Report on the 'Centrostephanus Forum 2018'

Media Release

Last Friday DPIPWE held the 'Centrostephanus Forum 2018'at Blundstone Area and Jon Bryan and Peter McGlone attended for the TCT.

The forum agenda included six speakers talking about controlling urchins through commercial harvesting, culling, use of underway robots (drones) to help with culls and liming of urchins.
There was no speaker talking specifically about the importance of retaining or increasing sufficient numbers of large rock lobster, which is the urchin's only significant natural predator. It seemed to me that DPIPWE were determined to find a technological answer to the urchin problem while down playing the natural biological control that is proven to work, the lobster. This is probably because DPIPWE did not want to give much attention to the need to restrict fishing.

Critically rock lobsters have to be much larger than the legal size before they can flip a mature urchin over onto its back and attack its soft underside. Legal size (measured by carapace length) is 110 mm for males and 105 mm for females. Lobsters need to be at least 140 mm to kill a mature urchin. To enable enough lobsters to get to this size will require additional restrictions on fishing as most are caught as soon as hey get to legal size. This is why the translocation of lobsters from the west coast to the east coast is ineffective as hey just get caught before they get large enough. 

The importance of lobsters came up but the agenda was heavily focused on less effective and highly expensive human interventions while down playing what scientists have been saying is the most effective response, to let lobsters grow large enough to control the urchins. Lobsters are the best strategy to prevent areas developing into urchin barrens and once there is enough large lobsters there is no need for human intervention. The other strategies are mostly limited to responding once areas become taken over by urchins and need to be repeated.

The forum heard speakers talking about culling trials (culling is where people are paid to kill urchins) including one at Wineglass Bay which succeeded but cost $1,6 million and will eventually need to be repeated. There was a report on the success of commercial harvesting trials which is building to a scale that could be very useful but it is limited to shallow waters, is hard to target divers to areas most important to control urchins and is dependent on government subsidies.

Robots are proposed to be trialed in Tasmania in February 2019, so it is hard to comment on this, other than to note that they can obviously go into deeper water for longer that human divers. If effective they will still need very expensive human support and maintenance and each robot will cost several hundred thousand dollars.

A Norwegian scientist spoke about their trials of using lime to kill urchins by piping the lime down and using video connection to ensure urchins are entirely covered. This gets close to 100% kill rate and can address urchin barrens in deep water. The big problem raised by many people was the potential to kill many other species that we want to protect. Young abalone were considered to be at risk. So it might be best restricted to areas where there is only urchins but too risky in areas where urchins are just establishing.

Peter McGlone
Tasmanian Conservation Trust