Food Supply

The diets of cetacean species in B.C. vary widely and include many fish species targeted by human fisheries. The health of these fish populations is governed not only by the amount of harvesting, but also by ocean regime shifts, climate change, coastal development, pollution and logging.

In killer whales, a strong link between available food supply and mortality was recently reported in Ford, et.al. (2005). In this paper, the researchers show that periods of population decline were primarily due to unusually high mortality rates in all ages of northern and southern resident killer whales. Not coincidentally, these times of high mortality occurred when chinook salmon abundance was low. The southern and northern resident populations feed primarily on chinook salmon.

The whales’ preference for chinook salmon is likely due to this species’ relatively large size, high fat content, and unlike other species of salmon, they are present year-round in the whales’ range. These killer whales may be especially dependent on chinook during winter, when chinook are the main salmon species available in BC’s coastal waters. It seems likely that during the winter resident killer whale populations may experience increased mortality as a result of nutritional stress if the quantity and/or quality of this prey resource declines.

The link between resident killer whales and chinook salmon is strong, but took many years of research to understand. In contrast, the importance of prey species to the survivial of other cetaceans is not well understood. Reductions in the availability of prey to at-risk cetaceans either through competition with fisheries, regime shifts, climate change or other factors is a serious concern.

WHAT YOU CAN DO

- eat sustainably caught fish (Oceanwise) (Sea Choice)
- follow the fishing regulations