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Isotopic Differences between the Left and Right Side Otoliths of Flatfish Indicating Growth rather than Environment

Yongwen Gao, Joseph Petersen, Robert Conrad and David L Dettman

This paper reports a new result for the isotopic differences between the left and right sagittal otoliths of Pacific halibut Hippoglossus stenolepis, a flatfish with both eyes on the right side. Using microsampling techniques we were able to collect subsamples from the nucleus and the 5th and 8th annulus from 63 pairs of halibut otoliths. Isotopic analyses of δ13C and δ13C showed that there was a significant difference between the left and right side otoliths from the nucleus in both Washington Coast and Puget Sound samples; but no significant difference from the 5th and 8th annuli of the same otoliths. These results were difficult to be explained as the differences in environmental parameters between ocean and estuary, but the mass accumulation from growth bias that was caused by gravitational force. The management implications on the results are clear: when using the nucleus of flatfish samples on stock structure investigations, one should consider the possible isotopic differences between the left and right side otoliths. However, when using the same samples for adult population, one may choose otoliths from both sides.