Setting economic target reference points for multiple species in mixed fisheries

This publication was produced by CSIRO for the Fisheries Research and Development Corporation with research and data support by ABARES.

The report develops a framework that can be used to assist managers to cost effectively develop target reference points that are consistent with the Commonwealth Harvest Strategy Policy for multispecies in mixed fisheries. The report addresses the problem of determining appropriate target reference points for target and by-product stocks in multispecies fisheries. The applicability of this framework is demonstrated using a case study fishery, the trawl component of the Southern and Eastern Scalefish and Shark Fishery.

The report uses generic logistic and exponential bio-economic models to produce a target reference point consistent with the current management framework taking into consideration a wide range of biological and economic conditions. The output was included in the development of a generic decision support framework using two cost effective approaches: regression tree analysis and the Bayesian Network approach. Sensitivity tests were also conducted on all 4 models. The project also develops a separate set of bio-economic models specific to the trawl component of the Southern and Eastern Scalefish and Shark Fishery examining the static and dynamic aspects of maximum economic yield.

The results from the generic models suggest that the key determinants of the target reference point of individual species in multispecies mixed fisheries are catchability, growth rates and share of total fishery revenue. Other variables, such as costs of fishing, prices and number of species in the fishery are also influential but to a lesser degree. For the case study fishery, both of the cost effective approaches performed well and achieved better results than the current default proxy target reference point. An incidental result from the study is that attempting to impose a target reference point on all species may not be necessary (or feasible) in multispecies fisheries. Instead, imposing a target on the dominant species (in terms of revenue share) for each sub-fleet results in outcomes close to optimal, and reduces conflicts in catches where target reference points are not perfectly aligned.