Understanding seal strandings

Rob Deaville

Rob Deaville leads a team investigating the causes of cetacean strandings around the UK. He looks at how a new grant from Natural England for performing seal post-mortems could increase our understanding of the threats they are facing. 

This blog contains graphic images which some readers may find distressing.

I help to manage a research programme called the Cetacean Strandings Investigation Programme (CSIP), which began in 1990. Working with lots of different partners, we investigate all cetaceans (whales, dolphins and porpoises), marine turtles and basking sharks found stranded around the UK coastline (under contract to Defra and the devolved governments in Scotland and Wales). Through this work, we’re trying to learn more about the threats these species face in UK waters.

More specifically, we’re interested in learning about the threats that are due to our activities, and whether we can reduce their impact on these charismatic and difficult to study marine species.

Seal disease outbreak

Although the investigation of stranded seals was originally part of our initial remit in 1990, they unfortunately dropped off it sometime ago. Within England, there’s been little systematic investigation of dead seals since the last outbreak of a disease called phocine distemper virus (PDV), in the summer of 2002, which killed thousands of seals across Europe. 

Sick seal on sandbank in The Wash (c) Alan Knight BDMLR
Sick seal on sandbank in the Wash. Image (c) Alan Knight/BDMLR.

At ZSL, we helped coordinate the UK wide response to PDV, taking in reports from members of the public of morbid (sick) and dead seals. We also carried out post-mortem examinations, trying to learn more about the disease and its potential impact on the UK’s seal populations. You can read more about our findings in our report to Defra.

Threats to the UK’s seals

During the year of the PDV outbreak, over 4,300 reports of dead seals were recorded in the UK. Staggeringly, this was a near tenfold increase on the number recorded over the previous year. 

Since then funding for seal post-mortems in England has become much more limited and only a small number have been opportunistically carried out by other institutions. This lack of information has decreased our knowledge of threats faced by seals.  

Seal with PDV awaiting post mortem
Seal with PDV awaiting post-mortem.

We do know that some of the potential threats may include fisheries by-catch (accidental entanglement in fishing gear), ship-strike and impacts from marine debris, as well as the possible risk of future outbreaks of diseases such as influenza A (H10N7) and phocine distemper virus. Research and modelling by other institutions also indicates that another outbreak of PDV may occur in the near future. 

Evidence has also recently emerged in parts of the UK and Europe of grey seals predating on a variety of other species, including harbour porpoises and common seals. This puzzling phenomenon warrants further scientific investigation. Below this post you will find images that illustrate the kind of injuries sustained by seals and porpoises when they are predated on by grey seals. These are graphic images, but as we are keen to better understand this phenomenon, we've illustrated what to look out for to help you with reporting. 

How can you help?

The new funding from Natural England is vital given our lack of knowledge of the impacts our seal populations may be facing. We’ll be able to conduct an intensive six-month investigation of seal mortality, recovering and examining bodies of seals from around the English coast. 

But to make the most of the funding we need your help. We’ve always depended on the public to help us find and investigate strandings. During 2014, 481 dead stranded seals were reported in the UK, 122 of them in England. But a recent map in our last annual report shows there is probably significant under reporting of dead seals in some parts of England compared to the rest of the UK. This may be because of the gap in investigations since 2002. The new funding and the work that will be carried out will hopefully help address this knowledge gap. 

So if you do come across a stranded seal (or any of the other marine species we study), please do contact us as soon as you can. All information is valuable and important, even if you think the body is too damaged or decomposed to be of interest to anyone.  

Strandings can be reported via the national hotline of 0800 6520333. Seal strandings can also be reported to us at strandings@zsl.org

You can also report any marine mammals you've seen in the Thames on our special online map.

 

*Graphic images follow*

 

Find out more about CSIP

 

 

 

 

 

Porpoise with grey seal related injuries
Porpoise at Winterton with grey seal related injuries. Image (c) Ben Garrod.

Common seal with possible predation injuries
Common seal at Blakeney Point with possible predation injuries. Image (c) National Trust.

This image shows a common seal with injuries that are potentially consistent with predation by grey seals. If anyone spots injuries like these in any other seals, it's imperative that you let us know as soon as possible, so we can assess and recover them if appropriate.

 

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