Climate-driven Oceanic Range Shift of Saint John River Atlantic Salmon Revealed by Multidecadal Stable Isotope Trends

David X. Soto^1,2,*, Michael J. Dadswell³, Kurt M. Samways¹, Richard A. Cunjak¹, and Tom McDermott⁴

¹Canadian Rivers Institute, University of New Brunswick, Fredericton, NB E3B 5A3, Canada. ²Current affiliation - Leibniz Institute for Zoo and Wildlife Research, Berlin 10315, Germany. ³Department of Biology, Acadia University, Wolfville, NS B4P 2R6, Canada. ⁴Marine Institute, Oranmore, Galway, Ireland. *Corresponding author.

Northeastern Naturalist, Volume 30, Issue 4 (2023): 521–539

First published early online: 26 December 2023

Abstract
Marine migration patterns of unique or regional stocks of Salmo salar (Atlantic Salmon) are poorly known. Atlantic Salmon (AS) utilizing the North Atlantic Subpolar Gyre (NASpG) for foraging and growth consist of stocks from the United States (41oN) to Greenland (64oN) in the western Atlantic and from Spain (41oN) to Norway (70oN) in the eastern Atlantic. Wide latitudinal range and unique riverine characteristics probably result in stocks selecting differing suites of marine sea-surface temperatures (SST) within the species’ known selection range (i.e., their Grinnellian niche). We analyzed trends in stable carbon isotope (δ13C) composition from archived scale tissues in relation to long-term variation of SST for the North Atlantic Ocean to identify marine feeding regions used by adult AS successfully returning to the Saint John River, Canada, during the period 1982–2011. Marine foraging regions were determined for individuals that spent 1 winter (1SW) or multiple winters (MSW) at sea. During 1982–1991 and 1992–2001, AS which successfully returned, exploited more southern regions of the NASpG, while returning adults from 2002–2011 exploited more northern regions. Historically presumed marine feeding regions, which were identified by the isotopic model as probable during 1982–2001, have experienced a warming trend, and data suggests that AS returning to the Saint John River have been migrating further north in the NASpG in response to recent global climate change. The northward range shift as the North Atlantic warmed is consistent with recent biogeographical changes found among other marine species also following their Grinnellian niche.

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