Modelling multi-species fishery dynamics (B4.4)

Task leader: Dr Gavin Begg, James Cook University.

Task associates:
Mr Duncan Souter, Queensland Seafood Industry Association
Mr Russell Martin, Great Barrier Reef Marine Park Authority.

Fishing for a range of fish species, termed multi-species targeting, is fairly unique in world commercial fisheries and presents a number of challenges to Queensland’s fisheries managers. Multi-species targeting needs to be considered when formulating management strategies so that the flexibility in fishing operations is taken into account, and that all targeted species are adequately protected. Little is known, however, about the effects of this target-switching behaviour on either the patterns of fishing by operators or the sustainability of the fish stocks upon which the fishery depends. The F&F team has been funded by the Fisheries Research and Development Corporation to investigate multi-species targeting in the Queensland reef line fishery and examine its effects on the distribution of effort and fish stocks.

This task builds on single species population and effort dynamics models developed for coral trout as part of the Effects of Line Fishing (ELF) Project, and extends them to include other main target species (especially red throat emperor) in reef line fishery.

In the first component, the existing simulation models will be extended to include the two primary demersal target species in the reef line fishery (common coral trout and red throat emperor). The extension to the population dynamics model will involve modification of the existing population dynamics model for coral trout to include the demographic parameters for red throat emperor. This extension will draw on the biological information for red throat emperor gained through the Effects of Line Fishing on the Great Barrier Reef (task B4.2) and Population dynamics and stock structure of the Red Emperor and other target species of the Queensland Tropical Reef Line Fishery (task B4.3.1) and will be based on the assumption that the population dynamics of the two species and their response to harvest differ. Biological species interactions are not included in the extension to a multi-species model.

The second component of the extension will be the incorporation of multi-species targeting behaviour into the fleet dynamics model. This will build on the fleet dynamics model developed for coral trout by including information on red throat emperor (catch rate, price, distribution, relative profitability, etc) in the decision rules for the spatial and temporal distribution of effort. The underlying assumption here is that fishers include such information in their considerations of where and when to fish, and that including this additional information in the fleet dynamics model will improve our understanding of effort dynamics in the past and our ability to predict responses to alternative strategies in the future.

Objectives:

1. Document the decision-making processes that influence effort distribution of GBR line fishers in response to varying amounts of catch of target and non-target species and characterise the factors that result in changes in targeting behaviour by Great Barrier Reef line fishers.

2. Develop computer simulation models that predict the spatial distribution of effort by commercial line fishers in response to changing levels of catch of target and non-target species in the Queensland Coral Reef Fin Fish Fishery.

3. Formally evaluate alternative harvest and conservation management strategies for coral trout and red throat emperor for the Queensland Coral Reef Fin Fish Fishery, given models of changes in fishing strategy related to the harvest of multiple species, either through target switching or retention of significant by-product.