INDO– PACIFIC: Australia

Dispersal, connectivity and marine reserves on the Great Barrier Reef

Researchers from James Cook University in Australia are currently undertaking a reef fish tagging project within the Keppel Island group in the southern Great Barrier Reef Marine Park (GBRMP). The tag, release and recapture project is aimed at shedding light on fish movements within and between reefs, larval dispersal, population connectivity and export effects of no-take marine reserves.

Recreational fishers worked with the research team to catch, tag and release over 6,500 reef fishes within Marine National Park (green) zones (no-take marine reserves) of the Keppel Island group during late 2007 and early 2008. The research was carried out during the peak spawning season for these species in the southern GBR region.

Fish were captured using hook and line, measured, externally tagged, fin clipped for a DNA sample and quickly returned to the water. Additionally, bar-cheek coral trout (Plectropomus maculatus), long-fin grouper (Epinephelus quoyanus) and stripey snapper (Lutjanus carponotatus) were injected with an enriched stable isotope barium chloride solution. The stable isotope functions as a trans-generational marker which is passed from female fish to their developing eggs. The marker is subsequently expressed as an unequivocal altered barium isotope signature in the otoliths of the offspring.

Beginning in April 2008, recruits of bar-cheek coral trout, long-fin grouper and stripey sea perch were collected from reefs in the area. Otoliths were removed from the recruit fish and scanned for the barium isotope marker using laser ablation inductively coupled plasma mass spectrometric (LA-ICPMS) analysis. When marked otoliths are detected, the natal reef of that fish can be identified and larval dispersal distances and directions calculated. DNA samples taken from the recruited fish are also being cross-validated with DNA samples from adult fish in a parentage analysis to complement the larval marking and recapture component of the study. Analysis of samples is currently underway; however preliminary results have been encouraging. Several barium tagged individuals have been detected within the samples scanned thus far and it is evident that there has been some dispersal of larvae from within no-take marine reserves to surrounding fished areas. Analysis of all otolith and genetic samples will be completed by late 2009. The larval dispersal data is being incorporated into a high resolution coupled bio-physical model for the southern GBR region.

A combination of underwater visual census (UVC) and recaptures of tagged adult fish is providing insights into rates of adult fish export (spill-over) from no-take marine reserves to surrounding fished areas. UVC was also used to quantify the size and number of fish involved in spawning aggregations and the relative number of tagged to untagged fish participating in the spawning aggregations. Data obtained on fish spawning aggregation sites will be entered into databases coordinated by the Great Barrier Reef Marine Park Authority and the Society for the Conservation of Reef Fish Aggregations (SCRFA). The adult fish movement component of the study should be completed by late 2009.

David Williamson
James Cook University, & ARC Centre of Excellence for Coral Reef Studies.
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