Whales shrank be­fore pop­u­la­tions crashed

Kuwait Times - - HEALTH & SCIENCE -

PARIS: The body size of some whale species di­min­ished by sev­eral me­ters decades be­fore 20th-cen­tury fac­tory fish­ing caused their pop­u­la­tions to col­lapse, re­searchers said Thurs­day. If that pat­tern holds true for other com­mer­cially harvested marine species, a drop in body size could serve as early warn­ing that pro­tec­tive mea­sures are needed, they re­ported in the jour­nal Na­ture Ecol­ogy & Evo­lu­tion. Once a pop­u­la­tion has crashed, re­cov­ery is dif­fi­cult at best: 25 years af­ter a mora­to­rium on Canada’s dec­i­mated north­west At­lantic Cod fish­ery, the sub-species has yet to bounce back.

Hunted since the 18th cen­tury, many whale species were saved from ex­tinc­tion by a leaky 1982 mora­to­rium that has still al­lowed more than 1,000 of the ma­jes­tic sea mam­mals to be killed ev­ery year. Re­searchers led by Christo­pher Cle­ments of the Univer­sity of Zurich looked at an­nual records-in­clud­ing size and num­ber caught-com­piled by the In­ter­na­tional Whal­ing Com­mis­sion and reach­ing back to about 1900, when new tech­nolo­gies emerged that turned the hunt into a har­vest.

“We show that dur­ing this pe­riod of com­mer­cial whal­ing, the mean body size of caught whales de­clined dra­mat­i­cally-by up to four me­tersover a 70-year pe­riod,” the study con­cluded. In­dus­trial whal­ing wiped out nearly three mil­lion of the an­i­mals dur­ing the last cen­tury, ac­cord­ing to a tally pub­lished re­cently in the jour­nal Marine Fish­eries Re­view.

Fac­tory ships

Cle­ments and his col­leagues fo­cused of four species that ac­counted for 80 per­cent of that haul: sei, fin and blue whales-the largest an­i­mals ever to roam the planet-are fil­ter feed­ers, and listed as en­dan­gered on the Red List of threat­ened species. The box-headed sperm whale is prob­a­bly most rec­og­niz­able as Ahab’s ad­ver­sary in Moby Dick. “Fish­ing pres­sure re­mained high un­til whale pop­u­la­tions col­lapsed and be­come com­mer­cially un­ten­able, where­upon whalers moved on to new species,” the study said.

For blue, fin and sei whales, body size started to shrink a cou­ple of decades be­fore the sud­den drop off in num­bers caught. For sperm whales, the de­cline in size was grad­ual across most of the cen­tury, show­ing up clearly at least 40 years be­fore an­nual catch lev­els plum­meted. “Early warn­ing sig­nals were present for all four species,” the re­searchers said. Adding catch fig­ures into the pic­ture strength­ened the pre­dic­tive power of their model, which they sug­gest could be ap­plied to fish and other marine an­i­mals un­der in­tense fish­ing pres­sure. But in the ab­sence of re­li­able catch data, changes in size and other phys­i­cal traits “may be used to pre­dict col­lapse,” the study con­cluded. Tens of mil­lions of sharks, for ex­am­ple, are killed ev­ery year for their fins, the size of which may pro­vide clues on the health of re­gional or global pop­u­la­tions for these toplevel preda­tors. Wild sole, salmon and lob­ster could also ben­e­fit from such an ap­proach.—AFP

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