Recent government modelling predicts that 32% of east coast rocky reefs that are vital to the recreational fishery will be lost to urchin barrens by 2021. Both abalone and rock lobster fisheries will be eliminated from these areas while the Tasmanian government fails to take any effective action.
Tasmanian east coast reefs and recreational rock lobster fishery are threatened by the expanding population of the long-spined sea urchin, Centrostephanus rodgersii, due to government mismanagement of the Tasmanian rock lobster fishery.
Urchin barrens do not support useful numbers of abalone or rock lobster and do not spontaneously recover over time. Established barrens will exist for the foreseeable future. Apart from being an ecological disaster, urchin barrens eliminate commercial and recreational fisheries for abalone and rock lobster. This is particularly significant for the recreational rock lobster fishery as 80% of recreational fishers target the east coast and the reefs initially most affected by Centrostephanus urchins are the shallow reefs down to 30 m that are most important to the recreational sector.
Decades of overfishing have resulted in the almost total removal of large rock lobster from east coast reefs. Large rock lobsters (carapace length greater than 138 mm) are the only effective natural predator of Centrostephanus urchins in Tasmanian waters. This is much larger than the current recreational size limits, which are 110 mm for males and 105 mm for females. Without rock lobster predation controlling their numbers, Centrostephanus urchins graze rocky reefs so intensively that kelp and other marine plants are removed. Normal reef habitat is replaced by urchin barrens where few species survive other than small filamentous algae and sea urchins.
In 2017 it was revealed that modelling by the Tasmanian government's scientific advisors from the University of Tasmania's Institute of Marine and Antarctic Studies (IMAS) predicts 32% east coast reefs will be covered by Centrostephanus urchin barrens by 2021. That disturbing prediction is actually very optimistic, as important factors that will make the situation even worse are not taken into account. The modelling does not take into account the permanent loss of productivity due to expanding urchin barrens or the effects of climate change on rock lobster reproduction and recruitment patterns, which are likely to be negative. Fleet dynamics, is also ignored. This means that fishing activity, which can be expected to preferentially target more accessible reefs or more productive reefs, is not modelled. The actual loss of reef is likely to be much greater than the model's prediction of 32% by 2021.
Understanding fleet behaviour is critical to assessing the government's claims that it is rebuilding stocks and that there is nothing to worry about. If stocks rebuild on a particular reef, for example, fishers will naturally target that reef as it provides the best fishing. Unfortunately that means that as a result, there is almost no chance of rock lobster surviving to grow large enough to become successful urchin predators.
Claims are regularly made that the east coast rock lobster stock is rebuilding due to recent management changes such as the east coast cap (the catch limit on the catch of rock lobster on the east coast) and the cut in the commercial state-wide total allowable catch (TACC). Unfortunately, the failure to deal with fleet dynamics means that this strategy will not protect reefs from Centrostephanus urchin barrens. Even if stocks rebuild in the short term, the ongoing loss of reefs to barrens will affect the fishery. As fishers preferentially target more productive reefs, rock lobster will be unlikely to survive the gauntlet of fishing to become large enough to control Centrostephanus urchins and prevent the spread of barrens.
Rock lobster stock biomass in two of the east coast commercial management areas has fallen to critical levels. Area 3 (see Figure 1) rock lobster stocks are currently at 10% of virgin biomass, that is the biomass (i.e. the mass of the area's rock lobster population) is just one tenth of the level before European fishing began. Area 2 biomass is at 9%.
For non-fishery scientists the biomass levels need to be put into context. Fishery managers in most fisheries would be very concerned if stocks of species they were managing fell to 40%. A decline to 10% would normally be considered to be disastrous, to the point where major fisheries closures and management restructuring would be considered. A fishery operating at just 10% of virgin biomass is not normally considered to be a healthy or productive fishery. There is less of a buffer during bad years when natural weather events, for example, may reduce numbers, and it takes longer to catch fish, or take your quota if you are in a quota-managed fishery.
Anyone who fished for rock lobster (well we used to call them crayfish or crays) in the 1970's or 1980's, as I did, knows how much harder it is now to catch your bag limit. For the commercial fishery, this low stock level imposes extra costs, makes the fishery less efficient and makes it harder for commercial fishers to make a profit.
The government's solution is to manage stocks so that they reach a target of 20% of virgin biomass, which is still too low. I have not been able to find any scientific journal articles on comparable fisheries where even 20% would be considered to be acceptable. Even as a member of the government's own Fishery Advisory Committees (FACs), Crustacean FAC and Recreational FAC, I have never seen a reasonable explanation why Tasmania should set the bar so low for this important fishery.
And remember, it is not just the rock lobsters at stake. Because large southern rock lobster are the only local predator of Centrostephanus urchins, they are critical to the ecologically and preservation of Tasmanian east coast reef habitats. The current management system means that there is little chance of rock lobster surviving to become large enough to prey on Centrostephanus urchins and control their numbers. The absence of large rock lobster will lead to ongoing loss of productive reef habitat to urchin barrens even if rock lobster biomass recovers substantially. And the continuing loss of habitat spells disaster for the rock lobster fishery over the next decade or so.
Some commentators claim that this problem is due to climate change. Climate change is no doubt making things worse, by creating better conditions for Centrostephanus urchins while making things worse for rock lobster. However, it is important to remember that this disaster is directly related to overfishing that has almost completely removed large rock lobster that are able to control urchin numbers. This has directly resulted in the expansion of urchin barrens, as has been clearly demonstrated in experimental work done by scientists from the University of Tasmania. Large rock lobsters can and do protect reefs from Centrostephanus urchin barrens.
I first warned the government about the threat to Tasmania's reefs and fisheries from Centrostephanus urchin barrens in the 1990's, both in written submissions and at FAC meetings. I have personally briefed fisheries ministers on this issue, including David Llewellyn, Brian Green and Jeremy Rockliff.
A fairly obvious first step in dealing with this problem would be to bring stakeholder representatives together to develop some effective strategies that would minimise impacts on fisheries. This is something that I have been suggesting to Tasmanian fisheries ministers for years.
To his credit, Brian Green actually organized this type of meeting, but failed to progress beyond a successful first workshop. More recently, at the end of 2017 I tried to arrange a stakeholder meeting. Scientists, recreational fishers, conservationists, commercial fishers and others agreed to attend. I also wanted to involve the Minister and his department. Unfortunately, despite initial enthusiasm, the commercial fishers pulled out and Minister Rockliff appeared to be unable to convince them to participate and would not involve his department without the support of the commercial sector.
Fisheries ministers since the 1990's have been aware of this ongoing failure in fisheries management. They have allowed the stocks of rock lobster to decline to unacceptably low levels and have not done anything useful to stop the expansion of urchin barrens. Despite the Tasmanian government being aware of the Centrostephanus urchin threat for years, we are now looking at losing 32% of Tasmania's east coast reef by 2021. And that is an optimistic prediction.
The situation is not hopeless. There are things that can be done. But there has been a lack of political will over the last two decades to provide leadership and incentives to deal with this problem. The impending loss of 32% of east coast reefs by 2021 should be enough to motivate action by the new fisheries minister, Sarah Courtney. If the government wants to destroy the iconic east coast recreational rock lobster fishery then it just has to maintain its current rock lobster management.
About the Author: Jon Bryan began fishing in the 1960's and started spearfishing on Tasmania's east coast in 1973 as a kid. He learned to scuba dive in 1978 and has logged over 4000 dives. He has dived in many places around the world, and on every continent except Africa. Spearfishing and collecting abalone and rock lobster eventually gave way to underwater photography. He studied marine biology and ecology as part of his science degree. As well as normal diving, Jon does deep technical diving using closed circuit rebreathers and mixed gas, and has done dives to 70 m in Tasmanian waters. Concerned about the decline in fish in places where he was an active fisher, he started doing part time work for the Tasmanian Conservation Trust on marine issues such as wild fisheries management and aquaculture in the 1990's. Jon was deeply involved with the campaign to stop the super trawler and continues to work part time for the Tasmanian Conservation Trust and is currently a member of all Tasmanian Government's Fishery Advisory Committees (FACs), including Recreational FAC and Crustacean FAC. He is also a committee member for the recreational fishing organisation TARFish.
Management Responses to Urchin Barrens and Overfishing
A number of options are available to deal with the urchin barren problem. Some of the more obvious are outlined below. I believe that the government and current Tasmanian fisheries minister should convene a stakeholders meeting to develop strategies to deal with urchin barrens and the threat to the recreational rock lobster fishery.
Increase Density of Large Rock Lobster
Managing the rock lobster fishery to build density of large rock lobster (carapace length greater than 138 mm) to 1/1000 m2. Research indicates that this density of rock lobster appears to provide protection to reefs from expansion of urchin barrens. According to one government report (Report to the Minister on the draft management plan for the Tasmanian Rock Lobster fishery Wild Fisheries Management Branch, Department of Primary Industries, Parks, Water and Environment, 2011) a closure of the east coast commercial fishery would achieve this in between 5 and 10 years.
Introduce Maximum Size Limits
Maximum size limits will protect the important large rock lobsters that are able to control urchin numbers and make all other management options more effective. Unfortunately, current fishing levels mean that it is unlikely for any significant numbers of rock lobster to survive to be big enough to be effective urchin predators, so by itself an maximum size limit would be ineffective.
At first glance, commercial harvesting Centrostephanus urchins for their roe seems like a win-win solution and is sometimes presented as the perfect answer to Tasmania's urchin problem. While harvesting urchins for food may reduce urchin numbers in some limited areas, it will not have a significant effect on the overall problem. The demand for Centrostephanus urchins is currently low. Harvesting also does not normally target urchins on fully developed barrens as they are starving and their roe (the bit that is edible) is of very quality and of no commercial value. Starving urchins on urchin barrens unfortunately survive indefinitely and maintain the barren. There is some potential for collecting starving urchins then feeding them in aquaculture facilities, for example, until they are marketable but the costs involved are a real problem in a competitive marketplace. In any case, the logistics of diving and OH&S considerations limit collection by divers to relatively shallow depths (perhaps 15 m) and commercial divers will never be able to work economically on much of the reef being damaged by urchins.
Culling by divers is effective but very expensive. Logistical and OH&S considerations again prevent divers from operating economically except in relatively shallow depths. A number of trials have been carried out to assess the effectiveness of diver culling. The most relevant was carried out in a section of Wineglass Bay. Urchins were effectively removed after divers went over the same area of reef three times. It cost over 1.5 million dollars to clear a relatively small area, deeper reef below 15 m were not be cleared due to OH&S considerations, and of course the urchins will just return unless the culling continues or major changes are made to the management of the rock lobster fishery.
Autonomous Underwater Vehicles or Robots
There is potential to use autonomous or remote controlled underwater vehicles to cull urchins. Trials have begun on using this type of technology on crown of thorns starfish on the Great Barrie Reef. This technology is in the early stages of development and needs much more time and money before it is effective. Even if they are developed, ongoing costs are likely to be high. Tasmania's reefs need a solution quickly.
Areas closures could be used to allow rock lobster populations to recover and the density of large rock lobster to increase to a level where they protect against the expansion of urchin barrens. The likely strategy would be to close areas until the density of rock lobster increases to effective levels, then have a maximums size limit to protect large rock lobster when fishing resumed.
As described above, a closure of the east coast commercial fishery would likely result in an increase in the density of large rock lobster in between 5 and 10 years. According to the government, there are 12 to 14 commercial fishers who claim they can only fish on the east coast due to the size of their boats. They can still lease out or sell their entitlements, or some sort of compensation could be arranged. Removing commercial fishing pressure would reduce the east coast catch by 75 % overall, and probably around 50 % in inshore waters. This would greatly reduce fishing pressure and make managing the fishery and the urchin barren problem much easier.
Managing Fleet Behaviour
Fishers preferentially target more accessible and/or more productive reefs. This is common sense and backed up by research. The problem is that this means that stock rebuilding and efforts to manage urchin barrens can be undermined by fleet behaviour. Mechanisms such as tagging need to be developed to ensure stocks recover and reefs are protected from expanding urchin barrens.
The Tasmanian commercial rock lobster fishery sector has taken around 1 billion dollars worth of fish out of this fishery over the last decade. It has also taken most of the rock lobster out of the east coast and must therefore be seen as primarily responsible for the current situation. A small percentage levy would provide useful funding to support management options or buy outs of entitlements.
An alternative option is to simply do nothing. Prior to the state election this seemed to be the current position of the government. Recent changes to bag limits, seasons and even the introduction of the east coast cap area (which limits catch in the most critical parts of the east coast) will not stop the ongoing destruction of reef and conversion of productive habitat to Centrostephanus urchin barrens. Very optimistic modelling by government scientists predicts 32% of east coast reefs will be covered by urchin barrens by 2021. Urchin barren can be expected to expand across much of the east coast reefs. The do nothing strategy will result in the destruction of the iconic recreational rock lobster fishery on Tasmania's east coast.
The Author: Jon Bryan began fishing in the 1960's and started spearfishing on Tasmania's east coast in 1973 as a kid. He learned to scuba dive in 1978 and has logged over 4000 dives. He has dived in many places around the world, and on every continent except Africa. Spearfishing and collecting abalone and rock lobster eventually gave way to underwater photography. He studied marine biology and ecology as part of his science degree. As well as normal diving, Jon does deep technical diving using closed circuit rebreathers and mixed gas, and has done dives to 70 m in Tasmanian waters. Concerned about the decline in fish in places where he was an active fisher, he started doing part time work for the Tasmanian Conservation Trust on marine issues such as wild fisheries management and aquaculture in the 1990's. Jon was deeply involved with the campaign to stop the super trawler and continues to work part time for the Tasmanian Conservation Trust and is currently a member of all Tasmanian Government's Fishery Advisory Committees (FACs), including Recreational FAC and Crustacean FAC. He is also a committee member for the recreational fishing organisation TARFish.