Catch per unit effort and some water quality parameters of Lake Kalgwai Jigawa state, Nigeria

Abstract This study investigated the catch per unit effort and water quality of Lake Kalgwai Jigawa state, Nigeria for the period of 10 month (July 2012‐June 2013). The man hours, gears used, and fish catches of the Lake was determined by assessing the fishermen operating on three major landing sites of the Lake, namely Marke (Site I), Dingare (Site II), and Kalgwai (Site III). Water samples from the landing sites were collected and analyzed. Concentration of fishers ranged from 41 (April) to 51 (September). The highest number of fishing hour was observed in August (64 hr), whereas the lowest was in March (49 hr). The average catch per fisher per day ranged from 107 kg/day (December) to 144 kg/day (August) during the study period. An average of 25 days was spent fishing in each month. The result also indicated similarities in the water qualities of all the three sampling sites per months. Based on the result gotten it was concluded that lake Kalgwa is not over fished and water quality are within recommended ranges for fish production.


| INTRODUCTION
Fish supply in Africa is in crisis. Per capita consumption in sub-Saharan Africa is the lowest in all regions and it is the only part of the world where consumption is declining. The main reason for this decline is the leveling off in capture fish production and the ever-growing population. World Bank (2004) had estimated that fish production must be increase by 27.7% over if a per capita fish supply of 6.6 kg/year is to be maintained in sub-Saharan Africa by 2015. However, if capture fisheries is to continue to provide the bulk of fish food for Africans sustained efforts would have to be made to support, promote, and protect smallscale labor-intensive (both coastal and inland) fisheries. Investments in applied research and capacity building will be required to improve and strengthen the socio-institutional mechanisms underpinning the fisheries management process. But investments to improve environmental management are also required to sustain fisheries, especially in inland fisheries where increasing pressure on land and water is leading to high environmental degradation. These inland fisheries provide the basis of the livelihoods and therefore the indirect support to food security for millions of people, (World Fish Center, 2005).
The poor and uneconomic management of reservoir and lake fisheries is another major issue of concern. Therefore, creation of dams provides an ecosystem for the proliferation of wide range of aquatic organisms including fish thus promoting socio-economic activities of the surrounding communities (Fawole, 2002). However, closing fishing areas and regulating the use of fishing gear can result in more profitable catches and higher incomes. For instance, a 12-year study on fish caught in three locations off the coast of Kenya showed that fishing close to an area with restrictions led to larger catches of fish with higher market value (Spore, 2011). Alternatively, sustainable fishing regulations have been found to facilitate replenishment of stocks.
Restricting catches, imposing a minimum size for fishing and halting fishing for a certain period each year are strategies that enable species to regenerates, whereas everyone benefits including fishermen and consumers. Fishermen at Lake Albert, Uganda, have witnessed a rapid change and firsthand benefits of a 20-month fishing ban imposed between March 2010 and January 2011 (Spore, 2012). Some species of fish that were seldom found overtime became dominate catches of the lake hence, market prices for this fish fell by 40%.
Fishes are generally poikilotherms (cold blooded) and therefore their metabolic rates are strongly influenced by the external environment conditions. The thermal tolerance of fish for instance could be lethal, controlling, and directly influencing the responses of fish (Fry, 1971). In many cases, changes in thermal conditions are also accompanied by changes in other water characteristics such as water levels, changes in composition and amount of food, changes in acidity and other chemical characteristics (Schindler, 2001). Therefore, seasonal influences and instances when such changes occur may be equally or even more severe than changes expressed on an annual basis (Pearson & Dawson, 2003). Fishes as been exploited as excellent bioindicators of water quality changes (Idodo-Umeh, 2002;Ogbeibu & Victor, 1989;Oguzie, 2003;Yamazaki, Tanizaki, & Shinikawa, 1996).
The justification lies in the fact that fish communities respond to episodic events and therefore integrate environmental conditions over time. This study is therefore designed to evaluate the catch per unit effort of Lake Kalgwai for 10 months in relation to the water quality parameters.  (Matthes, 1990). Its maximum surface area normally occurs at the end of the rain season in September. Thereafter, the water recedes so that minimum level is reached just before the start of rains in June. The extent of flooding varies from year to year and is mainly dependent on the amount of rainfall (Benthem, 1990). Hence fish production also varies depending on the extent of the volume of water during the season.

Kalgwai
This has brought an increased fishing activity especially in those villages surrounding the dam site.
The fish specimens used for the study were obtained through catch statistics at three major landing sites of the dam, namely Marke (Site I), Dingare (Site II), and Kalgwai (Site III), respectively. Fish species were randomly sampled and examined at each site fortnightly over a period of 10 months from July 2012 to June 2013 between 6:00 a.m. and 8:00 a.m. Fish identifications as well as measurement of weight and number of fishermen were taken directly from the landing sites according to identification keys provided by Thalwar and Jhingran (1991), FAO (1992), Olaosebikan and Raji (1998) and Bankole and Mbagwn (2000).
The body weight of each specimen was determined was measured in grams (g) using compact balance (Model MP-600A) sensitive electronic weighing scale. Catch per unit effort was determined using the formula: Water samples from the landing sites were collected using two liter capacity sampling bottle on monthly basis. The water samples were subjected to the following analysis as soon as possible after collection as described by APHA (1998). Analysis of variance (ANOVA) was used to test for significant difference at 95% confidence limit. Data were analyzed using Minitab 14 ® software for descriptive and summary statistics and Genstat Discovery Edition 4 for Analysis of Variance. Data were analyzed using one way analysis of variance for a completely randomized design. Some variates were analyzed using analysis of covariance where some dependent factors were found to be significantly different (p < .05). All significantly different means were separated using Fisher's least significant difference of means.

| RESULTS
The result of catch per unit effort is as presented in Tables

| DISCUSSIONS
The catch per unit effort of this study revealed the highest fish catch in February and March which was during the dry months with low rains. Similar trend was observed for the monthly total weight of fish catches. This could be attributed to the high volume of water in the dam during the rainy season and most of the species are dispersed due to the increase in surface area. This agrees with results from Jebba Lake (Halstead, 1971), Kainji Lake (Imevbore, 1975), Asa Lake (Vander-Heide, 1982) Asejire Lake (Sendacz, Kubo, & Cestarolli, 1985), and Ikwori Lake (Offem, Ayotunde, Ikpi, Ochang, & Ada, 2011) where larger ichthyofaunal densities were observed in the dry season.
Reasons for the variation were similar to those advanced in this study.
However, during the wet season, it is assumed that the high level of water and subsequent flood favored reproductive activities, hence, fish species were less vulnerable to catch because of high water levels and restricted movement. This assumption agrees with the report of Willoughby and Tweddle (1978) who stated that early rainfall and subsequent rise in water level trigger spawning activities of most fish species in African water bodies.
Diversity of gear was observed used by fishermen in this study. is suggestive that Kalgwai Lake is relatively shallow hence, may be connected to the high fish abundance noticed in the dam. Beyond this, Alabasster and Lyod (1980) had earlier opined that high depth might result in reduction in fish growth rate as a result of reduction in food availability in the ecosystem. Hence, the low depth of the lake in this study may be an advantage translated to higher food availability.
More so, the shallow depth of this study could also be linked to the