August 19, 2021 — The following was released by NOAA Fisheries:
The body condition of endangered Southern Resident killer whales reflects changes in Chinook salmon numbers in the Fraser River and the Salish Sea. This is according to new research using aerial photogrammetry from drones to track changes in their body condition over time.
The study, titled “Survival of the Fattest: Linking body condition to prey availability and survivorship of killer whales,” also found that poor body condition makes the whales more likely to die.
The new findings published today in Ecosphere highlight the value of monitoring these endangered whales through aerial photogrammetry. This method can detect individual whales declining in condition, which can provide an early warning system that they may die.
The 74 Southern Resident orcas make up three pods known as J, K, and L. Each pod is made up of distinct social and family groups.
The research showed that the body condition of J pod whales improved when Chinook salmon abundance was higher in the Salish Sea and in Fraser River tributaries. L pod body condition improved when Chinook salmon abundance was higher in Puget Sound tributaries, although that relationship was weaker than J pod and Fraser River Chinook. K pod whales had no clear relationship to the salmon populations examined in the study. However, whales in K pod also experienced little change in their body condition during the study period.
K and L pods spend more time foraging on the outer coast of Washington and Oregon than J pod. Their more varied diet is more challenging to relate to changes in their body condition. In contrast, J pod depends to a greater extent on Chinook salmon. Differences in body condition between the three pods reflects distinct foraging patterns, while the condition of individual whales provides insights into their health, researchers found.