Distinguishing Wild from Hatchery-Produced Juvenile Red Snapper with Otolith Chemical Signatures

Abstract

Otolith chemical signatures were evaluated as natural tags to distinguish wild from hatchery-produced juvenile red snapper Lutjanus campechanus. Otoliths were sampled from 59 hatchery-reared fish and 146 wild fish collected over the continental shelf from northwest Florida to Texas. One sagitta from each fish was cleaned, dissolved in ultrapure nitric acid, and analyzed with sector field inductively coupled plasma mass spectrometry to test for differences in otolith element:Ca ratios (Ba:Ca, Li:Ca, Mg:Ca, Mn:Ca, and Sr:Ca) between wild and hatchery fish. The second sagitta was cleaned, ground to a fine powder, and analyzed with stable isotope ratio mass spectrometry to test for differences in delta (δ) values of the stable isotopes ¹³C and ¹⁸O. Significant differences existed in otolith chemical signatures between hatchery and wild juveniles (multivariate analysis of variance, Pillai's trace: P < 0.001). Jackknifed classification accuracies from linear discriminant function analysis indicated that hatchery fish could be distinguished from wild fish with 100% accuracy based on otolith chemical signatures. The most important otolith chemistry feature in distinguishing hatchery from wild fish was δ¹³C, with the mean difference in δ¹³C between hatchery and wild fish (−2.6‰) being similar to the mean difference in δ¹³C between hatchery feeds and the predominant food of wild juveniles (−2.8‰). Overall, results suggest that otolith chemical signatures may be employed as effective natural tags for mass marking of future stockings of red snapper or other marine fishes to estimate the hatchery contribution to wild populations.