A full life history synthesis of Arrowtooth Flounder ecology in the Gulf of Alaska: Exposure and sensitivity to potential ecosystem change

In recent decades, Arrowtooth Flounder (Atheresthes stomias) has been the most abundant groundfish in the Gulf of Alaska and an apex predator with trophic links to many pelagic and benthic species. Its abundance and trophic status implies that a small change in survival may result in substantial uncertainty in the ecosystem, with potentially large effects across multiple species. A synthesis of Arrowtooth Flounder ecology in the Gulf of Alaska was undertaken to determine exposure to the environment during different life history stages, and to develop hypotheses regarding population response to environmental forcing. Historical data sets were used to identify mechanisms of interaction with the pelagic environment during the egg and larval phase, assess habitat utilization and trophic interactions from early settlement through adult life, and evaluate sensitivity and potential response of the population to climate-induced variability in the Gulf of Alaska ecosystem. Modeling approaches include Individual-Based Modeling of the planktonic drift phase from spawning to settlement, Generalized Additive Modeling to examine the effects of location, bottom temperature, and depth on the distribution and density of different size categories of fish, and Habitat Suitability Modeling which integrates presence-absence and environmental data to develop predictive maps of suitable habitat for early juveniles, late juveniles, and adults. A strategy of high endurance characterizes the early ontogeny phase. Spawning and hatching occur during winter in deep water where predation risk is relatively low, and cold temperatures along with intrinsically low metabolic rates ensure extended availability of yolk reserves, lowering the risk of larval starvation in a food-poor environment. Larval duration and drift is protracted, contributing to widespread delivery of larvae to coastal, continental shelf and slope waters throughout the Gulf of Alaska, as well as expected transportation into the Bering Sea through the Aleutian Island Passes. Connectivity between spawning and settlement areas is less directed and juveniles are more ubiquitous across depths than previously understood. Juvenile and adult Arrowtooth Flounder are habitat and prey generalists, with some ontogenetic shifts apparent. Based on this comprehensive ecological synthesis, a preliminary climate-related vulnerability assessment indicates low risk, high resilience overall for this species in the Gulf of Alaska. However, some stage-specific sensitivity is hypothesized primarily relating to the potential for exacerbated temporal mis-match between early larvae and suitable zooplankton prey with increased temperatures. Density-dependent effects during the juvenile to adult stage may constrain further increases in Arrowtooth Flounder biomass in the Gulf of Alaska. This comprehensive ecological approach to assessing environmental sensitivities across life history stages for a commercially and ecologically important fish species has substantial merit for furthering the ecosystem approach to fisheries management, especially in marine ecosystems where there are robust sampling programs across trophic levels.