The use of otolith chemistry to determine stock structure of three epinepheline serranid coral reef fishes on the Great Barrier Reef, Australia

We investigated the use of otolith chemistry to identify the stock structure of three epinepheline serranid coral reef fishes: Plectropomus leopardus, Cephalopholis cyanostigma and Epinephelus fasciatus. Chemical signatures of otoliths collected from the three species were compared on a broad regional scale and, for P. leopardus, also on a finer reef scale. The temporal stability in these signals was also examined by comparing two cohorts of P. leopardus, and C. cyanostigma and E. fasciatus from the same cohorts that were collected 2 years before and 2 years after a significant weather disturbance caused by a large tropical cyclone (Cyclone Justin) in March 1997. Results showed differences in otolith chemistry at various spatial scales, as well as between years and individuals collected before and after the cyclone. The results highlight the need to incorporate data from several years in studies using these techniques to discriminate temporary and possibly misleading signals from those that indicate persistent spatial structure in stocks. The difficulties in identifying stocks and stock boundaries in species with spatially complex population structures are discussed, as is the need for complementary analyses of life history characteristics to determine biologically and logistically appropriate management units.