Researchers used an interdisciplinary approach combining ecology and archaeological methods to study sea otters’ past behavior — ScienceDaily


An international research team has analyzed the use of large coastline rocks as an "anvil" to break the shell and the resulting shells. Researchers use ecological and archaeological methods to identify patterns of traits used by sea otters at these locations. By looking at past evidence of using anvil stones, scientists can better understand the use of sea otter habitats.

Sea otter is a particularly fascinating marine mammal known for using rocks to break shells. The sea otter is estimated to have 150,000-300,000 people, ranging from Baja California, Mexico, to the North Pacific coast to Japan. The fur trade has greatly reduced their number. In California, the population of the southern sea otter has been reduced to about 50 people, but large-scale conservation efforts have increased their number to about 3,000 today. However, southern sea otters are still considered to be threatened.

Sea otter is the only marine mammal that uses stone tools. They often use rocks to crack open shells when floating on the back, and sometimes use fixed rocks along the shoreline as "anvils" to break open mollusks, especially mussels. A joint project involving the Max Planck Institute for Human History, the Monterey Bay Aquarium and the University of California, Santa Cruz, has published a first interdisciplinary study in the science of . Report combining the ten-year observation and archaeological methods of marine otters, to analyze the use of this anvil by sea otters, also known as emergency anvils.

The sea otter uses the anvil to leave a unique wear and shell, which is characteristic of the sea otter

The researchers spent ten years between 2007 and 2017 observing the consumption of mussels at the Bennett Slough Culverts site in California. Their analysis shows that mussels are the most common prey in the area and the only prey for sea otters using fixed anvils. Sea otters use this stone to consume about 20% of mussels.

Interestingly, the careful analysis of fixed anvil stones using archaeological methods suggests that their use has led to an identifiable pattern of damage that differs from the pattern of damage caused by human use. For example, sea otters preferentially cause mussels to hit points and ridges on the rock and strike the rock from the location in the water rather than from the top of the land or rock.

The pattern of unanimous destruction on broken clam shells suggests that there may be "paws" in sea otters

In addition to the stone itself, the researchers carefully analyzed the clam shells around the fixed anvil. The researchers randomly sampled shell fragments from the middle of these shells, which may contain as many as 132,000 individual clam shells. They found a very consistent mode of damage, with the sides of the clam shell still attached, but broken through the diagonal on the right side of the casing.

"The shell fracture pattern provides a new way to distinguish between mussels that appear on abrupt anvils and mussels that are broken by humans or other animals," Natalie of Max Planck Institute for Human History. · Umini explained. “For archaeologists who have tapped past human behavior, it is important to be able to distinguish evidence of sea otter food consumption from evidence of human consumption.”

In combination with their use of anvil to analyze the video of the otter, the researchers can see that the otter evenly grabs the shells on both claws, but when hitting the shells on the anvil, their right claws are slightly overhanging. Above. Although the total number of leeches observed is small, these results suggest that leeches may exhibit chiral or "claw", as do humans and many other mammals.

The possibility of conducting an archaeological investigation of the acts of the sea otters of the past

The researchers hope that the study will be useful to archaeologists working with coastal residents to distinguish between the use of rocks by humans and sea otters and the consumption of marine resources. In addition, the study may be helpful in the future study of the geographic extent of fixed anvil use throughout the foreshore, and the extent to which this behavior extends to the past.

"Our research shows that the use of fixed anvils can be found in places where sea otters lived. This information can help document the existence and diet of seawater in the past," explains Jessica Fujii of Monterey Bay. aquarium.

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