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Killer whale killers: Human interactions threaten endangered populations

An analysis of 53 killer whale deaths between 2004 and 2013 includes those related to commercial shipping and fishing.

A review of more than 50 killer whale necropsies show that many deaths stem from human impacts.
Fiona Goodall/Getty

Doublestuf's body floated off the coast of Sechelt, British Columbia, for at least three days before it was spotted by a local. The motionless killer whale, a few feet shorter than a bus, was at first mistaken for an upturned boat. He belonged to the J pod, a group of endangered killer whales known as the southern residents. On Dec. 20, 2016, Doublestuf's body was towed to shore.

A whale carcass, like Doublestuf's, is a historical record. One man tasked with reading these records is Stephen Raverty, a veterinary pathologist at the Ministry of Agriculture's Animal Health Center in British Columbia. An examination of the corpse, a necropsy, is a laborious process that can involve upward of 20 people.

"We usually have six to eight hours in order to do the exam," Raverty said.  

In that time, the team members makes careful measurements of the whale's body, including the thickness and character of its blubber. They remove samples of skin and tissue for analysis and then cut open the animal's abdominal cavity to analyze its gut. They also search for the telltale signs that humans may be responsible for a whale's death. Rope furrows in the skin; foreign debris in the mouth. They carefully assess every inch of the gastrointestinal tract. 

"We're always on the lookout for evidence of human interactions," Raverty said.

In Doublestuf's case, the record showed a painful end for the 18-year-old mammal. The primary cause of death was, in veterinarian parlance, a "vessel strike." At some point, a ship collided with Doublestuf's upper left flank, causing extreme internal bleeding. He survived the initial insult but later succumbed to the injuries.

Although killer whales are found in every ocean of the world, they exist in many smaller populations known as ecotypes, with distinct genetic differences, feeding habits, sounds and social hierarchies.

The southern resident whales occupy a stretch of ocean along North America's West Coast, from Oregon up into Canada. The whales, including Doublestuf's mother, Oreo, and brother Cookie, come into inland waters in the spring and summer, hunting chinook salmon near coastal towns. Shipping lanes crisscross their territory. Ship noise, strikes and pollution are a major threat to the southern residents.

In 2020, only 74 southern resident whales remain. That's down from 98 in 1995.

Seeking to understand the whale's lives and deaths more clearly, Raverty and a collaboration of marine veterinarians and researchers, published on Wednesday a review of pathology reports from 53 killer whale strandings along the western coast of North America between 2004 and 2013. In this case, strandings refer to dead whales found on shore or close to it, rather than live animals. 

The study, one of the first of its kind, captures three distinct ecotypes and enables marine scientists to better understand how different populations of killer whales are living and dying. 


An emaciated female killer whale become stranded on Hawaii's shore in 2008.

PLOS/Raverty et al (2020)

It also enables an understanding of the significant human impacts on whale life. Doublestuf's case, in particular, highlights a concerning trend. Vessel strikes may be an underappreciated cause of death in killer whale populations, particularly for the vulnerable southern residents. The study finds that human interactions are directly impacting whales in all age groups. Identifying these anthropogenic impacts is the first step in mitigating them, according to the study.

In 22 of the 53 killer whales, the research team were able to identify a primary cause of death. "That comprises about 5 to 15% of the overall mortality within the population of killer whales," noted Raverty. Globally, killer whale numbers are estimated to be at around 55,000. 

An additional 15 cases, of which Doublestuf was one, were included after 2017 to help analyze how body length and cause of death might influence blubber thickness and the condition of the whale body.

The necropsies find varying causes of death, with metabolic and nutritional abnormalities accounting for the largest proportion of killer whale deaths in the group. Infections and inflammation also feature. Raverty discusses the evidence of Toxoplasma, a cat parasite known to infect mammals such as humans and livestock, in one particular case -- the first time the parasite has been confirmed by molecular analysis in an orca.

The details of the human interactions are grim reminders of the very real damage commercial fishing and shipping can have on ocean life. One calf, an Alaskan resident found in 2005, had ingested a large halibut hook that had punctured the back of its throat. 

"That provided a portal for bacteria to invade into the bloodstream and eventually the animal died of sepsis," Raverty says. Two sub-adults had markings consistent with vessel strikes and one adult female, T086, was hit by a ship's propeller -- only a portion of her carcass, containing the dorsal fin, was recovered.

Human impacts have been particularly terrible for the North Atlantic right whales. In recent years, as a result of global warming, the slow, docile whales have changed their behavior and -- like the killer whales -- have found their new territories invaded by ships. Only around 400 right whales remain, and ship strikes and entanglements have greatly contributed to their dwindling numbers. 

Just how much are humans affecting the killer whale populations? It's unclear. Raverty, and others, are beginning to investigate. According to the veterinarian, over 8,000 incidents between humans and marine mammals have been reported to the Marine Mammal Response Program in British Columbia in the past 12 years. His team will now begin to sift through the data with a particular focus on killer whales. 

"We're looking at levels of harassment, encroachments, different types of human interactions that may adversely affect these animals," Raverty said.

The information will help establish a baseline on incidents, much like the necropsies have established a baseline for population health data. Other groups around the world are studying the killer whale's gut microbes and fecal matter to get a better handle on the charismatic creature's health.

A whale's carcass is a rich historical record, and Raverty is methodical and empathic in the way he speaks about reading those records. He's conducted about 20 killer whale necropsies and describes the experience as humbling. But he also sees in the end of these creatures some opportunity to make a better future for those still swimming in the cold waters off the coast of British Columbia.

"We're always interested in terms of, how do we apply the knowledge derived from that examination of that animal back to population health," he said.

With around 40 to 50 strandings occurring each year in the northern Pacific, he will have his work cut out.