Application of otolith chemistry at multiple life history stages to assess population structure of Warsaw grouper in the Gulf of Mexico

PJ Sanchez,MA Dance,JR Rooker,B Falterman,J Pinsky,M Zapp Sluis,RJ Allman

doi:10.3354/meps13457

Abstract

Chemical markers in otoliths have been used to assess the stock structure of many marine fishes, but these natural markers have yet to be widely evaluated or applied to demersal fishes in offshore habitats where physicochemical gradients are generally less pronounced relative to nearshore waters. To address this, we quantified trace elements (Li, Mg, Mn, Co, Cu, Zn, Sr, Ba) and stable isotopes (δ13C and δ18O) in otoliths of Warsaw grouper Hyporthodus nigritus from 4 regions in the Gulf of Mexico (Texas, Louisiana, Alabama-NW Florida, and SW Florida). Region-specific differences in otolith chemistry were observed, and notable differences in several influential markers (Mn:Ca, Sr:Ca, and Ba:Ca ratios and δ18O) were present, particularly between the most distant regions investigated (Texas/Louisiana and SW Florida). Distinct regional signatures were observed for Warsaw grouper across 3 life history stages: first year (otolith core), most recent years (otolith edge), and lifetime (whole otolith), suggesting that individuals within certain regions share common environmental histories that may represent unique contingents or sub-populations. Findings also demonstrate that spatial variability within these markers was consistent enough to overcome any temporal variability within the geographic domains investigated for all 3 life history stages, highlighting their potential value for assessing the natal origin, exchange, and population structure of this species and potentially other members of the deepwater fish assemblage.

Highlights

A variety of techniques are used to assess the movement and stock structure of marine fishes, including genetic markers (Ruzzante et al 2000, Beltrán et al 2017), conventional and electronic tagging (Merten et al 2016, Rooker et al 2019), and natural tracers in fish hard parts (Rooker et al 2010, Wells et al 2010, Kitchens et al 2018)
Distinct chemical signatures and high overall classification success (~85% or above) to specific geographic regions indicate that the Warsaw grouper population in the Gulf of Mexico (GoM) likely consists of multiple stock components (Kalish 1989, Ashford et al 2012, Tanner et al 2016), with contingents or sub-populations emerging in the NW/NC/NE GoM and the SE GoM
The singlestock framework currently used to manage the population may not accurately represent the actual population structure of Warsaw grouper in the GoM, which compromises the management of the stock

Summary

Introduction

A variety of techniques are used to assess the movement and stock structure of marine fishes (see review by Cowen et al 2007), including genetic markers (Ruzzante et al 2000, Beltrán et al 2017), conventional and electronic tagging (Merten et al 2016, Rooker et al 2019), and natural tracers in fish hard parts (e.g. otoliths, spines, vertebrae) (Rooker et al 2010, Wells et al 2010, Kitchens et al 2018). Warsaw grouper Hyporthodus nigritus (Epinephelidae) are a species of concern in the western Atlantic Ocean due to harvest pressure from recreational and commercial fisheries (Farmer & Karnauskas 2013, Aguilar-Perera et al 2018, Shertzer et al 2018). These fish are periodic strategists within the Winemiller & Rose (1992) trilateral continuum (high fecundity, late maturity, and long lived) that spawn in the spring and summer along the outer continental shelf (Smith 1971, Manooch & Mason 1987, Parker & Mays 1998, Sanchez et al 2019). As the second largest grouper species in the western Atlantic Ocean (> 230 cm total length) and with an elevated trophic status (i.e. apex predator), Warsaw grouper exert topdown regulation and play an important ecological role in structuring deepwater communities (Shurin et al 2002)

Methods

Results

Conclusion