Ocean jackets (Nelusetta ayraudi) are distributed from North West Cape (W.A.) through southern coastal waters to the south of Queensland. They have not been recorded from Tasmanian waters. Seawards their distribution ranges from coastal embayments where juveniles school seasonally to waters just off the edge of the continental shelf (Hutchins and Thompson, 1983). They mainly inhabit the mid­water bottom habitat over either sandy bottom (S.A.) or reef areas (N.S.W.). There are indications from studies in South Australia that ocean jackets may leave the continental shelf to spawn in offshore waters (Grove-Jones and Burnell, 1991 ).

In the 1940s and 50's there was an intensive trap fishery in N.S.W. This fishery suffered a dramatic decline and was subsequently replaced by a snapper trap fishery in the same area. Some ocean jackets are still taken in N.S.W. but the catch, which is probably less that 100 tonnes p.a., is difficult to estimate because most of it is sold to local markets.

More recently a commercial trap fishery developed in South Australia. The catch rose rapidly to almost 900 tonnes in 1988/89 (Anon., 1989). Since then the catch has levelled out but ocean jackets remain one of the largest marine scale fisheries (by weight) in South Australia.

Given the rapid success of the ocean jacket fishery in South Australia and the good eating qualities of the flesh, expansion of the fishery into other areas is a possibility. The past dramatic collapse of the N.S.W. fishery, the recent flattening off of the catch in South Australia and the suggested cohesion of the schools (Grove-Jones and Burnell, 1990) raise questions about the genetic stock structure of the ocean jacket population(s) in Australia.

This study examines the genetics of N. ayraudi as revealed by isozyme analysis. It investigates the feasibility of carrying out a full scale project aimed at determining whether the ocean jackets in Australian waters belong to one large interbreeding population or whether two or more discrete genetic stocks exist. This information is crucial to biologically appropriate management of the species.