Sharks, especially great whites, have been in the news a lot recently after the tragic death of a surfer off Dee Why beach and an abundance of tagged sharks being detected off Stanwell Park. Much of the media response so far has followed a fairly predictable pattern and there will be much discussion in months ahead.

The protection of beach users is an emotional topic. Considerable amounts of money are spent each year on a growing number of techniques aimed at minimising the risk of shark attacks (or bites). Trying to work out which ones are effective is complicated by the vanishingly small incidence of human/shark interactions. There are millions of individual bathing events (including surfing, diving and other seaborne activities) each year and trying to determine patterns of risk is very difficult.

It's worth reflecting on what measures are taken in the Illawarra and ask some questions about what may or may not be effective and the tradeoffs involved. At the moment, the Department of Primary Industries has several measures being used, namely:

• Beach meshing – large mesh gillnets have been used for several decades at 51 NSW beaches from 1 September to 30 April each year. These nets are not designed to create a barrier for sharks but to reduce the population of target sharks (whites, bulls and tigers) down to some unstated level where they are deemed to not pose a major risk. We know from a long history of monitoring that catches of some species have declined precipitously and beach meshing was listed as a Key Threatening Process when the great white shark was listed as threatened. The nets also take a variety of non-target species, such as eagle rays, various shark species, turtles and dolphins.
• Drumlines – the so-called ‘Smart’ drumlines are baited hooks set under orange floats. These are maintained by contractors and, if something gets caught, they have to go to sea and release the animal and, if it is a target shark, place an acoustic tag in the fish so it can be picked up by listening stations.
• Listening stations – 37 buoys anchored along the coast that pick up a ‘ping’ from a tagged shark. The detection range is about 400-500m. The pings are then sent to users of the Shark Smart App so the recipient can be advised a shark is present.
• Drones – Surf Lifesaving NSW has been supplied with drones that they can use to either patrol for sharks or conduct investigations of shark-related activities.

The full cost of all this is unknown. Some aspects of the performance of the various approaches are reported publicly and some not. Catches in the mesh nets are required to be reported as a condition of approval for the program to interact with threatened species. The drumline catches are also reported, as are the detections (pings) and the number of shark sightings per hours of drone use. Comparing effectiveness is difficult due to different reporting units, plus the low level of shark attacks.

For the Illawarra region

The Illawarra’s shark nets and drumlines catch very few sharks but the listening station (noting I don’t collect pings from the Wollongong one) shows that sharks are more common than the nets/lines would imply. Clearly, the sharks caught by a drumline do not head out to sea and stay away.

The number of drones sighted by drones is very, very small. As I know from my own drone flights, sharks are difficult to find. However, once found they can generate some compelling imagery.

About the writer

Duncan Leadbitter is a director of fisheries and natural resource consulting company, Fish Matter, which advises industry, government and NGOs on the sustainable use of fish. Most of Duncan’s work is based in Asia, where he is involved in fisheries projects in Indonesia, Vietnam, Thailand, Philippines and India. He is a Visiting Fellow at the Australian Centre for Ocean Resources and Security at the University of Wollongong. A keen scuba diver, snorkeller, spearfisherman and photographer, Duncan has lived in Stanwell Park for 20 years.