Chemical tags in otoliths indicate the importance of local and distant settlement areas to populations of a temperate sparid, Pagrus auratus

Abstract

Understanding geographic origins of fish is essential to the management of fisheries and protection of critical juvenile habitats. We used natural chemical tags (Mn, Sr, and Ba), characterized from otoliths of 0+ snapper (Pagrus auratus) (approximately 1–3 months postsettlement), to determine the origins of 1- and 2-year-old (subadult) fish about to recruit to the Victorian fishery. We sampled subadults from eight areas across 700 km of coastline and within the major Victorian fishery, Port Phillip Bay. Maximum likelihood analyses indicated for both cohorts that most subadults in Port Phillip Bay and a significant proportion from west Victorian coastal waters had settled within Port Phillip Bay. The contribution of the Port Phillip Bay settlement area to coastal populations, however, decreased with distance to the west, varied between cohorts, and was negligible at locations over 200 km to the east of the bay. Comparison of elemental tags between 0+ fish of known settlement origin and the subadults indicated that unknown settlement areas may have contributed recruitment to one of the cohorts. These results have highlighted the importance of local settlement areas to sustaining the major Victorian fishery, but small juveniles can migrate large distances from this settlement area and contribute to coastal populations.