True blue crab count is on

Southern Gazette (South Perth) - - Front Page -

ABOUT 2000 blue swim­mer crabs are be­ing tagged in the first long-term study of the ed­i­ble crus­tacean’s stocks in the Swan and Can­ning rivers.

“We would very much like crab­bers to leave the tag un­touched, make records, and re­turn the crab to the wa­ter so we can find out where it goes next,” Fish­eries crab sci­en­tist David Har­ris said.

The three-year, $300,000 study is funded by the Bet­ter Ini­tia­tives Fish­ing Fund, and is fo­cus­ing on crab stocks in the rivers, Leschenault Es­tu­ary next to Bun­bury and nearby Geographe Bay.

“Stocks in the rivers are very healthy, but there is a high level of fish­ing pres­sure, which we are mon­i­tor­ing,” Mr Har­ris said.

Last month, re­searchers’ tag­ging in the Perth rivers started us­ing per­ma­nent T-bar tags in their work, which will con­tinue un­til June.

A four-month pi­lot sur­vey un­til Fe­bru­ary glued other types of tags to 1100 crabs, af­ter which re­ports in­di­cated the marked crabs com­prised about 10 per cent of all cap­tures.

But glued tags may fall off dur­ing ju­ve­nile crabs’ fre­quent moult­ing be­fore they ma­ture at about six months, while ma­ture crabs are thought to shed their shells each sum­mer.

Mr Har­ris said fish­ers with tagged crabs should record their cap­tures’ size and sex, tag num­ber, date, lo­ca­tion, depth and catch method.

Re­searchers need to know if the crab had eggs, whether it was re­turned to the wa­ter or kept for eat­ing, and whether it was a legal size.

Vol­un­teers can join the work aboard the re­search ves­sel as part of a Depart­ment of Fish­eries True Blue Swim­mer Sup­porter pro­gram.

Main pic­ture: Fish­eries tech­ni­cal of­fi­cer Josh Baker holds a T-bar tag and a blue swim­mer crab with the glued iden­ti­fi­ca­tion; inset: a blue swim­mer crab with a glued tag across its shell and a T-bar tag in­serted in its body.

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