Leeuwin Current eddies and potential impacts on Western Australian coastal fisheries
Beckley, L.E., Holliday, David, Muhling, B.A., Gaughan, D.J. and Waite, A.M. (2007) Leeuwin Current eddies and potential impacts on Western Australian coastal fisheries. In: AMSA2007, 9 - 13 July, Melbourne, Australia.
In the eastern Indian Ocean, the anomalous Leeuwin Current has been reported to influence fisheries production, although the exact mechanisms remain unknown. The current, which flows southwards along the shelf-break, intensifies during the autumn and generates numerous meso-scale eddies which propagate offshore into the Indian Ocean. Cyclonic, cold-core eddies may be significant for the input of upwelled nutrients whilst anticyclonic, warm-core eddies provide a mechanism for the entrainment of coastal water, and may cause offshore transport of neritic plankton. The potential impact of meso-scale eddies on Western Australian coastal fisheries depends largely on the spawning season of the target species as well as the duration of the pelagic larval phase. Most coastal finfish species have pelagic larval durations of a few weeks and if, after a short period of entrainment in eddies, they are able to return to the shelf, they could benefit from concentrated food resources within the eddies. On the other hand, if these larvae cannot escape as the eddy propagates offshore, then eddies probably result in increased natural mortality for neritic fishes. In contrast, rock lobster have characteristic phyllosoma larvae with pelagic durations of 9-11 months and, if entrained in eddies, could experience improved feeding conditions, in addition to being retained in the ocean adjacent to the area of adult distribution. Data from the SRFME biophysical oceanography study along the Two Rocks transect (2002-2005) and two research cruises aboard the RV Southern Surveyor undertaken to study the biological oceanography of Leeuwin Current eddies (October 2003 and May 2006) will be drawn upon to illustrate the above hypotheses.
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