Recent growth rate of larval pilchards Sardinops sagax in relation to their stable isotope composition, in an upwelling zone of the East Australian Current

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. © CSIRO 2005.