Management of multi-species tropical fisheries, Final Technical Report.
The final report summarises the purpose, activities and results (outputs) of the project. Detailed guidelines for management are given here. General conclusions from practical and theoretical studies are drawn (contribution of outputs). A second part of the report describes the detailed results. The effects of fishing on multispecies resources are not clearly understood. Models for assessing and managing them are frequently data hungry, and unsuitable for developing country fisheries institutions. This project aimed to assess fishing effects, derive biological management guidelines, and describe minimum data requirements for demersal bank and deep slope reef fisheries, a relatively simple multispecies example, but with widespread applicability. To achieve this, data typically collected by developing country fisheries institutions from artisanal fisheries were analysed for case study fisheries in Tonga (deep slope) and the Indian Ocean (banks). Available local literature described the socio-economic context of each fishery. Theoretical studies were performed using a multispecies model developed for the project. Input parameters for modeling were derived from case studies. For fisheries similar to those studied, fishing removes top predators and is postulated to lead to prey release with implications for management. No evidence for prey release or other multispecies interactions was found, but species composition changes due to technical interactions were significant. Theoretical studies predicted prey release from 5 years onwards into a new fishery, but its magnitude was less than variation typically observed in available data indicating that prey release would be undetectable. These results suggested that single, and aggregate single species models were adequate to derive management advice. They also indicated that data need not be collected on all species individually, but on the most important species and guilds of others. Improved data collection in relation to technological changes in the fishery was, however, required. Biological data collection on identified key species was also important. Management simulations have resulted in guidelines for selecting a suitable target fishing mortality for species where length at maturity is unknown and length at first capture cannot be controlled. The guidelines suggest a means of selecting the most important and vulnerable species for analysis, and a method for setting overall effort limits for a multi-species fishery, taking into account different targeting practices and conservation trade-offs. Simulations indicated that closures are primarily useful as a means of reducing effort. Pulse fishing provided no benefit and did not result in long term changes in species composition. Recovery rates for depleted stocks were shown to be lower for deep slope than for banks species. Predator control was shown not to be a viable management option. Outputs of the project were promoted through seminars, presentations at international meetings, scientific papers and technical reports, and will be presented to collaborating institutions through working groups.
Marine Resources Assessment Group Ltd, London, UK, 195 pp.