Stock discrimination of the J apanese S panish mackerel ( Scomberomorus niphonius ) based on the otolith shape analysis in the Y ellow S ea and B ohai S ea

Summary Geographic variability in sagittal otoliths shape of the J apanese S panish mackerel ( S comberomorus niphonius ) was studied to test whether stock discrimination might be possible using this method. It was hypothesized that S . niphonius would show little difference in otolith shape, likely as a result of mixing between seas. A total of 164 sagittal otoliths were collected from commercial fishing vessels between A pril and J une 2010 in three spawning grounds, that of Q ingdao in the middle Y ellow S ea, L vsi in the southern Y ellow S ea, H uanghua in the the B ohai S ea. To minimize the potential effect of the fish size among the three fishing grounds, a narrow size range (400–550 mm fork length) was selected. The discriminant function analysis conducted with standardized otolith shape indices and F ourier harmonics produced classification success rates ranging from 57.0 to 88.2% and worked well in the separation between the B ohai S ea group and the Y ellow S ea group. No significant differences were detected among the three groups for the L vsi spawning grounds. The otolith variables showed a distinct gradual variation tendency with the movement of fish schools from south to north. The results suggest that stock from the B ohai S ea could be managed as a separate entity from those found in the Y ellow S ea.