Gray whales are bottom feeders. Blue whales are krill feeders. Humpbacks, however, are opportunistic, feeding mostly on fish in the northern hemisphere and krill in the Antarctic. Humpbacks and blues have been observed in the same area in California eating krill together. Different whales found in the same general region are often doing very different things, harvesting different levels of the food chain, and feeding in different physical habitats.
Most whales are specialists.
Toxins With toxins entering into the environment, there are two main levels of threat to whales. For highly toxic pollutants, the danger for whales is that the toxins would kill their prey. If there is no whale food, there will be no whales. The second danger to whales from toxins is secondary effects. Hydrocarbon pollutants like PCB and DDT reside in fats.