Killer whales are continuing to die as a result of human interaction, including fishing-related injuries and vessel strikes, despite extensive global conservation efforts, scientists found in a new study examining more than 50 stranded whales.

Scientists analyzed pathology reports from 53 dead whales found in the eastern Pacific Ocean and Hawaii between 2004 and 2013, determining cause of death for 22. A significant number, including orcas of all age groups, were found to have died as a result of contact with humans.

After being injured by a halibut hook, one calf died of sepsis, according to the study. Two adults died from blunt force trauma due to vessel strikes.

The unusually comprehensive study, published Dec. 2 in PLOS ONE, aimed to provide a baseline understanding of health, nutrition and mortality in killer whales that ended up stranded.

The study was important for assessing human impact on small, endangered groups of killer whales that live close to large human populations, interact with recreational and commercial fishing and swim through established shipping lanes, according to the researchers.

“We think ‘Oh, we have noise pollution, we've taken away food sources,’ things like that,” Joseph K. Gaydos, senior author of the paper and science director for the SeaDoc Society, a program out of the University of California, Davis School of Veterinary Medicine, told The Academic Times. “We don't tend to think that we're hitting them with a boat or they’re being involved with fisheries interaction.”

Certain indirect human impacts on the whale population have been widely studied, but the traumas uncovered in the latest analysis shed new light on the wide variety of ways whales can suffer through human contact.

“Yet we found direct human causes of death in every single age class we looked at,” Gaydos continued. “That was striking for me, and reminded all of us that we need to pay attention to that.”

Human interactions were blamed for half of deaths from the well-known southern resident, or fish-eating, population, which is listed as endangered by Canada and the U.S.

"In British Columbia, we lost nine southern resident killer whales: two adults, two sub-adults and one calf died from trauma; one was a confirmed propeller strike, with one adult and two sub-adults from suspected ship strikes," said lead author Stephen Raverty, a veterinarian pathologist at the British Columbia Ministry of Agriculture, Food and Fisheries and adjunct professor at the University of British Columbia’s Institute for the Oceans and Fisheries.

One whale death was attributed to an infection secondary to satellite tagging, which scientists use to track whales’ movements — and log data that helps inform where the animals might need protections. 

Gaydos said the 20-year-old male likely already had a fungal infection that was exacerbated by the satellite-linked dart. But the high-profile incident in spring 2016 led to the indefinite suspension of the tagging program for southern residents, after a panel convened by the National Oceanic and Atmospheric Administration determined that the dart may have been the source of the infection. 

Whale habits and human impacts on the animals are difficult to study because they are elusive. They come to the surface only briefly, move over great distances and are difficult to find when they die. The new study of existing pathology reports required collaboration from researchers across the western part of North America.

Reproduction for whales is an area where many unknowns persist. However, scientists are aware that female orcas, which can live for a century, generally reproduce in their late 40s. Slowing the overall rate of reproduction, female whales take as long as 17 or 18 months to birth another calf if one of their calves dies.

It appears that female orcas develop strong bonds with their calves. Two years ago, a southern orca captured international attention by pushing along her calf which died 30 minutes after birth for 17 days. Experts said she was mourning. At that time, the southern residents numbered just 75.

Although more whales around the world may die from indirect human causes such as overfishing, environmental damage or shipping noise levels, those things are more difficult to change than, say, vessel traffic patterns that are resulting in whales being hit by propellers, Gaydos said.

“On endangered populations, we can have a big difference by just saving a few animals, and these sorts of specific direct interactions are the way to just save a few animals,” he said.

The study shows that calves also died from causes such as infectious disease, nutritional issues and congenital malformations, while sub-adults succumbed to malnutrition and infectious disease and adult mortalities stemmed from bacterial infections and emaciation.

“A lot of people think of saving whales as a rich, white endeavor. But really they are emblematic that we all depend on the ocean and the ecosystem, whether we know it or not,” Gaydos said. “It’s making oxygen, it’s regulating our climate, it makes our water cycles. We have to do a better job of taking care of that. The whales are just an example of, that we’re not doing as well as we should be right now.”

The study “Pathology findings and correlation with body condition index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013,” published Dec. 2 in PLOS ONE, was authored by Stephen Raverty, Province of British Columbia Animal Health Centre; Judy St. Leger, Cornell University; Dawn P. Noren, National Oceanic and Atmospheric Administration; Kathy Burek Huntington, Alaska Veterinary Pathology Services; David S. Rothstein, Marine Mammal Pathology Service; Frances M. D. Gulland, University of California, Davis; John K. B. Ford, Fisheries and Oceans Canada; M. Bradley Hanson, National Oceanic and Atmospheric Administration; Dyanna M. Lambourn, Washington Department of Fish and Wildlife; Jessie Huggins, Cascadia Research Collective; Martha A. Delaney, University of Illinois; Lisa Spaven, Fisheries and Oceans Canada; Teri Rowles, National Oceanic and Atmospheric Administration; Lynne Barre, National Oceanic and Atmospheric Administration; Paul Cottrell, Fisheries and Oceans Canada; Graeme Ellis, Fisheries and Oceans Canada; Tracey Goldstein, University of California, Davis; Karen Terio, University of Illinois; Debbie Duffield, Portland State University; Jim Rice, Oregon State University; and Joseph K. Gaydos, University of California, Davis SeaDoc Society.