'Goldilocks' Zone for Tiger Sharks is 22ºC, Say Scientists
A team of scientists led by researchers from Queen's University, Belfast, has determined that the optimal temperature for tiger sharks to thrive is 22 degrees centigrade, an important consideration to predict the presence of the species in waters where they may come into contact with humans.
Tiger sharks (Galeocerdo cuvier) are one of the few species of shark that are classed as dangerous to humans, and although attacks are rare – and fatalities even rarer – tiger sharks, along with other species such as the great white and bull shark, have been targeted in controversial, and wholly unnecessary, shark culling schemes, such as the mass killing of large sharks off the coasts of Queensland and New South Wales in Australia.
The study, led by Dr Nicholas Payne, a visiting researcher at Queen’s University Belfast and an academic at the Department of Life Sciences at the University of Roehampton in London, was carried out by tagging sharks in the waters surrounding Hawaii to measure their swimming performance, combined with several decades worth of 'catch data' from the eastern coast of Australia. It found that the 'coastal abundance and swimming performance' of tiger sharks were both highest at around 22°C – an indication that water temperature specifically affects the distribution of the animals.
Most sharks are poikilothermic (often colloquially described as 'cold-blooded'), which means that they are unable to regulate their own internal body heat, which is therefore maintained by the temperature of the surrounding water. Tiger sharks are mostly found near the coast in tropical waters, following warmer currents as the year progresses. The research aims to predict where the tiger sharks will turn up, and under what conditions, in a similar way in which the presence of other dangerous species is monitored.
'In parts of Northern Australia,' said Dr Payne, 'we close beaches and use public awareness campaigns to minimise injury caused by marine stingers; this management strategy is based on our knowledge that dangerous jellyfish only appear on those beaches under certain weather conditions, including when the water is warm.'
Likewise, rising ocean temperatures though climate change may cause the distribution of tiger sharks to alter, meaning that they may be found along beaches at times of year when they were previously not generally encountered. The report cites the example that tiger sharks 'are mostly caught at Australia’s popular New South Wales beaches (ie near Sydney) in the warmest months, but our data suggest similar abundances will occur in winter and summer if annual sea surface temperatures increase by a further 1–2°C.'
'How we manage risks associated with potentially dangerous shark species is a difficult issue for authorities,' said Dr Payne. 'Building our understanding of the biology and ecology of dangerous species might enable us to develop shark management strategies that don’t rely solely on killing sharks.'