KILLER WHALE BIOLOGY
biopsy sampling and DNA analysis
How can you tell whether a killer whale in a given area is after fish or whether it has marine mammal meals on its mind? This question has been problematic in trying to determine potential predation pressure on Steller sea lions, particularly when there is uncertainty about the number of killer whales that might be present. Because both resident and transient forms of killer whales inhabit the study area, a simple estimate of killer whale population size is not sufficient to provide an accurate picture of what is really going on.
While it is true that resident and transient killer whales usually differ slightly in appearance, this difference is not consistent enough to help in effectively distinguishing between members of the two populations. A more reliable way of separating the two groups is to compare sequences of mitochondrial DNA, also known as ‘maternal DNA.’ Since residents and transients have never been observed to intermingle non-aggressively, the population identity of a group can be inferred by sequencing mitochondrial DNA from only one of its members.
Analyzing biopsy samples collected for DNA analysis for persistent chemical pollutants such as PCBs has shown that members of some killer whale populations have extremely high concentrations of these toxins in their blubber. Because transients feed higher in the food chain, their levels are particularly high, but also members of the Southern Resident Population in Puget Sound and Georgia Strait show elevated PCB concentrations. This raises concerns about the effect of these chemicals on the health of the animals, especially with regard to their immune systems’ ability to fight off disease.