Abundance estimate and seasonal patterns of grey seal (<i>Halichoerus grypus</i>) occurrence in Brittany, France, as assessed by photo-identification and capture–mark–recapture

Gerondeau, Maureen; Barbraud, Christophe; Ridoux, Vincent; Vincent, Cécile

doi:10.1017/s0025315407054586

Cited by 21 publications

(22 citation statements)

References 25 publications

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“…The geometric mean of the MLEs of the survival probabilities at NR is 0.882. This is lower than the time-independent survival estimates of 0.98 for a southern North Sea colony (Gerondeau et al 2007), and 0.96 (estimated for Norwegian grey seals, Wiig 1991). It appears therefore that the survival probability at NR is generally lower than for grey seals at a number of different locations in several other studies, and may be a large contributing factor in the observed downward trend in pup production at this colony over the time scale of the study (Duck and Mackey 2005).…”

Section: Discussionmentioning

confidence: 54%

Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

2010

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In mark-recapture studies, various techniques can be used to uniquely identify individual animals, such as ringing, tagging or photo-identification using natural markings. In some long-term studies more than one type of marking procedure may be implemented during the study period. In these circumstances, ignoring the different mark types can produce biased survival estimates since the assumption that the different mark types are equally catchable (homogeneous capture probability across mark types) may be incorrect. We implement an integrated approach where we simultaneously analyse data obtained using three different marking techniques, assuming that animals can be cross-classified across the different mark types. We discriminate between competing models using the AIC statistic. This technique also allows us to estimate both relative mark-loss probabilities and relative recapture efficiency rates for the different marking methods. We initially perform a simulation study to explore the different biases that can be introduced if we assume a homogeneous recapture probability over mark type, before applying the method to a real dataset. We make use of data obtained from an intensive long-term observational study of UK female grey seals (Halichoerus grypus) at a single breeding colony, where three different methods are used to identify individuals within a single study: branding, tagging and photo-identification based on seal coat pattern or pelage.

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Section: Discussionmentioning

confidence: 54%

Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

2010

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“…Because of the heavily biased ratio of males in our sample, we could not explore gender-based differences in distribution patterns, although such differences are known to occur in this species, potentially reducing intra-specific competition (Breed et al 2006). Most adult females are known to leave MOL during the breeding season (Gerondeau et al, 2007), which is consistent with the very low pup production. While the number of tracked adult females from MOL was too low in our study to identify their breeding sites, one grey seal female photographed at MOL during summers 1998 to 2000 was previously photo-identified while breeding in the Blasket islands, western Ireland, in mid November 1996 (O. O'Cadhla & L. Hiby, pers.…”

Section: Distribution and Connectivitymentioning

confidence: 89%

Grey and harbour seals in France: Distribution at sea, connectivity and trends in abundance at haulout sites

Vincent

Huon

Caurant

et al. 2017

Deep Sea Research Part II: Topical Studies in Oceanography

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Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7 to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the northeastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200 km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.

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“…A small population of less than 200 individuals uses haul-out sites in Brittany, France [36], [40], [60], [61] which is further south than predicted. This sub-population inhabit water slightly warmer than the 95% range of mean SST but the average summer temperature is well within the 95% range of the in situ recorded SST values from the 81 seals in the sample used here.…”

Section: Discussionmentioning

confidence: 99%

How Many Seals Were There? The Global Shelf Loss during the Last Glacial Maximum and Its Effect on the Size and Distribution of Grey Seal Populations

et al. 2012

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Predicting how marine mammal populations respond to habitat changes will be essential for developing conservation management strategies in the 21st century. Responses to previous environmental change may be informative in the development of predictive models. Here we describe the likely effects of the last ice age on grey seal population size and distribution. We use satellite telemetry data to define grey seal foraging habitat in terms of the temperature and depth ranges exploited by the contemporary populations. We estimate the available extent of such habitat in the North Atlantic at present (between 1.42·106 km2 and 2.07·106 km2) and at the last glacial maximum (between 4.74·104 km2 and 2.11·105 km2); taking account of glacial and seasonal sea-ice coverage, estimated reductions of sea-level (123 m) and sea surface temperature hind-casts. Most of the extensive continental shelf waters (North Sea, Baltic Sea and Scotian Shelf), currently supporting >95% of grey seals, were unavailable during the last glacial maximum. A combination of lower sea-level and extensive ice-sheets, massively increased seasonal sea-ice coverage and southerly extent of cold water would have pushed grey seals into areas with no significant shelf waters. The habitat during the last glacial maximum might have been as small as 3% of today's extent and grey seal populations may have fallen to similarly low numbers. An alternative scenario involving a major change to a pelagic or bathy-pelagic foraging niche cannot be discounted. However, hooded seals currently dominate that niche and may have excluded grey seals from such habitat. If as seems likely, the grey seal population fell to very low levels it would have remained low for several thousand years before expanding into current habitats over the past 12,000 years or so.

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Abundance estimate and seasonal patterns of grey seal (Halichoerus grypus) occurrence in Brittany, France, as assessed by photo-identification and capture–mark–recapture

Cited by 21 publications

References 25 publications

Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

Grey and harbour seals in France: Distribution at sea, connectivity and trends in abundance at haulout sites

How Many Seals Were There? The Global Shelf Loss during the Last Glacial Maximum and Its Effect on the Size and Distribution of Grey Seal Populations

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