for Sunday Herald, 29 September 2013
Female
seals may be lured to a horrible death because they mistake the sound of ships’
propellers for a male seal saying he wants to mate.
That is one of the theories under investigation by scientists trying to solve Scotland’s seal murder mystery. They are testing the reactions of seals to the noises made by propellers.
In the last couple of years, investigators at the Sea Mammal Research Unit at the University of St Andrews have found out what has been killing large numbers of seals and porpoises with “corkscrew” injuries. But they can’t yet name the actual killers.
“The wounds are caused by some sort of blade rotating within a duct,” said the unit’s senior research scientist, Dr Dave Thompson. “The only mechanisms that fit this description and are found at all the locations are ducted propellers on ships.”
He pointed out that ducted propellers like Kort Nozzles and Azimuth pod drives were now commonly fitted to a wide range of vessels such as tugs, work boats, barges, mobile rigs and fishing boats. “Such vessels are widely used in coastal and offshore engineering works, port activities and fishing so it isn’t possible to identify any particular industry,” he said.
Ducted propellers are often computer controlled to enable vessels to maintain their positions at sea. This means that they are sometimes turned on and off, giving seals opportunities to approach them.
Because the characteristic corkscrew cut starts on the seal’s face, scientists think that they must be voluntarily moving towards the propellers, before being drawn into them and sliced to death.
“The reasons why seals would be attracted to such devices are not known,” said Thompson. As well as testing their responses to sounds, researchers are also using scale models of seals and propellers to find out which specific devices leave the telltale corkscrew cuts.
Dr Andrew Brownlow, a veterinary investigation officer at Scotland’s Rural College in Inverness, agreed that ducted propellers were the most likely culprits. “No other mechanism with the required characteristics has been identified,” he said.
He stressed, however, that more evidence was needed, and urged members of the public who find marine mammals stranded on the shore to report them “no matter what condition they are in”.
Sightings can be reported by phone, email and social media to the Scottish Marine Animal Stranding Scheme.
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