Sharks are back in the headlines this week following the attack of 17-year-old Cooper Allen off the coast of New South Wales.
In response there have been renewed calls for culling and even the establishment of a commercial shark fishery. Queensland premier Annastacia Palaszczuk offered to extend her state’s shark control program to include northern New South Wales beaches.
Any unprovoked shark bite is devastating for individuals and communities. Accepting Queensland’s offer of increased culling in New South Wales waters, however, will not automatically reduce the chance of these bites occurring.
So how does Queensland’s program stack up and should it be extended?
How does Queensland’s program work?
The program uses hundreds of hooked drumlines and tens of shark nets at popular beaches from Cairns to the Gold Coast. Equipment is checked every couple of days by government contractors, and target sharks that have been caught are killed with a firearm. The idea is to prevent sharks reaching the beaches and interacting with people.
The Queensland program has been running since 1962 as a public safety measure to reduce the risk of shark bites and attacks.
New South Wales already uses a similar program, which deploys nets set below the surface roughly 500m from the shoreline on 51 beaches from Wollongong to Newcastle between September and April each year.
The equipment is designed to target sharks of 2m or larger, but in reality indiscriminately kills animals of all sizes and species beyond the targets of white sharks, tiger sharks and bull sharks.
Do shark programs stop shark attacks?
A recent study has shown that unprovoked shark bites appear to have increased in recent years in eastern and southern Australia, but it is difficult to tease apart what environmental conditions are causing the increase, and even more difficult to predict when and where these conditions will next occur.
Important environmental conditions include sea surface temperature, freshwater runoff, turbidity (the cloudiness of water), currents and circulation patterns. While there are correlations between these factors and shark bites, that is all we know so far. Correlation does not mean causation.
The big problem is that there is currently no scientific evidence to link shark nets or drumlines to ocean safety.
It is not a matter of putting humans at the “top of the food chain” as Nationals president Larry Anthony (who represents the north coast in parliament) stated earlier this week.
It is a matter of whether (1) the strategies directly reduce the number of shark-related deaths, and (2) any reductions outweigh the ecological costs of these mitigation strategies.
Interestingly, shark-related fatalities have declined in Queensland since the state’s shark program began, but fatalities have declined in areas with and without shark mitigation equipment. The greatest decline actually occurred before deployment of nets and drumlines began.
And what about the sharks?
The dangers posed by Queensland’s shark program to shark populations are substantial. The vast majority of sharks that are caught by the program are threatened according to the International Union for Conservation of Nature. This includes target species such as white sharks and tiger sharks, and non-target species such as grey nurse sharks.
Some of these species are already listed by the New South Wales Fisheries Scientific Committee. The same committee has listed the state’s current program as a threatening process for marine wildlife. These species are in need of increased conservation and management rather than increased slaughter. Removing even a few of these larger predators can have unpredictable and cascading negative impacts on whole ecosystems.
Any removal of sharks are exacerbated by the slow growth and relatively low reproduction rate of these animals, which make them particularly vulnerable.
What Annastacia Palaszczuk is really offering New South Wales is to indiscriminately kill a large portion of species that should be protected by our state legislation.
What we should be doing is tagging and following the movements of these highly migratory species to understand where they go, and why.
Shark experts associated with the New South Wales government are trialling various forms of shark deterrent technology, some of which look are looking promising. Priority has been given to development of personal shark deterrents, such as electrical and magnetic devices, and protective wetsuits.
While things are progressing since the Shark Summit hosted by premier Mike Baird in September 2015, any solution is going to take time.
Authors: Jane Williamson, Associate Professor in Marine Ecology, Macquarie University