5.1 CAS DATA
This study observed that when the percent catches of the species are assessed on a yearly basis, there are insignificant declines/changes among the years under consideration as observed in figure 2 and 3 and more importantly from the p-value of 0.78 produced by one-way Anova which is greater than the confidence level at p-value = 0.05. The overall percent catch of the species/family of economic importance were almost similar. 2012 recorded the highest overall percent contribution of the species on average, although inconsistent for some species. The high variation observed in 2012 is probably because in 2012, only one round of CAS was conducted and at different time intervals (seasons). However, the ideal situation is to conduct the survey in all the four strata of the fishery at the same, but due to untimely release of financial resources, the survey was conducted at different times. As a result, the survey in stratum 1, 2 and 4 was conducted from 22nd to 31st August while in Stratum 3 from 9th to 18th November 2012. In 2013, most of the species recorded higher percent catches than 2014 which recorded the lowest percent catches on average. The highest percent catches on average for most species observed in 2012 despite the lowest CPUE, figure 14 is attributed to the lowest activity rate of that year on the lake, figure 15. This is in the sense that because less fishing activities took place that year, more fish were made available for the few people that undertook fishing activity. There were more chances for the fish to reproduce and survive against less chances of being caught. However, the high CPUE observed the same year entails that there were more effort expended and yet few fish were caught. Interesting to note is that according to the report by the Engineering Institution of Zambia Technical, 2015, of the three years being considered here, on average, 2012 had the highest rainfall level of about 485.8mm followed by 2013 which recorded 485.2mm and the lowest 485.00mm was observed in 2014, see appendix 1. The minimal difference observed among the years in terms of annual production is probably due to the differences in the amount of rainfall the lake and the country at large received during those years. It has been discovered that during periods of floods more food for fish is made available in water bodies, hence, more fish grow and reproduce. This is also supported by the findings of Sanyanga et al, (1994) that catches in a given fishery go down considerably during periods of droughts. Therefore, it follows that the rise in water levels leads to the rise in fish production also.
AT STRATUM LEVEL
The study further observed that there are high variations in terms of percent catch of Tilapia species at stratum level among the years under consideration. This is supported by the results obtained from one way analysis of variance where a p-value of 0.01 was obtained compared to the confidence level of p-value of 0.05. Statistically, this means that there has been a significant decline in the percent catches of Tilapia species among the individual strata of Lake Kariba. Figure 12 and 13 shows how the trends for the catches have been in each stratum for each year indicated. Interesting to note however, is the fact that Tilapia species are declining at a higher rate in stratum 4 compared to the other three strata of Lake Kariba. It is also noted that more tilapia species are found in stratum 4 as observed from the percent catches recorded for each year. According to frame survey conducted in 2011, the largest number of fishers are found in stratum 1 followed by stratum 3, then stratum 4 and the least number in stratum 2 (see appendix 17). The survey further showed that stratum 4 has the least total number of canoes and gears although it has more number of fishing villages together with stratum 3 compared to the other two. The largest percent catches of Tilapia species in stratum 4 is attributed to the fact that there are more baskets used as fishing gears in this stratum than the other three. Stratum 3 rather showed the lowest rate of species decline of all the strata, figure 13. The reason for high fish production in stratum 4 is probably due to the fact that Lake Kariba fishery is rapidly expanding in terms of cage fish farming as well as the upgrading of electricity generation facilities. These introduced economic activities have had a bearing in terms of fishing activity rate in the sense that these ventures have offered alternative livelihood in form of employment to fishers either on permanent or temporal basis mainly Stratum 4 ( Siavonga)
In line with the findings of Wallace and Fletcher (2005), the current study also observed that when the CPUE was high, more percent catches were recorded, likewise low CPUE yielded low percent catches of the species/family, compare figure 4 and figure 14.
5.2 GNS DATA
According to data obtained from GNS, the study observed that there has been a decline in the weight and length of individual Tilapia species in terms of grams and centimeters respectively. This is in line with the findings of Maunder et al (2006) that as fish are removed from a population, that population will decrease in abundance and the size of individual species decreases also. This also implies that the size of tilapia species and even those of other species will keep decreasing as long as fishing continues. Most of the fish will be caught before attaining maturity to reproduce, which may lead to total extinction of that particular species if there is no proper intervention.
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