Dr Susan Lawler
First published on The Conversation on 29 April 2013.
Last week, Victorian Fisheries announced changes to the fishing regulations for Murray Spiny Freshwater Crayfish to bring them in line with recent changes in New South Wales.
This is a quick turnaround, but will not be considered quick enough by fishers who have already made plans for the 1 May season opening. It was necessary because NSW fishers, whose season has been moved from 1 May to 1 June, were quite likely to shift their fishing trip to Victorian waters, thereby putting extra pressure on crayfish in some populations.
I have already written about how I felt about the new rules in NSW, which will go a long way toward addressing some of my concerns about the viability of this fishery. What I haven’t said before is how remarkable it is that these animals are part of a fishery at all.
In Victoria, the Murray Spiny Crayfish are on the threatened list of the Flora and Fauna Guarantee Act.
This means that when I want to collect this species, in addition to the usual research permits from Victorian Fisheries and my University’s ethics department, I need to get permission from the Department of Sustainability and Environment to handle this threatened species. That it is harvested and eaten by people for three months of the year on a humble fishing license is a highly unusual situation.
Obviously, many fishers believe this should continue and see their yearly crayfish trips as a right, rather than a privilege. In some cases, they are fishing in areas where the decline in numbers is not apparent, so they may wonder why these changes in regulations are necessary.
One of the new regulations is the introduction of a maximum size, which will mean that really big animals cannot be removed from the river. The reason this is necessary is that fishing pressure tends to remove all large males, which reduced the productivity of large females.
Basically, a large Murray cray female will not produce as many eggs when she mates with a smaller male. This can have a big impact on a population because the largest females are the most prolific breeders, producing up to a thousand young in a season under the right conditions. When they are forced to mate with a small male, their egg set will be much smaller, and the next generation is less secure.
Under the new regulations, it is hoped that some males are lucky enough to escape the pot until they exceed the maximum size limit, at which point they can live the rest of their long lives servicing those large females and keeping the population strong.
So even though, according to NSW Fisheries, recreational fishing does not appear to be the main cause of the decline of Murray crays, managing fishing pressure is the best way to ensure the species recovers from its current decline. Protecting habitat is another important component, but given that this would mean, in some cases, preventing drought, it may be beyond our ability to manage.
Just to be clear, the Victorian rules for Murray crayfish season now reflect those of NSW: a minimum size of 10 cm OCL (occipital carapace length: from the eye to the base of the tail), a maximum size of 12 cm OCL, reduced bag limits (to 2 ), reduced possession limits (to 4) and a delayed season opening to 1 June.
In my own discussions with fishers, many are motivated (as are my students) by the joy of meeting these remarkable creatures, and eating their catch is not as important as being able to introduce these animals to their children. A catch and release fishery would meet their needs, but ensuring compliance would be a significant challenge.
Our research at present is focussed on a river that is not part of a commercial fishery. We are examining the impact of various land uses (cropping, pine plantations, cattle) on the distribution of crays. We are also interested in the temnocephalan worms that use the crays as a substrate: these unique flatworms are not parasites, but rather partners in crime; the crayfish are their godfathers. By assessing the distribution of temnocephalans along a gradient, we hope to learn more about their ecology, which is linked to but not completely driven by crayfish abundance.
My two new Honours students have just begun their fieldwork and it has been a joy to watch them fall in love with these spiny, gorgeous, often grumpy creatures. I can therefore understand the pain that fishers feel when their fishing activities are curtailed. Just remember that the future of this species may depend on us leaving them alone in some areas.