When aerial surveys won’t do: Grey seal pup production in cryptic habitats of Wales

Thomas Stringell, Colin Millar, William Sanderson, Stephen Westcott, Amanda McMath

    Research output: Contribution to journalArticlepeer-review

    5 Citations (Scopus)
    142 Downloads (Pure)


    Grey seals (Halichoerus grypus) are a species of conservation importance that require Marine Protected Area management and population status assessment under the EU Habitats and Species Directive. Aerial surveys are commonly used to monitor grey seal pup production at their globally important UK colonies. However, in Wales more than half of pups are born in cryptic breeding habitats, such as sea caves. These cryptic habitats preclude the use of aerial monitoring methods and necessitate groundbased counts, which are costly in resources. In this study, we compare a ground-based pup production census with a reduced effort plot-sampling survey to estimate pup production, derive a total population size and assess cost effectiveness. Pup production in north Wales was estimated at 91 (95% CI: 70 – 112) by the plot-sampling design and was a good approximation of the ‘true’ value of 96 derived from the census. The total population size in north Wales was estimated at between 242 and 307 grey seals. The plot-sampling design reduced survey effort by 46% and saved 30% on logistical costs compared to the full census. We outline thesuitability of this method as part of a monitoring programme for grey seal pup production and suggest our approach may be applicable to other regions where grey seals use cryptic breeding habitat.
    Original languageEnglish
    Pages (from-to)1155-1159
    Number of pages5
    JournalJournal of the Marine Biological Association of the United Kingdom
    Issue number6
    Early online date12 Mar 2013
    Publication statusPublished - Sept 2014


    • Grey seals (Halichoerus grypus)
    • Special Areas of Conservation
    • Habitats Directive
    • monitoring
    • abundance estimation
    • plot-sampling
    • caves
    • pup production
    • Wales

    ASJC Scopus subject areas

    • Aquatic Science


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