West coast killer whales threatened by lack of fatty salmon
UBC study finds reduction in high-quality oily salmon influences decline in killer whale numbers.
Researchers say resident killer whales in southern British Columbia are not only threatened by the decline in the overall salmon population, but also by the reduction in fatty salmon from high quality, these whales' favorite meal.
A study by scientists at the University of British Columbia (UBC) concludes that not all salmon are created equal when it comes to feeding these animals, whose total population has been declining to 73 individuals.
Food quality matters, said the study's lead author, Jacob Lerner. Understanding differences in the energy density of salmon and their populations could help manage both the fish and the whales that feed on them, researchers point out in the study published in Nature last week.
The study indicates that although it is suspected that human activity is linked to the decline in the number of whales, in particular the water contaminants and noise pollution, much of the blame lies with the decline of the Fraser River Chinook population.
The most endangered types of Fraser River chinook salmon are also the most energy-dense prey for whales, the study found.
Jacob Lerner points out that scientists had started with the assumption that all Fraser River Chinook salmon were of equal value to Southern Resident Killer Whales.
However, they discovered that this is not true: fish have different levels of lipid content. Oily spring salmon tend to be higher in lipid, attracting killer whales that feed on them, while salmon that come later in the season have lower energy density.
Much research has focused on salmon abundance, but we thought it was important to try to understand how the energy density of Chinook salmon differs between different populations of Chinook salmon and when these different populations of chinook salmon are available to killer whales, explained Jacob Lerner.
According to researchers, chinook salmon from the Fraser River have different levels of lipid content.
The study found that southern residents should consume 30% more run salmon in the fall than in the spring, since early run fish tend to be larger and stronger. energy density.
To maintain the same energy level, the total Southern Resident population would need to eat about 80,000 more low-fat Chinook salmon each year, than if they ate high-lipid fish, said the researcher, a doctoral student in pelagic ecosystems at UBC.
Jacob Lerner said quantifying the lipid content of Fraser salmon plays a role in helping killer whales because migrating whales always return to the Salish Sea for spring and summer, coinciding often with the arrival of spring salmon.
We have identified a range of high, medium and low fat Fraser Chinook populations that can be used to better inform energetic patterns and manage the two species, he said in a press release.
Although the study focuses primarily on killer whales and their prey favorites, Jacob Lerner points out that it also highlights the effect of climate change on the entire food chain.
The study in Nature on the lipid content of Chinook Salmon and the implications for Southern Resident Killer Whales. )