The Effects of Age and Sex on the Energy Intake of Captive Sea Otters (Enhydra lutris): Implications for Captive Management and Species Conservation

Abstract

Sea otters (Enhydra lutris) are known ecosystem engineers that have significant impacts on their kelp forest and rocky intertidal communities due to their high levels of food intake. Quantifying sea otter food biomass and energy intake is a valuable way to understand potential ecological impacts of sea otter populations on ecosystems and for predicting future population trends and potential for expansion. While detailed, fine-scale, age-specific food intake is difficult to quantify in wild sea otters, there is a wealth of potential information available from otters under human care. This study used food and energy intake data from husbandry records of 10 sea otters collected over three decades at the Vancouver Aquarium. Within these husbandry records, daily food biomass intake and body mass measurements were recorded and converted to annual average food mass and gross energy intake (GEI). Age-, sex-, and mass-specific trends were also observed. Young sea otters had the highest relative ingested food mass, equivalent to ~26% of body mass, which decreased to ~20% in adult otters. Young otters similarly had the highest mass-specific GEI, where measures from near birth to year 1 were ~40% higher than at year 3, the age of sexual and physical maturity. There were also key differences in trends between sexes. Captive adult male sea otters were 25 to 42% larger than females and their GEI was 23 to 58% higher, although mass-specific GEI was almost identical for male and non-reproductive female otters at all ages, plateauing at ~650 kJ kg-1 d-1. Despite high levels of ingested food mass, GEI was only 5 to 15% higher than for other captive marine mammals and was comparable to previous estimates for wild sea otters. These estimates of ingested food mass and energy intake requirements are valuable when modelling the ecological impact of sea otter populations and for considering the potential effects of future environmental changes.