Genetic stock assessment of two southern African inshore sparids


Bronze bream (Pachymetopon grande) and black musselcracker or poenskop (Cymatoceps nasutus) are slow-growing, long-lived, sparid fish. They are endemic to South African inshore waters and their stocks support important recreational and subsistence fisheries along the southern and eastern coasts. Despite species-specific management interventions, both stocks have experienced declines in recent history. Such unsustainable resource use derives from management practices based on a poor understanding of stock dynamics and movement patterns. Both species are highly resident (at different life-history stages) along inshore reefs, suggesting that stocks would benefit from “no take” Marine Protected Areas (MPAs). Linefish abundance and diversity have increased in such areas, but an assessment of the efficacy and potential of these reserves as sources for adjacent exploited areas is limited by an incomplete understanding of recruitment, movement, residency and population structure of these fishes. In this study, supported by the International Foundation for Science (IFS), Drs. Paul Cowley, Monica Mwale and I will provide a genetic assessment of stock structure and variability for these two species. A fragment of the highly-variable mitochondrial DNA control region will be sequenced from approximately 300 individuals of each species. This assessment will complement ongoing tagging studies in the examination of migration, recruitment and residency. Using long-term sampling, this study can also elucidate temporal variation in recruitment and recent changes in genetic diversity and demography. By comparing "no take" areas with adjacent exploited areas, this study will consider whether MPAs are effective repositories of genetic diversity. The extent to which genetic criteria can inform linefish management protocols will also be considered. Conceptually, traditional stock assessments can be compared to those derived from genetic data, and the extent to which genetic criteria can be employed as target reference points in Linefish Management Protocols will be considered. As such the study has the potential to serve as a template for future studies of commercially important southern African species.

Funding: International Foundation for Science, Sweden
Duration: 2008 - 2010