Population Structure and Regional Connectivity of Young Snowy Grouper in the Gulf of Mexico and Western Atlantic Ocean

Abstract

Snowy Grouper Hyporthodus niveatus are long-lived, slow-growing demersal fish that occur throughout most of the western Atlantic Ocean. Currently, Snowy Grouper in U.S. territorial waters are managed as two stocks, one along the eastern Atlantic coast and one in the Gulf of Mexico (GoM), though population connectivity throughout the region is unknown. The population structure of juvenile Snowy Grouper in U.S. territorial waters was assessed with otolith chemistry analysis, both trace element (⁷Li, ²⁴Mg, ⁵⁵Mn, ⁸⁸Sr, and ¹³⁷Ba) and stable isotope (δ¹³C and δ¹⁸O), from three life stages (core [first-year deposition], edge [most recent deposition], and life [mean of lifetime deposition]) across four geographic regions (northwest GoM, northeast GoM, southeast GoM, and U.S. East Coast). Dissimilar element : Ca signatures were evident across regions for all three life history stages, with regional patterns in individual markers following expected differences in environmental chemistry based on the geographic location of dominant mesoscale features (Mississippi and Atchafalaya River system, Loop Current, and Gulf Stream) and associated physicochemical conditions. Moderate classification success of Snowy Grouper to collection region with lifetime signatures indicated that the population along the U.S. East Coast experienced different physicochemical conditions than individuals inhabiting the GoM. The close adherence in regional patterns of otolith chemistry with expected environmental chemistry indicates that movement of individuals is limited and population connectivity constrained in U.S. territorial waters.