Killer whales can be divided into three ecotypes based on their social structure, dialects and hunting strategies and diet: residents, transients and offshores The principal food of residents tends to be Chinook salmon, while transient killer whales feed on warm blooded prey like seals, sea lions and baleen whales such as gray whales. As you can see from the ecotype poster the differences are quite visible.
The current threats to resident killer whales are broadly defined as being:
- Environmental contamination,
- Reductions in the availability or quality of prey,
- Disturbance - both physical and acoustic disturbance.
Historic threats that affected killer whale populations include culling and being taken for captivity. Today, multiple threats interact to create stresses on the populations. With less food, toxins are more likely to metabolize and stresses such as noise and boat traffic are likely to have a greater impact as they reduce the chance of catching limited prey.
Due to their diet choice, the different killer whale ecotypes vary in their vulnerability towards persistent organic pollutants. Since PCBs (Polychlorinated biphenyls) and similar organic pollutants accumulate in the animal fat layer along the ‘food chain’, the transient orcas are in the most danger as they are feeding on other top-predators such as sea lions, porpoises and whales. Furthermore, resident and transient males accumulate higher levels of persistent organic pollutants in their fatty tissues (blubber) than females, since they are not able to offload their toxins to their offspring by nursing. The load in organic pollutants contains the risk in further vulnerability towards other health risks of orcas and top-down impacts on the whole ecosystem.
This Killer Whales Ecotypes & Forms poster was reprinted by NOAA/SWFSC and can be downloaded from free of charge. Poster created by Bob Pitman (text) and Uko Gorter (illustrations & design).