Abstract
The tilapia (Oreochromis niloticus, L. 1758) stock of Lake Hawassa, Ethiopia, was assessed to estimate sustainable yield (MSY) and optimum fishing effort (fopt) 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 for 514 days during 27-12-2003 to 24-05-2005 at the major landing site known as Fish market or AmoraGedel. The sampling days fell into two periods demarcated by the date (08-04-2004) when a management action was implemented, which reduced fishing effort by half (from1954 gillnets/day to below 800 nets/day). Thus, data obtained during 27-12-2003 to 08-04-2004 pertained to the period prior to effort reduction whereas the rest pertained to the period after the reduction. The two data sets were analyzed separately to get a basis to evaluate the effect of the management action of effort reduction. The assessment gave an estimate of current yield of 526.8 t/year for the period before effort reduction whereas 441.6 t/year afterward. The predicted MSY was 514.5 t/year and 441.6 t/year for the period before and after effort reduction, respectively. The respective F-factor is estimated to be 0.5 and 1.0.This suggested that the fishing effort before the reduction of effort (1954nets/day) was very high and, as already implemented, should have been reduced by half(i.e., an F-factor of 0.5).Therefore, the implemented management measure to reduce effort below 800 nets/day is appropriate. Likewise, since the estimated MSY of441.6 t/year for the period after the reduction would be obtained at an F-factor of 1.0, it was concluded that the current level of fishing effort of 696 gillnets/day can be maintained as fopt for sustainable exploitation of the stock.
Highlights
Global Ocean and inland water bodies are suffering from excessive overfishing exerted by an increasing demand of human population
The length based models are suitable for tropical fish stock assessment work as they do not require the tedious procedure of age determination, which is frequently difficult for tropical fish stocks
Status of the tilapia fishery of Lake Hawassa After measures were taken to reduce the fishing efforts, the number of nets set per day were drastically reduced by 2.8 times, i.e., from close to 2000 nets per day to about 700 nets per day
Summary
Global Ocean and inland water bodies are suffering from excessive overfishing exerted by an increasing demand of human population This strong demand, which was not controlled through appropriate management of fishing capacities, had led to a generalized fleet overcapacity and to overfishing, highlighted by declining catches worldwide (FAO, 2009a).In 2007, most of the stocks were either overexploited or depleted and yielded less than their maximum potential owing to excessive fishing pressure (FAO, 2009b).The general view seems to be that most of Ethiopian lakes are heavily exploited. After a decade it is only just over half that figure while the effort has not declined by nearly as much (LFDP, 1997) This proves that the lake was over fished in the past years. The main purpose of the study was to provide information on
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
