Influence of Human Activities on Fish Distribution, Composition and Abundance in Otamiri River, Imo State
Abstract
Otamiri River was carried out between July to October, 2018. The objective of the study was to identify those human activities that had been hindering the growth and survival of fish species in the river as well as ascertaining the species composition present in the river. The fish population were assessed using hooks and lines, gillnets, cast nets, traps etc as gears while one man dugout canoe as well as planked canoes were used as crafts. A total of 757 fish species which consist of 9 families, 10 genera and 15 species were described and identified. The family ranked highest as the most abundant fish species with 363 fishes, while Distichodontidae ranked the lowest with 5 fishes. The result of this study was further compared with other studies that had been carried out previously on the river where it was discovered that there had been a steady decline in number of fish species caught which were caused by most human activities such as sand and gravel mining, pollution, agricultural activities, deforestation etc.
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Introduction
The fish farm fauna of the Ecozone has changed dramatically since the Europeans first arrived in the 16000’s changes in the aquatic community structure have resulted from a variety of human activity including exploitation, habitat alteration, pollution, drains, canals, and introduction of non-native species. Often these factors act together to decimate native species and reduce the overall biodiversity of native aquatic ecosystems.
Unrelated or inadequately regulated commercial fishing quickly reduced populations of the lake sturgeon, and many species of native trout and whitefishes.
Species diversity is affected by habitat destruction which includes removal of ground water, land clearing and consequent sedimentation and water turbidity, more drastic variability of water levels, channelization, and removal of gravel and sand nutrient enrichment and addition of toxic contaminants. Populations of species which migrate up streams to spawn have been reduced or extirpated because dams have blocked access to spawning areas. In the 1800’s dams were built usually to provide a head water to operate a mill. A secondary effect was the pollution caused by the organic waste material dumped into the water by the function of these mills. Species have been unintentionally introduced through man-made canals (e.g Wenand Canal, the Eric Barge Canal and the Trent Canal) or transported and introduced with blast water. Human interest in only a limited number of recreational species. Unauthorized introductions have come from bait buckets, aquariums, and fish markets that import live fishes for human food.
Recent examples of unintentional introductions include two members of the Goby family native to the black and Caspian seas in Europe which have been transported and inadvertently introduced – with discharged ballast water of international vessels. The tuberose goby, proterorlinus marmoratus, was the first to be discovered in April 1990 in ST. Clair River followed shortly by the round goby, Neogobius melanostomus discovered in June 1990. (Grossman and Holm, 1998). The effects of this population explosion on the total biodiversity is not fully understood yet, but it is becoming apparent that the round goby will cause a significant decline of the native mottled sculpin and possible log perch and other darters through competition for food, space, spawning areas, or by direct predation on these species. These two species are excellent examples of the unpredictable consequences of introductions.
Conclusion
Degradation of lands adjacent to freshwater ecosystem can adversely affect biological communities through many mechanisms, for instance land use activities that eliminate vegetative covers, decrease infiltration rates or reduce moisture hold capacity of soil can adversely impact surface water quality. At Otamiri river dredging for sand and gravel have been going on for some years and this dredging helps in removing of some vegetative covering. Habitat destruction and degradation occurs when poorly managed agricultural lands, mineral extraction and construction of projects, in Otamiri, effluent from Fuason Alluminum Company, sewage from the college of Education, and soaking of cassava in the Otamiri River influence this factor.
During the dredging process, the spawning ground for some of the species must have been disrupted (causing them to migrate). Dredging also increase the depth while the width reduces some of fish families in earlier investigation. Another factor may be the season. Nwadiaro and Okereke (1993) did their investigation also during the rainy season and dry season periods, while this investigation was done during the dry season period. Some fish species might have migrate at this particular period may be in search of favorable weather condition or for breeding and or ecological reasons and this might be reasonable for the reduced catch in this study. Toxic substance in the cassava soaked in the river to be turbid which some fishes cannot tolerate. (Reeds et al., 1992) in Wiram Gulf discovered that there was evidence to suggest that over fishing with fine mesh net is partly to blame for the disappearance of haplochromis.
In conclusion, the declining rate of fish catch in Otamiri River need to be controlled in order to avoid losing most of the valuable fish species that are of great importance to fisheries. There might be need for legislation to check some of these obnoxious acts. Also some extension work should be done to educate people living along the river on the effect of what they do on the fish population and their long term to the aquatic ecosystem.