Of Singing Seals and Drones

I have two bat detectors on the Farne Islands – one on Inner Farne and one on Brownsman – and visit them several times a year to download data and check that they are still working properly.  The Farnes change character remarkably during the course of the year, bursting with life during the seabird breeding season, then strangely quiet after the terns and auks head off in August until the following spring.  But some of the islands have a third facet to their character – these are the seal breeding islands, chief amongst which are Brownsman and its tidally conjoined twin Staple Island.  Come October, for about 3 months these become the domain of the Grey Seals (Halichoerus grypus).  The lush growth of guano-fertilised herbage that in the height of summer covers everything that isn’t bare rock or fresh puffin-excavation is relentlessly trampled out of existence by hundreds of lumbering seal bodies so that parts resemble nothing so much as a First World War battlefield.

Brownsman in November – trashed by seals

The seals boss the islands, and this presents challenges on the final visit of the year to Brownsman.  There are only a couple of places where you can land a boat and whichever you use you have to run a seal gauntlet to get to the cottage where the rangers live and where the detector is located.  Mother seals are very protective of their pups, and bull seals are suspicious of anything approaching their females so there is considerable scope for inter-species misunderstandings.

Bull Grey Seal, suspicious of my motives
Cow seal, likewise

Seal pups start off as little creamy-white scraps with over-large heads, but within a few days of intensive suckling they swell into chubby white rugby balls.  Once she has them fat enough (after about 18 days during which time they have ballooned from ~14 to ~45 kilos) the female abandons them.  The bull seals are constantly patrolling the colony, fighting each other, squashing pups and sexually harassing the females, and by the time she heads off the female will be carrying the fertilised egg that will develop into next year’s pup.

Grey Seals are much the same weight as lions with strength and teeth to match – if they had legs rather than flippers we would be terrified of them.

Reasons to be thankful that seals do not have legs

Fortunately sex and child-rearing take place on land, and once they are in the water they are much more chilled, their curiosity making them a delight to scuba divers and snorkelers.

Dive Buddy off the Farnes – Photo by Ben Burville @sealdiver

Having been abandoned by their mothers the pups proceed to moult into their mottled adult coats, and are particularly delightful at this stage.  I don’t know if it is a term in general use, but the Farnes rangers call them ‘moleys’, which is very apt.

Moleys

The moleys tend to drift together into loose groups, now and again galumphing around playfully, but mostly just snoozing away the grey days and long nights of early winter until after three or four weeks they head off to sea to start looking for food.  Now I started my professional career studying coastal-living otters in Shetland.  Otter cubs go to sea when they are about 2 months old but accompany their mothers for another year or so, and still struggle to survive when they finally have to fend for themselves.  It has therefore always intrigued me that Grey Seals are able to dispense entirely with parental education and support – in which respect they are more like fish or amphibians than mammals (and even some of those would put Grey Seals to shame!)  One would have thought that to begin with young Grey Seals would not venture far while they ‘find their flippers’, but far from it.  Geolocator tagging has shown that these babies promptly set off on what may be the widest wanderings of their lives.  Pups tagged on the Isle of May in the Firth of Forth fan out into the North Sea and have been found as far afield as Holland and Norway within a few weeks of setting out.  They forage primarily on the seabed and the whole of the North Sea, which is relatively shallow, is their oyster – one male pup was even recorded diving to over 200m in the Norwegian Trench.

For the pups, this is a desperate race against time that pits their ability to learn how, where and when to dive and catch fish against those dwindling fat reserves that are providing them with energy and keeping the cold at bay.  Mortality is high and when you look at this equation you wonder why the moleys don’t head off to sea as soon as possible rather than lolling around on land for the thick end of a month and losing up to a quarter of their body weight in the process.  However evolution would have long since winnowed out the lingering habit if there had not been a very good reason for it.  That reason seems to be that their bodies need this time to use a hefty chunk of that puppy fat to fuel the development of the physiological adaptations they will need for sustained swimming, diving and foraging – it is a sort of pupal stage where a fat, guzzling milksop goes in at one end and a young marine predator, its blood and muscles charged with oxygen-carrying haemoglobin and myoglobin, comes out at the other!

Who are you calling a pupa?!
We’re not being lazy, honest!
Busy metamorphosing into a top marine predator
Myoglobin dreams……

The Grey Seal is a species that is doing very well at present.  Numbers around Britain and Ireland were very low in the early 1900s, possibly even as low as 500 when the Grey Seals (Protection) Act was introduced in 1914.  One hundred years later, the population is estimated to be in the order of 150,000 and still growing.  The biggest breeding colonies were, and still are, in the Orkneys and the Outer Hebrides and for a long time the only breeding colony on the east coast of Britain was the one on the Farnes.  This continued to be the case until 1956 when the first pup was born on the Isle of May, but that colony didn’t really take off until the late 1970s.  Then in the late 1990s they started breeding on the mainland, on the little boulder beaches at the feet of the towering cliffs of the Berwickshire coast centred on Fast Castle Head.  Much more surprising was the establishment in the 1980s of a breeding colony at Donna Nook on the Lincolnshire coast as this was utterly different habitat – vast open sandy beaches readily accessible from land – and there are now two sandy beach colonies in Norfolk as well, at Blakeney Point and at Horsey.  Tagging and genetic studies have shown that the Farnes is the ultimate source of these new colonies, several of which are now producing more pups that the motherland, Fast Castle being the largest.  While the rate of population growth has slowed around the north and west of Britain, it continues exponentially on the east coast with about 13,000 pups produced in 2014.  With 7 pups born this year, it looks as if Coquet Island, 30km to the south of the Farnes, is becoming the next new breeding colony.

This development of the habit of making use of sandy shores for breeding is an interesting one, not least because it holds the potential for competition with Common Seals (Phoca vitulina) which traditionally have been much more strongly associated with sandbanks and estuaries that have Grey Seals.  Indeed there seems a strong likelihood that the crashes in numbers of Common Seals in the Wash area, caused by outbreaks of Phocine Distemper Disease that first struck in 1988, opened up the way south for the Greys.  Now, it seems, the habit of using sandy beaches for hauling out is spreading back north through the population.

I have to admit to a very soft spot for Common Seals.  They shared the same (rocky) coasts as the otters I was studying so I saw quite a lot of them during my Shetland years.  They have very friendly puppyish faces and are much more playful than their grey cousins, being given to leaping clear of the water, flipper-slapping, snorting and serial porpoising.  They will come a long way into estuaries, right into freshwater, and one fine May morning I watched one fishing upstream of Newcastle just below the tidal limit of the River Tyne at Wylam, some 25km from the sea as the crow flies (and considerably more as the seal swims) looking quite at home in between the lush green river banks, bedecked with Cow Parsley and Dame’s Violet.  Indeed I think the least far-fetched explanation for the existence of the Loch Ness Monster is that it is based on whisky-fuelled sightings of a convoy of porpoising Common Seals spotted through Highland drizzle on a murky night.  Although much more numerous than the Grey Seal in global terms, they are less common than Greys in British waters so their home-grown English name is not particularly appropriate.  Far better is their international English name of Harbour Seal, and that is what I will refer to them as hereafter.  In fact I think I will go one step further by adopting our American cousins’ spelling i.e. dropping that superfluo(u)s ‘u’ and referring to them as Harbor Seals.

Anyway, not so long ago (the 1990s), if I wanted to watch Harbor Seals I would head for the tidal island of Lindisfarne (aka Holy Island), just up the coast from the Farnes.  At low tide a dozen or two would haul out on the sandbanks which form a sort of Northumbrian mini-Wash between Lindisfarne and the mainland, and splosh and cavort in the channels.  By about 2010 this had become impossible.  Not necessarily because the Harbor Seals are no longer there, but because they have now been swamped by literally hundreds of Grey Seals with their newly acquired sandbank habit.  It would take powerful optics and greater patience than I have to establish whether the Harbor Seals have actually been displaced, or if they are still in there amongst the throngs of Greys.  Now when the wind is in the west the whole of Lindisfarne is pervaded by the singing of the Greys – a delightful experience when you are sitting in the warm sunshine in the sheltered gardens of one of the coffee shops in the village.  Close to, you realise that this wonderfully evocative sound is actually the incessant, cantankerous wailing of seals telling their neighbours to keep their distance (it has been well said that they are gregarious but not sociable), but distance strips away the harsh notes and leaves only the mournful keening to caress the ear and fill the imagination with mermaids and lost souls.  The Greys are also hauling out in their hundreds on the mainland close by, at the northern tip of Ross Back Sands, and it is surely only a matter of time before they start breeding there as well.

To return to the Farnes, the Grey Seal pup production has surged over the last few years, reaching 2,295 in 2016, and a large chunk of that surge has happened on Brownsman (934 pups in 2016).  With the result that the rangers decided they could no longer run the risk of my getting marooned up a ladder by seals, and so this autumn I was restricted to Inner Farne and the issuing of detailed instructions to the Brownsman landing party.  I am pleased to say, though, that I still got my seal pup fix as they are now beginning to use St Cuthbert’s Cove, the little sandy beach next to the jetty on Inner Farne.

One of the pleasures of visiting the Farnes is the opportunity to talk to various scientists about their research there and my visit in late November coincided with one by Bethany Cowan, a marine science student at Newcastle University.  The mortality rate of Grey Seal pups on the Farnes is considerably higher than at most other North Sea colonies, and while the most likely explanation for this is their level of exposure to storms which can wash hundreds of pups away if they hit at the wrong times, there is a nagging concern that some of it could be due to the disturbance caused to the seals by the pup monitoring process.  There are several counts during the course of the pupping season during which any new pups are sprayed with dye to avoid double-counting and to get an estimate of on-site mortality.  This has been the fundamental methodology used since the 1950s so clearly if there has been any adverse effect it has not been significant enough to interfere with the North Sea population explosion.  Nevertheless, it is a potential animal welfare even if not a conservation issue, and allied with concerns about the human health and safety risks of the process, the National Trust had decided to experiment with the use of a drone to count the pups from the air.  Bethany’s study is into how seals respond to this new source of potential disturbance.  Cue the drone man – Tim Askew, a filmmaker specialising in filming with drones.  The Inner Farne bat equipment safely decommissioned I spent a happy couple of hours peering over Tim’s shoulders at a kittiwake’s eye view of the islands and of the seals loafing and diving in the clear waters, and with Bethany watching the behaviour of the seal mothers and pups on the beach.  With the coming and going of boats at the jetty, the seals here seem thoroughly habituated to people so  it was a more relaxed environment for seal-watching than Brownsman and it is a much better place for studying how seals react to one another rather than to humans.  However I have to say that following the adventures of one little pup whose mother had sloped off to cool down in the sea as he flopped his wailing way from one female seal to another in quest of milk was quite harrowing – mother seals do not treat milk-poachers kindly!

Do you think she’ll let me have some too?

As far as I could tell the seals were, at most, just mildly curious about the drone – looking up at this buzzy little flying object above their heads.  This is not really surprising, given that they have to share the islands with thousands of racketing seabirds for several months each year.  It certainly looks to me like this will be a situation where new technology will prove its worth.

Bethany: ‘That one’s been suckling for 8 minutes now’
Tim and drone
Flying drones over the sea requires extra concentration!
Getting a drone’s eye view

As for the Grey Seals’ future, I can’t help but think these may be their salad days.  At present they are the top predator in the North Sea, but it has not always been so.  In other parts of their range they are preyed upon by Killer Whales (Orcinus orca).  Currently these are, at best, only occasional visitors to the North Sea, but surely the burgeoning biomass of Grey Seals is such that the Killers will not continue to overlook this opportunity for ever.  More immediately, I suspect Brexit will pose a threat to them.  Back in the ’60s and ’70s when seal numbers were only a tenth of what they are now, they were perceived as an economic threat by the fishing community and there were several somewhat ineffectual seal culls which foundered in the face of public opinion and scientific uncertainty.  Post-Brexit, if we ‘take back control’ of our seas and British fishermen no longer have foreign fishermen to blame for catches failing to live up to hopes and expectations, then I think we can confidently expect the seals to become the scapegoat of choice once more.

References

Anderson, S (1990) Seals. Whittet Books.

Bennett, K et al (2010) Effects of age and body mass on development of diving capabilities of gray seal pups: costs and benefits of the postweaning fast. Physiol. Biochem. Zool. 83(6): 911-923.

Carter, M et al (2017) Intrinsic and extrinsic factors drive ontogeny of early-life at-sea behaviour in a marine top predator. www.nature.com/scientificreports

Noren, S et al (2005) Development of the blood and muscle oxygen stores of gray seals (Halichoerus grypus): Implications for juvenile diving capacity and the necessity of a post-weaning fast. Physiol. Biochem. Zool. 78(4): 482-490.

Sleate, E and Perrow, M (2008) An undercurrent of change for Norfolk’s seals. British Wildlife 19(5), 305-314.

Smout, TC and Stewart, M (2012)  The Firth of Forth: an environmental history.  Birlinn.

Special Committee on Seals (SCOS) 2016 report: http://www.smru.st-andrews.ac.uk/files/2017/04/SCOS-2016.pdf

Tooth, E (2017) The Farne Islands grey seal colony in 2016. Northumbrian Naturalist 82, 92-95.

Leave a Reply

Your email address will not be published.