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Tagging West Coast rock lobster in Elandsbaai

By Donia Wozniak, DST/NRF Intern, SAEON Egagasini Node mail.jpg facebook.jpg

West Coast rock lobster, Jasus lalandii (locally known as 'kreef'), is not nearly as abundant as it once was.

Overfishing, poaching, environmental factors as well as slower growth rates have contributed towards their decline, with population estimates currently at approximately 2% of pre-exploitation levels.

In 2016, the South African Sustainable Seafood Initiative (SASSI) included the heavily depleted West Coast rock lobster on their “Red List”, strongly discouraging consumers from buying it (http://wwfsassi.co.za/west-coast-rock-lobster-is-now-red-listed/). Nevertheless, more than 4 000 people in coastal communities rely on this commercially valuable species for their livelihoods (DAFF, 2016).

It is vital for research efforts to continue monitoring West Coast rock lobster populations, to better inform sustainable management of the rock lobster stock in the future.

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A lobster trap is hauled onboard (left) and lobsters are sorted (right). Females and undersized males are released overboard, with legally sized males kept aside for tagging.                          

A bucket full of lobsters awaiting to be measured and tagged before being released back into the ocean.

Research surveys

The Department of Agriculture, Forestry and Fisheries (DAFF) conduct annual research surveys during the closed fishing season (July-November). Researchers tag male West Coast rock lobsters to monitor their somatic growth rates. Growth rate data are used as one of the inputs into the Operational Management Procedure (OMP) assessment model, which provides future biomass projections of rock lobster populations, helping to inform fisheries management decisions (DAFF, 2016).

As an intern at SAEON’s Egagasini Node, I was recently given the opportunity to participate in one such survey as a scientific team member. Our destination was the Elandsbaai/Lamberts Bay area.

We set sail onboard the Research Vessel Ellen Khuzwayo for a 10-day cruise (3–13 September). Our aim was to tag 3 000 legally sized (75 mm carapace length) male, pre-moult lobsters for the purpose of collecting growth rate data.

Only males are tagged during these surveys as they grow faster than females, with females expending more energy on reproduction. Data for length frequency analysis were also collected, with information about sex, reproductive state and carapace length of a random sample of lobsters being recorded. These data are used as additional inputs into the size-structured assessment model, which is moreover used to scientifically inform management decisions of this resource (DAFF, 2016).

We got off to an early start each day, with breakfast at 06:30 and the first traps being hauled onto the deck from 07:00. Baited with hake heads, the lobster trap nets were set each day at depths around 20-40 m. There were seven lines of traps in total, with each line consisting of 10 traps.

Lobsters were sorted by size each time a trap was hauled in and at the end of each line, the lobsters were measured and tagged with a uniquely coded tag. My duties mostly included recording the data. If any of the tagged lobsters are recaptured by the commercial fishers once the fishing season begins, they are to report the size and tag number of the lobster to authorities, making it possible to calculate the rate of growth over the release-recapture time period.

Activities on deck usually wrapped up around lunchtime, with the afternoon spent catching up on sleep, reading or relaxing in the messroom.

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Calm seas and good weather persisted throughout the cruise.

Participation in this cruise was highly informative and an eye-opening experience. To top it all off, good weather throughout the trip with frequent visits from whales and dolphins made it not just enjoyable, but memorable as well.

The collection of this kind of data is invaluable for monitoring the species and contributing towards informing management of the status of the resource, hopefully enabling a sustainable future for the West Coast rock lobster fishery.

Further reading

Department of Agriculture, Forestry and Fisheries (2016). Status of the South African Marine Fishery Resources 2016.

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