Social Structure of Marine Otters: Inter and Intraspecific Variation

Otters are a semiaquatic clade that stands out among carnivorans. Of 13 otter species, only three are known to cooperate, although most species exhibit some form of sociality. The observed variation in social structure among species, especially those in marine environments, makes this taxon suitable for studying the proximate and ultimate factors underpinning sociality. Here we review evidence for social behavior in otters with an emphasis on two species: the North American river otter (an inland and coastal generalist) and the sea otter (a marine specialist). In addition, we provide new information on a marine population of river otters in coastal Alaska using telemetry, camera traps, and social network analysis. Our results provide new insight into the contexts for river otter social behavior, confirm previous observations on individual variation in social behavior, and highlight differences between males and females. We additionally review the published data on sea otter social behavior. We discuss potential directions for hypothesis testing in otter social systems with an emphasis on drivers of individual variation in social behavior, especially potential insights from the fields of sociogenomics and proteomics.