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Aspects of the reproductive biology of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana, were studied from September 2014 to August 2015. The current study was aimed at providing information useful for managing the mussel fishery in this locality and also that would form the basis for designing appropriate culture methods for the species. Microscopic examination of fresh smears of gonadal material, as well as histological preparations of the gonad, were used to study the sexuality and breeding pattern of the species. Monthly gonadal and condition indices were also determined. Perna perna exhibited gonochoristic sexuality with a sex ratio of approximately 1:1 throughout the study period. Sexes were identifiable at shell lengths of 15.0–19.9 mm. Five stages of gonadal development were identified in both sexes. Gametogenic activity was continuous throughout the year, with two major spawning activities, from April to June and from August to December. These periods coincided with the major and minor rainy seasons, respectively, as well as the major upwelling period in August. Condition indices suggest that the mussels were in better condition for harvesting in March and August prior to the major spawning events. 相似文献
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The brown mussel, Perna perna, is an ecologically important species which has a great potential for aquaculture in Ghana. Though it is harvested from the wild for consumption locally, there is no information on its population parameters to guide its management and subsequent culturing. The species inhabiting Iture rocky beach near Cape Coast (Ghana) was therefore investigated to elucidate its growth and other population parameters. Specimens had shell length ranging from 5.00 to 78.0 mm, a modal shell length class of 35.0–39.9 mm, and exhibited negative allometric growth. The asymptotic length (L∞), growth coefficient (K), and growth performance index (Φ') were 80.10 mm, 0.49 per year, and 3.49, respectively. The recruitment pattern showed that P. perna has year-round recruitment with a single peak between April and July. Total mortality (Z) was estimated at 2.79 per year, while natural mortality (M) and fishing mortality (F) were 0.87 and 1.92 per year, respectively. The calculated exploitation level of the population (E = 0.69) suggests possible overfishing of the mussels at Iture rocky beach. These results could serve as baseline information for management of the mussel population in Ghana. 相似文献
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Ecosystem-based management of marine fisheries requires the use of simulation modelling to investigate the system-level impact of candidate fisheries management strategies. However, testing of fundamental assumptions such as system structure or process formulations is rarely done. In this study, we compare the output of three different ecosystem models (Atlantis, Ecopath with Ecosim, and OSMOSE) applied to the same ecosystem (the southern Benguela), to explore which ecosystem effects of fishing are most sensitive to model uncertainty. We subjected the models to two contrasting fishing pressure scenarios, applying high fishing pressure to either small pelagic fish or to adult hake. We compared the resulting model behaviour at a system level, and also at the level of model groups. We analysed the outputs in terms of various commonly used ecosystem indicators, and found some similarities in the overall behaviour of the models, despite major differences in model formulation and assumptions. Direction of change in system-level indicators was consistent for all models under the hake pressure scenario, although discrepancies emerged under the small-pelagic-fish scenario. Studying biomass response of individual model groups was key to understanding more integrated system-level metrics. All three models are based on existing knowledge of the system, and the convergence of model results increases confidence in the robustness of the model outputs. Points of divergence in the model results suggest important areas of future study. The use of feeding guilds to provide indicators for fish species at an aggregated level was explored, and proved to be an interesting alternative to aggregation by trophic level. 相似文献
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