Interdecadal variability in predator–prey interactions of juvenile North Pacific albacore in the California Current System

Abstract

Predator-prey interactions are critical components of multispecies models, and most attempts to quantify these interactions in pelagic marine environments rely on observational diet studies. In conjunction with 3 historical studies, a new diet study quantifies decadal patterns of predator-prey interactions for juvenile North Pacific albacore Thunnus alalunga in the California Current System (CCS). Juvenile albacore in the CCS eat young-of-year prey and derive 68 to 89% of nutrition from fishes, 9 to 30% from cephalopods, and the remainder from crustaceans. Despite resurgence in abundance of Pacific sardine Sardinops sagax in the CCS, only Northern anchovy Engraulis mordax, Pacific saury Cololabis saira, and cephalopods have consistently been important to albacore diet. These results support theoretical predictions of optimal foraging models that albacore will prefer hunting in cold, near-shore waters containing anchovy and saury while minimizing foraging in warmer, offshore waters of sardine habitat. A bioenergetics model is used to calculate daily and annual consumption rates. The importance of calculating an ensemble prey energy density (ED n ) value for steady-state consumption models is demonstrated, and the relationship between ED n and consumption rates is generalized to other marine predators. Low variability in ED n consumed by juvenile albacore translates into equally stable consumption to biomass (Q:B) ratios over decades.

Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in the Pacific Ocean off Baja California, Mexico, determined from archival tag data analyses, including unscented Kalman filtering

“…Large concentrations of Pacific sardines occur during the summer off northern BC, corresponding with the peak in productivity in that area. There may be a switch in the composition of the diet of yellowfin toward higher percentages of Pacific sardines, when anchovy are at relatively low levels of abundance, as noted by Glaser (2010) regarding the diet of north Pacific albacore from off northern BC. It appears the seasonal latitudinal movements of yellowfin along the coast of BC are driven by suitable environmental conditions, and synchronized with the occurrence of high concentrations of suitable prey within those areas.…”

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

“…Energy density and protein values were obtained from the literature (Donnelly et al, 1993;Sidwell, 1980; see also Glaser, 2010) and are provided in Table 1. The three metrics were compared univariately.…”

“…Finally, many fishing vessels used live bait (sardine, anchovy, and occasionally Pacific mackerel), and bait was counted and measured but excluded from analyses. Bait was easily identified because a record of the bait used on each boat was kept, bait was of a nearly-uniform length (much larger than the real prey; Glaser, 2010), and bait was ≤5% digested.…”

“…Albacore diet in the CCS is diverse, and studies have identified northern anchovy (Engraulis mordax), Pacific saury (Cololabis saira), Pacific hake (Merluccius productus), euphausiids, and various species of cephalopod as significant prey. Of these studies, only Iversen (1962), Pinkas et al (1971), and Glaser (2010) describe diet habits at high taxonomic resolution.…”

“…The diet habits of North Pacific albacore in the CCS have been described by five quantitative studies since 1949 (Bernard et al, 1985;Glaser, 2010;Iversen, 1962;McHugh, 1952;Pinkas et al, 1971). These studies failed to report or analyze data at the scale of the individual predator.…”