Almost one-fifth of the whale sharks (Rhincodon typus) in Western Australia’sNingaloo Reef Marine Park show major scarring or fin amputations, with thenumber of injured animals increasing in recent years, new research reveals.
Distinctive scar patterns strongly suggest many of the injuries are caused byboat collisions, says whale shark scientist Emily Lester from the AustralianInstitute of Marine Science (AIMS).
To make the finding, Ms Lester, a PhD candidate at the University of WesternAustralia (UWA), and colleagues from AIMS and the Department of Biodiversity,Conservation and Attractions (DBCA), reviewed still and moving images of 913whale sharks taken by Ningaloo tour boat operators between 2008 and 2013.
Of these, 146 or about 16% showed some form of serious injury.
“Some of the major scars were probably bite marks from predators, but mostwere the marks of blunt trauma, lacerations or amputations arising fromencounters with ships, particularly propellers,” Ms Lester said.
Whale shark diving is an important part of the Western Australian tourismindustry, delivering an estimated at $12.5 million in economic activity forthe Ningaloo Reef region.
However, because the species swim for thousands of kilometres beyond themarine park boundaries exactly where the injuries were sustained is unknown.
“Mitigating the impact of scarring from vessel collisions is challenging,particularly outside of our jurisdiction of State waters,” said DBCA researchscientist and co-author Dr Holly Raudino.
The results of the research show injuries recorded during 2012 and 2013 almostdoubled compared to 2011.
“One possible explanation is that there is an increase in shipping activitythroughout the whale sharks’ range – inside Ningaloo and out – and collisionsare becoming more frequent,” said Ms Lester.
The data in the study cannot reveal the number of fatal ship collisions,because whale sharks are ‘negatively buoyant’, meaning that when they die theysink to the ocean floor.
“A collision between a large ocean-going vessel and a whale shark wouldn’t befelt by the ship, as a result, it’s likely that we’re underestimating thenumber of mortalities from ship strike, since our study could only documentsharks that survived their injuries,” Ms Lester said.
Dr Raudino, whose expertise is marine fauna, added that the first step inreducing these interactions would be by “identifying hotspots of where thesecollisions are occurring through spatial modelling”.
The research is published in the Marine Ecology Progress Series.
Image: Jess Hadden. The tail of a whale shark (Rhincodon typus) showingmassive scarring.
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