While researching how our southern resident orcas hunt and capture fish, I came upon an interesting article that shows that the northern resident orcas (which live in British Columbia waters, generally north of the Fraser River) alter their hunting strategy depending upon prey availability, and that this is tied into large scale climatic variability. But when I checked to see if the southern residents showed a similar pattern, I encountered a really different, and surprising pattern.
According to a thesis, the local orcas don't seem to change their strategy in relation to climatic changes, but do extend the range and effort required to find adequate prey when it is scarce. And not all the pods showed the same changes in the same circumstances.
What is surprising is that the orcas did not concentrate their hunting efforts where salmon were most abundant, as measured by the capture rate by fishing boats. In other words, where fishermen had the most success was not necessarily where the orcas chose to hunt...although it became a 'chicken or egg' issue - did the fishermen have more success because the orcas weren't there? Or were there other features of the environment that were less desirable for the orcas at those places? Is there an aspect of the killer whale's culture at play, since they are different even from their "cousins" north of the border?
I looked at some other populations of fish-eating orcas, and again I found interesting variations between areas. When hunting herring, a population of orcas in Norway has
School of Herring (Creative Commons Photo)
been observed to keep schools of the fish near the surface. The whales flash their white undersides towards the fish and emit bubbles, which has the effect of driving the fish school to form into a 'ball'. The orcas then strike at the herring school with their tails, stunning and killing the fish, which the whales then eat one at a time. (I had no idea that herring can get to be 18" long!)
In Iceland, another population of orcas feeds very similarly upon herring, but in addition to emitting the bubbles the whales produce a loud droning type sound, possibly to help confuse and further compress the fish school (for video and a soundtrack, go here).
In the Russian waters of Avacha Gulf, orcas force tight schools of mackerel in a similar fashion, but then take turns swimming into the middle of the fish 'ball'.
In and around the Mediterranean Sea, a population of orcas hunts bluefin tuna (which are huge, 620 lbs is spawning size) by chasing them until the fish becomes exhausted...and in more recent times the whales have learned how to strip a fish from fishermen's long lines as the tuna are brought up from depth. Annoying to the fishermen, perhaps, who receive thousands of dollars per fish, but a sensible adaptation from the whales' point of view.
The following is from comments sent to me by Howard Garrett (see previous post), of OrcaNetwork, which speaks to the varied ways the orcas live and find fish:
When Rendell and Whitehead wrote Culture in Whales and Dolphins (2001) they summed up the findings that each orca community eats its own severely restricted diet, uses their own discrete repertoire of vocalizations, and maintains their own prescribed mating practices. The paper, published in the Journal of Behavioural and Brain Sciences, established that: "The complex and stable vocal and behavioural cultures of sympatric groups of killer whales (Orcinus orca) appear to have no parallel outside humans and represent an independent evolution of cultural faculties."
But they didn't want to venture any guesses about how orcas communicate, or how they transmit their cultural rules and traditions. They realize that "...understanding process (cultural transmission) is crucial to our understanding of the product (culture)" but they just don't even want to talk about it: "...no attempt is made to deduce what particular form of social learning underlies the observed patterns." And…"we know virtually nothing about the actual learning mechanisms cetaceans employ."
Then they hint at what they suspect: "Human culture is intimately linked to both language and symbolism, but there is currently no empirical basis for discussing the role or non-role of language and symbolism in cetacean culture …"
And they say: "Cetacean cultures appear to possess other attributes that have otherwise been restricted to humans. In particular, we are aware of no phenomena outside humans comparable to the distinctive, stable and sympatric vocal and behavioural cultures which appear to exist at several levels of killer whale society."
Over the next month we will continue to explore the intelligence and culture of the orcas as we discuss the proposed guidelines for increased protection of our locally endangered population.
