Caught crab is an Asian pest

Western Suburbs Weekly - - Opinion - By JON BAS­SETT

A KEEN-EYED crab fish­er­man iden­ti­fied the Swan River’s fourth con­firmed pest Asian pad­dle crab near Matilda Bay, Craw­ley on De­cem­ber 22.

How­ever, Depart­ment of Fish­eries Depart­ment of Fish­eries marine biose­cu­rity of­fi­cer Mar­ion Mas­sam said there was no in­di­ca­tion the pest was spread­ing in the es­tu­ary, after three of the poi­sonous in­vaders were net­ted about 7km down­stream at Mos­man Bay in 2012.

“Th­ese are just the odd in­di­vid­u­als who have tried to colonise an area, and the fact that the depart­ment has de­vel­oped a good in­for­ma­tion net­work, re­ceives fish­ers’ in­tel­li­gence, means it can re­spond to a catch and get the an­i­mal iden­ti­fied straight away, and mount a re­sponse,” Ms Mas­sam said.

Aus­tralia has no Asian pad­dle crab breed­ing pop­u­la­tions but num­bers in Auck­land Har­bour are enough for the species to be re­ported in com­mer­cial catches, after an ini­tial dis­cov­ery in the late 1990s.

The Mos­man Park catches prompted Fish­eries’ net­ting and pub­lic ed­u­ca­tion, and follow-up trap­ping three, six and 12 months later, which caught no Asian pad­dle crabs, 1139 na­tive blue swim­mers, 273 four-lobed swim­mers and one ex­am­ple each of a three­spot and co­ral crab.

Ms Mas­sam said lar­vae in a ship’s bal­last, in­di­vid­ual crabs inside hulls or lar­vae drift­ing from the north on the Leeuwin Cur­rent were the most likely sources of Asian pad­dle crabs but it was almost im­pos­si­ble to iden­ti­fy­ing a cul­prit among hun­dreds of ves­sels vis­it­ing or mov­ing around WA each year.

Find­ing a fe­male would change Fish­eries’ re­sponse to the threat, which she said was presently sus­pected to be “iso­lated males drop­ping off a boat”.

Since 2013, Fish­eries has re­ceived about 400 calls from crab­bers with sus­pect crabs but many were the na­tive four-lobed swimming crab that has no spines be­tween its eyes, while the Asian pad­dle crab has sharp spines be­tween the eyes and six spines down each side

Of­fi­cer Mar­ion Mas­sam with the caught Asian pad­dle crab and (be­low, left) an Asian pad­dle crab and (right) a na­tive four­lobed swimming crab.

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