectivity of local traps and hook and line reported in this study
agrees with the earlier findings of Ockiya (1996) in
Kolo Creek and Ikomi and Sikoki (1998) in River Jamieson.
These gears were mostly used by fishermen in the flooded areas particularly
during the wet season.
The low catches in fish abundance during the rainy season encountered in this
study disagrees with the results of Idodo-Umeh (2003)
in Asa River and Ikomi and Sikoki (1998) in Jamieson
River, who observed more fish catches in the wet season than the dry season.
The results of this study have shown that Tagwai Lake like most other water
bodies in the state has a great potential for fisheries exploitation. The gear
selectivity observed among the fish species showed that the use of multiple
gears may probably be the best approach to such studies as fish composition
in the nearest future.
Finally, since fish abundance in this study might show significant variations
in season and time of the day, it is therefore recommended that these factors
be put into consideration in future exploitation of the fish species of Tagwai
Lake. In addition, future research effort should be geared towards the investigation
of the biology of the species of the lake, as a pragmatic approach to enhance
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