Loyalty pays: potential life history consequences of fidelity to marine foraging regions by southern elephant seals

Choices made by foraging animals should maximize energy intake, although ‘irrational’ short-term behaviours are common. One explanation for this is that environmental variation may lead to the evolution of behaviours that benefit individual reproductive output, but only over long timescales. Long-term (multiyear) fidelity to foraging regions in extremely variable environments may confer ecological benefits to individuals, such as familiarity with resources, even when energy gain is not consistently high in all years. We examined the annual foraging ranges (sometimes exceeding 3.5 million km2) of female southern elephant seals, Mirounga leonina, over 4 years and found that individuals used preferred regions year after year. We hypothesized that the degree of fidelity in a particular year was related to the foraging success (as measured by mass gain) in the previous year; however, there was no significant relation between the two. Despite this high variation in annual foraging success, the regions revisited in consecutive years provided higher potential food production as measured by higher variance in sea surface temperatures over two decades (a surrogate measure of ocean productivity). The evolution of long-term fidelity assisted by simple navigational rules may confer energetic advantages over an individual's lifetime and explain the existence of seemingly nonadaptive short-term behaviours.