Through the stomach of a predator: Regional patterns of forage in the diet of albacore tuna in the California Current System and metrics needed for ecosystem-based management

Abstract

Foraging habits of predators can reveal patterns in prey ecology and guide ecosystem-based management by informing species interactions. This study describes the diet habits of albacore tuna in three regions (north, central, south) of the California Current System (CCS) and estimates the total predation mortality imposed on twenty prey taxa. The northern CCS was defined by predation on decapods, euphausiids, anchovy and hake. The central CCS was defined by predation on squid, hake and Pacific saury. The southern CCS was defined by predation on anchovy. We estimate North Pacific albacore consumed each year, on average, 54,000mt of decapods and euphausiids, 43,000mt of cephalopods, 84,000mt of juvenile hake, 1600mt of myctophids, 21,000mt of juvenile sardine, 10,000mt of juvenile rockfishes, almost 43,000mt of Pacific saury, and over 107,000mt of juvenile anchovy. While variability in predation certainly exists, this and prior studies show that diet habits of albacore are fairly stable through time. The northern CCS appears to be a more significant source of energy for albacore. When designing ecosystem-based approaches to the management of CCS-based fisheries, we recommend that the forage contribution of saury, hake and anchovy to the albacore population be considered.