The deal with grey seals: human disturbance at haul-out sites

Student Spotlight - Rachel Roberts

Undergraduate Research at Scotland's Rural College (SRUC)

Email: rachelmroberts86@gmail.com   LinkedIn: https://www.linkedin.com/in/rachel-roberts-54b41b146/ 

Download the PDF of the poster here

Background

The number of grey seals (Halichoerus grypus) using Forvie National Nature Reserve (NNR) as a haul-out site has dramatically increased since 2010, making this Reserve the largest non-breeding haul-out site in Scotland. The site, therefore, offers visitors a great opportunity to view Britain’s largest carnivorous mammals in all their grunting, corpulent splendour.

Despite their many afforded protections under the EU Habitats Directive, monitoring of disturbance to resting grey seals at the site has been minimal. Scotland’s Land Reform Act 2003 grants people the statutory right to roam or access most land and inland water within Scotland for recreation purposes. With the introduction of COVID, more people than ever before are being recorded visiting the site; a trend that is suspected only to continue.

The aim of my research was to assess whether people visiting the site along its more visitor-friendly south shore may be causing distress to resting seals on the north shore, as well as evaluate the significance of other potential stress-inducing factors.

What’s the big deal?

Depending on the distance from which visitors approach, interactions between grey seals and visitors can cause disturbance to resting seals, resulting in a vigilance or even flushing response. Repeated provocation of these behaviours can cause hormone irregularity due to chronic cortisol and thyroid hormone secretion in the bloodstream, negatively impacting upon their expenditure of energy.

Furthermore, grey seals undergo an annual moult where they shed old fur and grow in new coats. During this time, they are vulnerable to hypothermia if they are flushed into the cold sea waters without any insulation. Such behaviours may force individuals to abandon the site altogether in favour of less suitable sites for their long-term survival.

Observing the seals

 Data were collected on the Ythan estuary’s south shore between October 2020 to March 2021. I filmed a total of 116 minute-long observations, where I recorded the number of seals within the ‘bob’ (my preferred collective noun used for seals), and then measured how long each of the seals exhibited a particular behaviour, along with manually recording the number of people present and their estimated distances from hauled-out seals. Seals were considered to exhibit a behaviour if an active movement (e.g. vigilance, flushing, locomoting, or interacting) persisted for more than ten seconds, a resting response was sustained, or overwhelmingly displayed a behaviour by a majority of the bob at once (e.g. highly vigilant or flushing).

Given the site’s recent popularity among seals and visitors alike, I also sought to investigate whether the number and distance of visitors on the south shore of the estuary (separated by a water channel from seals) appeared to cause a greater vigilance response in resting seals than when visitors accessed the northern estuary shore.

Analysing the data

Unsurprisingly, the closer visitors on the north shore got to hauled-out seals, the more vigilant and eventual flushing behaviour seals exhibited. Interestingly though, the number of people on either the north or south did not significantly affect seals resting. Furthermore, the only other factor which proved significant in predicting seal vigilance was the height of the tide (higher tide levels = higher vigilance among resting seals).

A smaller bob size did not appear to be a factor in predicting seal vigilance, suggesting that seals at Newburgh don’t feel any more vulnerable to predation when fewer individuals are available to scan for threats. Dogs on the south shore, even when off-lead, did not provoke an increase in vigilance response from seals, though previous interactions between off-lead dogs on the north shore and seals have been reported.

Future of seals at the site

Follow-up studies to determine what conditions make this haul-out site so popular among seals can help inform management plans and feed into regulations and visitor behaviour guidelines at the Ythan as well as other sites that are vulnerable to anthropogenic pressures.

What do you think? Is our statutory right to roam worth the expense of dispelling our remaining native fauna to other areas, or even losing them altogether? Or would installing a barrier tarnish the natural seascape?

For further questions or comments, feel free to get in touch at Rachelmroberts86@gmail.com