Foraging Behavior and Success of a Mesopelagic Predator in the Northeast Pacific Ocean: Insights from a Data-Rich Species, the Northern Elephant Seal

Abstract

The mesopelagic zone of the northeast Pacific Ocean is an important foraging habitat for many predators, yet few studies have addressed the factors driving basin-scale predator distributions or inter-annual variability in foraging and breeding success. Understanding these processes is critical to reveal how conditions at sea cascade to population-level effects. To begin addressing these challenging questions, we collected diving, tracking, foraging success, and natality data for 297 adult female northern elephant seal migrations from 2004 to 2010. During the longer post-molting migration, individual energy gain rates were significant predictors of pregnancy. At sea, seals focused their foraging effort along a narrow band corresponding to the boundary between the sub-arctic and sub-tropical gyres. In contrast to shallow-diving predators, elephant seals target the gyre-gyre boundary throughout the year rather than follow the southward winter migration of surface features, such as the Transition Zone Chlorophyll Front. We also assessed the impact of added transit costs by studying seals at a colony near the southern extent of the species’ range, 1,150 km to the south. A much larger proportion of seals foraged locally, implying plasticity in foraging strategies and possibly prey type. While these findings are derived from a single species, the results may provide insight to the foraging patterns of many other meso-pelagic predators in the northeast Pacific Ocean.

Variation in adrenal and thyroid hormones with life-history stage in juvenile northern elephant seals (Mirounga angustirostris)

“…Although these findings may reflect species differences, our findings suggest this difference might reflect the feeding regimens entrained in captive animals. The lack of diel pattern seen in wild juvenile elephant seals is consistent with the fact that elephant seals feed intensively at night (Robinson et al, 2012) and do not show diel patterns to behavior when hauled out on shore .…”

Route Fidelity during Marine Megafauna Migration

“…Northern elephant seals were also tracked using PTT satellite tags (Robinson et al, 2012) which were attached to the head of each seal during onshore residence in Año Nuevo State Park (ca. 37.11 • N; 122.33 • W), California, U.S.A.…”

Escaping the oligotrophic gyre? The year-round movements, foraging behaviour and habitat preferences of Murphy’s petrels

“…Unlike the foraging habitats of Murphy's petrels in the South Pacific, during winter and spring, strong westerlies cause mixing of nutrient-rich waters and help maintain productivity in the absence of sunlight (Bograd et al 2004). Additionally, birds appear to use the NPTZ, which spans the Subarctic and Subtropical Frontal Zones, and is an important foraging and migration habitat for many species due to aggregations of mesopelagic prey (Robinson et al 2012). For example, DVM squid seasonally migrate from spawning areas in the subtropics to the Subarctic Frontal Zone to feed on myctophid fishes (Watanabe et al 2004, Ichii et al 2009).…”