Toxins, Noise, Food Scarcity & Disease:
Life as a Southern Resident Killer Whale

By Desiree Aguiar and Jasjeet Dhanota

You would be hard-pressed to find a more charismatic species in the Salish Sea than the killer whale. They are beloved by locals and tourists alike, but despite their acclaim, they are struggling amid a confluence of major obstacles. The endangered southern resident killer whale ecotype a staple of the Salish Sea has it especially tough.

There are three types of killer whales in the Salish Sea, and each one has a distinct diet: The transients eat marine mammals, the offshores specialize in eating sharks and the residents (both northern and southern) eat fish – typically salmon.

Unlike transient and offshore killer whales, which usually only pass through the area in search of food, southern resident killer whales generally remain in the Salish Sea from late spring through the fall. Their population has been carefully monitored for decades, and in the late 1990s it dropped by 17 percent over the span of just four years. The decline has continued, although at a less severe rate.



The SeaDoc Society has teamed up with National Oceanic and Atmospheric Administration (NOAA) and other organizations to investigate why these remarkable creatures are in decline and what can be done to help them.

When considering whale health, it’s helpful to think about what makes a healthy human.  

“It’s rare that we get sick when we're taking good care of ourselves,” said Dr. Joe Gaydos, Director and Chief Scientist of the SeaDoc Society, which is a program of the Karen C. Drayer Wildlife Health Center at UC Davis. “But when you're sleep-deprived and haven’t had enough of the nutritious food your body needs, you’re more likely to get sick, especially when you come into contact with someone who has a cold. Disease often works in concert with these other compromising factors.”

Such is the struggle of the southern resident killer whale: food scarcity, noise sensitivity and harmful toxins have all made killer whales more susceptible to disease.

“You really have to put everything together to understand what’s affecting these whales,” said Dr. Stephen Raverty, Director of the Marine Ecosystem Health Program in Vancouver and Veterinary Pathologist with the British Columbia Animal Health Center.

SeaDoc, along with Dr. Raverty and Dr. Judy St. Leger, a veterinary pathologist with Sea World, has developed a standardized necropsy protocol to assess how disease might play a role in the population's decline. The protocol allows researchers to efficiently gather specific information from every stranding, which is vital, because each death, however sad, is an opportunity to learn something.


Population estimates suggest that the southern resident killer whale population was as high as 200 individuals at the start of the 1900s, but it plummeted in the 1960s and 1970s when 36 southern residents were captured for marine parks. The population has fluctuated ever since.

Canada listed southern resident killer whales as endangered in 2004 and the United States followed suit in 2005, highlighting the obvious truth that conservation issues like this one transcend political boundaries.

There are three family groups of southern resident killer whales. They are identified as J, K and L pods. According to census data from the Center for Whale Research, the southern resident killer whale population is currently estimated at 81 individuals.

Exciting side note: There were 78 when we started this story, but three babies were recently born!

Frequent whale strandings have prompted scientists to look deeper into what could be making the Salish Sea a difficult environment for the whales. They are conducting cause-of-death investigations that they hope will demystify the life-threatening issues the whales are facing.

“The most striking thing we find from these necropsy examinations is that all of the elements of life – from the food these animals eat to the environment they live in – have an effect on them,” says Dr. St. Leger. “The richness of the information we can collect is both remarkable and critical.”

But despite the increase in research and conservation efforts over the past ten years, the population on the whole has continued to decline.


Food scarcity

Southern resident killer whales eat many types of fish, but their preferred diet is Chinook salmon. Unfortunately, many populations of Chinook are endangered due to overfishing and habitat loss or degradation.

“You have one endangered species that must feed on another endangered species to survive,” said Gaydos. “That’s a big challenge. Scarcity of food definitely has an effect on the health and fitness of the whales.”

Underwater noise

In addition to the low Chinook supply, southern resident killer whales are dealing with significant underwater noise in the Salish Sea, which makes it difficult for them to echolocate their prey.

“They live in an acoustic world,” said Gaydos. “They navigate and find food with their ears, but noise caused by boat traffic can inhibit their ability to effectively do that.”

Whales rely on special calls to communicate with other members of their pod, but the noise from vessel engines has forced them to vocalize slower and louder when the boats are nearby, just like when people speak slower and louder in a noisy room.

“The vessel traffic also diminishes their ability to detect salmon,” added Gaydos. “So not only is their food source endangered, but noise obstructs their ability to find the shrinking supply of fish that remains.”


On top of the high noise levels and low salmon availability, southern residents face yet another danger, and it might be the most challenging of the three: toxins.

“These are legacy chemicals that we’ve dumped into the ecosystem,” said Gaydos. “They are persistent chemicals, so they remain in the sea for a very long time and are having an effect on killer whales.”

Though the use of certain chemical toxins like PCBs and DDT is now illegal, chemicals remain in the water from past usage. Those chemicals can depress killer whales’ immune systems, making them more susceptible to diseases.

Washington has gone a step beyond federal law and banned some forms of flame-retardants (called PBDEs) that may pose health risks for killer whales and other marine life. While such decisions are undoubtedly good for the future, they don’t do anything about the toxins that are already in the system.

Since southern resident killer whales are at the top of the food chain, those legacy toxins accumulate in their blubber at high concentrations. The toxins also concentrate in the fat-rich milk of mothers, meaning female whales pass the chemicals on to their offspring, possibly compromising health and development from an early age.

Necropsies have revealed high levels of PCBs and DDT compounds in stranded whales. In some cases, high contaminant burdens are believed to have depressed whales' immune systems, making them more susceptible to infectious disease.


The SeaDoc Society approaches the study of killer whales the same way it approaches all other wildlife in the Salish Sea: they consider the problem as it relates to the ecosystem as a whole. The health and behaviors of animals, people and the environment are collectively weighed as Gaydos and his team work toward healing the sea.

Taking this One Health approach, SeaDoc has helped illuminate the role disease plays in killer whale deaths. A decade ago, Gaydos and his collaborators were surprised to learn that only four diseases had ever been written about in wild killer whales.

“At the same time we looked at elk, which had almost 200 diseases,” said Gaydos. “We know it’s not that killer whales don’t get diseases; it’s that we just hadn’t learned about them.”

But in the decade that followed, much has been learned. The number of known diseases in wild killer whales is growing, as is the understanding of how those diseases affect recovery. This work has spawned action that could help alleviate the struggle moving forward.

Some runs of Chinook salmon that southern residents prefer to eat are now listed as endangered, which will help prevent overfishing of the whales' primary food source. Recent regulations require that vessels stay a minimum of 200 yards away from the whales to reduce impact on their ability to communicate and find food. Banning contaminants that are known to be harmful to killer whales and other animals in the ecosystem will limit future exposure to toxins that weaken their immune systems.

In addition to those signs of progress, the standardized necropsy protocol has already led to the collection of more reliable and consistent data from killer whale deaths, which has made it easier for scientists to share their findings across organizations.

“It’s important because, when an animal dies, you want to learn as much as you can from that experience,” said Gaydos. “Information gathered from one animal’s death could prevent another animal from dying in the future.”

There are only 81 southern residents, so every single one matters. 

More from Volume 6: The Salish Sea

Multimedia and graphics by Chris Ancheta and Justin Cox