To Understand Whales, Follow the Prey
This summer has been a strange one. How often have we heard those words in recent years for one reason or another? It could be persistently damp climate and flooding, or wildlife of one kind or another breaking the supposed rules of what we think we know about them. This time it’s orcas. Or, more accurately: a lack of orcas.
Where have all the Kamchatka orcas gone? WDC’s Far East Russia Orca Project /FEROP team working in Kamchatka, Russia, has had the slowest orca season since we started working here 14 years ago. The resident killer whales, more than 500 of them who habitually show up in Avacha Gulf, are all but absent. We’ve seen a few sperm whales and two gray whales but there have only been a few killer whale sightings — nothing like our usual daily sighting rate throughout the summer.
Having lots of time on our hands, our FEROP team began talking with local fishermen. We’ve learned that this is also a record poor year for pink salmon, the preferred salmon of our orcas. We still have a few weeks to go in our field season, but we’re wondering now if there has been a substantial relocation of our formerly reliable orcas or worse: a die-off. It may not be till next season or later that we get any idea of whether they will return to former numbers.
At the same time, news has come from the other side of the North Pacific, in British Columbia and Washington State waters, where the southern resident Vancouver Island orcas have similarly disappeared for long periods. According to Monika Weiland’s Orca Watcher Blog, the orcas have turned up on fewer days in 2013 than in any year since 1990. These southern resident orcas depend on Fraser River Chinook salmon. This salmon, too, is having a poor year. Susan Berta, in a reply to Monika’s blog, talks about how, in the past, the orca numbers have dipped following the low years for the Chinook salmon. The problem is that with only 82 orcas in that population, we cannot afford to lose any more.
Of course, orca prey have cycles of fat and lean; in the ocean, all food moves around, dependent on what it subsists on, and thus the orcas must keep moving, too. What we don’t know is how bad the food source would have to get before at least some of them are able to adjust their prey preferences. Would it just be the fittest individuals that manage to survive and change their habits? Certainly, there is a greater margin of safety with our larger population numbers in Kamchatka (500 plus) than with the southern community. But killer whales everywhere appear to live in populations, or breeding units of from fewer than 100 to no more than a few hundred. That’s why the capture of a third to a half of the southern resident population, as Susan Berta points out, was so disastrous — a legacy these orcas are still dealing with, and may yet not overcome.
These cycles are not just peculiar to fish-eating orcas. The transient marine-mammal eating orcas off the Commander Islands are reportedly not showing up as often as usual this summer. The blue whales off the west coast of Iceland are feeding farther offshore these days than they were in the late 1990s. And, in the past few decades, the well-studied humpback whales in Glacier Bay and on Stellwagen Bank have had a number of disappearances, sometimes for a full summer feeding season or two. The immediate theories then were that boats, shipping, noise, or even whale watching may have driven the whales away, but in these cases, at least, the decline or disappearance of prey appeared to be the main factor in the whales’ disappearance. In Stellwagen Bank, it was possible to show that the whales simply moved further offshore where they could feed on sand lance and eventually, when it returned to Stellwagen, the whales returned as well.
When whales disappear, “follow the prey” is not the only answer or route to understanding, but it is proving to be useful as the first line of enquiry. Now we need to find out more about the health of prey species, what they do, where they go, why they do what they do. Follow the prey soon becomes: Follow the prey of the prey…
