South­ern killer whales starv­ing while their cousins in Alaska feast

North­ern or­cas thriv­ing be­cause they get first crack at largest chi­nook

Vancouver Sun - - CITY - RANDY SHORE [email protected]

Killer whales na­tive to the waters of north­ern B.C. and Alaska are se­lec­tively eat­ing mil­lions of large, nu­tri­tious chi­nook salmon long be­fore the fish make their way to the feed­ing grounds fre­quented by our dwin­dling south­ern res­i­dent killer whales, ac­cord­ing to new re­search.

Con­ser­va­tion ef­forts aimed at both killer whales and chi­nook salmon may be hav­ing “un­ex­pected con­se­quences,” said the study’s lead au­thor Jan Ohlberger, from the Univer­sity of Washington’s School of Aquatic and Fish­ery Sciences.

The prob­lem is that boom­ing pop­u­la­tions of north­ern res­i­dent killer whales and Alaska res­i­dents are get­ting first crack at the best chi­nooks, those more than 75 cen­time­tres long.

Un­like the smaller south­ern group that in­cludes ap­prox­i­mately 73 whales, there are 300 north­ern and 2,300 Alaska whales, about three times as many as 30 years ago.

“Chi­nook from the Columbia River and B.C. river sys­tems move north along the coast to the Gulf of Alaska, where they put on most of their mass,” said co-au­thor Daniel Schindler, a UW pro­fes­sor of aquatic and fish­ery sciences.

“It’s pretty clear that Alaska killer whales and north­ern res­i­dents get first shot at (the chi­nook) be­fore they head south through a gaunt­let of preda­tors, and that’s when the dregs show up in the Sal­ish Sea,” he said.

In re­cent years, Cana­dian and Amer­i­can re­searchers have ob­served that the south­ern res­i­dents ap­pear to be mal­nour­ished. Three mem­bers have per­ished this year, in­clud­ing one that showed ob­vi­ous signs of de­pleted body fat.

All three res­i­dent killer whale groups pre­fer large chi­nook. To­gether, they eat about 2.5 mil­lion adult chi­nook salmon per year.

That level of con­sump­tion has led to a de­cline in the body size of chi­nook and the num­ber of large chi­nook over the past 40 years, ac­cord­ing to the study pub­lished Mon­day in the Pro­ceed­ings of the Na­tional Acad­emy of Sciences.

Fish­ing pres­sure has eased over that same pe­riod, with lit­tle ef­fect.

Chi­nook have de­clined 10 per cent in length and at least 25 per cent in weight, which is likely af­fect­ing their abil­ity to re­pro­duce. Smaller fish are less at­trac­tive to the res­i­dent killer whales, which typ­i­cally don’t eat chi­nook un­til they’re at least 60 cen­time­tres in length.

“Killer whales don’t show a lot of in­ter­est in chi­nook un­til they reach a cer­tain size, and then they fo­cus in­tensely on those in­di­vid­u­als,” said Ohlberger.

Both chi­nook salmon and res­i­dent killer whales have been the tar­get of in­ten­sive con­ser­va­tion mea­sures, but the suc­cess of the north­ern or­cas ap­pears to be com­ing at the ex­pense of the chi­nook and south­ern res­i­dent whales. Eleven B.C. chi­nook stocks are con­sid­ered en­dan­gered or threat­ened.

“We can’t ex­pect ev­ery species to be abun­dant. There are lim­its and trade-offs,” he said. “Th­ese are ecosys­tems that are in flux, and things are go­ing up and down all the time, even with­out human in­flu­ences.”

The re­cov­ery of seal and sea lion pop­u­la­tions in the Sal­ish Sea has also been im­pli­cated in the gen­eral de­cline of the chi­nook pop­u­la­tions.

How­ever, in the UW anal­y­sis, most ar­rows point to the north­ern res­i­dents.

“Most of the dis­cus­sion about the south­ern res­i­dents in Van­cou­ver and Seat­tle al­most pre­tends that they ex­ist in their own universe,” said Schindler. “In fact, they are com­pet­ing (for food) with whales else­where that are do­ing re­ally well, with in­cred­i­bly high pop­u­la­tion growth rates.”

Tak­ing a wider view of the north­ern Pa­cific, or­cas are thriv­ing, he said.

“There are more or­cas out there now than there have been in decades,” he said. “The south­ern res­i­dents could be suf­fer­ing from com­pe­ti­tion or changes to their en­vi­ron­ment.”

CANDICE EM­MONS/NORTH­WEST FISH­ERIES SCIENCE CEN­TER

Many of the 73 or so south­ern res­i­dent killer whales that can be seen off the coast of Van­cou­ver ap­pear to be mal­nour­ished with signs of de­pleted body fat.

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