Stock discrimination of pilchards Sardinops sagax by stable isotope ratio analysis of otolith carbonate

  • Edmonds J
  • Fletcher W
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Abstract

Measurement of the ratios of the stable isotopes 1 8 O: 1 6 O and 1 3 C: 1 2 C, by standard mass spectrometric techniques, in the otolith carbonate of samples of pilchards Sardinops sagax from coastal waters adjacent to the 4 main fishing ports of southwestern Australia (Fremantle, Albany, Bremer Bay and Esperance) provided location-specific signatures which showed that Fremantle fish could be regarded as a separate stock from those taken at the other 3 locations, and fish from Esperance constituted a different stock from those fish taken at Albany and Bremer Bay. The isotope signatures for fish from the different locations persisted through time, and it could be concluded that they comprised separate stocks for most of the purposes of fisheries management. Values for ratios of stable oxygen isotopes in pilchard otolith carbonate indicated that they were probably deposited close to equilibrium and therefore reflected ambient water temperatures as governed by latitude and movements of the Leeuwin Current. This suggested that the measurement of ratios of stable oxygen isotopes can be a valuable method for the discrimination of management units of adult fish where the range of distribution of a species covers waters of different temperatures.

Author-supplied keywords

  • Otolith carbonate
  • Sardinops sagax
  • Stable isotopes
  • Stock discrimination
  • Western Australia

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Authors

  • J. S. Edmonds

  • W. J. Fletcher

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