Trends in the Size of British Grey Seal Populations

Summers, Carol

doi:10.2307/2402599

Cited by 36 publications

(23 citation statements)

References 8 publications

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“…The population of grey seals in Britain, based on using pup counts as an index of abundance, has been increasing steadily since records began in the early 1960s (Summers 1978). Each year, the Sea Mammal Research Unit (SMRU) in St. Andrews, Scotland conducts aerial surveys of the major grey seal breeding colonies in Britain to determine the number of pups born (pup production; Duck 2004).…”

Section: Introductionmentioning

confidence: 99%

The status of grey seals in Britain

Duck

Thompson

2013

NAMMCOSP

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Grey seal pup production in Scotland was estimated through annual aerial surveys of the main grey seal breeding colonies. Between 3 and 7 counts of pups were obtained for each colony at intervals through the course of the breeding season. Pup production for individual colonies was estimated from the series of counts using a maximum likelihood model. At 3 colonies, 2 in England, annual pup production was estimated using ground counts. Between the early 1960s and the early 1990s, grey seal pup production progressively increased. At colonies in the Inner and Outer Hebrides, production appeared to stabilize during the 1990s and has remained so. Pup production at colonies in Orkney and in the North Sea has continued to increase but in recent years the rate of increase has declined. This may imply that the UK grey seal population is reaching some limit to its size. The observed changes in pup production imply that some density dependent factors are affecting the British grey seal population. Changes in either juvenile survival and/or female fecundity are the most likely options. Without knowing which of these, or what combination of these factors, is operating, estimating total population size is complicated.

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Section: Introductionmentioning

confidence: 99%

The status of grey seals in Britain

Duck

Thompson

2013

NAMMCOSP

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“…However, in species with less tightly synchronous breeding, or for which time ashore is short, single counts may not be a representative index. The reliability of such an index is dependent on capturing the true peak, which is difficult to achieve if the timing of the breeding varies spatially or annually (Summers, 1978;Williams, Frederick, & Nichols, 2011), and on a constant relationship between the peak and total production. Number of births (production) can be calculated by counting each individual born through the season, either by marking positions (on ground or on photographs) if young are 'tied' to one site (e.g.…”

Section: Introductionmentioning

confidence: 99%

Monitoring long‐term changes in UK grey seal pup production

Russell

Morris

Duck

et al. 2019

Aquatic Conservation

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1. The population size of many species, particularly those in the aquatic environment, cannot be censused directly. Counts, during the breeding season, of one component of the population (e.g. breeding females) are often used as an index to allow investigation of trends. In species, such as grey seals (Halichoerus grypus), for which births are not tightly synchronous, single counts of pups represent an unknown proportion of the total number of pups born (pup production), and thus of breeding females (i.e. each pup born represents a breeding female).2. Grey seals pup at large colonies around the coast of the UK. Information on their populations is required under national and international legislation.3. In the UK, pup production has been monitored at some colonies since 1956. Currently, large colonies (~90% of UK pup production) are monitored either using ground (~10%; annually) or aerial surveys (~80%; annually until 2010, and thereafter biennially).4. Here, the model used to estimate pup production at aerially surveyed colonies from 1987 to 2010 is described; structured pup counts from multiple surveys are combined with knowledge of life-history parameters to model birth curves.5. The resulting trends in pup production up to 2010 (aerially surveyed colonies) and 2016 (ground surveyed colonies) are examined.6. In 2010, over 45,000 pups were estimated to be born in the UK. Pup production appeared to have reached an asymptote in the Inner Hebrides, Outer Hebrides and Orkney, whereas it is still increasing exponentially in the North Sea. Although density-dependent processes acting at sea are likely to be responsible for these regional trends, we suggest that the substantial variation in trends within regions are likely caused by processes acting at the colony level. Some long-established colonies, including Special Areas of Conservation, are exhibiting decreasing trends. 7. Special Areas of Conservation often serve as de facto monitoring sites and are the focus of management efforts. The observed temporal and spatial variability in patterns of colony growth rates highlight the potential risks of using such sites to develop wider management policies.

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“…The grey seal (Halichoerus grypus) inhabits both temperate and sub-artic habitats on the west and east Atlantic coasts and in the Baltic Sea, breeding colonially on a variety of habitats including ice, sand-flats, sandy and pebble beaches, grassy island tops and caves (Summers 1978 ;Stobo and Zwanenburg 1990 ;Hiby et al 1992 ;Caudron 1998). The relief of hunting pressure and the depopulation of coastal and offshore islands (Boyd 1963 ;Summers et al 1978) have contributed to many grey seal populations in the west (Zwanenburg and Bowen 1990) and east Atlantic (Summers 1978;Summers et al 1978 ;Hiby et al 1996) regions to increase in size in recent decades.…”

Section: Introductionmentioning

confidence: 99%

“…The relief of hunting pressure and the depopulation of coastal and offshore islands (Boyd 1963 ;Summers et al 1978) have contributed to many grey seal populations in the west (Zwanenburg and Bowen 1990) and east Atlantic (Summers 1978;Summers et al 1978 ;Hiby et al 1996) regions to increase in size in recent decades.…”

Section: Introductionmentioning

confidence: 99%

“…The increase in west Atlantic and other east Atlantic grey seal populations has reinforced the potential for conflict between grey seals and fisheries (Summers 1978;Harwood and Croxall 1988 ;Harwood 1992;Thompson 1992). An additional conflict has recently arisen from the tourism industry (Baines et al 1995 ;Lidgard 1996;Young 1998) and the effects of global climate change pose a new, although as yet little understood threat to marine mammal populations and their future conservation (Würsig and Ortega-Ortiz 1999).…”

Section: Introductionmentioning

confidence: 99%

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The status of breeding grey seals (Halichoerus grypus) on the east and south-east coasts of Ireland

Lidgard¹,

Kiely²,

Rogan³

et al. 2001

Mamm

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A two year survey was conducted to estimate the population status of grey seals on the east and south-east coasts of Ireland and to document the types of habitat used. Surveys were concentrated around the known breeding sites of Lambay Island on the east coast and the Great Saltec on the south-east coast, during the breeding seasons of 1997 and 1998. The standard technique of through-counting was used to estimate pup production and mortality. Population estimates were calculated from the total pup production using the multipliers given in the grey seal life-history table. The total grey seal pup production was estimated at 41 and 49 for the east coast group, and 100 and 128 for the south-east group in 1997 and 1998, respectively. The population estimate for the east coast group was between 172 and 221 and between 448 and 576 for the south-east group. Estimated pup mortality for the east coast group was 7.3 % and 2.0 % and 3.0 % and 8.6 % for the south-east group in 1997 and 1998, respectively. Most pups were found on beaches, however data from the Great Saltee suggests that beach-cave sites were the preferred habitat early in the breeding season. This study has provided up-to-date information on an otherwise little studied marginal colony.Resume. -Apres deux ans d'enquete on a pu estimer le Statut des populations de phoques gris sur les cötes est et sud-est de l'Irlande, et recenser le type d'habitat qu'ils utilisent. Les observations ont etc centrees autour des lieux de reproduction connus de Tile Lambay sur la cote Orientale et de la Grande Saltee sur le cöte sud-est, au cours des Saisons de reproduction de 1997 et 1998. Une technique de comptage standard a ete utilisee pour estimer la production et la mortalite des jcunes. Les estimations de populations ont ete faites d'apres la production totale de jeunes, en utilisant les donnees de la table qui concerne le phoque gris. La production totale des jcunes phoques gris, en 1997 et 1998 respectivement, a ete cstimee ä 41 et 49 pour le groupe de la cötc est, et 100 ä 128 pour le groupe sud-est. La population du groupe de la cöte est a ete estimee entre 172 et 221 et cclle du groupe de la cöte sud-est cntre 448 et 576. La mortalite des jeunes du groupe de la cöte est a ete estimee en 1997 ä 7,3 % et en 1998 ä 2,0 %; celle des jeunes du sud-est est ä 3,0 % pour 1997 et 8,6 % pour 1998. La plupart des jeunes ont ete trouves sur les plages; cependant les donnees concernant Tile de Grande Saltee suggerent que les sites de grottes de plage etaient habitat prefere au debut de la saison de reproduction. Cette etude a apporte des informations d'actualite sur une colonie marginale peu etudiee.

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Trends in the Size of British Grey Seal Populations

Cited by 36 publications

References 8 publications

The status of grey seals in Britain

The status of grey seals in Britain

Monitoring long‐term changes in UK grey seal pup production

The status of breeding grey seals (Halichoerus grypus) on the east and south-east coasts of Ireland

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