Sea Otters Boost Foraging Success, Dental Health with Tools

Using tools, like shells and rocks, to open their often thick-shelled mollusk prey increases foraging success in sea otters and protects their teeth from damage by allowing the animals to eat prey that would otherwise be difficult to obtain. The findings suggest that this behavior is a necessity for the survival of some otters in environments where competition is high and preferred prey is in short supply. Sea otters are well-known tool users. Aside from crushing prey with their teeth, sea otters have been observed using rocks, shells, human litter, and even the hulls of boats to bash open hard prey, including marine snails, sea urchins, or clams. In general, sea otters prefer to forage on prey that are not only rich in energy but also easy to process. However, in areas where the animal occurs at high densities, intraspecific competition can lead to easy-to-access prey becoming depleted, driving some otters to specialize on alternative pretty types, which influences their reliance on tool use for foraging. Using longitudinal data from 196 radio-tagged sea otters, Chris Law and colleagues investigated whether tool use enhances the foraging success of individual southern sea otters (Enhydra lutris nereis) by allowing them to increase the diversity of harder-shelled prey and increases fitness by preventing dental injury. In general, Law et al. found that tool-use frequency enabled the use of a wider variety of prey, which led to higher energy consumption rates and reduced tooth wear. However, this pattern was not linear – some infrequent tool users had more damaged teeth than otters that did not use tools at all, likely due to diet specialization. Individuals that prefer prey where tools are needed tend to use tools to access all prey types. In contrast, those that prefer prey that can be accessed without tools risk damaging their teeth – and, by extension, reducing their overall fitness – because they tend to not use tools unless absolutely necessary. Unique to female otters, the more an animal relied on tool use, the more often it processed harder prey, increasing the foraging success of female otters, suggesting that tool-using behavior is disproportionally more beneficial for females, perhaps by enabling them to overcome the physical constraints of processing harder prey given their smaller body size and weaker biting strength. In a related Perspective, Barbara Klump discusses the study in greater detail.