Stock assessment of fishery target species in Lake Koka, Ethiopia
Effective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to...
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| Format: | Article |
| Language: | English |
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Vicerractoría Investigación
2015-09-01
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| Series: | Revista de Biología Tropical |
| Subjects: | |
| Online Access: | http://www.scielo.sa.cr/scielo.php?script=sci_arttext&pid=S0034-77442015000300755&lng=en&tlng=en |
| _version_ | 1797762246404734976 |
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| author | Gashaw Tesfaye Matthias Wolff |
| author_facet | Gashaw Tesfaye Matthias Wolff |
| author_sort | Gashaw Tesfaye |
| collection | DOAJ |
| description | Effective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to sustain their fisheries and the benefits for the society. In Lake Koka (Ethiopia), very little is known about the vital population parameters and exploitation status of the fishery target species: tilapia Oreochromis niloticus,common carp Cyprinus carpióand catfish Clarias gariepinus.Our study, therefore, aimed at determining the vital population parameters and assessing the status of these target species in Lake Koka using length frequency data collected quarterly from commercial catches from 2007-2012. A total of 20 097 fish specimens (distributed as 7 933 tilapia, 6 025 catfish and 6 139 common carp) were measured for the analysis. Von Bertalanffy growth parameters and their confidence intervals were determined from modal progression analysis using ELEFAN I and applying the jackknife technique. Mortality parameters were determined from length-converted catch curves and empirical models. The exploitation status of these target species were then assessed by computing exploitation rates (E) from mortality parameters as well as from size indicators i.e., assessing the size distribution of fish catches relative to the size at maturity (L m),the size that provides maximum cohort biomass (Lopt) and the abundance of mega-spawners. The mean value of growth parameters L x, Kand the growth performance index 0' were 44.5 cm, 0.41/year and 2.90 for O. niloticus,74.1 cm, 0.28/year and 3.19 for C. carpioand 121.9 cm, 0.16/year and 3.36 for C. gariepinus,respectively. The 95 % confidence intervals of the estimates were also computed. Total mortality (Z) estimates were 1.47, 0.83 and 0.72/year for O. niloticus, C. carpioand C. gariepinus,respectively. Our study suggest that O. niloticusis in a healthy state, while C. gariepinusshow signs of growth overfishing (when both exploitation rate (E)and size indicators were considered). In case of C. carpio,the low exploitation rate encountered would point to underfishing, while the size indicators of the catches would suggest that too small fish are harvested leading to growth overfishing. We concluded that fisheries production in Lake Koka could be enhanced by increasing Etoward optimum level of exploitation (E opt)for the underexploited C. carpioand by increasing the size at first capture (Lc)toward the L opt range for all target species. |
| first_indexed | 2024-03-12T19:25:30Z |
| format | Article |
| id | doaj.art-3a8a5c86ab83409d97e3d4605cde32c3 |
| institution | Directory Open Access Journal |
| issn | 0034-7744 |
| language | English |
| last_indexed | 2024-03-12T19:25:30Z |
| publishDate | 2015-09-01 |
| publisher | Vicerractoría Investigación |
| record_format | Article |
| series | Revista de Biología Tropical |
| spelling | doaj.art-3a8a5c86ab83409d97e3d4605cde32c32023-08-02T04:53:32ZengVicerractoría InvestigaciónRevista de Biología Tropical0034-77442015-09-01633755770S0034-77442015000300755Stock assessment of fishery target species in Lake Koka, EthiopiaGashaw TesfayeMatthias WolffEffective management is essential for small-scale fisheries to continue providing food and livelihoods for households, particularly in developing countries where other options are often limited. Studies on the population dynamics and stock assessment on fishery target species are thus imperative to sustain their fisheries and the benefits for the society. In Lake Koka (Ethiopia), very little is known about the vital population parameters and exploitation status of the fishery target species: tilapia Oreochromis niloticus,common carp Cyprinus carpióand catfish Clarias gariepinus.Our study, therefore, aimed at determining the vital population parameters and assessing the status of these target species in Lake Koka using length frequency data collected quarterly from commercial catches from 2007-2012. A total of 20 097 fish specimens (distributed as 7 933 tilapia, 6 025 catfish and 6 139 common carp) were measured for the analysis. Von Bertalanffy growth parameters and their confidence intervals were determined from modal progression analysis using ELEFAN I and applying the jackknife technique. Mortality parameters were determined from length-converted catch curves and empirical models. The exploitation status of these target species were then assessed by computing exploitation rates (E) from mortality parameters as well as from size indicators i.e., assessing the size distribution of fish catches relative to the size at maturity (L m),the size that provides maximum cohort biomass (Lopt) and the abundance of mega-spawners. The mean value of growth parameters L x, Kand the growth performance index 0' were 44.5 cm, 0.41/year and 2.90 for O. niloticus,74.1 cm, 0.28/year and 3.19 for C. carpioand 121.9 cm, 0.16/year and 3.36 for C. gariepinus,respectively. The 95 % confidence intervals of the estimates were also computed. Total mortality (Z) estimates were 1.47, 0.83 and 0.72/year for O. niloticus, C. carpioand C. gariepinus,respectively. Our study suggest that O. niloticusis in a healthy state, while C. gariepinusshow signs of growth overfishing (when both exploitation rate (E)and size indicators were considered). In case of C. carpio,the low exploitation rate encountered would point to underfishing, while the size indicators of the catches would suggest that too small fish are harvested leading to growth overfishing. We concluded that fisheries production in Lake Koka could be enhanced by increasing Etoward optimum level of exploitation (E opt)for the underexploited C. carpioand by increasing the size at first capture (Lc)toward the L opt range for all target species.http://www.scielo.sa.cr/scielo.php?script=sci_arttext&pid=S0034-77442015000300755&lng=en&tlng=encrecimientomortalidadtasa de explotaciónlongitud óptima (L opt)mega-desovantesindicadores de tamaño |
| spellingShingle | Gashaw Tesfaye Matthias Wolff Stock assessment of fishery target species in Lake Koka, Ethiopia Revista de Biología Tropical crecimiento mortalidad tasa de explotación longitud óptima (L opt) mega-desovantes indicadores de tamaño |
| title | Stock assessment of fishery target species in Lake Koka, Ethiopia |
| title_full | Stock assessment of fishery target species in Lake Koka, Ethiopia |
| title_fullStr | Stock assessment of fishery target species in Lake Koka, Ethiopia |
| title_full_unstemmed | Stock assessment of fishery target species in Lake Koka, Ethiopia |
| title_short | Stock assessment of fishery target species in Lake Koka, Ethiopia |
| title_sort | stock assessment of fishery target species in lake koka ethiopia |
| topic | crecimiento mortalidad tasa de explotación longitud óptima (L opt) mega-desovantes indicadores de tamaño |
| url | http://www.scielo.sa.cr/scielo.php?script=sci_arttext&pid=S0034-77442015000300755&lng=en&tlng=en |
| work_keys_str_mv | AT gashawtesfaye stockassessmentoffisherytargetspeciesinlakekokaethiopia AT matthiaswolff stockassessmentoffisherytargetspeciesinlakekokaethiopia |