Albacore Tuna Diet and Foraging Ecology in the Northern California Current

Albacore tuna are an important commercial and recreational fish species that demonstrates high levels of variability in their abundance and distribution. Currently, the mechanisms leading to this variability, which influences catch and profitability, are poorly understood. One important but not well-characterized driver is likely to be foraging ecology (diets), including offshore of Washington and Oregon on the U.S. West Coast, which is a key feeding ground for juvenile albacore. This study examines albacore diet and spatial feeding ecology over an extended time-period covering a range of oceanographic conditions. Sampling years include El Niño, La Niña, El Niño neutral, and the anomalous marine heatwave of 2013 - 2016. Analysis of albacore gut contents from offshore of Washington and Oregon show potentially complex feeding behavior and high interannual variability in prey assemblages. Juvenile albacore diet appears to be less stable through time than assumed from previous studies. Prey include young of the year fish consisting of northern anchovy Engraulis mordax, Pacific saury Cololabis saira, rockfish Sebastes spp., and Pacific sardine Sardinops sagax, as well as cephalopods and crustaceans. Future ecosystem models may need to account for these more complex feeding behaviors. These results will contribute to adaptive fishery management strategies.