Orcas face a variety of deadly threats—many stemming from human interactions, according to pathology reports on more than 50 killer whales stranded over nearly a decade in the northeast Pacific and Hawaii.
A study analyzing the reports in PLOS ONE indicates that understanding and being aware of each threat is critical for managing and conserving killer whale populations. It also presents a baseline understanding of orca health.
The whales include those from healthy populations as well as endangered species, such as the southern resident whales regularly sighted off the coasts of British Columbia, Washington, and Oregon.
Scientists determined the causes of death for 42% of 53 whales stranded between 2004 and 2013. For example, one calf died from sepsis following a halibut hook injury. Another starved from a congenital facial deformity. Two whales died from the blunt force trauma of vessel strikes. Additional causes of death include infectious disease and nutritional deficiencies.
Despite the absence of a single common cause of death, the study found a common theme: Human-caused deaths occurred in every age class—from juveniles to subadults and adults.
“Nobody likes to think we’re directly harming animals,” says Joe Gaydos, a wildlife veterinarian with the Karen C. Drayer Wildlife Health Center in the School of Veterinary Medicine at the University of California, Davis and director of the SeaDoc Society.
“But it’s important to realize that we’re not just indirectly hurting them from things like lack of salmon, vessel disturbance, or legacy toxins. It’s also vessel strikes and fish hooks. That humans are directly killing killer whales across all age classes is significant; it says we can do a better job.”
Gaydos and lead author Stephen Raverty, a veterinary pathologist with the BC Ministry of Agriculture, co-developed a standardized killer whale necropsy protocol in 2004. Revised in 2014 with help from Judy St. Leger, a pathologist working for SeaWorld, the guide helped improve examinations of deceased whales.
“The results from systematic necropsies of dead killer whales in this review is unique and will establish critical baseline information to assess future mitigation efforts,” Raverty says. “This work contributes to a better understanding of the impacts that ongoing human activities and environmental events have on killer whales.”
The authors acknowledge the report is an incomplete picture of orca health and mortality. Necropsies can only be performed on whales found in an adequate state to receive them, and even then, scientists can’t always determine the cause of death.
But the report offers one of the most comprehensive looks yet at the multitude of human and environmental threats affecting killer whales and can help inform strategies to better protect them.
Additional researchers from Cornell University, NOAA Fisheries, Alaska Veterinary Pathology Services, Marine Mammal Pathology Service in Maryland, UC Davis One Health Institute, Fisheries and Oceans Canada, Washington Department of Fish and Wildlife, Cascadia Research Collective, University of Illinois-Brookfield, Portland State University, Oregon State University, the British Columbia Ministry of Agriculture, and SeaDoc Society contributed to the work.
NOAA Fisheries and the John H. Prescott Marine Mammal Rescue Assistance Grant Program funded the work. Additional support came from Fisheries and Oceans, Canada; Vancouver Aquarium Research Program; SeaDoc Society; SeaWorld; Animal Health Center of the BC Ministry of Agriculture; Washington Department of Fish and Wildlife; and numerous and numerous First Nations, Alaska Native, and Inuit communities.
Source: UC Davis