Two small research areas that were closed to rock lobster fishing, so that researchers could investigate the Centrostephanus urchin barrens that threaten much of Tasmania's rocky reef systems, are at risk of being opened to fishing even while they remain vital to the fight against the destruction of reef habitat and important fisheries.
Centrostephanus barrens currently represent the greatest threat to Tasmanian reefs and recreational abalone and rock lobster fishing.
About six years ago, two small areas of reef were closed to rock lobster fishing and stocked with large rock lobsters. The research areas at Elephant Rock, near St Helens, and at North Bay, on the Tasman peninsula, were set up so that the relationship between large rock lobsters, Centrostephanus rodgersii sea urchins and urchin barrens could be investigated. Large rock lobster, with a carapace length of 140mm or greater, are the only significant predator on large, barren-forming Centrostephanus rodgersii sea urchins.
Centrostephanus urchin barrens form when urchin population density increases to the point where most of the marine plants that normally cover shallow rock reefs, or invertebrate animals such as sponges on deeper reefs, are grazed so intensively that they disappear. Instead of being the base for rich habitats made up of beds of kelp or sponge gardens, rocky reefs become devoid of all life but filamentous algae and remnants of plants and invertebrates that have been lucky enough to avoid being eaten. In some Tasmanian locations this has happened to more than 90% of the reef habitat.
The barrens are not only an ecological disaster but a fisheries one as well. The habitat destruction means that abalone and rock lobster become too scarce to support either commercial or recreational fishing. It is not known what effects these barrens may have on other fisheries.
Much of Tasmania’s rocky reef, particularly along the east and south-east coast, including the Tasman Peninsula and Bruny Island, appears to be at risk of turning into urchin barrens over the next 10 or 20 years, unless better management practices are adopted. Extensive barrens can form in shallow water down to at least 60m and include reefs that are especially important to recreational fishers and divers, as well as some elements of the commercial rock lobster and abalone fisheries.
Once a large Centrostephanus barren becomes established in Tasmanian waters, it is likely to remain in perpetuity, as there are no natural processes that will reverse this process.
While climate change has no doubt contributed to increasing numbers of Centrostephanus urchins and associated barrens, the main cause of this disaster is overfishing, which in many areas, has let very few rock lobster large enough to be capable of preying on the urchins. The two research areas have provided vital information on the relationship between rock lobster density and urchin barrens, which indicates that the best way to limit the expansion of barrens is likely to be to change management of the rock lobster fishery, to increase numbers of large rock lobsters.
It has taken something in the order of $3 million and years of effort to set up these research areas; if they were opened up to fishing, they would probably be impossible to replace as funding on the scale required would be unlikely under current and foreseeable economic conditions. For example, the Tasmanian Conservation Trust understands that a major source of fisheries research grant money in Australia, the Fisheries Research and Development Corporation (FRDC), has ruled out funding more Centrostephanus urchin research in Tasmania.
It would also be impossible to replicate the time-series of data that has been collected, and might be collected in the future at the current research areas; new research areas would take many years to develop to the same state. The existing sites still continue to change and provide an ongoing opportunity to investigate the development of and potential control of Centrostephanus barrens, and the effectiveness of management measures over time; this would be impossible to replicate elsewhere in a reasonable time frame.
Centrostephanus barrens threaten reefs that are vital to recreational fishers and others. A much greater area of reef has already been lost to Centrostephanus barrens than is covered by these two small research areas. Much more reef habitat will be lost forever unless more effective management measures are developed.
When the areas were first closed the government made the commitment to close them for only three years. This was extended for a further three years. Their value as research tools has justified the closure extensions. Research scientists from IMAS (Institute for Marine and Antarctic Studies) continue to support the ongoing closure of these areas. So if these research sites are so useful why is the Tasmanian Government considering opening them to fishing?
Some fishing interests would like access to the large rock lobsters in these areas, but that access is likely to be short-lived, before the rock lobster are fished out and the reefs in the research areas inevitably degenerate into just another series of urchin barrens.
The scientific reserves at Elephant Rock and North Bay should remain closed for as long as they might contribute to research, or at least until demonstrably successful measures have been identified to control the expansion of barrens. The size of the closed areas is insignificant compared to the area of reef that has already been permanently lost.These areas have taken too much time and money to set up, and continue to provide too much valuable scientific information for them to be opened up to fishing and quickly destroyed just so a small minority of fishers can catch a few rock lobsters.
The Tasmanian Conservation Trust has written to the Department of Primary Industries, Parks, Water and Environment to make the points outlined in this article, and ask that the research areas are retained. We have also been trying to secure a meeting with Primary Industries Minister Jeremy Rockliff to discuss this and other issues related to overfishing of rock lobsters and the destruction of Tasmania’s reef habitat. We are waiting on a response.
Tasmanian Conservation Trust