Hu­man be­hav­iour is at the root of orca plight

The Western Star - - SCIENCE - David Suzuki David Suzuki is a sci­en­tist, broad­caster, au­thor and co-founder of the David Suzuki Foun­da­tion. Writ­ten with con­tri­bu­tions from David Suzuki Foun­da­tion Se­nior Com­mu­ni­ca­tions Spe­cial­ist Theresa Beer. Learn more at www.david­suzuki.org.

News about orca mother Tahle­quah car­ry­ing her dead new­born for 17 days through the Sal­ish Sea this sum­mer was heart­break­ing, and right­fully cap­tured the world’s at­ten­tion. It high­lighted the plight of one of Canada’s most en­dan­gered marine mam­mals. The south­ern res­i­dent killer whale (orca) pop­u­la­tion has dropped by 25 per cent in two decades. Just 74 re­main, and none has suc­cess­fully given birth in three years.

The south­ern res­i­dents’ sur­vival de­pends on chi­nook salmon, their pri­mary food. In the Fraser River, one of B.C.’s most im­por­tant salmon rivers, 11 of 15 chi­nook stocks are highly de­pleted and re­quire con­ser­va­tion ac­tion. Habi­tat de­struc­tion, fish­eries, con­tam­i­nants, agri­cul­tural runoff, warm­ing and acid­i­fy­ing wa­ters from cli­mate change, and dis­ease threats from open net­pen salmon farms all play roles in chi­nook de­cline. Com­mer­cial and recre­ational fish­eries com­pete with whales for salmon, and their pres­ence, along with all ocean traf­fic, dis­rupts the feed­ing whales.

Sports fish­ing groups at­tribute chi­nook de­clines to seals and sea lions and are call­ing for culls. But blam­ing seals doesn’t ex­plain low chi­nook re­turns.

Peo­ple nearly elim­i­nated har­bour seals from B.C.’s coast in the 20th cen­tury. Preda­tor con­trol and over-hunt­ing for the com­mer­cial fur trade brought pop­u­la­tions to fewer than 10,000 in the 1960s. After seals were pro­tected in 1970, num­bers in­creased to near 1880s pre-ex­ploita­tion lev­els, at about 110,000, and have re­mained sta­ble since the late 1990s. Re­cov­ery of seal pop­u­la­tions can be con­sid­ered a good news story.

It’s tempt­ing to look for sim­ple lin­ear so­lu­tions such as a cull, but it’s highly un­likely to have the de­sired out­come. The com­plex­ity of marine food webs re­quires a non-lin­ear view that in­cludes mil­lions of eco­log­i­cal pos­si­bil­i­ties. Ac­cord­ing to one study, only four per cent of a har­bour seal’s diet is salmon, and an even smaller pro­por­tion is chi­nook. Seals eat all species of ju­ve­nile salmon, and only rarely the adult salmon recre­ational fish­eries tar­get. They also eat small fish, such as hake, which are ma­jor salmon smolt preda­tors, as well as fish that com­pete with chi­nook. It’s plau­si­ble that a seal’s pres­ence in­creases rather than de­creases chi­nook num­bers.

Tran­sient or­cas have been seen more of­ten than their res­i­dent cousins in B.C.’s coastal wa­ters over the past decade. Their pop­u­la­tion is thought to have in­creased to about 300. These or­cas pre­fer to eat har­bour seals, re­quir­ing the caloric en­ergy of about one seal a day.

Many peo­ple call­ing for seal and sea lion culls also point to in­creased hatch­ery pro­duc­tion as the best so­lu­tion to plum­met­ing wild salmon stocks. But dur­ing more than 130 years of West Coast hatch­eries, fish­eries have col­lapsed and wild salmon pop­u­la­tions have de­clined. The pro­lif­er­a­tion of hatch­eries be­tween 1900 and 2014, among other fac­tors, led to a 97 per cent re­duc­tion of wild Puget Sound steel­head.

Pa­cific salmon are an adap­tive species, ca­pa­ble of mea­sur­able ge­netic vari­a­tions within 17 gen­er­a­tions and able to ad­just to the vari­able nat­u­ral en­vi­ron­ments where they were born. Ar­ti­fi­cially se­lect­ing par­ents in a hatch­ery re­moves much of the nat­u­ral se­lec­tion nec­es­sary to en­sure ef­fec­tive adap­ta­tion. The lat­est sci­ence also shows even short pe­ri­ods of time spent in an ar­ti­fi­cial en­vi­ron­ment changes hatch­ery fish, mak­ing them less fit for sur­vival and car­ry­ing genes that may harm wild stocks if hatch­ery fish make it to spawn­ing grounds.

Hatch­ery fish can never re­ally be wild. Their pres­ence can do more harm than good. Those that sur­vive com­pete with wild fish for food, and in some cases may eat smaller wild fish. With more than five bil­lion hatch­ery salmon re­leased each year, con­cerns have been raised about the over­all car­ry­ing ca­pac­ity of the North Pa­cific Ocean and lim­ited food sup­plies. Of­ten the use of hatch­eries re­sults in a drive for more fish­ing to jus­tify hatch­ery costs or to avoid tak­ing nec­es­sary ac­tions such as re­duc­ing catch and restor­ing habi­tat to re­build wild fish pop­u­la­tions.

Com­mis­sioner of the En­vi­ron­ment and Sus­tain­able Devel­op­ment Julie Gelfand called the fed­eral gov­ern­ment’s mea­sures to pro­tect en­dan­gered or­cas re­ac­tive, lim­ited and late. Hu­mans are the main threat to wildlife.

We must take re­spon­si­bil­ity and change our de­struc­tive ways. If we want or­cas and other species to sur­vive, we should look in the mir­ror and change our own be­hav­iour.

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