Lurk­ing sharks lead to spike in seal stress

The Herald (South Africa) - - NEWS - – Dave Cham­bers

THE pres­ence of great white sharks off the West­ern Cape sends seals’ stress lev­els rock­et­ing.

US sci­en­tists who stud­ied seals on six is­lands for three years say lev­els of a stress hor­mone in their fae­ces rose sharply when the oceans’ apex preda­tor was lurk­ing.

In par­tic­u­lar‚ re­searchers from the Uni­ver­sity of Mi­ami found that stress lev­els peaked when seals were at risk of un­pre­dictable and lethal at­tack from great whites as they left the safety of an is­land’s in­ner perime­ter and passed through a gauntlet of sharks to reach off­shore feed­ing grounds.

“These re­sults un­der­line the eco­log­i­cal im­por­tance of apex preda­tors‚” study leader Neil Ham­mer­schlag‚ who spe­cialises in ecosys­tem sci­ence, said.

“Any re­sult­ing loss in health or sur­vival of prey due to preda­tor-in­duced stress could have cas­cad­ing ef­fects on the en­tire ecosys­tem and food web‚” he wrote in the jour­nal Ecol­ogy.

He said Cape fur seal colonies were the ideal place to study the hy­poth­e­sis that preda­tors could ex­ert con­trol over their prey us­ing a stress re­sponse be­cause of the dense great white pop­u­la­tions.

“Our find­ings showed seals ex­hib­ited high stress when great whites were hunt­ing and the seals had no way of an­tic­i­pat­ing or ef­fec­tively pre­vent­ing a pre­da­tion at­tempt.”

Pic­ture: YOUTUBE

APEX PREDA­TOR: A great white

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