Tool use by sea otters

The sea otter, Enhydra lutris, is a member of the Mustelidae that is fully aquatic. Sea otters are the smallest of the marine mammals, but they are also the most dexterous. Sea otters are known for their ability to use stones as anvils or hammers to facilitate access to hard-to-reach prey items. There are three recognized subspecies of otters, all of which exhibit tool use behavior in some capacity. Tool use behavior is more associated with geographic location than sub-species. Most behavioral research has been conducted on Enhydra lutris nereis, the Californian otter, and some has been conducted on Enhydra lutris kenyoni, the Alaska sea otter. Sea otters frequently use rocks as anvils to crack open prey, and they are also observed to rip open prey with their forepaws. While laying on their backs, otters will rip apart coral algae to find food among the debris. The frequency of tool use varies greatly between geographic regions and individual otters. Regardless of the frequency, The use of tools is present in the behavioral repertoire of sea otters and is performed when most appropriate to the situation.

It is not possible to pin-point the moment in history in which sea otters began using tools consistently. It is hypothesized that certain behaviors were selected for, in the process of evolution, which led to this incredibly useful adaptation. The first instance of a rock as a tool may have occurred when an otter was unable to access a prey item at the bottom of the ocean and used a rock to facilitate access to the object. Similarly, an otter at the surface of the water may have chosen to crush two bivalves against each other when faced with an inability to crush the prey items with the forelimbs or teeth. Shellfish are found on rock structures at the bottom of the ocean, so collecting multiple rocks and shellfish from the bottom of the ocean in one diving episode and crushing the objects together on the surface may have led to the association of rocks with crushing shells of foods items. If a behavior which was performed in a conflict situation happened to open a prey item, an otter may have attempted to repeat the behavior and therefore learned to repeat the behavior consistently.

Sea otters commonly exhibit swimming behavior where they swim on their backs. The features which facilitate swimming on the back also facilitate tool-use. Otters that do not use tools still feed on their backs. This habit of feeding on the surface with the chest up facilitates a flat surface for resting rocks and pounding items together (1). Once discovered and consistently performed by one or some otters, the tool-use behavior may have spread through a population of nearby otters by horizontal social learning.

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