Lauren Peel, a UWA Zoology graduate and shark enthusiast, presented an interesting talk on sharks at the meeting held on 9th August.
Her talk introduced us to some aspects of sharks and their behaviour gained from her experiences participating in white shark research work based in Mossel Bay, South Africa. These fuelled her enthusiasm to learn more about white sharks and work to understand the best ways to manage interaction between their natural and predictable behaviour as wild animals and the maritime recreational activities of people. To this end Lauren is returning to South Africa in a voluntary role to continue her studies.
Sharks have an evolutionary lineage of about 420 my; shark’s teeth are found as fossils in certain sedimentary rocks. Sharks are elasmobranchs, having cartilaginous skeletons, and are related to rays. There are approximately 450 species of sharks of which 182 can be found in Australia’s oceans. Their life spans are estimated at between 30 and 50 years (but could be more) and male white sharks can be 4.5 m in length. Approximations of shark numbers off the WA coast are estimated at about 700 with no evidence of numbers increasing. Sharks off WA are migratory and they are most likely to be encountered off Perth in the period October to December.
As an apex predator, sharks are important in maintaining balanced and healthy food webs. Their removal has been shown to impact specialist fishing; one example is the collapse of the scallop industry in the Atlantic. Sharks are dominantly fish eaters rather than marine mammal eaters and feed opportunistically; they are known to dive up to a kilometre but possibly deeper. Sharks are found throughout the oceans of the world and as a large group there are many species having specialist adaptations; the hammerhead, for example, has electro-receptors and vision through 360 degrees. Generally sharks have a good sense of smell, with the odour of decaying shark a known deterrent.
Sharks are hunted in huge numbers, estimated at about 273 million killed each year. Hunting by cruel methods includes the abominable ‘finning’ trade. Sharks, of all kinds, are captured and restrained whilst their fins are cut off, then often released. This results in their suffering for a product used as a textural additive to foods of an ingredient that is essentially tasteless. Whale sharks are also included in this hunting trade.
Shark attacks on people are actually small in number, but media reports produce bad press with sensationalised and exaggerated reports. These often reinforce dangers by repeating the small number of attacks and illustrating articles with pictures of the open jaws with ragged teeth of a Great White shark. Other human medical problems and accidents rate far higher than the 1:3,748,067 chance of fatal encounters with sharks.
Some sensible personal measures that can be taken to avoid confrontation include: not swimming or diving at twilight, in murky waters, near food, with pets, and no spear fishing. Surface swimmers are most vulnerable as the visual optics of sharks are best focussed upwards. Some control measures have included the official culling of a shark seen often in an area and aerial patrolling of swimming beaches. Patrolling seems effective and is non-invasive and swimmers can be warned to leave the sea. There are also a few personal repellents and devices that can be carried, some producing electrical fields as well as specially designed patterned swimwear suits and wet suits that appear to break up the human body outline of what could be potential prey. Sharks are colour blind and perceive only in black and white. The testing of such suits could also lead to a shortage of trial volunteers. Lauren mentioned the use of shark nets as used in NSW. Nets are not designed to construct a safe swimming enclosure and have resulted in high levels of bycatch. Between 1985 and 2011, for example, nets caused the deaths of 20,000 sharks, 2,100 turtles, 552 dugongs, 216 dolphins and a human drowning. During the period 1905 and 1962 there were two human fatalities and from 1962 to 2003, three in the same areas.
Lauren’s presentation both entertained and educated us and clearly emphasised the need for further research of this large but little understood group of animals. Education is essential to manage the interactions between people and sharks in their natural habitat. There are many web sites that focus on factual information to assist in overcoming some fears about sharks.
Susan Stocklmayer