Episodic High‐Latitude Occurrence of Walleye Pollock ( Gadus chalcogrammus ) in the Central Arctic Ocean Associated With Warm Subsurface Conditions: Multi‐Year Environmental DNA and Larval Evidence

Abstract

ABSTRACT Episodic high‐latitude occurrences of subarctic fish due to Arctic warming present significant challenges for managing high‐latitude ecosystems. In this study, we present four consecutive years (2021–2024) of integrated environmental DNA (eDNA) monitoring and larval surveys for walleye pollock ( Gadus chalcogrammus ) conducted aboard the Korean icebreaker IBR/V Araon in the Chukchi Sea (CS) and Central Arctic Ocean (CAO). Of the 342 eDNA samples from 180 stations (55°N–76°N, spanning the Bering Sea, CS, and CAO, including underway surface‐pump stations), walleye pollock eDNA was detected in 25 samples (7.3%), with annual detection rates ranging from 2.8% to 13.2%. In 2024, eDNA was detected at 75°58′N, representing the northernmost molecular record for this species and extending beyond the previous northernmost trawl record (75.44°N). Larvae were collected in 2021 ( n = 5; standard length [SL]: 3.4–5.1 mm) and 2022 ( n = 3; SL: 9.7–14.6 mm) but were absent in 2023 and 2024 despite peak eDNA detection, indicating that northward pollock occurrence has not yet resulted in successful local reproduction. eDNA‐positive stations exhibited significantly warmer bottom temperatures than negative stations ( U = 2845, p = 0.0012; odds ratio [OR] = 1.74/°C [95% confidence interval (CI): 1.25–2.44]). Detection rates and the spatial distribution of positive stations differed markedly between years: In 2023, two stations yielded positive detections over a 1.2° latitudinal span, whereas in 2024, seven stations were positive spanning 10.8° (65°N–76°N), although interannual variation in detection rates was not statistically significant. Overall, these findings provide the first multi‐year molecular evidence that walleye pollock occur episodically at higher latitudes than previously documented, with detections spatially correlated with warmer subsurface bottom temperatures. This pattern is consistent with ongoing atlantification, which may promote the occurrence of pollock at higher latitudes. However, a causal relationship cannot be established because hydrodynamic transport data were not available.