Culling or mitigating the great whites?
The recent fatal shark accident in SW Australia where 17 year old surfer Laetitia Brouwer died after a bite in the leg by a Great White Shark has ignited the culling debate in Australia. Hard liners in the debate have blamed the government to listen to much to the ‘insane shark conservation policies that have cost another life', and insist on measures to bring down the number of great whites sharks at the beaches.
Left: A sonar buoy emitting signals in a shark protected environment*
But what measures should be taken by the government to effectively protect swimmers and surfers along such an extended coastline comprising south west, south as well as south east Australia? The primary cause of the increased fatalities of the last decade seems to be the increasing numbers of beach visitors, not of the great white sharks. The favorite beaches of surfers and swimmers are spread over a large stretch of coastline in Australia, many of which are unsupervised. Unfortunately, there still is no effective warning system signaling the areas where a visit of great whites could be a potential hazard in the holidays season or -even better- on a certain day or week-end.
A direct invasive intervention measure that has proven sofar to be relatively effective is shark culling via shark nets and drumlines with baited hooks that are anchored to the sea floor. Larger sharks that are caught are killed, smaller ones released. In both Queensland and New South Wales culling is permitted in cases where sharks are deemed to present a serious threat to public safety. Opponents however have expressed concerns about the impact of culling on on both targeted and non-targeted threatened sharks species, and as ‘bycatch’ of species like dugongs, dolphins, turtles and other fish. Many sharks caught since 2001 were not great whites, or were caught in areas where no fatalities have ever occurred. In addition, culling may only be effective for more territorial shark species. But great whites are not territorial, except in areas that lie in the vicinity of their favorite hunting grounds such as islands harbouring colonies of seals or sea lions. Although they show some fidelity to sites meant for pupping and mating, much of their time seems to be spent with following long migratory routes in the open seas. Human surfers and swimmers on a beach may occasionally attract their attention when they are patrolling the coastline, but are not on their menu.
Only a minority of the population in Australia including New South Wales seems to support culling of sharks, and among Australians there is a rising trend toward greater balance between wildlife, marine life and national values. It still remains a curious fact that a fatal accident caused by a wild animal elicits much more emotion and publicity than a fatal traffic accident. Apparently the hazards of our modern industrial society are accepted more easily by mankind than an occasional attack of a great white mistaking a human for a prey entering its territory.
Alternative non invasive measures labelled as Shark Mitigation that are now in development include technologies such as sattelite and acoustic signaling of the presence of sharks in certain risk areas. For online measures of shark movements battery operated SPOT (Smart Position and Temperature Transmitting) tags are attached to the sharks dorsal fin. These tags transmit a signal or ‘ping’’ to a satellite array whenever the dorsal fin breaks the surface of the water. The New South Wales Government has even developed software like the Shark Smart app to provide beachgoers with real-time data of sharks' movements. Shark tagging and related shark tracking devices have proven to be higly useful tools to study migratory patterns of individual sharks. Some amazing results have recently been obtained by researchers working with great whites at Isla Gualape in Mexico (See: http://www.marinecsi.org/). But to make it work as a accident prevention tool will require tagging of numerous great whites, which may not be feasible considering the enormous size of their habitat.
Online shark tracking could work however as a supplementary tool to use in combination with other techniques. An interesting and perhaps more feasible option are strings of sonar buoys that are stationed in potential danger areas like beaches often visited by swimmers or surfers. These solar-powered surface buoys provide power as well as communication functionalities. A buoy or chain of buoys will constantly emit sonar signals. When the sonar detects a large fish entering the guarded area, it will tranmit the signal to a satellite receiver which in turn relays it to a beach station (see insert).
On the longer term shark mitigating technology aims to develop a shark monitoring network that relies on several parallel sources of information, including not only data derived from tagged shark detection but also from local sonar buoys, air patrols and sight detection by beach guards. This information would finally become assembled and digitally mapped on a shark activity map. Visitors could inspect the map with their Sharksmart app to check any recent activity before using the beach or going out to surf.