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NW Fishletter #390, February 4, 2019

[2] New Baby Orca, New Study Offer Hope For Survival

As whale watchers were celebrating sightings of a new baby orca in Puget Sound on Jan. 10, fisheries scientist Gregory Ruggerone took comfort knowing that--despite the loss of a baby orca last year--this newest member of the endangered southern resident killer whales has a better chance of surviving its first year.

A research scientist at Natural Resources Consultants and a member of the Independent Scientific Review Panel, Ruggerone and three other scientists just completed a study finding that newborn orcas are twice as likely to survive in odd years--as in 2019--than they are in even years--like 2018.

They also found that overall mortality rates among both newborns and older whales are more than three times higher in even years compared with odd years. From 1998 to 2017, when the population dropped from 98 to 75 whales, these orcas saw only 16 successful births in even years--half as many compared with odd years, when 32 have survived their first year. The mortality rate for both newborn and older whales was 3.6 times higher--or 61 whales--in even years compared with just 17 whales that have died in odd years.

Scientists believe this biennial mortality is not just coincidence. To Ruggerone, who has spent years studying pink salmon and the impact that their every-other-year abundance has had on the ocean environment and other species, he and other authors of the study believe that somehow--even though orcas don't eat them--pink salmon are playing a key role in the orca's plight. But they're not yet sure whether that impact is positive or negative.

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Whale watchers spotted a new member of the SRKWs L pod in Puget Sound on Jan. 10. Courtesy: Center for Whale Research

"The data are quite simple and straightforward, and in my mind, totally unexpected," Ruggerone told NW Fishletter.

And while it's not clear why the whales are more likely to survive in years when pink salmon are ultra-abundant, the authors of the study have some ideas. "The biennial pattern is there. We need to understand it, because it could help us recover the whales," Ruggerone noted.

The new baby was spotted Jan. 10, and brings the southern resident population to 75 individuals. It is a member of the L pod, and is being identified by the Center for Whale Research as L124, calf of 31-year-old L77. The mother has had two prior calves--the first died the same year it was born in 2010, and the second is a living female born in 2012, the nonprofit group reports.

"Approximately 40 percent of newborn calves do not survive their first few years, but we hope that this one makes it to maturity," the group's website says.

It's been three years since the southern residents have successfully produced a new member. The population includes the J, K and L pods. The L pod, now with 35 individuals, is the largest. Unlike the J pod--which lost a baby and an adult female last year and spends most of its time in the inner Salish Sea--the K and L pods travel the West Coast, preying on salmon as far south as California.

Following news of the new baby orca, the Washington Fish and Wildlife Commission adopted a new policy at its Jan. 11-12 meeting directing Fish and Wildlife managers to consider the dietary needs of orcas when setting this year's salmon fishing seasons.

"While state fishing seasons have long been subject to federal review, this new policy confirms that WDFW must play a leading role in orca recovery," Ron Warren, head of the agency's fish program, said in a prepared statement. "This year we plan to work with the National Marine Fisheries Service to develop new tools to assess the effects of fisheries on available prey for endangered orcas."

The agency is also asking the state Legislature for funds to improve salmon habitat and increase hatchery salmon by 24 million juveniles over the next two years, and is planning to increase production by 50 million in the 2021-2023 biennium budget.

The commission's policy also directs staff to enforce boating regulations and take steps to protect orcas from fishing vessel traffic disruptions.

Ruggerone said further investigation is needed before the indirect link between pink salmon abundance and orca survival can be used to develop other policies to help the southern resident population.

His study, published in the Jan. 3 edition of Marine Ecology Progress Series, notes that annual returns of pink salmon number about 17.8 million fish in odd years, and drop to about 400,000 fish in even years.

"This is the only biennial pattern in the physical or biological environment of the northeastern Pacific Ocean of which we are aware that could potentially drive the demographic pattern observed in [southern resident killer whales]," the study states.

One hypothesis as to why orcas do better in odd years is that they have a harder time finding their much-preferred prey--Chinook salmon--which are deeper in the ocean when there is a layer of highly abundant pink salmon closer to the ocean's surface. Pink and Chinook salmon both migrate through the same areas of the Salish Sea at the same time in summer and early fall. "Reduced foraging efficiency of the whales would lower their nutritional status, which would be expressed in the following even year because these large mammals have a strong physiological buffering capacity," the study suggests.

An alternative hypothesis is that pink salmon, when they are highly abundant, are indirectly helping the whale's ability to survive, even if they're not eating them directly. "[A]t present, we do not have a mechanistic explanation for how pink salmon would enhance SRKW foraging on Chinook salmon," the study said. The study also says that this biennial pattern also coincides with shifts in the orcas' foraging distribution.

The study's authors note that the biennial pattern linking orcas' birth and mortality rates to even or odd years cannot be explained by vessel disturbance, toxic contaminants or Chinook abundance, and that the extreme biennial abundance of pink salmon has been tied to effects on other species and ecosystem processes.

In prior studies, Ruggerone and other scientists found that the peaks and ebbs of annual pink salmon runs are causing the ocean's tiny plants and animals--its phytoplankton and zooplankton--to rise and fall dramatically each year.

His study and others have also found that increasing numbers of wild and hatchery pink salmon throughout the Pacific could be significantly impacting seabirds and other salmon species, including the growth and survival of sockeye, Chinook, coho and chum salmon, and steelhead. Pink salmon are now more abundant in the Pacific than at any other time since monitoring began in 1925. -K.C. Mehaffey

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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