Where are the hake going? How age, environmental signals, and shelf habitat shape Pacific Hake (Merluccius productus) summer distribution

Rebecca Thomas, Julia Clemons, Stéphane Gauthier, Alicia Billings, Chelsea Stanley, Dezhang Chu, Elizabeth Phillips, John Pohl, Sabrina Beyer, Stephen de Blois

Sustainably managing a multinational fishery on a transboundary, relatively long-lived and migratory fish stock is challenging, especially in a changing ocean environment. In a warming world, Pacific hake (Merluccius productus, Merluccidae), jointly managed by the U.S. and Canada, have been hypothesized to move north. However, in recent years the proportion of Pacific hake in the northern part of their historical range has been declining. Because Pacific hake have a complex migration pattern depending on age and other factors, we developed models to relate the effects of fish age, length, biomass, El Niño conditions, and Pacific Decadal Oscillation (PDO) indices on interannual shifts in the latitudinal distribution of the Pacific hake stock, using fisheries-independent survey data spanning 30 years (1995-2025). We found that older Pacific hake and warmer PDO conditions significantly contributed to explaining the proportion of migration into the northern part of their range during summer months. Over the 30-year time series, Pacific hake exhibited a southward shift in their northern extent, along with a decrease in area occupied, suggesting a change in movement patterns and overall contraction of the stock. Distance from the continental shelf break positively correlated with age for fish up to 8 years old. We estimated that 95% of the Pacific hake biomass occurred within 31 nautical miles of the shelf break, and that the distribution of Pacific hake extends farther offshore as biomass increases. These results provide insight on interannual shifts in the distribution of Pacific hake that can inform predictions for future management strategies.