Wednesday, February 1, 2023

Rock lobster whites run starts in the Two Rocks to Cervantes region

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The whites run when juvenile western rock lobsters undergo a synchronised moult in late spring actually starts in the Two Rocks to Cervantes region before getting underway later in northern areas such as Kalbarri.

During the whites run recreational fishers, who need a licence, flock to the Two Rocks marina and other areas so they can head out to check their pots.

Commercial boats also operate in the area and a charter boat offers western rock lobster tours as part of a trial introduced by the McGowan Government in 2019 to boost rock lobster fishing tourism and make more local lobsters available.

Department of Department of Primary Industries and Regional Development (DPIRD) offshore crustaceans principal research scientist Simon de Lestang said why the whites run started between Two Rocks and Cervantes was unknown, but the variation between years correlated very well with water temperatures.

The Two Rocks area has been closely associated with the western rock lobster (or crayfish as it used to be known) industry for more than 100 years and it is likely the date and reasons around when the whites run will start have long been debated.

Some rock lobster fishers think the full moon influences the start of the whites run.

But Dr de Lestang disagrees.

“The link with the moon phase has been studied and found not to exist,’’ he said.

He said the main factor driving the annual whites run was water temperature in August-September.

“The warmer it is, the earlier they moult and migrate.

“Swell also affects their behaviour, a big swell can make them move early and fast.’’

Some of the veteran fishers are said to recall a season about 40 years ago where there was a late start to the whites run but then the season ran longer.

Dr de Lestang said generally a later start to the annual whites run meant the run continued longer into the new year.

“However, some years we seem to get a very fast movement, if a big storm/swell comes in.

“In these years, the run can be over very fast.’’

A year-round monitoring program estimating the number of post-larval stage lobsters (puerulus) settling on inshore reefs along the Western Australian coast helps inform predicted catches up to four years in advance and also provides estimates of the breeding stock levels.

The monitoring program started in 1968 north of Dongara and since then other puerulus collector sites have been added with eight locations between Kalbarri and Cape Mentelle now sampled every month including sites at Alkimos, Lancelin and Jurien.

Dr de Lestang said the sites were sampled every full moon and the site data presented on an interactive weblink

According to a Fisheries fact sheet during the puerulus stage western rock lobster settle onto seaweed floating around nearshore reefs on their way to settling into crevices and holes within the reef systems and once there within days they develop the red colour associated with western rock lobsters.

Through a series of moults they grow to become juvenile rock lobsters feeding and growing on the shallow onshore reefs for the next three or four years.

At this point, they undergo a synchronised moult in late spring, when they change their normal red shell colour to a creamy-white/pale pink and are called ‘whites’, until they return to their normal red colour at the next moult a few months later.

The whites phase of the western rock lobster’s life cycle is a migratory phase.

“Once their new lighter-coloured shell has hardened, they set out on a two-pronged migration,’’ says the fact sheet.

“The vast majority head west and undergo a mass migration into deeper water, where they resettle on deeper reefs.

“A small percentage makes a longer migration to the north, usually following the continental shelf.

“In large groups, the lobsters set out on their march, trekking at night, until they reach the spawning grounds, occasionally 100km or more away from where they started and in water up to 100m deep.

“Above them, the western rock lobster fishing season has started.’’

This article appeared on Yanchep News Online on 27 November 2022.

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