Journal of FisheriesSciences.com

Abstract

Thirty-seven (37) species belonging to fifteen (15) families were identified during twelve months period of study (2020/21), on river Benue valley. Fish biodiversity and abundance showed a significance increase with increasing fishing efforts. The highest catch per unit effort was observed in Gongola/Benue confluents in Numan and kocheyel with more than 80.89kg/day and 78.29 kg/day with a cumulative fish weight of more than 432347.8kg per annum and 341931kg respectively. The lowest catch per unit efforts was observed in Parda and Gwakra with 24.97kg/day and 29.59 kg/day and a cumulative fish weight of 114321.5kg and 122008.2kg per annum respectively. Fishing gears used during the study indicates frequent use of gill/cast nets with 45% rate and traps at 43% rate, and other gears like hooks and line showed the lowest catch at 12%. The percentage composition of boats/canoes used during fishing was highest in Wurobokki at 25% and lowest in Parda with 13% rate. The highest number of fish species was observed in the family Claridae with five different spp and a cumulative number of 13119 fish followed by family Mormyridae with five spp with a cumulative number of 12075 fish and then followed by family, Cichlidae with four spp and a cumulative fish amounting to 12015. The lowest fish spp observed was Distichodoidae, Arapaimidae and Malapteruridae. Therefore, the most dominant fish amongst the family family were Claridae and Mormyridae and the near extinction fish family was Channidae. The dominant fish amongst the species were Alestes boremose followed by Schilbe intermedius, hydrocynus and Oreochromis. The decreasing number of fish species observed amongst the family Channidae was an indication that the river was under fishing pressure. Meanwhile, the mean physic-chemical parameters in the study areas revealed a normal water quality parameters throughout the year, except for the conductivity and total dissolved solid whose levels were high during raining season and low in the dry season. Results of the fish abundance indicates positive correlation with the water quality in all the stations studied. Hence, there were fish abundance and a sustainable livelihood amongst the fishermen.

Keywords

Abundance; Biodiversity; Species; family; Catch; Drag nets

Introduction

In Nigeria fresh waters, lakes ecosystem have two groups of fishes identified based on their adaptive strategies [1]. Migratory fishes, they occupy environmental variability and exhibit a high fecundity and a short breeding period at the beginning of floods, the spawners concentrate in few sites, later disseminate in the whole river, where genetic mixing is enhanced. Most of those fishes have low fecundity, but can breed several times in a year; their young once survive due to parental care ranging from territorial behaviour associated with nest building to mouth brooding and their abundance depends on the variability of the hydrological cycle both in space and time strategies. In Nigeria considering that all natural lakes and reservoirs are supplied with fish from the inflowing rivers, it is expected that the rivers will have high fish species diversity, but are not visible in the adjacent floodplains and wetlands, after each flood season during which the fishes breed. Thus the natural phenomena cause by drought or damming will disrupt the natural cycle of flooding which is bound to affect fish species diversity both in the natural, artificial and the wetlands [2]. At the dry season when the tide is low at brackish, coastal shores and in the freshwater fishing is very intense and low fishing is seen during raining season, decreasing exploitation when fishes are dispersed in the wetlands. All these lead to fishers to modify their fishing gears according to space and time diagram based on the hydrological cycle, being river Niger and Benue take their courses in the Sudano-sahel savannah they have high fish biodiversity composed of small sized fishes [3].

Water quality is the first most important limiting factor in fish production. It is also the most difficult production factor to understand, predict and manage. Water is not just where the fish live. Its quality directly affects feed efficiency, growth performances, the fish health and survival. Most fish deaths, disease outbreaks, poor growth, poor feed conversion efficiency and similar management problems are directly related to poor water quality. Water quality refers to anything in the water, be it physical, chemical or biological that affects the production of fish [4]. The chemistry of lake water is a cumulative reflection of catchment geology, weathering and erosional processes as well as anthropogenic inputs [5]. Pollution arising from anthropogenic substances is capable of altering a lake ecosystem and reduces its economic productivity. Organic wastes and other nutrient inputs from sewage and industrial discharges, agricultural and urban runoff can result in low oxygen level. Nutrient input often leads to excessive algal growth; when the algae die, the organic matter is decomposed by bacteria, a process which consumes a great deal of oxygen that could lead to oxygen depletion [6]. Low concentration of dissolved oxygen is known to be one of the major problems of faunal and floral survival in the aquatic environment, because it creates anoxic condition. High water temperature is known to enhance the growth of microorganisms. However, changes in temperature can have critical effect on living organisms. Relative depth of water at a particular site in a water body is one of the major physical factors controlling the water quality. Therefore, temperature and water depth relationship can provide vital information on Lake Ecosystem [7]. Water lakes and reservoirs are static (lentic), they water sources have different physical, chemical and biological characteristics which correspondingly affect the quality of fish [8-10]. In virtually every case a change in one of these factors may result in change to one or more of the other factors. Even though, there are many water quality variables in fish production only a few of these usually play important role. However, some parameters interact with other and influence the overall water quality [11]. The quality of water plays a vital role in the production of any water body. The fertility of water is related to its chemical properties which will determine the primary production such as planktons and micro-benthic invertebrates and that water quality influences fish survival, production and growth performance and the overall biological production of the water body and organisms, greenness appearance is one of the indicators of primary productivity and good water quality parameters. The importance of chemical factors is owing to their lethal and sub-lethal effect on aquatic organisms and also owing to their effect on biological productivity i.e. productivity of the organism in the food chain. The chemical aspects of water include dissolved gasses such as oxygen, carbondioxide and concentration of various ions.

The objective of this study was to determine fish biodiversity and abundance in relation to water quality (Figure 1).

Figure 1: Study area.

Materials and Method

The direct method was used to obtaining data for the Biodiversity and fish abundance by deploying observers. Species composition and weights of fish. Areas and time fished were also recorded as described by. The fish samples were identified by identification key. Catch per Unit Efforts was estimated using the formula below. APHA (1995) was used to analyze physic-chemical parameters in all the lakes.

CPUE = Weight of fish species caught (Kg) /Time in hour.

Results were analysed and presented in a tabular and charts form. Microsoft excel 2010 and IBM SPSS statistics with the statistical tools employed.

Results and Discussion

Thirty-seven (37) species belonging to fifteen (15) families were identified in 2020/21. Fish biodiversity and abundance showed a significance increase with increasing fishing efforts. The highest catch per unit effort was observed in Gongola/Benue confluents in Numan and kocheyel with more than 80.89kg/day and 78.29 kg/day with a cumulative fish weight of more than 432347.8kg per annum and 341931kg respectively, Table 1. The lowest catch per unit efforts was observed in Parda and Gwakra with 24.97kg/ day and 29.59 kg/day and a cumulative fish weight of 114321.5kg and 122008.2kg per annum respectively. Fishing gears used during the study indicates frequent use of gill/cast nets with 45% rate and traps at 43%, and other gears like hooks and line showed the lowest catch at 12%. The percentage composition of boats/ canoes used during fishing was highest in Wurobokki at 25% and lowest in Parda with 13% rate Figure 1. The highest fish of different spp was observed in the family Claridae (five spp) and a cumulative number of 13119 fish followed by Cichlidae five spp with a cumulative number of 12015 fish and then followed by family Mormyridae (four spp) and a cumulative fish amounting to 12075. The lowest fish spp observed was Distichodoidae, Arapaimidae and Malapteruridae. The most dominant fish family in the study areas were Claridae and Cichlidae and the near extinction fish family was Channidae. The dominant fish amongst species was Alestes boremose followed by Schilbe intermedius, hydrocynus and Oreochromis respectively. The decreased number of fish species observed amongst the family Channidae was an indication that the river is under fishing pressure because, they were one of the most common families of fish species found mostly in abundance in Nigerian freshwaters and one of the most highly utilized fish species by fish consumers. Fish were caught by mesh nets and hooks. Drag/cast/gill nets and traps showed the highest gear utilization, while hooks and line appeared to be the lowest (Tables 1 and 2, Figure 2)

Figure 2: Percentage composition of boats and canoes in study areas.

Field survey (2021)

Field survey (2021) Key :< 1=Extinct; 1-50 = Rare; 51-100 = Few; 101-200 = Common; 201-400 = Abundant; >400 = Dominant

Field survey (2021)

Study of the mean physic-chemical parameters revealed a seasonal water quality variations. The mean conductivity and Total Dissolved Solid appeared to be very high during the raining season that was between months of March and September and dropped in the dry season that was between the months of October and February. All other parameters especially temperatures, transparency, ph., Dissolved Oxygen and depth revealed a steady levels throughout the year (Figures 3 and 4).

Figure 3: Fish species abundance on river Benue valley.

Figure 4: Fish composition by family on river Benue valley, North-eastern Nigeria.

Field survey (2021)

The fish stock abundance on the river valleys was observed to be dependent on the fishing efforts, gears selectivity and species population density, fishing methods and season of the year. The highest catch per effort was 80.89kg and lowest of 24.97kg indicated that fishing efforts in a water body will be higher if the effort was small and catch was much and it depends on the weight of fishes caught divided by the time spent. The number of fishermen recorded against the boats used on all the stations, showed that some fishermen had more than one canoe and hired them to fishers to gain and check their gears and some were used for commercial transport to nearby markets and farms, despite the conditions of availability of canoes some fishermen used foot to cast their gears at shallow waters. Gill/cast nets were recorded as the highest in number used on the river and that could be attributed to the high catch per unit effort and the prohibition of the use of less than 76 millimeters of nets mesh size to construct any fishing gears or used on the river. There were different fishing gears and traps used on the river and the frequency indicated high level of computation amongst the fishermen due to over dependency on the water and increase their chances to survival since fishing is one of the major means for survival as well as reducing the chances of been redundant, where one gear failed to catch fish the other will do. Total of 15 families and 37 species of fishes were recorded and Claridae Cichlidae family was among the dominant family in all the study areas. These may be due to their certain characters like high productivity rate, high sense of parental care after hatching, ability to breed in a swampy habitat with plenty organic matter to feed on by their fry, breed early during floods at the margins of advancing water, high fecundity, growth, and have high feeding ratio on aquatic macrophytes. These coincides with findings of and Polypteridae, Distichodontidae, channidae and Malapteruridae family were in an extinct form and could be attributed to over fishing. Fish were abundant in the dry season than rainy season, and that could be either because fish generally exhibit restricted movement during the rainy season to undergo breeding and thus become scattered into lakes for reproduction, feeding and escape being captured and or eaten by predators and also fish harvesting is usually very high at all the stations (Figure 5).

Figure 5: Physic-chemical parameters on river Benue Nigeria.

Conclusion

The families of fishers were extended and the physico-chemical and biological properties of the river valleys were within the recommended standard levels for maximum fish production.

Multiple gears were used to catch different fish species and family Distichodontidae, polypteridae, channidae, Malapteruridae and spp clarias lazera were becoming extinct at the lakes.

Recommendations

The production of mesh size net of less than 76millimeter should be discouraged to prevent overfishing of small fishes. Agricultural activities around the lakes should be discouraged because of possible residual deposit of agrochemicals that can lead water quality declination.

Limitations of the study

Even though the method used provides the most reliable data but, it is the most expensive and requires relatively well-trained personnel to manage and report the data accurately.