Every August we do a special informational page in the local paper,
the San Juan Journal, all about the endangered Southern Resident Killer Whales. This year, Director Ken Baclomb is the author. We thought we would share them with all of you who don't have access to the San Juan Journal!
This is the second installment:
the San Juan Journal, all about the endangered Southern Resident Killer Whales. This year, Director Ken Baclomb is the author. We thought we would share them with all of you who don't have access to the San Juan Journal!
This is the second installment:
What do Orca Whales Like to Eat?
In the previous article in the Whale Pages, we presented the fact that the whales we call Killer or Orca represent a complex of many distinct populations that may prove to qualify as species; and, here we present the fact that these distinct populations specialize or “like to eat” particular prey species. All of the populations of so-called Killer whales are predatory animals currently assigned to one species (Orcinus orca, Linnaeus, 1758), and they must eat to survive; but, the preferred prey species for each population varies according to what is locally abundant and available in the marine ecosystem within swimming range. The classic studies regarding what “Killer” whales like to eat came from examination of stomach contents of these whales that were stranded in various locations around the world, or taken by whalers. The food items were fish, squid, seals, porpoises, other whales, etc. that led to the early conclusion that Orcinus orca was euryphagous, that is they fed upon a wide variety of prey and could switch diet if a particular variety became scarce. More comprehensive recent studies, including those done by the Center for Whale Research, indicate that each branch of the Orca family tree tends to strongly lean toward a prey species that is locally available and sufficiently abundant year-round for a very long time (many whale lifetimes). This tendency is termed stenophagy – a narrow variety of prey species; and, over the evolutionary time scales available from thousands of whale lifetimes it has resulted in very distinct differences in the anatomy and morphology of the various whale populations.
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| Transient killer whale with a harbor seal in it's mouth- Photo by Dave Ellifrit |
“Transient”
Orcinus
orca whales may indeed be properly called “killers” (at least by the
seals, sea lions and porpoises they consume), and they have very robust jaw
structure with relatively big teeth (the better to bite you with, my dear).
Their lifestyle is rather nomadic, as they travel with the seasonal migrations
and/or the seasonal birthing and weaning cycles of their prey species. These
mammal predator whales typically venture into the waters around the San Juan
Islands in autumn and winter months when harbor seals are weaned (and
unsuspecting), and when sea lions overwinter in the Salish Sea. Typically the
“transients” travel in relatively small groups of 3-15 relatives and
associates, and they are usually stealthy (non-vocal, so the prey species
cannot hear them). This year (2013) we have witnessed an unprecedented influx
of “transients” around the San Juan Islands, some coming from as far as
California and Alaska. There are about 250 “transient” killer whales in the
Center for Whale Research catalogue for this area.
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| Southern Resident, L84, with a salmon in his mouth- Photo by Dave Ellifrit |
Orcinus
orca whales may be properly called “Orca”, a term that is more fitting
with the image of a peaceful non-stress-inducing population of mellow fish-eating
predators with less robust jaw architecture and smaller teeth than “transient”
killer whales. The “resident” lifestyle is adapted to the migrations and
seasonal abundance of salmon in the eastern North Pacific Ocean. The salmon
most available year-round within the “resident” swimming range are Chinook, or
Kings, which happen to be the largest and most nutritious species of salmon in
the world (formerly weighing up to 125 pounds each!). Chinook lifestyle, in
turn, is predatory upon smaller fishes that are in greatest abundance on the
continental shelf of the Pacific Ocean near the edge of upwelling currents.
Chinook salmon have been taken in Human fisheries by the millions each year for
the past century, and most wild populations of these fish are now “Endangered”
with many already extinct. The “resident” Orca whales typically venture into
the waters around the San Juan Islands in pod and multi-pod associations
(Superpods) from May to September when the mature Chinook salmon are bound primarily
for the Fraser River for spawning, though a few migrate to other river systems
in the Salish Sea. Thus, we have an Endangered whale species obligate feeding
upon an Endangered salmon species – a revolting development unforeseen by dam
builders, habitat usurpers, and fishermen. As of 2013, there are currently 82
southern “resident” Orca whales in this population, down from nearly 100 twenty
years ago, and down from more than 200 that we have catalogued. We have
demonstrated that the “resident” Orca survival is significantly linked to
Chinook abundance, and the government managers on both sides of the US/Canada
border should take more notice of this inconvenient truth before it is too
late. This year (2013) during the summer when whale-watching is historically
best, we have witnessed an unprecedented absence of “residents” around the San
Juan Islands, and a continuing downtrend in their population number concurrent
with a near collapse of Fraser River Chinook.
Ken Balcomb
Director
Center for Whale Research
