Recent growth rate of larval pilchards Sardinops sagax in relation to their stable isotope composition, in an upwelling zone of the East Australian Current
Shinji Uehara A B , Augy Syahailatua B and Iain M. Suthers A CA School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
B Kuroshio Research Division, National Research Institute of Fisheries Science, 6-1-21 Sanbashidori, Kochi 780-8010, Japan.
C Corresponding author. Email: i.suthers@unsw.edu.au
Marine and Freshwater Research 56(5) 549-560 https://doi.org/10.1071/MF04221
Submitted: 20 August 2004 Accepted: 12 April 2005 Published: 22 July 2005
Abstract
The recent growth rate and stable isotope composition of larval pilchards, (Sardinops sagax, 6–29 mm standard length), captured in surface and near-surface waters, were examined in coastal upwelling and non-upwelling regions of the East Australian Current over two cruises during the austral summer of 1998/1999. Compared to the non-upwelled regions, larvae were larger in the upwelling regions, and yet the back-calculated recent growth over 2 days before capture was significantly less on both cruises. This surprising result is consistent with slower larval growth of this species near coastal Japan and California, where strong year classes may form in offshore waters. δ15N ratios were significantly correlated with larval length, indicating ontogeny in their diet. In November, slower growers in upwelled waters were enriched in δ15N and depleted in δ13C, consistent with expected ratios from diets derived from deeper water. The pilchard’s early life history off eastern Australia is proposed and compared with that off eastern Japan.
Extra keywords: age, back-calculation, condition, daily growth increments, fish larvae, Kuroshio, recent otolith growth, sagitta, Tasman Front, western boundary current.
Acknowledgements
We acknowledge the support of the Australian Research Council, and the National Research Institute of Fisheries Science (NRIFS), Japan. We thank the excellent seamanship of the captain and crew of the R.V. Franklin and the remarkable CSIRO support staff. Richard Piola provided considerable technical expertise during the cruise, Matt Taylor provided laboratory support and Jocelyn Dela Cruz provided the microzooplankton data. Laurent Vigliola kindly assisted with the modified Fry back-calculation. Two anonymous referees greatly improved the manuscript.
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