EFFECT OF CLIMATE CHANGE ON CLARIID FISHERIES RESOURCES OF KAINJI LAKE, NIGERIA
ABSTRACT
Climate change is believed to have major implication on agricultural production, fisheries resources and food security especially in the aquatic ecosystem of the sub-tropical and tropical regions. However, in Nigeria serious emphasis has not been paid on studying the impacts of this change on fishery production and fisher folk livelihood. The data used in the study include two years (2012 – 2013) generated primary data on (rainfall and temperature) secondary data spanning 20 years climatic record 1994 – 2013 on (rainfall, temperature, flood regimes and fish yield of Kainji lake obtained from National Institute for Freshwater Fisheries Research (NIFFR), New-Bussa. Questionnaire responses revealing knowledge attitude practice (KAP) of fisher-folks on climate change and fish yield were also used. Monthly sampling analysis of physico-chemical parameters in four stations (Damsite-Fakun, Tarda, Garafini and Malale), plankton status analysis and gonad developmental cycle (maturation stages) examination of Clarias anguillaris from Kainji Lake were done using standard methods. Data generated were used to establish relationships between primary productivity of the lake and climatic variables. The result of weather trend analysis showed that there was general rising trend in temperature, which suddenly declined since 2012. The rainfall was not only variable but onset and cessation pattern had shifted. Its occurrence was very inconsistent and its intensity increased. The prediction from “fitted model”, forecast future increase of rainfall, decrease in temperature and decrease in fish yield. The analysis and comparison of physico-chemical parameters, weather elements and plankton abundance showed moderate,r positive and negative linear correlations between the variables. The mean values of the physico-chemical parameters recorded were; temperature air and water (36.23oC ± 0.8oC, 29.75oC ±1.15oC), pH (7.14 ± 0.28), electrical conductivity (122.04 ± 19.06 µsho/sec), dissolved oxygen (8.31 ± 1.65 mg/l), biochemical oxygen demanded (3.98 ± 1.36 mg/l), total hardness (33.38 ± 4.95 mg/l) and alkalinity (20.35 ± 2.18 mg/l). These parameters measured showed marked significant (P<0.05) variations between different stations, seasons, and months. The mean values recorded were within the recommended range by WHO except for electrical conductivity and alkalinity which indicated that the lake was moderately polluted. Kainji Lake water is soft and support moderate productivity. In plankton analysis; ten taxa of zooplankton were identified from seven classes (Ostracod, Calanoid, Amphiphod, Copepod, Cypris larva, Sicula, Nictychia, Nauplius, Rotaria and Daphnia). The classes are Ostracoda, Maxillopoda, Amphipoda, Cephalopoda, Trematoda, Bdelloida and Branchiopoda, while the phytoplankton identified were six taxa from five families (Diatom, Dinophagillate, Ceratium, Spirogyra, Bactrachospermum and Fragillaria) and their classes are Bacillariophyceae, Dinophyceae, Zygnematophyceae, Florideophyceae and Fragilariophyceae. Maxillopoda and Bacillariophyceae were the dominant class and family. The analysis of plankton showed significant relationship with weather elements (temperature and rainfall) and physico-chemical parameters. The dissected Clarias anguillaris, showed gonad developmental cycle, with six maturation stages. The gravid stage was recorded in the month of September and October coinciding with “white flood”. Mean condition factor (K) range of 1.27 ± 0.22 – 2.67 ± 1.33 was recorded which indicated that these fishes were in good condition in their natural habitat in all the months except for the month of February (0.96 ± 0.33). Regression and correlation coefficient of length-weight relationship gave an absolute mean of 0.575 which indicated that the fishes had allometric growth pattern. The knowledge, attitude and practice of fisher folks revealed that they were artisanal, full time fishermen. They had experienced fluctuating, variable and unpredicted weather pattern which had great negative impact on their fishing activities. They recorded decline on catch per unit effort and confessed scarcity of the clariid in the lake. Their social and economic activity was getting low and many had taken adaptive measures of using different gears, sometime alternating them and in some cases abandoned fishing for upland farming and other vocation for livelihood. Kainji Lake ecosystem is responding to the threat of climate change and efforts should be made to mitigate this menace both in the short and long terms.