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Fish biology and ecology in area closure planning

This PhD project examines some of the biological and ecological aspects of key fish species to provide data for spatial closure (MPA) planning. Primarily this study is looking at:

  • small scale patterns in coral trout reproductive activity;
  • coral trout spawning aggregations;
  • movement patterns of coral trout and baldchin groper through acoustic tracking; and
  • acoustic tracking of Mulloway to spawning aggregations.

The biological examination of coral trout (Plectropomus leopardus), being conducted at the Houtman Abrolhos Islands, has revealed some interesting preliminary results in patterns of spawning activity.

Both downloadable documents show the relative proportion of gonad (GSI; Figure A) and fat (FSI; Figure B) to total weight for fish caught during the 2006 spawning period for one island groups at the Houtman Abrolhos Islands. Only fish inside the Reef Observation Area (Finfish protected area; outlined in pink) and just outside are reproductively active during the spawning period (Figure A). Those same fish however have a low fat content (Figure B) where as those fish from the west part of the island group have considerably higher fat content for their body weights but aren't reproductively active. This is a preliminary finding and will be explored more in coming seasons to see if the pattern is consistent both temporally and spatially. This may have important ramifications in the design or protected areas, or possibly the impacts of protected areas on species biology.

Coral trout form spawning aggregations. One such aggregation has been discovered at the Houtman Abrolhos Islands and will be examined through the next few spawning seasons to see if it conforms to patterns shown by coral trout on the east coast. It will provide valuable information should temporary spawning closures be required to protect this highly prized species enabling appropriately timed closures of a sufficient duration.

Fish movement is a critical part of understanding the geographic scale of protection required. The coral trout (P. leopardus) and baldchin groper (Choerodon rubescens) have showed differing response to closure, which is thought to be a result of their different movement patterns (Nardi et al 2004). This aspect of my PhD, conducted towards the end of 2007, will involve acoustically tracking several individuals from both species in a protected area at the Houtman Abrolhos Islands to determine their home ranges and habitat preferences.

The mulloway (Argyrosomus) is known to form spawning aggregations in the Swan River. Understanding the timing of this aggregation and fish movement to and from it is critical should any protective measure be required. This would allow temporal closures to be implemented to provide maximum protection to the fish, while minimising impacts on fishers. Initial range test of acoustic equipment has begun in the river and acoustic tracking will begin when the mulloway move into the river (approximately October 2006).

Researchers

Mr Jason How
Associate Professor Glenn Hyndes
Department of Fisheries Western Australia, Jill St John

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