Three dead sea otters with gunshot wounds have washed ashore on the southern California coast in the past month, prompting wildlife officials to offer a $10,000 reward for information that could lead to the arrest of their killer.

Southern sea otters are protected as a threatened species under the Endangered Species Act. These recent otter killings are significant to conservationists who are engaged in efforts to preserve the natural habitat of the southern California coastline, and wildlife experts are taking them seriously.

“Initial necropsy results indicate the otters sustained gunshot wounds and died several days to several weeks prior to washing ashore,” said the California Department of Fish and Wildlife in a statement. “The US Fish and Wildlife Service Forensics Laboratory is conducting a thorough examination to aid in the investigation.”

Thus far, wildlife officials know that the sea otters were males, killed by a human with a weapon and not by natural causes. All three otters died in late July or early August. Another sea otter, discovered more recently, may have been killed in the same manner. The penalty for killing a southern sea otter is a $100,000 fine and a possible jail sentence.

In 2015, an elderly southern California man was sentenced to 150 hours of community service for shooting an air rifle at a baby otter, the Santa Cruz Sentinel reported. The otter was not hit by the projectile and was not injured.

The southern sea otter was listed as threatened in 1977. Although once abundant, the sea otter population along the California coast has declined to about 2,800 otters, as of 2012. At its peak, likely during the 18th century, the otter population is estimated to have numbered approximately 16,000. Recovery efforts do appear to be working but are slow, with the population growing only five to six percent per year.

Nevertheless, even small gains are a victory for the southern sea otter. At the dawn of the 20th century, the species was believed to be extinct in California due to the popularity of otter pelts in garment and hat manufacturing.

Recovery efforts are important for both the species and the environment. According to a US Fish and Wildlife report on sea otter populations in British Columbia, the otter is a keystone predator in West Coast marine habitats, meaning that its effect on the habitat is much greater than would be expected for its population size.

Sea otters prey on urchins, a species that in turn consumes kelp. The presence of sea otters in the environment manages urchin populations and helps kelp populations flourish. Without the otters, the urchins overpopulate and devour kelp forests.

Otters also help manage abalone (sea snails), another heavy consumer of kelp. With a strong population of sea otters around, kelp forests are able to provide food in the form of drift algae for a number of other species, including commercially harvested fish and shellfish.

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Sea otters are particularly vulnerable to human threats, including habitat contamination (such as oil spills) and boating and fishing accidents.

A worldwide survey of endangered and threatened animals earlier this year found that three-quarters of the world’s approximately 8,000 imperiled species were in that position due to human factors, including overexploitation of the species and exploitation of natural habitats.