Document Type

Article

Date of Original Version

2002

Department

Biological Sciences

Abstract

Many coastal fishes use inshore nursery habitats as juveniles, but it is often difficult to define which nursery areas supply most recruits to adult populations. We tested whether trace element concentrations in otoliths can be used to identify which of 2 nursery habitats (bays or shallow open coast) were occupied by juvenile California halibut. Juveniles from bays in 1998 had concentrations of Cu and Pb in their otoliths that were higher than those in open coast juveniles of the same year. This broad-scale difference between bay and open coast juveniles remained intact when bay juveniles from 1994 to 1997 were added to the comparison, and juvenile halibut could be assigned to their nursery habitat of origin quite accurately (83%) using otolith concentrations of Cu and Pb. At a finer spatial scale, otolith concentrations of Cu and Pb differed among individual bays, and fish from the same bay could differ among years, precluding their use as markers of nursery habitat use at these scales. Like halibut otoliths, sediments from bays had higher concentrations of Cu and Pb than open coast nursery sites, and this difference was consistent over 11 yr. Otoliths and sediments from individual bays, however, showed no correlation in Cu and Pb concentrations. The concentration of Cu and Pb in sediments and their deposition in otoliths were thus loosely matched at a broad scale, though the underlying cause of this link is not known. A discriminant model, parameterized using Cu and Pb levels in juvenile otoliths, was used to classify prior nursery habitat use by 19 larger halibut (of unknown origin). Eleven of these halibut had high levels of Cu and Pb in the part of the otolith deposited as a juvenile, and were classified as of bay origin. The other 8 halibut had low otolith Cu and Pb levels in the juvenile portion of their otoliths and were classified as having used open coast nurseries. Overall, our results suggest that this approach has the potential to allow identification of nursery habitat use by California halibut at a broad scale (bay vs open coast) but not at a fine scale (individual bays).

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