Seal mutilation investigation continues

Seal mutilation investigation continues2Over four years ago, our website columns reported over 100 seals appearing as corpses strewn on our Scottish and East Anglian beaches. The victims had suffered ‘Corkscrew Deaths’, the term given to the deep evenly spaced lacerations running as a linear spiral down their bodies. Similar findings were reported later from the German sea coast. There could be many more deep on remote coastlines and under the sea.

There are particular concerns over harbour seals, which have suffered steep declines around Scotland in recent years. Populations on the east coast and in Orkney and Shetland plummeted by up to 85 per cent between 2000 and 2010.

Trencher at work

Trencher at work

A number of theories have been suggested, as to the probable cause. MARINET wondered if the creatures, who are naturally very inquisitive, could have possibly been sucked into and trapped by the bed suction intake of the dredgers, or, what seemed even more likely, that the trenching machines employed to cut out the channels in the sea bed for laying cables, pipes etc. were responsible. Either the suction dredging or the trenching could have disturbed and revealed the bottom lying flatfish, which would then have been spotted by the hungry seals, which could then be sucked in and trapped by the mechanism.

Others thought that unguarded ducting propellers were responsible, due to the animals becoming sucked in then trapped between the propeller blades and the casing and so slashed to death and beheaded. These are now widely used in shipping and the offshore industry, to position boats more efficiently at low speed. Cannibalism was also considered as a possibility.

Greenland sharks (who are not carnivorous and who normally inhabit the deepest far north waters and feed from sea bottom detritus remains) were also considered, as changing sea temperatures might have changed their behaviour and placement.

During the investigation, a number of examples of juvenile grey seals with typical spiral injuries were recently unexpectedly seen to be the result of adult grey seal predation. The full report of this is available from: http://www.smru.st-and.ac.uk/documents/2162.pdf

Seal mutilation investigation continues3The Sea Mammal Research Unit researchers discovered supporting evidence for predation, as they observed an adult male grey seal in the Firth of Forth killing and cannibalising young grey seals and leaving distinctive spiral lacerations around their bodies. Combined with recent similar evidence from Germany, this suggests such behaviour is not an isolated incident and could explain the unusual clusters of injured seals found in Scottish waters.

Whilst such evidence does not eliminate any possibility of ship ducting propellers ever being involved, it now seems less likely that they are a key factor.

This information should help to inform regulators, developers and others, enabling them to take it into account in their activities. Marine Scotland intends to continue funding research to monitor the seal population for further injuries and any additional evidence about the causes.

Official advice was changed last month, as a result of this evidence. New advice, given internally to staff at Scottish Natural Heritage and other government wildlife agencies across the UK, concluded that ducted propellers may not be responsible for corkscrew injuries, so mitigation measures and monitoring may not be necessary.

However, the new advice also accepts that “it would be premature to completely discount the possibility that some of the corkscrew injuries are caused by interactions with propellers”.

Now the mystery surrounding the spate of corkscrew seal deaths in Scottish waters has spilled over into a war of words between the governments and a coalition of environmental and conservation groups, who are urging the Scottish and UK governments to give further attention to the use of unguarded ducting propellers in the shipping industry, because they believe that they could see more seals killed by corkscrew injuries.

These environmental groups are now saying that propellers cannot yet be ruled out as causes of injury so it is ‘premature’ to change shipping advice. They say that previous precautionary warnings not to use ducted propellers near seal conservation areas and to avoid the breeding season should be reinstated.

“We need to do more, not less, to turn around the declines in seals, so the… advice is premature and inappropriate,” said Sarah Dolman, North-east Atlantic programme manager for Whale and Dolphin Conservation.

“We urgently need a UK-wide strategy to recover seal populations that should include monitoring at haul-out sites, post-mortem examinations to determine all causes of death and peer-review of all previous work on corkscrew injuries including historical analysis. Precautionary mitigation guidance should be in place until all causes of death are clearly understood.”

Conservationists also point out that there is no evidence to date that grey seals are killing adult harbour seals with corkscrew injuries. More than 30 of those found with the injuries have been harbour seals.

The shipping industry, however, attacked campaigners for ignoring the new evidence on seal predation. “It is frustrating that now the evidence does not suit their theories they continue to blame the industry regardless,” said David Balston, policy director at the Chamber of Shipping.

“The evidence now shows natural factors are to blame for seal deaths. It is time environmental campaign groups stopped demonising the industry,” he argued. “We should have a constructive debate but one that is based on science and evidence, not ideology.”

According to the Scottish Government, the new research was clear evidence that grey seals were likely to be the main cause of corkscrew deaths, rather than propellers. A government spokeswoman said “However, Marine Scotland will continue to monitor our seal population for further injuries and any evidence about the causes. We will continue to monitor interactions between harbour seals and shipping, including the potential for any disturbance or collisions.”

The government is also funding a major research project to identify the causes of the decline in harbour seals.


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