Field work update: seals

There can be few sounds in the British Isles more evocative than the cries of seals echoing around a rocky cove on a grey, bleak island morning. Standing quietly and peering into the autumnal drizzle, Skomer feels smaller and more remote than its actual position less than a mile from the busy Pembrokeshire mainland. Perhaps it’s not surprising that seals have long since featured in Celtic and Norse folklore. Selkies are described as melancholic mystical creatures with the ability to shape shift between human and seal, and often described as having the souls of drowned sailors trapped within...

Known primarily for its bustling seabird colonies during the summer months, Skomer Island and its surrounding waters are also an important breeding site for the Atlantic grey seal Halichoerus grypus. Approximately 4% of the UK population of Atlantic grey seal, breed in Wales. Of these, most are found in Pembrokeshire which has the largest breeding population in southwest Britain (Stringell et al., 2014).

Once the seabirds have returned to sea for the winter, staff and volunteers monitor all the main pupping sites around the island as part of the seal fieldwork programme from late July until mid November.

Skomer’s seal monitoring programme

Since Skomer’s seal monitoring programme started in 1983, observations have been carried out annually generating estimates for:

1.       Productivity (number of pups born)

2.       Survival (of these, how many survive)

3.       Population (how many seals are present during the breeding season)

Pups are followed through regular observation from vantage points above key pupping beaches. The busiest sites around The Neck are covered every two days, with quieter beaches visited every four days. To maintain consistency and provide optimal conditions for finding pups, monitoring is undertaken two hours either side of low water (though at the height of the pupping season fieldwork can stretch to six hours or more per visit).

A widely used classification guide (Smith, 1966) is a useful tool for estimating the age and condition of each pup. Pups take roughly 21 days to become fully weaned and independent. This three week period is divided into five: Class I (1-5 days), Class II (6-10 days), Class III (11-15 days), Class IV (16-20 days) and Class V (21+ days). Class I pups are small and thin with a clearly defined neck, whereas healthy Class IV pups are barrel shaped and are usually moulting their white coat revealing a glossy first year pelage. Each pup is also given a condition score from 1 to 5, with 1 described as thin and weak, and 5 being exceptionally round and well fed.

To estimate the island population, counts of adult seals are also carried out every two days, with these counts split into three categories: male, female and immature. Numbers of weaned pups are also recorded. All the island seal data is transferred from notebooks to a database after each site visit from which annual statistics can easily be generated. 

To date, this season Skomer has recorded 239 pups across 14 sites.

Our colleagues at the marine conservation zone (MCZ) based in Martin’s Haven monitor the local mainland beaches the same way. By using the same methodology, island and mainland data can be combined to provide a comprehensive picture for the whole marine conservation area.

Any data set increases in value, the longer the timeframe, and the more consistent it remains. That Skomer has over 40 years of continuous data for Atlantic grey seals is just another of the many reasons that makes it such a valuable place for conservation science.

Autumn fieldwork

Unlike summer seabird monitoring which is undertaken on fine, dry days with little wind, seal monitoring is much more of an all weather sport. Seal ‘rounds’ are conducted regardless of wind and rain, and in the poorest weather can bear a considerable likeness to caving back home in some of Derbyshire’s muddier potholes!

To keep a low profile and avoid disturbance requires a considerable amount of careful crawling around  amongst the honeycomb structure of abandoned seabird burrows. Adults and pups have an impressive ability to get into the most convoluted of places, so a careful scan from different vantage points is essential to cover all possible hiding places. Often braced against the weather, with the added difficulty of peering through misty optics in the driving rain this can be a considerable challenge, but one which gets easier with the experience gained from multiple visits. Waterproof notebooks are order of the day, with boots, full waterproofs and warm layers. Autumn days are varied though, and for each soaking visit, there are plenty of others which are still and calm, or even bright and sunny.

Like most fieldwork, each visit brings a rollercoaster of emotions: from odd moments of mild peril such as chasing a notebook caught by a sudden gust of wind, to the exhilaration of being out in all weathers and seeing big Atlantic seas thundering into the island cliffs. Then there’s despair at seeing adult seals with horrific injuries sustained through entanglement with fishing gear, and the brutal reality of seeing bloody pups lying still - attacked and killed by aggressive bulls - or wedged tightly amongst large boulders having been drowned by big waves and high spring tides. Then there’s also amusement, even joy, in watching a young pup gently playing with a tuft of grass at the top of a beach, exhibiting surprise and frustration each time it blows back in its face after being batted away. Or a weaned pup playing in the shallows and chasing its tail on a warm, calm afternoon.

With the rapid increase in technology for wildlife monitoring, observational fieldwork such as this is rapidly becoming seen as archaic. But for all the benefits new technology brings, I think much can still be learnt using this approach, and that useful data can still be collected simply with a pair of binoculars and a notebook. I count myself lucky to have been able to spend time observing seals through this autumn whilst contributing to the 42^nd season of data collection for the project. 

- Will Whittington, field worker