What Causes Clusters of Unprovoked Shark Bites? Associate Professor Daryl McPhee Head – Higher Degree Research Today…..
• A brief introduction to trends in unprovoked shark bite. • Discussion of a number of factors which may influence the location and timing of bite clusters. • What can be done?
Global Trends in Unprovoked Shark Bites (1982-2012)
90 y = 2.0494x - 4043.7 80 R² = 0.90093
70
60
50
40
30
20 No. of Unprovoked Shark Bites 10
0 1982 1987 1992 1997 2002 2007 2012 Year
Source: McPhee (2014) Unprovoked Shark Bites: Are They Becoming More Prevalent? Coastal Management 42(5): 478-492. We fear what our ancestral history has prepared us to fear.
Four We fear influences on We fear what what’s our we cannot immediate. intuitions control about fear.
We fear what’s most readily available in memory. Source: Dr Alison Kock, Cape Town Shark Spotters Program Why the Clusters?
• Compare the cognitive need for a single reason with reality. – There is no single factor that explains the occurrence of a cluster of shark bites. – There is no effective predictive tool. – There are a range of factors operating at a several different scales that are inter-related. Why the Clusters?
Human population increase? Per Capita Trends in Unprovoked Shark Bite in Australia 0.8
0.7
0.6
0.5
0.4
0.3
0.2 Shark attack per 100,000 people
0.1
0 1980 1985 1990 1995 2000 2005 2010 2015
Chapman, B.K and McPhee, D.P. (2016) Global shark attack hotspots: Identifying underlying factors behind increased unprovoked shark bite incidence. Ocean and Coastal Management 133: 72-84. Why the Clusters?
Shark population increase? Shark Population Increase?
• Perhaps the most contentious of the reasons. • People are constantly reporting increased sightings of sharks. – Perhaps amplified by social and traditional media. • The white shark is a nationally listed threatened species (Vulnerable) under the EPBC Act. – Same conservation status as the greater bilby, numbat, green and golden bell frog, and populations of the koala. Shark Population Increase?
• We cannot determine if white shark populations have increased since protection because we don’t know what the population was at the time of protection. – While protected since the 1990s, white sharks are slow growing with low reproductive output. • No information on trends in bull shark numbers. • Information on tiger sharks demonstrates declining abundance on the Australian east coast. Why the Clusters?
Changes to Human Patterns of Water Use Changes to Human Patterns of Water Use • Growth of kite surfing in New Caledonia. • More scuba divers and more access to remote locations. • Patterns of surfing has largely stayed the same, although some expansion into more remote locations? • Shark-cage diving. Why the Clusters?
Changes to Shark Habitat Use and Feeding Changes to Shark Habitat Use and Feeding • Myth regarding overfishing of prey and unprovoked shark bite. • Some correlation between enhanced prey abundance and white sharks. – Falls short of causation. • Habitat changes unclear, with the exception of Recife in Brazil where port construction that displaced sharks was the most important factor. • Signage. What to Do? What to Do?
• Barrier nets for bathers where it is practical to do so, and where the community wants them. – Costs including maintenance. • Encouraging the use of independently scientifically tested individual deterrents. • Formal consideration of a significant risk of increased shark bite from coastal developments in shark bite areas is warranted, but not necessarily high priority. An example of the Eco Shark Barrier in place at Coogee Beach (WA) Source: www.ecosharkbarrier.com.au/case-studies/coogee-beach-trial-perth-western- australia/ Results of Independent Testing of the Shark Shield
Device On = 0.16 Device Off = 0.90
Device On = 0.08 Device Off = 0.70
Probability = 0 Probability = 1 Certain NOT TO happen Certain TO happen
Data from Huveneers et al. (2013) Thank you and questions.