We then calculated an index of spatial overlap across a uniform grid by multiplying standardized predictions of species’ abundance. We restricted analyses to fish measuring 30 to 69 cm fork length and used a delta modeling approach to quantify species-specific presence-absence and catch-per-unit-effort as a function of survey year, tow location, depth, and bottom temperature. To assess the potential for competition between Pacific Halibut and Arrowtooth Flounder, we evaluated their degree of spatiotemporal and dietary overlap in the Gulf of Alaska using bottom trawl survey and food habits data provided by the Alaska Fisheries Science Center (NOAA 1990 to 2017). Among the prevailing hypotheses for reduced size-at-age is intensified competition with Arrowtooth Flounder ( Atheresthes stomias), a groundfish predator that exhibited nearly five-fold increases in biomass between the 1960s and mid-2010s. Pacific Halibut ( Hippoglossus stenolepis) support culturally and economically important fisheries in the Gulf of Alaska, though recent decreases in mean size-at-age have substantially reduced fishery yields, generating concerns among stakeholders and resource managers.
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