Modelling the potential transport of tropical fish larvae in the Leeuwin Current |
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| Authors: | A Pearce D Slawinski M Feng B Hutchins P Fearns |
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| Institution: | 1. Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia;2. Western Australian Department of Fisheries, PO Box 20, North Beach, WA 6920, Australia;3. CSIRO Marine and Atmospheric Research, Private Bag 5, Wembley, WA 6913, Australia;4. Western Australian Museum, 49 Kew Street, Welshpool, WA 6106, Australia;1. Department of Ocean Sciences, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA;2. Cooperative Institute of Ocean Research, Exploration and Technology, Harbor Branch Oceanographic Institute, Florida Atlantic University, Fort Pierce, FL 34946, USA;1. Remote Sensing Group, Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK;2. National Oceanography Centre, European Way, Southampton SO14 3ZH, UK;3. Scottish Association for Marine Science, Oban, Argyll PA37 1QA, UK;1. School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia;2. BioMedware Inc., 121 W. Washington St., 4th floor-TBC, Ann Arbor, MI 48104, USA;3. Centre for Marine Ecosystems Research, School of Natural Sciences, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia;1. Centre for Fish and Fisheries Research, School of Veterinary and Life Sciences, Murdoch University, South Street, Perth, Western Australia 6150, Australia;2. Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PLI 3DH, United Kingdom;1. Edith Cowan University, 270 Joondalup Drive, Joondalup, WA, 6027 Australia;2. Department of Primary Industries and Regional Development, PO Box 20, North Beach, WA, 6920 Australia |
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| Abstract: | Application of an individual-based particle tracking model to the migration of tropical fish larvae along the continental shelf between the Houtman Abrolhos Islands and Rottnest Island (Western Australia) has shown that there is potential for the southwards advection of passive particles/larvae in the Leeuwin Current system throughout the year. However, seasonal variations in the prevailing wind field result in corresponding seasonal changes in the surface current flow (both alongshore and cross-shelf) on the continental shelf, leading to a pulse of modelled particles arriving at Rottnest Island during the autumn months. This matches, within a month, the observed April/May peak in annual recruitment of 2 species of damselfish (Abudefduf sexfasciatus and A. vaigiensis), at the time when the Leeuwin Current is strengthening. It is assumed that the larvae are in the uppermost 20 m of the water column and that there are no vertical diurnal movements.The model has a 10 km grid spacing, and so can resolve some of the current gradients across the continental shelf. Comparison of the modelled near-surface currents with ADCP measurements at 2 current mooring sites as well as with a broader range of historical current measurements off south-western Australia indicates that the alongshore net transport is reasonably well reproduced by the model, whereas agreement with the cross-shelf flow is not as good (this may be partly attributed to the paucity of high-quality near-surface current measurements in the area of study). Because of limitations in our knowledge of the swimming ability, choice of swimming direction and habitat selection of larval fish, as well as the inability of the model to reproduce the small-scale circulation around Rottnest Island, the swimming capacity of the late-stage larval fish is not specifically included; they are considered as potential settlers once they have reached within 20 km of the Island.The observed inter-annual variability in recruitment is not as well matched by the model as is the seasonal pattern, but this is almost certainly due to uncertainties in biological factors such as spawning strength, food and predation en route, which are not known.The modelled results are also applied to a more general discussion of the transport of eggs and larvae of commercial fish and invertebrate species on the Western Australian continental shelf, and it is shown that the seasonality and position on the shelf of the spawning may play a large role in the movement (and hence survival and ultimate recruitment) of different species. |
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