Fraser River Chinook salmon are so vital to the endangered Southern Resident killer whales that the U.S. government defines the Salish Sea as their “core summer habitat.” In a new study, scientists examined 17 years of sightings to understand better how the whales’ presence or absence is related to the changing abundance of Fraser River Chinook salmon.
What was the study?
Scientists analyzed sightings from reputable sources—submitted between April 1 and October 31 each year from 2004 to 2020. They then compared the Southern Resident killer whales’ presence in the Salish Sea against Canadian government data on the number of Chinook salmon returning to the Fraser River over the same time period.
What did they find?
"The number of days each pod was observed in the core summer habitat between April 1 and October 31 declined steadily between 2004 and 2020 for all pods."
In the early 2000s, at least one pod from was present 50-75% of the days between April 1 and October 31; in recent years, this has fallen to just 5-15%.
For example, J Pod, who relies on this food source more than K and L Pods—and hence are usually more often in the Salish Sea—was present for a record 164 days in 2005. In 2016, J Pod visits hit a historic low of just 36 days.
In 2009, K Pod spent 124 days in the Salish Sea, but in 2017 made only 10 visits. There were 103 sighting days for L Pod in 2000; in 2019, there were just 10.
As chinook salmon abundance declines, Southern Resident killer whales have become increasingly absent in the Salish Sea.
How does this decline in visits by the Southern Resident killer whales relate to Chinook salmon abundance? Unsurprisingly, the average daily Fraser River Chinook salmon count declined by over 50% over the same period.
Sadly, these are the most energy-rich the whales might eat all year, as “Fraser River Chinook generally have larger individual body sizes and, therefore higher energetic value as prey, than other Salish Sea Chinook stocks.”
As the researchers noted, the increasing absence of this prey “may be driving Southern Resident killer whales to forage in other areas outside of the core summer habitat (e.g., in their typical winter range) rather than risk encountering low prey density that they experienced in prior years.”
In other words, these highly intelligent whales learn, adapt, and move their hunt to the outer coast. Yet, studies show that these alternate prey sources may be inadequate to meet the whales’ energy needs, particularly to bulk up and build their blubber stores for the leaner winter and early spring months when prey is even harder to find.
Now, as these richest prey sources dwindle and their arrival shifts back to later in the year, the whales return to the Salish Sea in poor body condition, and the skinniest of these are the least likely to survive, let alone thrive.
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What, then, are the solutions to this crisis? Quite simply, the study’s authors recommend limiting commercial fishing. The Canadian government has already taken such measures in their waters; however, these fish must also swim through U.S. waters to get to the Fraser River, and these areas are not closed to fishing.
Additionally, the U.S. government could restrict fishing to increase the number of high-in-fat Chinook salmon returning to U.S. river systems such as the Columbia in Washington State. Yet many are caught in the Southeast Alaska Chinook fishery before they can return to spawn. Sadly, this fishery will continue this year despite a recent court judgment that found this fishery endangers predator and their prey.
We must hold the government accountable for this Endangered Species Act violation while continuing to ask they halt fishing to save endangered salmon AND compensate fishermen for their loss of income. It’s essential if we are to secure a future for wild Chinook salmon and healthy Southern Resident killer whales.
