Tuesday, July 10, 2018

Puget Sound Orcas Suffer Demographic Decline

Orca pods addicted to Chinook Salmon suffering: Starvation and Habitat Threats Stalk Killer Whales
SEATTLE — For the last three years, not one calf has been born to the dwindling pods of black-and-white killer whales spouting geysers of mist off the coast in the Pacific Northwest.

Normally four or five calves would be born each year among this fairly unique urban population of whales — pods named J, K and L. But most recently, the number of orcas here has dwindled to just 75, a 30-year-low in what seems to be an inexorable, perplexing decline.

Listed as endangered since 2005, the orcas are essentially starving, as their primary prey, the Chinook, or king salmon, are dying off. Just last month, another one of the Southern Resident killer whales — one nicknamed “Crewser” that had not been seen since last November — was presumed dead by the Center for Whale Research.

In March, Gov. Jay Inslee issued an executive order directing state agencies to do more to protect the whales, and in May he convened the Southern Resident Orca Task Force, a group of state, tribal, provincial and federal officials, to devise ways to stem the loss of the beloved regional creature. “I believe we have orcas in our soul in this state,” he said. At another point, he wrote of the whales and Chinook salmon that “the impacts of letting these two species disappear would be felt for generations.”

In the late 1990s, there were nearly 100 of these giant whales in the population. Following the salmon, they migrate in the Salish Sea to the northern coast of British Columbia and often surface in the south at Puget Sound within sight of downtown Seattle, especially during the spring and summer months. The males, which can weigh up to 22,000 pounds, typically live about 30 years, and females, up to 16,000 pounds, survive longer — up to 50 or 60 years, although one J-pod member, Granny, lived to be 105 years old.

Not only are there fewer calves in recent years, but signs of inbreeding also point to a weakening population. In the 1970s and 80s, theme parks like Sea World captured nearly 4 dozen orcas from the region, possibly shrinking the pods’ gene pool. In the last three decades, just two males fathered half the calves in the last three decades, and only a third of the females are breeding, just once every decade instead of every five years. Researchers worry that reproducing females are aging out of the population, and will not be replaced.

Some conservationists are concerned that the orcas’ decline is another sign of a marine ecosystem in collapse. Beginning in 2013, something known as “The Blob” — a gigantic mass of nutrient poor, extremely warm water — warmed the Pacific from Mexico to Alaska, as much as six degrees above normal. Several years ago, starfish succumbed to a wasting disease and vanished from tide pools.

Much is still unknown about the plight of these orcas, but biologists and conservation managers have zeroed in on several main factors — and they are all connected.

The biggest contributing factor may be the disappearance of big king salmon — fish more than 40 inches long. “They are Chinook salmon specialists,” said Brad Hanson, team leader for recovery efforts for the Northwest Fisheries Science Center here, part of NOAA. “If they could, they would eat Chinook salmon 24/7.” Orcas gobble 30 a day. Hunting enough smaller prey requires a lot more energy.

Of most concern are the lingering effects of chemicals and pesticides, including the now banned DDT, as well as PCBs and PPDE, widely used in flame retardants and found through the world. The pollutants accumulate in salmon as they feed, and when the whales eat salmon they also ingest PCBs at even higher levels. “It’s very lipophilic, which means it stays in the fat, and the females transfer a huge proportion of the contaminant burden to their offspring,” Hanson said. “About 85 percent gets transferred to calves through lactation.”

And while much of the pollution is from the region’s industrial past, Boeing disclosed this spring that over the past five years it had discharged highly toxic PCBs into the Duwamish River, which flows into Puget Sound, thousands of times over the legal limit.

These toxins suppress the whales’ immune systems, making them more susceptible to disease. They can also impede reproduction. That may be why tests show a high number of females who have become pregnant have failed to calve.

However, the decline of the whales cannot be pegged, experts say, to contaminants alone. A separate population of transient whales near here eat mammals that eat fish, and so consume concentrate contaminants at even higher levels — many times as high as the resident pods. Yet they are thriving, which has left scientists scratching their heads. Global populations are robust as well.
They throw out a lot of other potential problems, mostly man made as possible causes of the declines, but without much evidence. My best guess is that a dearth of Chinook Salmon is largely responsible for the decline. The Chinook Salmon decline, in turn is likely the result of over-fishing, land use  and climatic cycles which are driving their growth and reproduction. In particular, the Pacific Decadal Oscillation seems to be highly correlated to Chinook Salmon success:

It's also interesting to note that Orcas are smart enough that pods have different "cultures", or learned food preferences. These pods prefer Chinook Salmon, but others specialize in seals and and sea lions, and at least two are known to kill and eat large sharks, including Great Whites.

Somehow, gene flow is maintained across the various pods, since they have not (yet) evolved into separate species, so some whales must switch between pods somehow. Maybe these whales should reconsider their life style.

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