Sea Otters’ Tools Tell Us A Lot About Their Archaeological History

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Researchers studied the archaeological history of otters, and by combining ecology with different archaeological methods, found that sea otters’ tools tell us a lot about how these animals survived throughout their history, offering distinctive evidence of how they used their habitat.

A group of scientists from around the globe studied large rocks around the shore used as sea otters’ tools. Interestingly, these animals used the rocks during feeding by opening shells and consuming the shell contents. Using different approaches, researchers found patterns in the characteristics of the way the sea otters used the rocks and could better understand how the sea otter use the habitat that they live in.

Sea otters are marine mammals which often use different tools such as rocks to break shells open, evolving to use the best of their habitat. Estimates suggest that sea otters once numbered from 150,000 to 300,000 individuals living from Baja California, Mexico to the northern Pacific Rim to Japan. Unfortunately, fur trade caused these estimates to drastically reduce. Nevertheless, massive conservation efforts increased the declining numbers to about 107,000 today. Still, the southern sea otter is considered threatened.

Aside from using small rocks to open seashells on their chests, sea otters’ used tools from the beach to crack mollusks open. An international project reported in the journal Scientific Reports combines ten years of observation data of sea otters’ tools, analyzing the archaeological methods they use to survive. The observations lasted from 2007 to 2017, watching otters consuming mussels at the Bennett Slough Culverts site in California. These observations revealed that otters mostly feed on mussels at that site, also being the only prey they used stationary anvil stones to break open the shells.

Additionally, researchers studied the mussel shells that were left close to the stationary anvils, taking shell fragments from the shell middens. Careful observations revealed that they used carefully planned damage patterns; the two sides of the mussel shell were still attached, with a diagonal fracture on the right side of the shell.

“The shell breakage patterns provide a novel way to distinguish mussels broken by sea otter pounding on emergent anvils from those broken by humans or other animals,” Natalie Uomini of the Max Planck Institute for the Science of Human History said in a statement. “For archaeologists who excavate past human behavior, it is crucial to be able to distinguish the evidence of sea otter food consumption from that of humans.”

Observing the usage of sea otters’ tools, scientists recorded them in footage and carefully watched how otters held the shells evenly using both paws, but revealing a pattern where they would smash the shells using the anvils with the right paw slightly positioned on top, suggesting otters could have “handedness” as humans do.

The researchers believe that this study is important for archaeologists and other scientists who study coastal populations, as well as making a consistent difference between otter and human use of rocks. Moreover, this study could be used as a strong foundation for future studies looking at the geographical prominence of stationary anvil use by former sea otters, looking at how far into the past this practice was used.

“Our study suggests that stationary anvil use can be detected in locations previously inhabited by sea otters. This information could help to document past sea otter presence and diet in locations where they are currently extirpated,” explains Jessica Fujii of the Monterey Bay Aquarium.

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