Divergent foraging strategies between populations of sympatric matrilineal killer whales

In gregarious species, collective behavior maximizes individual fitness
benefits while minimizing costs. Despite the relevance of behavior to
conservation, the link between the robustness of behavioral patterns
across populations and population health is poorly understood. We studied
the collective foraging behavior of two closed, sympatric populations of
piscivorous killer whales, leveraging two contemporaneously-collected data
sets from suction cup-attached bio-logging tags, to quantify patterns of
fine-scale foraging movements and their relationships with demography. We
reveal striking plasticity in collective foraging behavior between
populations. Prey capture rate and foraging efficiency were greater for
males in the endangered Southern Resident (SRKW) population, yet greater
for females in the Northern Resident (NRKW) population. The presence of a
calf (≤ 3 y) reduced the number of prey captured by adult females in both
populations, with the greatest effect in SRKW, in which no mothers with
calves captured prey while bearing tags. SRKW adult males with a living
mother tended to capture more prey than those whose mother had died,
whereas the opposite was true for NRKW adult males. Moreover, males
generally tended to forage in areas with deeper bathymetry than females,
and SRKW captured prey deeper than NRKW. These population-level
differences in sex-specific foraging behavior challenge the existing
paradigm that mothers are disproportionate foragers in gregarious killer
whales, underscoring that an endangered population is employing a
potentially unstable collective foraging strategy mismatched to recovery.
Thus, our study provides a mechanistic link between fine-scale, collective
foraging behavior and population health in an apex marine predator.