A warmer North Pacific Ocean might be partly to blame for king-salmon-eating killer whales struggling in the Salish Sea of the Pacific Northwest, but climate changes appear to be opening rich, new hunting grounds for some of their northern cousins.
The report buttresses the observations of hunters and scientists from along Alaska’s remote and desolate northern Bering Sea, Chukchi and Beaufort Sea coasts.
“They’ve always been around based on local knowledge, but the aerial surveys essentially never saw them until the last decade,” said Craig George, an elder scientist based at the top of the world in Utqiaġvik, the community formerly known as Barrow.
“In the last five years, the first bowhead (whale) calf kills have been recorded,” George said Saturday. “So I’m pretty convinced the killer whale densities have increased in the northeast Chukchi and there may be more killer whales now. Grays and bowheads are at historic levels, and fin (whales) humpbacks are now common in the Chukchi. Lots of food around for killer whales.”
The wolves of the sea, killer whales – orcas to some – would naturally try to exploit a new prey base, and the hydrophone data would indicate that is what is happening.
“Killer whale calls were detected every year from 2009 to 2015,” she wrote. “Signals were detected with increasing frequency in fall months (September to November) annually from 2009 to 2015, and in every month from June through November from 2013 to 2015.”
The hydrophone provides but a snapshot of a tiny part of the picture of what is going on in the region.
“The acoustic detections reported here are from a single site in the southern Chukchi Sea that is located where Bering Sea waters from both the eastern and western sides of the Bering Strait converge,” Stafford noted. “The detection range for killer whale calls under very low ambient noise conditions is on the order of at most 10 kilometers (6.2 miles), therefore only a very small proportion of the southern Chukchi Sea was monitored during this study.
“The occurrence documented here should be considered a minimum estimate of the time spent in the Chukchi Sea.”
Data collection was hampered by, among other things, the fact that “mammal-eating killer whales tend to be silent when hunting, only producing calls during social interactions or after a successful kill or when pursuing large prey,” Stafford wrote.
The thinking is that killer whales on the hunt travel silently so as not to alert prey of their presence in the area.
Given the limitations on the hydrophone data, Stafford expressed a belief killer whale numbers in the increasingly ice-free Alaska Arctic might be far higher than indicated.
“In the eastern Canadian Arctic, particularly the Hudson Bay area, killer whale sightings have increased exponentially since the 1950s,” she observed. “This increase has been partially attributed to decreases in seasonal sea ice at ‘choke points’ where heavy, multiyear sea ice has restricted their access in the past.
“The proportion of bowhead whales with killer whale rake marks, which are scars caused by an unsuccessful predation event, increased from 1986 to 2012 with an estimate of 10 percent of adults seen between 2007 and 2012 exhibiting interaction with killer whales.”
Residents and transients
Commercial fishermen in the Bering Sea have for years been complaining about a boom in whale numbers there. A 2014 study published in PLOS One concluded those fishermen were losing more than $500 per day to killer whales that had become masters at stealing fish off longlines.
These whales, however, are resident fish eaters, and interactions that bring them into contact with fishermen make them easier to track.
“We have over 700 individual resident killer whales photographed and catalogued in the waters stretching from southern Southeast Alaska to Kodiak Island and over 1,500 from the Aleutian Islands and Bering Sea shelf edge, and we are still discovering more with every field effort,” noted Alaska whale authority Craig Matkin wrote in the Journal of the American Cetacean Society.
Much less is known about the so-called transients that prey on other whales and marine mammals.
Although northern fur seals which breed in the Pribilof Islands are known to be prime prey for the transients, Maktkin said, only about 50 have been individually identified.
“Just what they do when they leave the Pribilofs is not certain,” he wrote, “but there is no doubt they travel substantial distances. One satellite-tagged whale headed southward more than 1120 miles into the subtropical transition region of the central North Pacific, nearly halfway to Hawaii.”
There have been indications, however, that the population has grown large enough to alter ecosystem in some places.
“We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales’ foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus ‘fishing-down’ this element of the marine food web,” they said. “The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis.”
Matkin, who estimates there are 350 killers using the waters around rookeries and haulouts, has questioned that. If they whales were only eating sea otters and sea lions, he wrote, they might be able to decimate those populations, but all indications are that the whales are feasting on a multitude of prey.
“…Our observations suggest some seasonal specialization (or) gray whales at migration time, or fur seals at breeding time,” he observed. “(But) stable isotope analysis of skin biopsy samples has shown that the spring/summer diet of transient killer whales in the Aleutian Islands is not composed exclusively or even primarily of Steller sea lions or sea otters, a finding
supported by field observation data indicating that gray whales, minke whales, and northern fur seals comprise a substantial portion of the their diet.
“Additionally, transient killer whales sampled in the Bering Sea have stable isotope signatures consistent with a largely cetacean diet (of) Dall’s porpoises, minke whales, and gray whales. We have not observed actual consumption of sea otters in this region, although there are a few accounts from other researchers.”
Available prey
Opportunistic hunters, the killer whales could well have shifted their hunting toward more plentiful prey after Western Alaska sea lion numbers plummeted in the 1980s and whales became more common.
The population of eastern grey whales has been increasingly steadily since the 1990s, and expanding ever northward into new habitat as Arctic Ocean ice retreats.
NOAA scientist Sue Moore suggested in 2016 that it was “boom times” for all the baleen whales in the Arctic and near-Arctic. Killer whales feed on those whales along with other marine mammals.
“A ‘new normal’ climate is emerging in the Pacific Arctic marine ecosystem, coincident with the dramatic loss of sea ice at a rate which accelerated after 2000,” Moore observed. “Overall, the region has lost 75 percent of sea ice by volume and 50 percent in late-summer surface cover, coincident with the extension of the open-water period by four to six weeks.”
“Satellite data suggest that this biophysical transformation supports increased rates of phytoplankton net primary production by 42 percent in the Chukchi Sea and 53.1 percent in the Beaufort Sea, probably in response to reduced sea ice thickness and extension of the open-water period,” she wrote.
Increasing volumes of phytoplankton, in turn, “probably supports higher rates of secondary production, including the mesozooplankton and forage fish prey of baleen whales,” Moore concluded. “This suggested link between sea ice loss and increased prey production is supported by limited observations in the Chukchi Sea, where the abundance and biomass of mesozooplankton was higher in reduced-ice years (2007/2008) compared with years with extensive sea ice (1991/1992).”
As the base of the pyramid-shaped food web grows, so too do the number of predators on up the web – salmon, pollock, pinnipeds, the little whales, the big whales, and finally at the top of the heap the highly predatory killer whales.
“At present,” Moore concluded, “conditions in the Pacific Arctic appear to be favourable – i.e. ‘boom times’ – for all five species of baleen whales.”
Indications are that the boom times for baleen whales might now have trickled down to the killer whales coming north to join the mix in the bloody jungle that is the natural world, where the richness of an ecosystem, or lack thereof, is usually most obvious in the volume of killing taking place.
Whether these changes are a good thing or a bad thing for the Arctic going forward only time will tell.
“Baleen whales also act as ecosystem engineers and their recovering numbers may actually buffer the marine ecosystem from destabilizing stresses associated with rapid change,” Moore wrote. “With more baleen whales recycling nutrients vertically and horizontally and, with increasing numbers of bowhead and grey whales re-suspending sediments during epibenthic and benthic foraging, the Pacific Arctic marine ecosystem will probably continue to change in ways now difficult to predict.”
So far, however, the warming of the Bering Sea and waters to the north has brought good times for any number of species from baleen whales to killer whales to salmon.
Bristol Bay at the southern edge of the Bering Sea is witnessing unprecedented returns of sockeye salmon, and Russia’s Kamchatka Peninsula on the eastern edge of the sea was overrun by the 2018 pink salmon return.