Otherwise healthy harbour and grey seals and harbour porpoises are dying around the UK coastline due to injuries resulting from a sudden traumatic event, reported this weekend. Injuries are thought to be consistent with impact by ducted propellers on numerous maritime vessels, such as tugs, self-propelled barges and rigs, various types of offshore support vessels and research boats.
In the last 5 years, more than a hundred seals and porpoises were found on the coast of the UK with similar injuries consisting of a single continuous curvilinear skin laceration spiralling down the body (known as corkscrew injuries).
Injuries of this type date back to 1993 when 95 dead seals stranded on Sable Island, Nova Scotia. In 1998, more than 1,000 immature harp seals washed ashore on Prince Edward Island in the Gulf of St Lawrence.
‘Hot spots’ are in east Scotland, north Norfolk and Strangford Lough in Northern Ireland.
These cases are just the tip of the iceberg, where only seals or porpoises that die in coastal waters are washed ashore and not all of these will be found, reported, then diagnosed.
The deaths of harbour seals as a result of these injuries mean that several local and potentially regional population have suffered declines. Breeding females comprise a large proportion of dead seals and without sufficient females of breeding age it is not possible to maintain or recover a population.
In particular, there is a small and dramatically declining harbour seal population off the east coast of Scotland, protected by the European designation, the Firth and Tay SAC. The Firth of Tay count in 2011 was the lowest ever recorded (77 seals) and was 38% lower than the 2010 count. This SAC population has declined at an average rate of 20% per year since 2002 with the 2011 count 89% lower than the peak count in 2000. In the Firth of Tay and Eden Estuary harbour seal SAC in 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. This level of mortality is considered to be significant such that, it is likely to affect the population’s ability to recover from its currently declined level, according to Statutory Agency advice.
Sea Mammal Research Unit analysis of the likely future trends in population in this population suggests that it will go extinct by 2040 and probably much sooner unless the cause of the additional mortality is removed.
Further research is clearly necessary to confirm the exact causal mechanism that results in these deaths. The Scottish government is investigating the causes of death.
But whilst the research is on-going, no mitigations have currently been put in place and so the deaths continue.
WDC and nine other UK and Scottish charities wrote to the UK and Scottish government this week to as for the following, as a matter of urgency:
1) Dedicated collection of stranded marine mammals from all around the UK coastline.
2) Raise awareness with the maritime industry, require obligatory recording and reporting of position and drive use when in areas already known to be risk hotspots, reducing any time holding at station and carrying monitoring equipment and a commitment to avoid certain engine use patterns when close to seal populations
3) Further immediate mitigation is required in those areas where incidents are on-going
4) Guidance for developers should be expanded to include porpoises
You can read more here.