Sharks go­ing down

Port Douglas & Mossman Gazette - - NEWS -

SHARK numbers are in se­ri­ous de­cline with the sur­vival of some species threat­ened, ac­cord­ing to a study con­ducted on the Great Bar­rier Reef by an Aus­tralian group of marine sci­en­tists.

The pop­u­la­tion mod­el­ling study con­ducted by Pro­fes­sor Sean Con­nolly, Mizue Hisano and Doc­tor Wil­liam Rob­bins from the ARC Cen­tre of Ex­cel­lence for Coral reef Stud­ies and James Cook Univer­sity in­ves­ti­gated shark growth, birth and mor­tal­ity rates to cal­cu­late pop­u­la­tion growth rates.

“The study was only on whitetip and grey reef sharks,” Pro­fes­sor Con­nolly said.

“They are slow breed­ing an­i­mals of­ten hav­ing just one or a small num­ber of pups ev­ery other year.

“This means they do not re­cover from over fish­ing eas­ily.”

The cause of the ap­par­ent pop­u­la­tion de­cline sits firmly in the lap of com­mer­cial fish­ing, ac­cord­ing to Pro­fes­sor Con­nolly.

Some of the over­fish­ing is a re­sult of sharks be­ing a by-catch of tar­get species such as coral trout, and some be­cause of shark fish­ing.

The main value in a shark is in shark fin and there is strong ev­i­dence of il­le­gal fish­ing for shark fins within the Great Bar­rier Reef with finned shark car­casses be­ing found.

“Grey reef sharks and whitetips to a slightly lesser ex­tent are ag­gres­sive feed­ers, so they will at­tack a bait quicker than a species like coral trout,” Pro­fes­sor Con­nolly said.

“Com­mer­cial fish­er­men need to vir­tu­ally clear out the shark pop­u­la­tion be­fore they can start catch­ing their tar­get species.”

The find­ings of the study are sup­ported by ev­ery­day ob­ser­va­tions by dive op­er­a­tors such as Aris­to­cat that have been div­ing on the reefs off Port Dou­glas for over 20 years.

Jared Dun­stan is a dive in­struc­tor on Aris­to­cat and of­ten dives into the wa­ters around Agin­court Reef 12 or more times a day.

He is con­vinced reef shark numbers have de­clined dra­mat­i­cally in the last five years.

“Five years ago, we’d see sharks on vir­tu­ally ev­ery dive. Now, we’re lucky if we see one a day,” he said.

“I used to see blacktip reef sharks reg­u­larly, but I can’t re­mem­ber the last time I saw one.

“The sharks I see to­day are also no­tice­ably smaller than they used to be.”

Smaller, younger sharks is in­dica­tive of a pop­u­la­tion be­ing over­fished,” said Pro­fes­sor Con­nolly.

“Sharks aren’t liv­ing long enough to grow to full size.

“There are mea­sures that can be taken to re­duce the im­pact on shark pop­u­la­tions with­out ban­ning all com­mer­cial fish­ing or dra­mat­i­cally ex­tend­ing no go zones across the en­tire reef.

“Firstly, en­force­ment au­thor­i­ties need greater power to stop and search boats they sus­pect of il­le­gal fish­ing, and se­condly we need to stop tar­get­ing sharks.”

Un­der threat: the grey reef shark

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