title: Direct quantification of energy intake in an apex marine predator suggests physiology is a key driver of migrations.
abstract: Pacific bluefin tuna (Thunnus orientalis) are highly migratory apex marine predators that inhabit a broad thermal niche. The energy needed for migration must be garnered by foraging, but measuring energy intake in the marine environment is challenging. We quantified the energy intake of Pacific bluefin tuna in the California Current using a laboratory-validated model, the first such measurement in a wild marine predator. Mean daily energy intake was highest off the coast of Baja California, Mexico in summer (mean ± SD, 1034 ± 669 kcal), followed by autumn when Pacific bluefin achieve their northernmost range in waters off northern California (944 ± 579 kcal). Movements were not always consistent with maximizing energy intake: the Pacific bluefin move out of energy rich waters both in late summer and winter, coincident with rising and falling water temperatures, respectively. We hypothesize that temperature-related physiological constraints drive migration and that Pacific bluefin tuna optimize energy intake within a range of optimal aerobic performance.
authors.affiliation: Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, Oceanview Boulevard, Pacific Grove, CA 93950, USA. ; Sveriges Lantbruksuniversitet, Sötvattenslaboratoriet, Stångholmsvägen 2, Drottningholm 178 93, Sweden.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Whitlock
authors.affiliation: Environmental Research Division, Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA), 99 Pacific Street, Suite 255A, Monterey, CA 93940, USA.
authors.forename: Elliott L
authors.initials: EL
authors.lastname: Hazen
authors.affiliation: Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, Oceanview Boulevard, Pacific Grove, CA 93950, USA.
authors.forename: Andreas
authors.initials: A
authors.lastname: Walli
authors.affiliation: Monterey Bay Aquarium, 886 Cannery Row, Monterey Bay, CA 93940, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Farwell
authors.affiliation: Environmental Research Division, Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA), 99 Pacific Street, Suite 255A, Monterey, CA 93940, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Bograd
authors.affiliation: Environmental Research Division, Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA), 99 Pacific Street, Suite 255A, Monterey, CA 93940, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Foley
authors.affiliation: Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, Oceanview Boulevard, Pacific Grove, CA 93950, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Castleton
authors.affiliation: Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, Oceanview Boulevard, Pacific Grove, CA 93950, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Block
keywords: Bio-Logging; Foraging ecology; Migration; Physiology; bluefin tuna; heat increment of feeding