The proposed work is fundamental for assessment and sustainable, optimal harvest of Australia’s Spanish mackerel resources. This goal requires accurate information on which management decisions can be based. This project therefore seeks to describe the stock structure of a national shared resource, with a view to the development of complementary management approaches.

The NT, WA, Qld, Torres Strait and NSW have separate management regimes for the mackerel fisheries in their waters. However, our lack of information on stock structure means that the appropriate scale of management units is just not known. It is unlikely that it will coincide with current administrative boundaries. Basic questions such as whether management actions in one state will impinge on the fisheries of others cannot yet be answered. With such uncertainty, for example, would declines in one area reflect interception during migration, or over-fishing of spawners in another area? Different responses to such questions may require fundamentally different management approaches. Hence the Northern Australia Fisheries Management meeting of May 1997 recognized that stock definition was required for effective assessment and management of this species.

Most fishery assessments assume a randomly mixed unit stock; an alternative is to explicitly include spatial dynamics. Possibly with the exception of the east coast, there is no real basis for defining Spanish mackerel unit stocks. In none of the Australian fisheries are spatial relationships sufficiently understood to be addressed in assessments. The proposed research is requisite for basic stock assessment, and the first step in developing spatially structured models and management.

Spanish mackerel are also taken across our northern boundaries, in Indonesia, Papua New Guinea, and Pacific Island states. The proposed research is the basic work necessary to develop the methodology and information base for future research into these shared stocks, and for future studies into fine-scale spatial dynamics.

Recently available information suggests the Spanish mackerel fishery is growing rapidly in both commercial and recreational sectors. This underlines the need for this work as a basis for rational management. Commercial catches in WA and NT have increased substantially in recent years, and prices continue to rise. A recent recreational survey in NT revealed that recreational Spanish mackerel catches are of similar order to commercial catches. The species is a favoured target in the rapidly-growing and lucrative fishing tour sector.

The need for good for stock assessment is thus growing. Each state has responded with FRDC- or internally-funded programs. The results of this project could substantially change the directions of these projects, by establishing whether the assessment and management should be on a joint basis across states, or whether they should be on a more regional basis.