Owing to the fact that shark nets are a non-discriminatory fishing process, it is not only sharks which are caught up; the nets trap many other species which swim too close and become entangled - this is known as bycatch. Dolphins, dugongs, turtles and whales are some of the species known to be caught up in shark nets (1, 2).
There is a great deal of controversy of whether or not netting a beach has any effect on reducing shark attack numbers. The construction of the nets does allow animals to swim below and around and some shark net programs have found a large degree of the entangled sharks to actually be on the beach side of the net! (3)
In Australia, shark nets have been in place along the Queensland coast as part of the Government's Shark Control Program (SCP) since 1962. In the last 10 years 6,252 sharks have been caught as a part of this program, over a third of which were tiger sharks (Galeocerdo cuvier) (4). The remaining numbers are made up of another 36 species of shark, 22 of which are grey nurse sharks (Carcharias taurus). Also known as the ragged tooth shark, C. taurus is a common aquarium shark and a popular shark to dive with owing to its placid nature.
Of more concern are the number of endangered species which are killed by shark nets - the SCP reported catching many species listed as Vulnerable in the IUCN Red List such as the grey nurse shark, the shortfin mako (Isurus oxyrinchus) and the whale shark (Rhincodon typus) (5). Most shark species exhibit slow growth rates and tend to take a long time to reach maturity, which means that once their numbers are depleted it is difficult for them to rebuild the population.
The New South Wales (NSW) Shark Meshing Program (SMP) reported "72 interactions" with non-target species, vs. only "32 interactions" with target species. The non-target species included entanglement by Port Jackson Sharks (Heterodontus portusjacksoni), Southern Eagle Rays (Myliobatis australis) and 2 species of turtle (6). Two humpback whales were also entanglesd and whilst they swam away, they remained entangled as they swam and thus their survival is by no means assured.
Like all shark net projects, the NSW SMP is under scrutiny to perform in an ecological manner and to reduce bycatch numbers, and they do implement certain methods to attempt to reduce interactions with non-target species - for example the shark nets are removed for the whale migratory seasons from May to August. However, the fact remains that shark net programs are responsible for the death of a great many species of sharks, marine mammals and reptiles and are acting in response to a threat which is more perceived than real. In 2013, 10 people died globally from shark attacks (7) vs. an estimated 388,000 deaths from drowning worldwide annually and - the biggie - approximately 1.24 million annual deaths from road traffic accidents (8). It just seems as though the money and time of any government could be better invested in tackling the real dangers which exist in society, instead of using methods which are incredibly destructive to the marine environment in order to simply make people feel better about going in the water.
1. Qld's Fisheries Department defends shark nets amid trapped whale worries
2. Dolphin deaths a tragic find for local kayakers
3. Fisheries Scientific Committee
4. Department of Agriculture, Fisheries & Forestry - Shark Catch Numbers
5. IUCN Red List
6. Shark Meshing (Bather Protection) Program 2012-13 Annual Performance Report
7. International Shark Attack File (ISAF)
8. World Health Organisation - Factsheet - Drowning
