Drum line (shark control)

A drum line is an unmanned aquatic trap used to lure and capture large sharks using baited hooks. They are typically deployed near popular swimming beaches with the intention of reducing the number of sharks in the vicinity and therefore the probability of shark attack. Drum lines are often used in association with shark nets, used to offer further protection by enclosing designated swimming areas. The combination of drum lines and shark nets has been successful in reducing shark attacks in the areas protected by them. Since the shark nets and drum lines have been put into use (in the 1960s) there has only been one death caused by a shark attack on a protected beach.^[1][2][3] In January 2014, drum lines were introduced in Western Australia to catch potentially hazardous sharks. The topic of shark culling became a nationwide controversy and sparked public demonstrations and vocal opposition, particularly from environmentalists, animal welfare advocates and ocean activists.^[4][5][6][7]

Description

The drum line consists of a floating drum (a barrel) with two lines attached to it. One line is attached to an anchor on the sea floor, while the other features a large baited shark hook. The drum is filled with a rigid polyurethane foam, which keeps it buoyant and prevents it from being stolen for use as a storage vessel.^[8] To attract sharks, the hooks are baited with red mullet and false jacopever. Since the objective of the drum line is to prevent sharks from approaching popular beaches (and not to attract them) only about 500 grams of bait is added to each hook. Thus sharks are only attracted to the baits from the immediate vicinity.^[9]

History

Drum lines were deployed with the intent of preventing shark attacks in Queensland, Australia in 1962.^[10] They continue to be used in Queensland, and continue to kill sharks (and also kill by-catch species such as dolphins).^[11][12] They were then used by KwaZulu-Natal (South Africa) and have been killing sharks there for the past 50 years.^[13] They have been used intermittently in Western Australia in an "imminent threat" policy (having previously been used there throughout 2014);^[14][6] New South Wales and Réunion use shark nets to kill sharks.^[15][16]

Advantages

Permanent or semipermanent deployment of shark-fishing gear off high-use beaches (which includes drum lines) have been very successful in reducing the incidence of shark attack at the protected beaches.^[17] More recently, drumlines have also been used with great success in Recife, Brazil where the number of attacks has been shown to have reduced by 97% when the drumlines are deployed.^[18] While shark nets and drum lines share the same purpose, drum lines are more effective at targeting the three sharks that are considered most dangerous to swimmers: the bull shark, tiger shark and great white shark.^[19] Drum Lines physically attract sharks from within the immediate vicinity using bait^[20] while shark nets allow the sharks to swim over or around them.^[21] The bycatch, or unintended catch, of drum lines is considerably less than that of shark nets.^[22]

Disadvantages

Drum lines are also responsible for bycatch. During shark attack mitigation off Recife, Brazil over a 4 year period (October 2007 to December 2011) the total bycatch and the percentage released alive was:^[23]

• Spotted eagle ray - 4 - 100%
• Marine catfish - 244 - 75%
• Blacknose shark - 26 - 12%
• Marine turtles - 4 - 100%
• Barred grunt - 3 - 67%
• Sting rays - 14 - 93%
• Goliath grouper - 13- 100%
• Nurse shark - 130 - 99%
• Moray eels - 11 - 19%
• Snappers - 6 -67%
• Devil rays - 6 - 50%
• Brazilian sharpnose shark - 1 - 0%

During the same period 38 potentially aggressive sharks were also hooked, including tiger sharks (34) and bull sharks (4). The overall survival rate of potentially aggressive sharks was 70% (relocated and released).^[23]

The combination of drum lines and shark nets do not directly lead to extinction, but they also may not give the population room to recover from being endangered of extinction.^[24]

However, it should be noted that bycatch from drum lines is minor compared to bycatch from other human activities. For example, Australia’s commercial shark fishing industry is taking over 1200 tonne of shark out of our various fisheries each year: everything from gummy shark to mako, and very likely a few white sharks as well. The NSW prawn trawling industry alone results in 64 tonne of shark as bycatch each year. Six percent of what’s caught in the tuna longline fisheries in northern Australia is shark.^[25]

There is also evidence of dolphins stealing bait on numerous occasions, thus rendering the drum lines useless.^[2][26]

Drum lines have been cited as not being an effective strategy to keep people safe, while simultaneously killing thousands of sharks and other wildlife in the marine ecosystem — in particular, the ongoing killing of sharks in Queensland (under its "shark control" program) has been criticized.^[10] This program has been called a cull.^[4]

Smart drumlines

On Réunion regular operation of the smart drum lines began in August 2015 and they are used in conjunction with bottom long lines. A smart drum line is based on the traditional drum line design, but it includes technology that can alert rangers to the capture of marine life, who can then attend the device if sea conditions permit. in Reunion, fishermen usually attend the drum lines within 90 minutes of an alert and 90 per cent of animals caught on the hooks survive.^[27] There are now around 15 of these smart-drumlines along the coast of Réunion Island.^[28]

Controversy

Great white sharks are targeted by Western Australia's controversial shark culling policy.

Prior to 2014, drum lines were only utilised on Australia's eastern coast and in South Africa where the numbers of attacks reduced dramatically.^[2][17] In 2014, the Western Australian government reacted to the loss of seven human lives in the years 2010-2013 and installed drum lines along around 200 km^[29] of its 20,000 km long coastline^[30] (around 1%). The policy has been the subject of national and international protests, coming under fire from marine conservationists and animal welfare advocates and their supporters. The policy is commonly referred to as the Western Australian shark cull.

Drum lines have been criticized on animal rights grounds, not only for its negative effect on the environment and killing of endangered species, but also criticism of the belief that humans are more "important" than non-humans (speciesism), as well as its non-scientific approach.^[5][6][7]

A number of people opposed to the program have sabotaged various drum lines throughout Queensland to save sharks, despite the risk of being fined.^[31]

References