Tool use by sea otters
Sea otters are known for their ability to use stones as anvils or hammers to facilitate access to hard-to-reach prey items.
Extremely young pups cannot swim or dive due to their natal fur coating, so they must be anchored to the mothers at all times.
[3] Sea otters belong to the order Carnivora, whose members possess typical carnivoran teeth, or shearing carnassials.
Sea otters have replaced their carnassial teeth with bunodont post-canines to improve their food crushing ability.
Forelimb structure, particularly musculature and skeletal anatomy, are potentially adapted for, "tactile sensitivity and tool use associated with detection, handling, and consumption of prey".
Being buoyant along the length of the body allows otters to lie on their backs and manipulate food, tools, and young while on the surface of the water.
[6] Underneath the arm of each sea otter, at the axilla, is a flap of skin that can store stones and food.
[4] It was found that orphaned juvenile sea otters in a research facility spontaneously developed stone tool use, without observing any models.
[8] Together, both studies suggest a genetic component to stone behaviours in otters – as this would explain both its occurrence without models and its cross-occurrence across species that do not observe each other.
Once an otter has adult-like swimming and diving behavior, can procure food by itself, and self-groom, it is considered independent.
This is exacerbated by the fact that for the first three months of life, otter pups cannot swim or dive effectively.
[9] Sea otter pups display a propensity for manipulating objects between their paws and regularly pound rocks and little bits of coral against their bodies in a random and curious manner.
[6] Pups express the same preferences in tools, technique, and diet as their mothers, which is potential evidence of vertical social transmission.
The scientists spent six days observing the Californian otters in Point Lobos State Park, California.
Over the course of their time, they observed 30 separate instances of tool use behaviors, most of which involved otters using rocks to crack mussels.
[12] Otters of the Northern Pacific consume mostly sea urchins and fish, thereby exhibiting less tool use behavior.
[6] Scientists have studied areas of California where up to 80% of abalone shells display crack patterns that are suggestive of breakage against rocks performed by otters.
[6] In areas near the Aleutian Islands, less tool use is recorded and sea otters consume much more fish.
The diet in these areas also includes sea urchins, which otters can break with their forepaws, mollusks, and crustaceans.
Hard prey items can be pounded against the anvil to create cracks and facilitate access to flesh.
Tool composite is the term given to the combination of two rocks as an anvil and a hammer, separately, but used on the same prey item at once.
Californian otters show multiple techniques with differences that are tailored specifically to eating bivalves and crabs.
[13] A study that compiled seventeen years' worth of observational data demonstrated a significant difference between the occurrence of tool use in Amchitka Island, Alaska and Monterey, California.
[10] In a study conducted from Alaska to Southern California, sixteen otter populations demonstrated that individual diet specializations are much more likely to be present in environments of rocky habitat over soft sediment substrates.
[13] In an aforementioned study, which compiled 17 years of observational data on otters from southern California to the Aleutian Islands, it was discovered that anywhere from 10% to 93% of individuals in a population use tools.
Individuals in California have learned how to tear open aluminum cans that float in the water from incidents of pollution.
However, they have the ability to manipulate their prey enough to avoid the paralytic shellfish poisoning toxins so that they do not consume lethal amounts.
Alaskan sea otters prey heavily on the butter clam, which has the ability to retain toxins obtained from dinoflagellate blooms.
