TY - JOUR
T1 - Assessing the exploitation status of main fisheries resources in Ghana’s reservoirs based on reconstructed catches and a length-based bootstrapping stock assessment method
AU - Abobi, Seth Mensah
AU - Mildenberger, Tobias Karl
AU - Kolding, Jeppe
AU - Wolff, Matthias
PY - 2019
Y1 - 2019
N2 - The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii, which are among the most exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs in northern Ghana, were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). The results suggest that the 3 species studied are heavily exploited in all 3 reservoirs, but with no alarming signs of overexploitation. The fishing effort at Golinga is comparatively low as a result of insignificant fishing during the agriculture season, which relates to low exploitation rates. Sarotherondon galilaeus and C. zillii have the highest and lowest biomass (t/km2) respectively in all the 3 reservoirs. The small shallow reservoir (Golinga) has the highest biomass of the target resources per unit area. According to a second assessment approach, based on length-based indicators, all species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the 2 reservoirs and suggests that a further increase in fishing effort should be prevented. Further monitoring of these fisheries will be needed for the improvement of assessments and thus management advice.
AB - The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii, which are among the most exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs in northern Ghana, were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). The results suggest that the 3 species studied are heavily exploited in all 3 reservoirs, but with no alarming signs of overexploitation. The fishing effort at Golinga is comparatively low as a result of insignificant fishing during the agriculture season, which relates to low exploitation rates. Sarotherondon galilaeus and C. zillii have the highest and lowest biomass (t/km2) respectively in all the 3 reservoirs. The small shallow reservoir (Golinga) has the highest biomass of the target resources per unit area. According to a second assessment approach, based on length-based indicators, all species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the 2 reservoirs and suggests that a further increase in fishing effort should be prevented. Further monitoring of these fisheries will be needed for the improvement of assessments and thus management advice.
KW - BFSA
KW - Ghana
KW - Length-based indicators
KW - Reservoirs
KW - Stock assessment
KW - TropFishR
U2 - 10.1080/10402381.2019.1616340
DO - 10.1080/10402381.2019.1616340
M3 - Journal article
VL - 35
SP - 415
EP - 434
JO - Lake & Reservoir Management
JF - Lake & Reservoir Management
SN - 1040-2381
IS - 4
ER -