Winter is the peak season for marine mammal strandings along our coasts. Anna Turns explains why
As one of Devon Wildlife Trust’s Stranding Network volunteers, I always keep a bag of rather strange kit in my car boot: it includes surgical gloves, tape measure, numbered tags, clipboard and welly boots. This kit really came into play this winter, when I attended four strandings along the Salcombe to Thurlestone stretch of South Devon coastline.
I received the first call from the Strandings Co-ordinator at Devon Wildlife Trust’s Strandings Network in October, who reported a dead seal pup which had stranded on the Salcombe estuary. Fellow volunteer Maya Plass and I went to Salcombe to collect the relevant data and photos for the strandings database. Information like this is invaluable in assessing the health of marine mammal populations, while identifying the cause of death is important – often it can be due to boat propellers or fishing line caught around the animal; other times it may be disease or attack from another animal.
On first impressions, the young grey seal pup looked well-nourished and still had its signature white coat. From nose to tail, the pup measured 115cm long, so it was probably about one month old. This pup showed no sign of disease, with healthy teeth and no signs of lesions or parasites. But underneath its right fore flipper it had suffered a 10cm-long deep gash, plus its metatarsals (toes) were all broken on its left rear flipper. Main threats to marine animals are collisions with vessels, disease, disturbance, marine pollution, entanglement in fishing gear and, most significant, accidental by-catch. This seal showed no sign of entanglement in fishing line or rope, and we suspect it was damaged by a boat propeller, then died from its serious injuries.
Grey seal pups are born in autumn with a dense, soft, silky white fur. Within about a month, they shed their pup fur and grow dense waterproof adult fur, then soon leave for the sea to learn to fish for themselves. But in their first crucial month as ‘whitecoats’ they are dependent on their mothers for survival.
Maya and I tagged the seal with a DWT numbered tag (made of biodegradable plastic), to show it has already been surveyed in case the seal is washed up again elsewhere.
In early November, Maya and I attended a harbour porpoise stranding on South Milton Sands beach, just west of Salcombe. Unfortunately, it was first seen a few days before we were notified, so it was quite decomposed by the time we arrived. (The sooner we can take the data, measurements and photos, the more information we can obtain.)
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Severe decomposition meant that it was not possible to identify sex, nutritional state, age or possible cause of death. On the up side, the body provides an additional food resource for beach strandline visitors: scavenging birds by day and small mammals by night. The carcass was left on the beach, half-buried in seaweed by movement of the tide, and the following day there was no trace of the body.
Just a few weeks later, we received a call from the National Trust, beach owners at Soar Mill Cove, a remote beach at the mouth of the beautiful Soar Mill valley. Unfortunately, a seal had been found on this beach one week earlier. On arrival, we found the seal in a cold freshwater stream which had acted as a preservative so the seal’s skin was in relatively good condition, although bloated. The young seal had suffered internal bleeding and the eyes had been scavenged. There was no sign of external injury or disease, so it could possibly have died as a result of recent stormy conditions, then got washed up with the tide. Malnutrition, disease or a combination of factors could have contributed, but the exact cause of death was hard to decipher.
In mid-January, I attended a common dolphin stranding at Hope Cove. On arrival, I found an adult female in pristine condition which must have only died a couple of hours earlier. Close-up views of its distinctive ‘hour-glass’ markings and streamlined shape showed just how well-adapted these marine mammals are to life in the ocean. It is strange how something can look beautiful, even when strandings like this are so incredibly sad.
Because the six-foot-long carcass was so fresh and intact, without any sign of disease or external injuries, the Institute of Zoology arranged to collect it the next day for post-mortem in London. To prevent it being washed away with the next high tide or scavenged by animals overnight, we carefully loaded the dolphin onto a trailer and kept it on our driveway under tarpaulins as protection until Rob Deaville from the Institute of Zoology arrived the next morning.
“As aquatic animals, cetaceans (whales, dolphins and porpoises) can be difficult to study, the investigation of strandings through post-mortems gives us a unique opportunity to increase our understanding of their biology, and help us learn more about the threats that cetaceans might face in UK waters,” Rob explains.
Predators at the top of the food chain, like cetaceans, are a strong indicator of the health of our marine environment, and the more information that can be collected the better, in terms of leading towards an improvement in their conservation status.
“Over the last 20 years, there have been almost 600 dead stranded cetaceans reported on Devon’s coasts. 146 of these were examined at post-mortem and cause of death varied from bycatch to pneumonia and attack by other cetacean species,” continues Rob.
Preliminary results from this post-mortem showed that the Hope Cove dolphin was a pregnant adult female that had apparently stranded alive, but had no significant underlying conditions. “There were no stomach contents or evidence of recent ingestion of prey, so it did not appear to have been feeding close to shore and then caught out by receding tide. So, it’s a bit of a mystery so far, but follow-up tests might help explain why it live stranded,” says Rob.
Although each stranding has been an invaluable chance to learn more about the biology of wild animals that many people would only see fleetingly at sea, they also represent stark warnings that these animals are fragile and every conservation effort is crucial.
You Can Help!
Save these contacts in your mobile phone so you can report marine strandings immediately. Dead…If you find a dead dolphin, porpoise, whale, seal, shark or turtle, ring Devon Biodiveristy Records Centre immediately on 01392 274128 (office hours) or ring the Natural History Museum’s Strandings Line on 0207 942 5155. The DBRC, which is hosted by Devon"Wildlife Trust, runs a network of volunteers who record the animal before it is taken by the tide. Removal of the body is the responsibility of the beach owner (for private beaches) or Environmental Health (for public beaches). • Keep dogs and children away. • Do not touch the body as dead animals may carry diseases.• Do not put the body back in the sea. …or AliveIf you find marine mammals stranded alive, ring British Divers Marine Life Rescue immediately on 01825 765546 (24-hour hotline) and trained teams will be scrambled to help rescue the animal. dbrc.org.uk