WDC has called on the UK Government to take immediate action after the release of more evidence linking the deaths of large numbers of healthy seals and harbour porpoises to injuries consistent with impact by ducted propellers used by a range of shipping vessels.
Between June 2008 and July 2012, 106 dead harbour seals and grey seals were found around the coast of the UK with a single continuous circular skin laceration spiralling down the body, and numerous harbour porpoise strandings have also been found with the same ‘corkscrew’ cuts to the skin similar to the seal cases.
These injuries have been linked to the ducted propellers used by vessels such as tugs, self-propelled barges and rigs, various types of offshore support vessels and research boats. Studies reveal that in some cases, there was an apparent correlation between the appearance of carcasses on shore and the presence of work boats operating in the vicinity.
Incidents like this in the UK were originally reported from 2008, but examination of historic data shows that injuries may have been occurring long before then and, in certain cases, appear also to coincide with the recent expansion of the offshore renewable energy industry and the associated increase in work boat activity.
Worryingly, it seems most likely that these cases are the tip of the iceberg. Only seals or porpoises that die in coastal waters are washed ashore and not all of these will be found, reported, then diagnosed. Therefore, assuming many carcasses do not make it ashore, the potential impact could be much greater and, in the case of declining harbour seals could even be having negative effects on population levels.
Seals and porpoises could be attracted by the noise that these propeller systems make. Hot spots are in east Scotland, north Norfolk and Strangford Lough in Northern Ireland, particularly during the breeding season.
The harbour seal population off the east coast of Scotland is dramatically declining despite protection measures. The Firth of Tay count in 2011 was the lowest ever recorded (77 seals) and was 38% lower than the 2010 count. This population has declined at an average rate of 20% p.a. since 2002 with the 2011 count 89% lower than the peak count in 2000.
In the Firth of Tay and Eden Estuary harbour seal Special Area of Conservation (east Scotland), 11 harbour seals carcasses with corkscrew injuries have been found between July 2009 and August 2010, representing approximately 9% of the total population. An analysis of the likely future trends in this population suggests that it will go extinct by 2040 and probably much sooner unless the cause of the additional mortality is removed .
“The injuries suffered by seals and harbour porpoises around the UK are horrific,” says Sarah Dolman, head of Scottish policy at WDC. Whilst we recognise that research is ongoing to investigate specific causes, and do not wish to point the finger of blame, measures can and should be put in place immediately to prevent further deaths.
“We are calling for the dedicated collection of stranded marine mammals from all around the UK coastline, including improved beach monitoring in England and Wales where there is currently no formally funded post-mortem surveillance system for seals.”