Oral Presentation- Symposium 12th International Mammalogical Congress

Diet, body condition, and reproductive success: winners and losers in sea otter societies (#33)

James Estes 1 , Michelle Staedler 2 , M. Tim Tinker 3
  1. University of California, Santa Cruz, Santa Cruz, California, United States of America
  2. Monterey Bay Aquarium, Monterey, California, United States of America
  3. US Geological Survey, Reston, Virginia, United States of America

Sea otters exhibit marked individuality in prey choice when or where resources limit further population growth. Inasmuch as caloric content, search time, and handling time typically vary among prey species, the net rate of value (e.g., energy) returned from foraging should also vary among individual sea otters, thus producing the expectation of dietary covariation in fitness on the one hand and selection for a dietary optimum on the other. Here we use Bayesian survival analysis to explore the effects of diet, mother’s age and body condition on reproductive success (probability of pup survival), using data from a 38 year study of 310 tagged female sea otters in central California. Dietary patterns of individual sea otters aggregated into six clusters based on proportional abundance in the diet of 14 prey types. Average weaning success was similar among diet clusters. However, within clusters (and across the entire data set) there were positive relationships between female age, body condition and weaning success.  Moreover, of the 189 adult females for whom we observed multiple (2 to 10) birth cycles, we found that individual females tended to vary consistently in terms of their likelihood of successfully weaning pups, even after accounting for effects of body condition and mother’s age.  Although fertility rate is essentially constant among adult female sea otters, most individuals fall into one of two classes: the winners (those who regularly succeed in weaning their offspring) and the losers (those who regularly fail).