AIRF project update “Decadal re-survey of long-term lobster experimental sites to inform Centrostephanus control” (AIRF Project 2019_08)
Principal Investigator: Dr. Scott Ling, Ecology & Biodiversity, IMAS
Update 19 May 2020
This AIRF project is re-surveying baseline sites established during a previous Fisheries Research Development Corporation project (FRDC#2007/045) which investigated the effectiveness of rebuilding large lobsters to mitigate risk of urchin overgrazing. Changes observed from 2008-2014 show decline in urchin abundance inside the dedicated no-take Fisheries Research Areas of Elephant Rock Research Area (ERRA) and North Bay Research Area (NBRA) established in 2008/2009; https://dpipwe.tas.gov.au/sea-fishing-aquaculture/recreational-fishing/area-restrictions/fisheries-research-areas. By 2014 it was apparent that the rebuilding of large predatory-capable lobster stocks within intact kelp beds (but containing incipient barrens) was much more effective at reducing risk of barrens formation than was rebuilding of lobster stocks in an attempt to recover widespread barrens. Re-survey of these sites in 2019/2020 presents a critical opportunity to:
- Examine decadal trends in the ability of lobster stocks to be rebuilt on urchin barrens and within kelp beds containing incipient barrens;
- Examine the longer-term effectiveness of lobster rebuilding strategies on preventing and re-mediating unproductive Centrostephanus barren grounds.
While large lobsters can prey on urchins, preliminary results 10 years down the track again indicate that increasing rock lobster numbers alone will not result in the recovery of extensive urchin barrens as shown at the Elephant Rock Research Area; during this time lobsters have been unable to reduce urchin numbers to the point where kelp and other seaweed can re-establish. A full-blown extensive barren requires the removal of almost all the urchins from the site to be removed over an extended period to allow the algal habitat and fisheries to recover.
Large predatory lobsters in sizable numbers are however able to effectively limit urchin populations in healthy kelp beds, minimising the risk of barrens formation in the first instance. Large lobster populations can also limit urchin populations on emerging barrens, which then helps the recovery of seaweeds and minimises the risk of further expansion of barrens.
Project Scope and Deliverables
Update of what has been achieved thus far relative to AIRF funded deliverables:
Deliverable #1. Diver resurveys of size/ age and abundance of lobsters, urchins, abalone and kelp bed cover at North Bay Research Area and Elephant Rock Research Area (plus a total of 4 control sites).
Update: All diver surveys of size and abundance of lobsters, urchins, abalone and kelp bed cover have been completed for NBRA plus control sites (see attached images). Urchin, abalone and kelp cover has been surveyed for ERRA plus control sites; with surveys of urchin size yet to be completed. The remaining fieldwork is scheduled for October/November.
Scott Ling surveying kelp beds – German Soler
Scott Ling measuring Centro – M.Khodajouei
AIRF project lead Dr. Scott Ling (top) surveying urchin abundance within kelp beds; (bottom) measuring a large Centrostephanus rodgersii within the North Bay Research Area during January 2020. Photographic credit (top) German Soler; (bottom) Mohammad Khodajouei.
Deliverable #2. Lobster potting at ERRA and NBRA (plus a total of 4 control sites) to determine the capacity to rebuild lobster stocks (size and abundance of lobsters) on urchin barren grounds and within kelp beds containing incipient barrens.
Update: Lobster potting has been completed for NBRA and adjacent control sites (as of Feb 2020; see image). ERRA scheduled to be sampled in November 2020 to achieve seasonally consistency of surveys with historical baseline sampling for this location.
Dr. Scott Ling tagging a large southern rock lobster that was sampled from within the North Bay Research Area during February 2020. Photographic credit Jennie Smith.