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Sea otters were once typical sight between Baja California and Japan, but the fur trade almost wiped them out. The sea otter population in southern California, which once numbered between 150,000 and 300,000, has dropped to at least 50. Now, there are 3000 thanks to conservation efforts, but their status is still under threat.
They are the only marine mammal that uses stone tools and rocks to break shells. Sea otters are known to break seashells on their belly with the help of rocks floating on their backs, but they have also been observed using rocks along the shore as "anvils" to break mussels, clams and crabs.
A research team observed sea otters for 10 years between 2007 and 2017 and filmed them at the Bennett Slough Culverts site, a tidal estuary in central California. The site includes six large metal drainage pipes surrounded by rocks. The pipes connect two wet areas and the molds attach to the sides of the pipes.
The otters plummeted for the mussels, came back to the surface, squeezing a tuft against their bosoms and opening them with their teeth or pebbles. They could grow from 25 to 75 mussels at the hour, depending on the number of otters present. Otters spent about an hour feeding at a time, and between 35% and 55% of their time eating.
Mussels were the food of choice for otters in the area and they used fixed stone anvils to open 20%. Of the 421 rocks studied in the region, 77 had distinct wear patterns, where otters used them to open mussels.
Otters seemed to prefer rocks closer to land with peaks and ridges.
The otters would float standing in the water, support a mussel and hit it against the stone. After enough strikes to weaken it, the otters used their teeth to open the shell. Then the otter would float on his back, savor his hard-earned food and perform a "cleaning roll" to remove the shell pieces.
The researchers also studied the mussel shells left around the rocks, creating accumulations called "clusters of shells". Some contained up to 132,000 shells. The shells also exhibited a distinctive type of damage in which both sides of the shell were still attached, but a diagonal crack passed through the right side of the shell.
In the video, the researchers found that the animals held the shells evenly between their paws, but when the shell struck the rock, their right paw was slightly shifted upward. This is similar to the tendency of a human to favor one or the other hand, called "righteousness". In this case, the researchers call this "paw".
"Shell breakage models offer a new way to distinguish broken mussels from hammered sea otters on anvils that emerge from those broken by humans or other animals," Natalie said in a statement. Uomini, author of the study, Science of Human History. "For archeologists who are exploring past human behavior, it is essential to be able to distinguish evidence of sea otter food consumption from that of humans."
In the future, knowing what these distinctive markings look like can help archaeologists determine how humans and sea otters could have used rocks in coastal areas. He could also trace the history of sea otters today gone missing by examining where they extend their use of anvils.
This could help expand the field of animal archeology, which was previously focused on primates.
"Our study suggests that fixed anvil use can be detected in places previously inhabited by sea otters. This information could help document the presence and feeding of the otter from the sea. past sea in places where they are currently gone, "said author Jessica Fujii's study of the Monterey Bay Aquarium. in a report. "The recovery of past behavioral traces from animals helps us understand the evolution of behaviors such as the use of the stone anvil, which is rare in the animal kingdom and extremely rare in animals." We hope this study opens a new path for animal archeology. "
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