Prediction of bio-economically sustainable yield and optimum fishing effort for the Nile &lt;i&gt;tilapia&lt;/i&gt; (&lt;i&gt;Oreochromis niloticus&lt;/i&gt; L.) fishery of Lake Hawassa, Ethiopia

Yosef Tekle-Giorgis

doi:10.4314/ejst.v11i1.5

Abstract

The Nile tilapia ( Oreochromis niloticus , L. 1758) stock of Lake Hawassa, Ethiopia, was assessed to estimate bio-economically sustainable yield (MSY and MEY) and optimum fishing effort (f opt ) using length-based analytical models (Jone’s Cohort Analysis and Thompson and Bell). Pertinent data (length, weight, catch, effort, etc.) were collected on a daily basis between May 2012 and June 2013 from the two landing sites, where fishermen at the northern and the southern part of the lake land their catch for retail. The assessment revealed an estimated current yield of 240.23 t/year and 216.33 t/year for the southern and northern part of the fishery of the lake, respectively. The predicted biologically maximum sustainable yield (MSY) was 240.2 t/year and 218.7 t/year for the southern and northern fishery, respectively, which were obtained at an F-factor of 1 and 1.5, respectively. On the other hand, the maximum economic return was generated from the southern and northern fishery at an F- factor of 0.8 and 1.4, respectively. Therefore, the level of effort at the time of sampling (F-current) should be reduced by 20 % for the southern fishery while the current effort of the northern fishery can be expanded by 40% in order to obtain the maximum economically sustainable yield. Accordingly, the optimum level of fishing effort (f opt ) to be exerted at the lake level was estimated at about 650 nets per day in order to exploit O. niloticus stock of Lake Hawassa sustainably. Keywords: Analytical yield prediction models, Lake Hawassa, MEY, MSY, optimum fishing effort , O. niloticus , stock assessment

Highlights

The commercial fishery of Lake Hawassa primarily rests on Oreochromis. niloticus that contributes about 90% of the total annual catch (LFDP, 1997; Elias Dadebo, 2000; Tadesse Fetahi and Seyoum Mengistou, 2007)
Overall 123,086 and 99,360 nets were operated per year at the southern and northern parts of the fishing grounds, respectively. With these levels of fishing efforts, an estimated total number of 1,098,817 (240.2 tons) and 684,195 (215.4 tons) of O. niloticus was landed at Amora-Gedel and TikurWuha landing sites, respectively (Table 1)
Since fishermen have to bring their catch to the retail site early in the morning, the southern part of the lake, which is located close to the fish landing site, is the most intensively fished part of the lake

Summary

Introduction

The commercial fishery of Lake Hawassa primarily rests on Oreochromis. niloticus that contributes about 90% of the total annual catch (LFDP, 1997; Elias Dadebo, 2000; Tadesse Fetahi and Seyoum Mengistou, 2007). The commercial fishery of Lake Hawassa primarily rests on Oreochromis. Some commercially important fish species like O. niloticus have become victims of overexploitation. 1990’s, the fishery of Lake Hawassa has been continuously expanding with a rise in the number of fishermen and fishing gears. Following this progressive increment of fishing effort, the annual fish yield in the early 1990’s reached its peak at about 900 t/year (LFDP, 1997). The yield has been continuously declining and reached about 50% of the maximum record, indicative of a dwindling fish population size probably resulting from overexploitation in the last two decades (LFDP, 1997; Reyntjens and Tesfaye Wudneh, 1998)

Methods

Results

Conclusion