Great white shark attacks on California sea otters are on the rise, according to the USGS.

California sea otters (Enhydra lutris nereis) appear to be experiencing an increase in mortality rates as a result of bites from white sharks (Carcharodon carcharias), according to a USGS press release. Tooth fragments and bite wound characteristics were used to identify white sharks as the species primarily responsible for the attacks on the otters.

USGS and DFG biologists and veterinarians have been documenting sea otter deaths since 1968. The data recorded indicates that shark bites accounted for about 8% in the 80s and early ’90s. However, that number rose to about 15% by the late 90s. Current estimates place the percentage of sea otter deaths caused by shark bites at approximately 30%.

Other natural causes of otter deaths recorded include mating trauma, starvation, infection, and heart disease. Additionally, boat strikes and gun-shot wounds were also among the reported causes of death for the federally listed threatened species.

For more information, check out the full report at USGS.gov.