15. May, 2017

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.