MEPS 620:119-138 (2019)  -  DOI: https://doi.org/10.3354/meps12966

ABSTRACT: In North Pacific marine ecosystems, Pacific capelin Mallotus catervarius are abundant and ecologically important planktivorous fish in pelagic food webs. Environmentally driven changes in their distribution and abundance can affect the availability of capelin to predators, but there is limited information that describes how changes in ocean temperature are related to fluctuations in capelin range and density. A spatiotemporal, generalized linear mixed model was used to quantify the influence of temperature-related covariates on the occurrence and density of age-1+ capelin over the continental shelf in the central and western Gulf of Alaska (GOA) during a period of warm and cold years between 2000 and 2013. Variability in capelin distribution was explained by temperature factors that vary between bathymetric zones. Capelin are predicted to concentrate in moderately stratified waters (i.e. a temperature difference of 3 to 7°C) over shallow banks (<100 m bottom depth) and within deeper troughs (≥100 m). The optimal temperature range for capelin occurrence and catch rates was 8 to 10°C; steep declines occurred in waters warmer than 10.5°C. In contrast to expected northern latitudinal shifts during warm years, capelin shifted northeastward towards the Kodiak Archipelago during the coldest study year, and interannual variation in mean densities was not related to regional mean temperatures. Our findings demonstrate a spatially complex response by capelin to temperature variability over the GOA shelf, and highlight the importance of including potential differences in oceanographic properties among bathymetric zones that may influence distributions of pelagic species.

KEY WORDS: Bathymetry · Diel correction · Forage fish · Habitat · North Pacific · Spatiotemporal · Thermal stratification