The corkscrew massacre: how seals and porpoises are being cruelly killed by propellers

from Sunday Herald, 29 September 2013

The deaths are cruel, violent and gruesome, and they are threatening the survival of some of Scotland’s rarest wildlife.

Seals and porpoises around the coast are being killed in large numbers because they get trapped between ships’ propellers and their covers, according to the latest scientific research for the Scottish government. The animals die from distinctive “corkscrew” cuts spiralling around their bodies.

Scientists have concluded that the slaughter could have contributed to dramatic declines in harbour seal populations on the east coast and is “unsustainable”. But they are still investigating exactly which offshore industries might be to blame.

This weekend a powerful coalition of ten environmental and animal welfare groups is demanding an end to the killing. They are calling on ministers to ban the use of the propellers in new offshore developments, and to restrict their use by ships in areas where seals are at risk.

“Hundreds of seals and porpoises have died needless and horrific deaths all around our coasts,” said Sarah Dolman, Northeast Atlantic programme manager for Whale and Dolphin Conservation.

“The future is especially bleak for declining harbour seals where, despite European protection, some local populations are facing extinction. On the ground action to prevent any more seals and porpoises from dying cannot wait.”

As many as 80 dead seals have been washed up around Scotland’s shores, confirmed killed by corkscrew injuries, as well as four porpoises. Most of the bodies have been found in the last five years, and scientists say they may be only a small proportion of those who have died, as many carcasses could have been lost at sea.

The animals all suffered a deep gash encircling their bodies. Or, as scientific reports put it, “a single continuous
 curvilinear skin laceration spiraling down the body” in which “the resulting spiral strip of skin and blubber was detached from the underlying tissue.”

Confirmed corkscrew seal deaths

The majority of the seals that died so painfully have been found along the east coast between North Berwick and Dundee, with another cluster around Orkney. Corkscrew deaths have also been recorded in a few other locations on the east and west coasts.

The victims were often adult female seals, sometimes pregnant. Of the 80 confirmed corkscrew deaths, 32 were harbour seals, some populations of which have been in sharp decline, and 48 were grey seals, which are more common (see table below).

In the past a wide variety of culprits have been blamed for causing the injuries, including sharks, killer whales, fishing equipment, naval submarines, tidal turbines, dredgers and even malevolent people with sharp knives. But these have all been ruled out by scientists from the Sea Mammal Research Unit at St Andrews University.

In their latest report for Marine Scotland, part of the Scottish government, they have pointed the finger at particular types of ducted propellers, widely used in marine vessels for many offshore industries. “It’s basically a shipping issue,” said Dr Dave Thompson, the unit’s seal biologist. 

“Seals travel widely out at sea to forage but all of them come inshore to rest, moult and breed. This produces large concentrations of seals at certain times and places. Many vessels with ducted propellers work close to shore and all of them need to enter and leave ports and may then come into areas with large numbers of seals.”

Dr Andrew Brownlow, a veterinary investigation officer at Scotland’s Rural College in Inverness, argued that the corkscrew deaths were having “a serious detrimental effect” on local populations of harbour seals. “This is most notable in the Firth of Tay where seal numbers have declined 90% since the early 1990’s,” he said.

“Eighty per cent of spiral trauma cases reported have come from this area and cases show a strong bias towards pregnant females. Given harbour seal numbers in this area are already critically low, any additional mortality, especially of breeding females, is a serious problem.”

According to Brownlow, the number of confirmed corkscrew deaths was probably just the tip of the iceberg. “It is quite possible that we are seeing a small proportion of what may be a more widespread but generally unobserved occurrence,” he told the Sunday Herald.

“We have no reliable way of estimating what proportion of the casualties we are seeing, but given cases have to float, make landfall, be spotted and finally reported, it is probable a significant number of animals are being missed.”

The ten groups that have written to Marine Scotland demanding action to stop the killing include Whale and Dolphin Conservation, Wildlife Trusts, Marine Conservation Society and OneKind, the Edinburgh animal rights group. They are supported by the National Trust in England, which has seen 45 seals killed by corkscrew injuries washed up in or around its reserve on the north Norfolk coast. 

The trust’s north Norfolk manager, John Sizer, said: “These deaths can severely impact on the population of a species and we are seeking urgent action from the government’s marine and conservation agencies to find the cause and put a stop to these horrific deaths.”

The groups’ joint letter argues that the best way to prevent more deaths is to prohibit the use of ducted propellers as part of the license conditions for new developments. It also suggests that offshore industries should been asked to report and restrict the use of the propellers close to seal populations.

Offshore industries expressed concern about the deaths, but none accepted responsibility. “The death of any sentient marine mammal, particularly after sustaining such horrific injuries, is something that no mariner would wish to see,” said David Balston, the safety and environment director for the UK Chamber of Shipping.

“The UK Chamber has, over the last two years, tried therefore to engage with the lead researchers working in this area, offering our expertise and that of our members to find a practical solution, but without success.”

The offshore oil and gas industry also promised to work with others to develop mitigation techniques, if they were deemed appropriate. “There is insufficient data to enable a definitive conclusion to be drawn on the reasons for these injuries,” said a spokesman for Oil and Gas UK.

The fishing industry body, Seafish, stressed that fishing methods were not to blame, and pointed out that there were no large-scale fishing operations in the areas where most seals had died. It was “unjust” for people to accuse the fishing industry, said a Seafish spokeswoman.

Scottish Renewables, which represents companies developing offshore wind, wave and tidal technologies, pointed out that some of the seal deaths pre-dated its activities. It said that work should continue to identify the causes and “any changes in working practices or design required to protect marine wildlife.”

The Scottish government highlighted other reasons for the decline of harbour seal populations, but agreed it was important to find out exactly what was causing corkscrew deaths. “Good progress is being made narrowing down the cause, but we do not yet have conclusive results,” said a government spokeswoman.

“The Scottish government will consider possible mitigation measures once researchers have completed their investigations and confirmed the specific set of circumstances of these unusual seal mortalities.”

Confirmed corkscrew deaths of seals in Scotland

year / grey seal / harbour seal

1985 / - / 2
1998 / - / 1
2004 / 2 / -
2008 / 1 / 2
2009 / 1 / 4
2010 / 17 / 9
2011 / 13 / 7
2012 / 14 / 7

Totals / 48 / 32

source: Sea Mammal Research Unit, University of St Andrews