Otolith chemistry and redistributions of Northern cod: evidence of Smith Sound – Bonavista Corridor connectivity

Abstract

Stable oxygen isotope assays of otoliths (δ 18 O oto ) from migrant Atlantic cod (Gadus morhua Linnaeus, 1758) that overwintered in Smith Sound, Newfoundland, during 1995–2006 differed from those of nonmigrating summer residents and cod from Placentia Bay and Halibut Channel but did not differ from those of cod from the adjacent offshore Bonavista Corridor in summer. All fish sampled were of the 1990 year class (founder of the Smith Sound aggregation) at ages 8–10 years. Hence, overwintering Smith Sound and summering Bonavista Corridor cod likely experienced similar temperatures and salinities in each year of life, representing different migration stages of an intermixed group. Moreover, predictions of δ 18 O oto from near-bottom ocean temperatures and salinities differed between inshore and offshore sites and, in general, matched observed signatures of inshore and offshore cod. The Bonavista Corridor cod, however, were an exception, having δ 18 O oto signatures suggestive of inshore exposure. Our findings provide direct evidence of metapopulation structure in the Northern cod and are consistent with offshore rebuilding having been spurred by dispersal of cod from inshore Smith Sound.