Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland

Monica Arso Civil; Sally Tapp; John Dickens; Izzy Langley; Helen M. Hiley; Maeva Terrapon; Emily Hague; Rebecca C. Hewitt; Line S. Cordes; Isla M. Graham; Barbara J. Cheney; Paul M. Thompson; Ailsa Hall; Carol E. Sparling

doi:10.1002/ece3.72349

Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland

Monica Arso Civil^*, Sally Tapp, John Dickens, Izzy Langley, Helen M. Hiley, Maeva Terrapon, Emily Hague, Rebecca C. Hewitt, Line S. Cordes, Isla M. Graham, Barbara J. Cheney, Paul M. Thompson, Ailsa Hall, Carol E. Sparling

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

Understanding the demographic drivers behind observed changes in wild populations is key to inferring intrinsic and extrinsic causes behind such changes. In Scotland, harbour seal populations have undergone regional declines since the early 2000s. Here we apply mark-recapture models to photo-identification data collected during the breeding season at haulout sites representative of three areas with contrasting population trajectories to estimate sex-specific apparent adult survival and fecundity rates. Apparent adult survival rates were lower at the declining site of Burray, located within the North Coast and Orkney Seal Monitoring Unit (SMU), which has declined by 85% since the mid-1990s: female survival = 0.844 (95%CI 0.803-0.878), male survival = 0.826 (95%CI 0.751-0.883) (photo-ID data collected in 2016-2022). At stable or increasing sites, estimated apparent adult survival rates were higher: at Dunvegan, located in the West Coast SMU, a region that has been generally increasing since monitoring started in the mid-1990s: female survival = 0.878 (95%CI 0.810-0.924), male survival = 0.842 (95%CI 0.756-0.902) (photo-ID data collected in 2016-2022); at Loch Fleet, located in the Moray Firth SMU which has shown no trend since 2003: female survival = 0.941 (95%CI 0.922-0.956), male survival = 0.919 (95%CI 0.888-0.942) (photo-ID data collected 2006-2021). Mark-recapture fecundity rates were generally high at all sites (0.809 to 0.883), with the lowest estimated fecundity at the declining site of Burray. The results indicate that the causes of the decline are likely acting on adult survival, while evidence that a decrease in fecundity is driving the observed declines had less support. The estimated vital rates inform current research into potential causes of the declines and can be incorporated into stage-structured population dynamics models to investigate whether the hypothesized mechanisms for decline are supported by the data.

Original language	English
Article number	e72349
Pages (from-to)	1-20
Number of pages	20
Journal	Ecology and Evolution
Volume	15
Issue number	10
Early online date	25 Oct 2025
DOIs	https://doi.org/10.1002/ece3.72349
Publication status	Published - Oct 2025

Keywords

Capture-recapture
Fecundity
Phoca vitulina
Photo-identification
Population dynamics
Survival
Vital rates

Access to Document

10.1002/ece3.72349Licence: CC BY

Civil-et-al-2025-Reduced-adult-survival-estimated-Ecol&Evol-15-e72349-CCBY
Copyright © 2025 The Author(s). Ecology and Evolution published by British Ecological Society and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Final published version, 3.09 MBLicence: CC BY

Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland (dataset and R code)
Arso Civil, M. (Creator), Tapp, S. (Contributor), Dickens, J. (Contributor), Langley, I. (Contributor), Hiley, H. M. (Contributor), Terrapon, M. (Contributor), Hague, E. (Contributor), Hewitt, R. (Contributor), Cordes, L. (Contributor), Graham, I. (Contributor), Cheney, B. (Contributor), Thompson, P. (Contributor), Hall, A. J. (Creator) & Sparling, C. E. (Creator), University of St Andrews, 5 Jun 2025
DOI: 10.17630/bd7fe8db-10e3-45ee-b067-19c9182f23e5
Dataset

File

Cite this

Arso Civil, M., Tapp, S., Dickens, J., Langley, I., Hiley, H. M., Terrapon, M., Hague, E., Hewitt, R. C., Cordes, L. S., Graham, I. M., Cheney, B. J., Thompson, P. M., Hall, A., & Sparling, C. E. (2025). Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland. Ecology and Evolution, 15(10), 1-20. Article e72349. https://doi.org/10.1002/ece3.72349

@article{6ec84b63cd63455dbdfb1cccb4d75b1d,

title = "Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland",

abstract = "Understanding the demographic drivers behind observed changes in wild populations is key to inferring intrinsic and extrinsic causes behind such changes. In Scotland, harbour seal populations have undergone regional declines since the early 2000s. Here we apply mark-recapture models to photo-identification data collected during the breeding season at haulout sites representative of three areas with contrasting population trajectories to estimate sex-specific apparent adult survival and fecundity rates. Apparent adult survival rates were lower at the declining site of Burray, located within the North Coast and Orkney Seal Monitoring Unit (SMU), which has declined by 85% since the mid-1990s: female survival = 0.844 (95%CI 0.803-0.878), male survival = 0.826 (95%CI 0.751-0.883) (photo-ID data collected in 2016-2022). At stable or increasing sites, estimated apparent adult survival rates were higher: at Dunvegan, located in the West Coast SMU, a region that has been generally increasing since monitoring started in the mid-1990s: female survival = 0.878 (95%CI 0.810-0.924), male survival = 0.842 (95%CI 0.756-0.902) (photo-ID data collected in 2016-2022); at Loch Fleet, located in the Moray Firth SMU which has shown no trend since 2003: female survival = 0.941 (95%CI 0.922-0.956), male survival = 0.919 (95%CI 0.888-0.942) (photo-ID data collected 2006-2021). Mark-recapture fecundity rates were generally high at all sites (0.809 to 0.883), with the lowest estimated fecundity at the declining site of Burray. The results indicate that the causes of the decline are likely acting on adult survival, while evidence that a decrease in fecundity is driving the observed declines had less support. The estimated vital rates inform current research into potential causes of the declines and can be incorporated into stage-structured population dynamics models to investigate whether the hypothesized mechanisms for decline are supported by the data.",

keywords = "Capture-recapture, Fecundity, Phoca vitulina, Photo-identification, Population dynamics, Survival, Vital rates",

author = "{Arso Civil}, Monica and Sally Tapp and John Dickens and Izzy Langley and Hiley, {Helen M.} and Maeva Terrapon and Emily Hague and Hewitt, {Rebecca C.} and Cordes, {Line S.} and Graham, {Isla M.} and Cheney, {Barbara J.} and Thompson, {Paul M.} and Ailsa Hall and Sparling, {Carol E.}",

note = "Funding: NatureScot; Scottish Government. Grant Numbers: MMSS/002/15, MMSS/003/20; Highlands and Islands Enterprise; Moray Offshore Windfarm (West) Ltd; Moray Offshore Windfarm (East) Ltd; Crown Estate; Beatrice Offshore Windfarm Ltd.",

year = "2025",

month = oct,

doi = "10.1002/ece3.72349",

language = "English",

volume = "15",

pages = "1--20",

journal = "Ecology and Evolution",

issn = "2045-7758",

publisher = "John Wiley & Sons, Ltd",

number = "10",

}

TY - JOUR

T1 - Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland

AU - Arso Civil, Monica

AU - Tapp, Sally

AU - Dickens, John

AU - Langley, Izzy

AU - Hiley, Helen M.

AU - Terrapon, Maeva

AU - Hague, Emily

AU - Hewitt, Rebecca C.

AU - Cordes, Line S.

AU - Graham, Isla M.

AU - Cheney, Barbara J.

AU - Thompson, Paul M.

AU - Hall, Ailsa

AU - Sparling, Carol E.

N1 - Funding: NatureScot; Scottish Government. Grant Numbers: MMSS/002/15, MMSS/003/20; Highlands and Islands Enterprise; Moray Offshore Windfarm (West) Ltd; Moray Offshore Windfarm (East) Ltd; Crown Estate; Beatrice Offshore Windfarm Ltd.

PY - 2025/10

Y1 - 2025/10

N2 - Understanding the demographic drivers behind observed changes in wild populations is key to inferring intrinsic and extrinsic causes behind such changes. In Scotland, harbour seal populations have undergone regional declines since the early 2000s. Here we apply mark-recapture models to photo-identification data collected during the breeding season at haulout sites representative of three areas with contrasting population trajectories to estimate sex-specific apparent adult survival and fecundity rates. Apparent adult survival rates were lower at the declining site of Burray, located within the North Coast and Orkney Seal Monitoring Unit (SMU), which has declined by 85% since the mid-1990s: female survival = 0.844 (95%CI 0.803-0.878), male survival = 0.826 (95%CI 0.751-0.883) (photo-ID data collected in 2016-2022). At stable or increasing sites, estimated apparent adult survival rates were higher: at Dunvegan, located in the West Coast SMU, a region that has been generally increasing since monitoring started in the mid-1990s: female survival = 0.878 (95%CI 0.810-0.924), male survival = 0.842 (95%CI 0.756-0.902) (photo-ID data collected in 2016-2022); at Loch Fleet, located in the Moray Firth SMU which has shown no trend since 2003: female survival = 0.941 (95%CI 0.922-0.956), male survival = 0.919 (95%CI 0.888-0.942) (photo-ID data collected 2006-2021). Mark-recapture fecundity rates were generally high at all sites (0.809 to 0.883), with the lowest estimated fecundity at the declining site of Burray. The results indicate that the causes of the decline are likely acting on adult survival, while evidence that a decrease in fecundity is driving the observed declines had less support. The estimated vital rates inform current research into potential causes of the declines and can be incorporated into stage-structured population dynamics models to investigate whether the hypothesized mechanisms for decline are supported by the data.

AB - Understanding the demographic drivers behind observed changes in wild populations is key to inferring intrinsic and extrinsic causes behind such changes. In Scotland, harbour seal populations have undergone regional declines since the early 2000s. Here we apply mark-recapture models to photo-identification data collected during the breeding season at haulout sites representative of three areas with contrasting population trajectories to estimate sex-specific apparent adult survival and fecundity rates. Apparent adult survival rates were lower at the declining site of Burray, located within the North Coast and Orkney Seal Monitoring Unit (SMU), which has declined by 85% since the mid-1990s: female survival = 0.844 (95%CI 0.803-0.878), male survival = 0.826 (95%CI 0.751-0.883) (photo-ID data collected in 2016-2022). At stable or increasing sites, estimated apparent adult survival rates were higher: at Dunvegan, located in the West Coast SMU, a region that has been generally increasing since monitoring started in the mid-1990s: female survival = 0.878 (95%CI 0.810-0.924), male survival = 0.842 (95%CI 0.756-0.902) (photo-ID data collected in 2016-2022); at Loch Fleet, located in the Moray Firth SMU which has shown no trend since 2003: female survival = 0.941 (95%CI 0.922-0.956), male survival = 0.919 (95%CI 0.888-0.942) (photo-ID data collected 2006-2021). Mark-recapture fecundity rates were generally high at all sites (0.809 to 0.883), with the lowest estimated fecundity at the declining site of Burray. The results indicate that the causes of the decline are likely acting on adult survival, while evidence that a decrease in fecundity is driving the observed declines had less support. The estimated vital rates inform current research into potential causes of the declines and can be incorporated into stage-structured population dynamics models to investigate whether the hypothesized mechanisms for decline are supported by the data.

KW - Capture-recapture

KW - Fecundity

KW - Phoca vitulina

KW - Photo-identification

KW - Population dynamics

KW - Survival

KW - Vital rates

U2 - 10.1002/ece3.72349

DO - 10.1002/ece3.72349

M3 - Article

SN - 2045-7758

VL - 15

SP - 1

EP - 20

JO - Ecology and Evolution

JF - Ecology and Evolution

IS - 10

M1 - e72349

ER -

Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland

Abstract

Keywords

Access to Document

Fingerprint

Datasets

Reduced adult survival estimated in areas of decline of harbour seal populations in Scotland (dataset and R code)

Cite this