Designing Aquatic Protected Areas - the Use of Otolith Microchemistry to Determine Stock Structure of Reef Fish Metapopulations

Mikaela Bergenius, Peter Doherty, Michael Kinsford and Garry Russ

CRC Reef, TOWNSVILLE, AUSTRALIA

Theme: TH2

Scale and boundary effects that influence critical life-history processes such as larval dispersal, connectivity and metapopulation structure are important considerations in the design of aquatic protected areas (APAs) for the conservation and enhancement of exploited reef fish populations. Adult reef fish populations tend to be relatively sedentary, but are regarded as 'open' because replenishment of one subpopulation (or stock) might be dependent on recruits from other subpopulations. Identifying the source of these recruits is crucial to understanding the connectivity between subpopulations, but has proven difficult. While information on stock structure of exploited tropical reef fish is urgently needed, the choice of technique for stock identification must be carefully considered in relation to the objectives of the APA. For example, if the aim of the APA is to protect genetic biodiversity then information on the genetic structure of fish stocks is necessary, but if it is to prevent overfishing and localised depletion then other phenotypic or population dynamic measures may be more informative. In this contribution, we investigated the use of otolith microchemistry to identify stock structure in common coral trout, Plectropomus leopardus, metapopulations in the Great Barrier Reef World Heritage Area. The use of trace elements incorporated into fish otoliths from the water column has proven successful in defining temperate fish population structures and tracing migration paths, but equivalent studies on reef fish populations are rare. We compared the otolith microchemistry signal in coral trout on a broad regional and finer reef scale. We also examined the temporal stability in these signals by comparing the otolith microchemistry signal of two cohorts at all spatial scales. As a difference in the otolith microchemistry of adult reef fish would indicate the possibility of back-tracking movement, as well as identifying the origins of newly recruited fish, we discuss the potential of using this technique for examining dispersal and connectivity between subpopulations. For exploited reef fish metapopulations, APAs should be designed to encompass those reefs which function as necessary sources of larval supply to other inter-connected reef fish populations.