Rapid increase of the grey seal (<Emphasis Type="Italic">Halichoerus grypus</Emphasis>) breeding stock at Helgoland

Over the past 25 years, the grey seal (Halichoerus grypus) population in the North Sea increased on average at 5% per year, while founding a number of new colonies. Based on published data, this note compares recent trends in pup production at nine breeding sites, with focus on the German island of Helgoland. Since 1997, numbers born at Helgoland increased at 35% per year (95% CI: 29–42), reaching an all-time high of 53 in 2007. Yet, this was less than 1% of all grey seal offspring in the North Sea area. Some other small stocks had similarly high growth rates of 20–50%, which must be explained by immigration from the larger colonies, as sustained autochthonous increase cannot exceed 13% per year in the species. Further, the Helgoland breeding stock increased significantly faster than the neighbouring colonies at Amrum (13%) and in the Dutch Wadden Sea (20%), indicating higher offspring survival and/or higher relative influx of migrants. This is attributed to the fact that at Helgoland newborn seals are safe from floodwater. In the other two sites, in contrast, pups are born on sandbanks and are thus often hit by winterly storm tides, which poses a risk to their survival. Because of the favourable breeding conditions at Helgoland, this new colony is expected to soon become an important stronghold of the grey seal in the Dutch-German North Sea area.     

Aerial surveying of grey seal breeding colonies on the Blasket Islands, Co. Kerry, the Inishkea Group, Co. Mayo and the Donegal Coast, Ireland

The status of Ireland's grey seal population and its relationship with that of Britain and Western Europe, are poorly understood. The existing population estimate for grey seals in Ireland is outdated and urgency exists to establish a reliable national population estimate for this species, listed as an Annex II species under the EU Habitats Directive. Prior to the initiation of a survey on a national scale, the success or otherwise of aerial techniques in surveying grey seal breeding habitat on the Irish coastline first needs to be established. Previously, surveys were boat-based and were susceptible to adverse weather conditions frequently encountered during the autumn breeding season. The feasibility of using aerial techniques to survey grey seal breeding colonies in Ireland was tested during the breeding season of 2003.     

The 1988 and 2002 phocine distemper virus epidemics in European harbour seals

We present new and revised data for the phocine distemper virus (PDV) epidemics that resulted in the deaths of more than 23 000 harbour seals Phoca vitulina in 1988 and 30,000 in 2002. On both occasions the epidemics started at the Danish island of Anholt in central Kattegat, and subsequently spread to adjacent colonies in a stepwise fashion. However, this pattern was not maintained throughout the epidemics and new centres of infection appeared far from infected populations on some occasions: in 1988 early positive cases were observed in the Irish Sea, and in 2002 the epidemic appeared in the Dutch Wadden Sea, 6 wk after the initiation of the outbreak at Anholt Island. Since the harbour seal is a rather sedentary species, such 'jumps' in the spread among colonies suggest that another vector species could have been involved. We discussed the role of sympatric species as disease vectors, and suggested that grey seal populations could act as reservoirs for PDV if infection rates in sympatric species are lower than in harbour seals. Alternatively, grey seals could act as subclinical infected carriers of the virus between Arctic and North Sea seal populations. Mixed colonies of grey and harbour seal colonies are found at all locations where the jumps occurred. It seems likely that grey seals, which show long-distance movements, contributed to the spread among regions. The harbour seal populations along the Norwegian coast and in the Baltic escaped both epidemics, which could be due either to genetic differences among harbour seal populations or to immunity. Catastrophic events such as repeated epidemics should be accounted for in future models and management strategies of wildlife populations.     

A Novel Tool to Mitigate By-Catch Mortality of Baltic Seals in Coastal Fyke Net Fishery

Developing methods to reduce the incidental catch of non-target species is important, as by-catch mortality poses threats especially to large aquatic predators. We examined the effectiveness of a novel device, a “seal sock”, in mitigating the by-catch mortality of seals in coastal fyke net fisheries in the Baltic Sea. The seal sock developed and tested in this study was a cylindrical net attached to the fyke net, allowing the seals access to the surface to breathe while trapped inside fishing gear. The number of dead and live seals caught in fyke nets without a seal sock (years 2008–2010) and with a sock (years 2011–2013) was recorded. The seals caught in fyke nets were mainly juveniles. Of ringed seals (Phoca hispida botnica) both sexes were equally represented, while of grey seals (Halichoerus grypus) the ratio was biased (71%) towards males. All the by-caught seals were dead in the fyke nets without a seal sock, whereas 70% of ringed seals and 11% of grey seals survived when the seal sock was used. The seal sock proved to be effective in reducing the by-catch mortality of ringed seals, but did not perform as well with grey seals.     

Geographic variation of the major histocompatibility complex in Eastern Atlantic grey seals (Halichoerus grypus)

Pathogen-driven balancing selection maintains high genetic diversity in many vertebrates, particularly in the major histocompatibility complex (MHC) immune system gene family, which is often associated with disease susceptibility. In large natural populations where subpopulations face different pathogen pressures, the MHC should show greater genetic differentiation within a species than neutral markers. We examined genetic diversity at the MHC-DQB locus and nine putatively neutral microsatellite markers in grey seals (Halichoerus grypus) from eight United Kingdom (UK) colonies, the Faeroe Islands and Sable Island, Canada. Five DQB alleles were identified in grey seals, which varied in prevalence across the grey seal range. Among the seal colonies, significant differences in DQB allele and haplotype frequencies and in average DQB heterozygosity were observed. Additionally, the DQB gene exhibited greater differentiation among colonies compared with neutral markers, yet a weaker pattern of isolation by distance (IBD). After correcting for the underlying IBD pattern, subpopulations breeding in similar habitats were more similar to one another in DQB allele frequencies than populations breeding in different habitats, but the same did not hold true for microsatellites, suggesting that habitat-specific pathogen pressure influences MHC evolution. Overall, the data are consistent with selection at MHC-DQB loci in grey seals with both varying selective pressures and geographic population structure appearing to influence the DQB genetic composition of breeding colonies.     

Assessing the impact of bycatch on dolphin populations: the case of the common dolphin in the eastern North Atlantic

Fisheries interactions have been implicated in the decline of many marine vertebrates worldwide. In the eastern North Atlantic, at least 1000 common dolphins (Delphinus delphis) are bycaught each year, particularly in pelagic pair-trawls. We have assessed the resulting impact of bycatch on this population using a demographic modeling approach. We relied on a sample of females stranded along the French Atlantic and western Channel coasts. Strandings represent an extensive source of demographic information to monitor our study population. Necropsy analysis provided an estimate of individual age and reproductive state. Then we estimated effective survivorship (including natural and human-induced mortality), age at first reproduction and pregnancy rates. Reproductive parameters were consistent with literature, but effective survivorship was unexpectedly low. Demographic parameters were then used as inputs in two models. A constant parameter matrix proposed an effective growth rate of -5.5±0.5%, corresponding to the current situation (including bycatch mortality). Subsequently, deterministic projections suggested that the population would be reduced to 20% of its current size in 30 years and would be extinct in 100 years. The demographic invariant model suggested a maximum growth rate of +4.5±0.09%, corresponding to the optimal demographic situation. Then, a risk analysis incorporating Potential Biological Removal (PBR), based on two plausible scenarii for stock structure suggested that bycatch level was unsustainable for the neritic population of the Bay of Biscay under a two-stock scenario. In depth assessment of stock structure and improved observer programs to provide scientifically robust bycatch estimates are needed. Effective conservation measures would be reducing bycatch to less than 50% of the current level in the neritic stock to reach PBR. Our approach provided indicators of the status and trajectory of the common dolphin population in the eastern North Atlantic and therefore proved to be a valuable tool for management, applicable to other dolphin populations.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

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

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.     

An assessment of population size and distribution of harbour seals in the Republic of Ireland during the moult season in August 2003

The status of Ireland's harbour seal Phoca vitulina vitulina population is poorly understood. The most recent national population estimate dates back to the breeding season in 1978 and did not cover the entire coastline. Reliable up-to-date information on the abundance and distribution of harbour seals in Ireland is necessary to assess the conservation status of the species and for the effective identification, management and monitoring of special areas of conservation required for harbour seals under the EU Habitats Directive. To provide comprehensive current information on Ireland's harbour seal population, a geographically extensive survey was conducted along the coastline of the Republic of Ireland during the species' annual moult in August 2003. This complemented a similar survey of Northern Ireland, which was conducted in 2002. Using thermal imaging technology, haul-out groups of harbour seals and grey seals Halichoerus grypus were identified from the air, aerial-counts were obtained and compared with simultaneous ground-count data from selected sites. Harbour seal distribution recorded during the 2003 moult season was concentrated in the south-west, west and north-west of the country. This national survey yielded a minimum population estimate for the Republic of Ireland of 2905 harbour seals, delivering an effective baseline for current and future population research.     

Increasing numbers of harbour seals and grey seals in the Solent

Harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) both occur within the UK, but display regional contrasting population trends. While grey seals are typically increasing in number, harbour seals have shown varying trends in recent decades following repeated pandemics. There is a need for monitoring of regional and local populations to understand overall trends. This study utilized a 20‐year dataset of seal counts from two neighboring harbours in the Solent region of south England. Generalized additive models showed a significant increase in the numbers of harbour (mean 5.3–30.5) and grey (mean 0–12.0) seals utilizing Chichester Harbour. Conversely, in Langstone Harbour there has been a slight decrease in the number of harbour seals (mean 5.3–4.0). Accompanying photographic data from 2016 to 18 supports the increase in seal numbers within Chichester Harbour, with a total of 68 harbour and 8 grey seals identified. These data also show evidence of site fidelity of harbour seals in this area, with almost a quarter of animals resighted within the past three years. Overall, this long‐term study indicates an increasing number of both harbour and grey seals within the Solent. However, more research is required to identify the drivers of this trend.     

Trophic niche overlap between sympatric harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) at the southern limit of their European range (Eastern English Channel)

Sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) are increasingly considered potential competitors, especially since recent local declines in harbour seal numbers while grey seal numbers remained stable or increased at their European core distributions. A better understanding of the interactions between these species is critical for conservation efforts. This study aimed to identify the trophic niche overlap between harbour and grey seals at the southern limit of their European range, in the Baie de Somme (BDS, Eastern English Channel, France), where numbers of resident harbour seals and visiting grey seals are increasing exponentially. Dietary overlap was identified from scat contents using hierarchical clustering. Isotopic niche overlap was quantified using δ¹³C and δ¹⁵N isotopic values from whiskers of 18 individuals, by estimating isotopic standard ellipses with a novel hierarchical model developed in a Bayesian framework to consider both intraindividual variability and interindividual variability. Foraging areas of these individuals were identified from telemetry data. The three independent approaches provided converging results, revealing a high trophic niche overlap due to consumption of benthic flatfish. Two diet clusters were dominated by either small or large benthic flatfish; these comprised 85.5% [CI95%: 80.3%–90.2%] of harbour seal scats and 46.8% [35.1%–58.4%] of grey seal scats. The narrower isotopic niche of harbour seals was nested within that of grey seals (58.2% [22.7%–100%] overlap). Grey seals with isotopic values similar to harbour seals foraged in coastal waters close to the BDS alike harbour seals did, suggesting the niche overlap may be due to individual grey seal strategies. Our findings therefore provide the basis for potential competition between both species (foraging on benthic flatfish close to the BDS). We suggest that a continued increase in seal numbers and/or a decrease in flatfish supply in this area could cause/amplify competitive interactions and have deleterious effects on harbour seal colonies.     

Morphometrics,body condition,and growth of the ringed seal (Pusa hispida saimensis) in Lake Saimaa: Implications for conservation

Morphometrics and growth of the critically endangered Saimaa ringed seal (Pusa hispida saimensis), which inhabits a freshwater lake in Finland were studied using data from 344 carcasses. This study presents the first detailed information on ringed seal pup growth and body condition from birth to the age of one year. Newborn pups were on average 68 cm long and weighed 5 kg. Pups attained the majority of their first year growth during the nursing period. Body condition and growth declined after weaning, but pups recovered from postweaning nutritional deprivation at the age of 8 mo. The seals achieved their maximum body length, girth, and mandible size around the age of 4 yr, and asymptotic body mass two years later. Baculum growth indicated that males reached sexual maturity at age 5–6 yr. The Saimaa ringed seals' asymptotic body length and mass were 132 cm and 59 kg, respectively, which is similar to medium sized marine ringed seals. Saimaa ringed seals' survival to adulthood is extremely low due to high bycatch mortality; furthermore climate change may hamper pup growth and elevate mortality. Therefore we recommend continuation of fishing closures to improve pup survival.     

Where have all the fathers gone? An extensive microsatellite analysis of paternity in the grey seal (Halichoerus grypus)

Microsatellites were used to conduct an extensive analysis of paternity of grey seals from two Scottish breeding colonies at North Rona (n = 1189) and the Isle of May (n = 694), spanning more than a decade. A maximum of 46% of pups at North Rona and 29% of pups at the Isle of May could be allocated a father, even though the majority of candidate males for specific study sites within each colony were believed to have been sampled. Based on the paternities which could be assigned, both colonies showed evidence of reproductive skew, apparently due to the presence of approximately five males who were exceptionally successful. Some males were assigned paternities at least 10 years before, and colleagues 10 years after, being sampled, implying a reproductive lifespan of at least 10 years, and there are indications that the real maximum lies in the range 15-20 years. Male grey seals appear to have at least two breeding strategies they can adopt. On land, some males benefit from a traditionally polygynous system. However, between 50 and 70% of grey seal pups born at a particular colony are not fathered by males who are likely to be sampled by us, implying that these males seldom venture ashore here. We conclude that aquatic mating may play a much larger role in the grey seal than has previously been thought.     

Trichinella nativa in grey seal Halichoerus grypus: spill-over from a highly endemic terrestrial ecosystem

Trichinella spp. infections of marine mammals pose a human health risk in Arctic regions where game meat is an important part of the diet. In the last decade, the grey seal population of the sub-arctic Baltic Sea has reached a level at which hunting is possible and seal meat is now available for food. We conducted a survey on the occurrence of Trichinella spp. in grey seals Halichoerus grypus (n = 171) and ringed seals Phoca hispida botnica (n = 56) of the Baltic Sea in the coastal waters of Finland, a highly Trichinella sp. endemic area. Muscle samples were examined by a mechanically assisted digestion method during 2006-2010. One grey seal was positive for Trichinella nativa , while all samples from ringed seals were negative. Even though just 1 grey seal was infected, the finding here emphasizes the importance of proper meat inspection of seals intended for human consumption, especially in areas with high infection pressure.     

Diet composition and seasonal feeding patterns of a freshwater ringed seal (Pusa hispida saimensis)

The Saimaa ringed seal (Pusa hispida saimensis) is one of the few freshwater seal populations worldwide. The major conservation issue of this critically endangered population is bycatch mortality. We used digestive tract content and stable isotopes (δ¹³C and δ¹⁵N) to estimate the diet and seasonal feeding patterns for gaining better understanding of the seals feeding habits and potential conservation implications. The diet was similar across age groups. Altogether 15 fish species were identified and the most important were smelt (Osmerus eperlanus), ruff (Gymnocephalus cernuus), perch (Perca fluviatilis), vendace (Coregonus albula) and cyprinids. The high δ¹⁵N values suggested that the seals lose weight during winter and spring. Additionally the drop in δ¹⁵N values indicated that pups start to recover from postweaning stress and gain weight around the age of 6 mo. The isotope values differed regionally, which emphasizes that samples from consumers and prey should be collected from the same regions to improve interpretation of the stable isotopic results. Overall, diet composition suggests minimal to nonexistent competition with commercial or recreational fishing. However, observed weight loss of pups during summer may be related to higher risk of bycatch and this should be taken into account when planning temporal fishing closures.     

Giardiasis in pinnipeds from eastern Canada

Cysts of Giardia sp. were detected in feces from the rectum of 20 of 74 pinnipeds examined from the eastern coast of Canada in 1997 and 1998 using a monoclonal antibody technique. Infected pinnipeds included 15 adult harp seals (Phoca groenlandica), four adult grey seals (Halichoerus grypus), and one juvenile harbor seal (Phoca vitulina). Cysts were not detected in 15 seal pups <1-yr-old. The highest prevalence (50%) occurred in adult harp seals collected near the Magdalen Islands in the Gulf of St. Lawrence. The overall prevalence of Giardia sp. in grey and harbor seals, excluding pups, from the Gulf and St. Lawrence estuary was 23%. Feces from 11 beluga (Delphinapterus leucas) and one northern bottle-nosed whale (Hyperoodon ampullatus) stranded in the St. Lawrence estuary were negative for Giardia sp. cysts. The significance of Giardia sp. in marine mammals, shown here for the first time in eastern coastal Canada, is unknown.     

Philopatry, Site Fidelity and Local Kin Associations within Grey Seal Breeding Colonies

Abstract Colonially breeding animals such as grey seals typically have a discrete number of breeding sites. The extent to which offspring are philopatric (return to breed at their natal site) and the prevalence of philopatry by sex of pup has fundamental consequences for the social and genetic structure within and between each colony.
Grey seals born and marked by tagging and cohort brands at colonies on North Rona, Outer Hebrides since 1960 and at the Isle of May, Firth of Forth since 1981 have shown philopatry. Overall re-sight rates of 1620 pups tagged at North Rona and 1667 pups at the Isle of May ranged from 0 to 17%. Although most evidence of philopatry relates to females, males at each colony displayed philopatry. In addition, females born at N. Rona pupped closer to their natal sites than would be expected by chance (p = 0.005), providing evidence of fine scale natal site fidelity. Females born at the Isle of May did not show the same degree of fine scale natal site fidelity, but there was considerable individual variation. The spatial scale of philopatry shown by seals differed according to the local area within each island. Fidelity of known adult females to pupping sites at both colonies was high. In addition, we found an instance of mother and daughter pupping together away from the daughter's natal site.
These data: (i) provide evidence of philopatry in both sexes at each site; (ii) describe occurrences of fine scale philopatry at both sites; (iii) show that mothers and offspring occupied the same areas on the colony, suggesting the possibility of highly related groups within colonies, which would provide conditions for kin-specific altruistic behaviours; (iv) suggest the possibility of individual or kin recognition, even though contact between mothers and offspring has been thought to cease after the 18 d lactation period.     

Population status, trends and a re-examination of the hypotheses explaining the recent declines of the southern elephant seal Mirounga leonina

1. Between the 1950s and 1990s the southern elephant seal Mirounga leonina underwent large decreases in population size throughout most of its breeding range in the Southern Ocean. While current population estimates suggest a recent recovery, some breeding populations have continued to decrease in recent years (Macquarie and Marion Islands), others have either remained stable (South Georgia, Kerguelen and Heard Island) or have increased (Peninsula Valdés, Argentina). 2. Intrinsic hypotheses for patterns of regional decline include factors that are affected by density-dependent mechanisms: (i) paucity of males, (ii) population ‘overshoot’ and (iii) pandemic disease. Extrinsic hypotheses include (iv) predation, (v) competition with fisheries concerns, (vi) interspecific competition, (vii) environmental change and (viii) human disturbance. Of the eight hypotheses proposed and examined here, we conclude that three can be discounted (i, v, viii), three are unlikely, but may require more testing (ii, iii, iv) and two are plausible (vi, vii). 3. The interspecific competition hypothesis is difficult to test because it requires the simultaneous monitoring of species that overlap directly with elephant seals, many of which have not been identified or little is known. However, an analysis of the relationship between log variance and log abundance (Taylor's power law) for populations of southern and northern elephant seals suggests that interspecific competition is not a significant factor in the decline of the southern elephant seal. 4. The hypothesis that decreases in southern elephant seal populations between the 1950s and 1990s were caused by the environmental change is the easiest to test and most plausible of the hypotheses. We propose a framework by which to test this hypothesis to determine how food availability affects individual survival.     

Differential adult survival at close seabird colonies: The importance of spatial foraging segregation and bycatch risk during the breeding season

Marine megafauna, including seabirds, are critically affected by fisheries bycatch. However, bycatch risk may differ on temporal and spatial scales due to the uneven distribution and effort of fleets operating different fishing gear, and to focal species distribution and foraging behavior. Scopoli's shearwater Calonectris diomedea is a long‐lived seabird that experiences high bycatch rates in longline fisheries and strong population‐level impacts due to this type of anthropogenic mortality. Analyzing a long‐term dataset on individual monitoring, we compared adult survival (by means of multi‐event capture–recapture models) among three close predator‐free Mediterranean colonies of the species. Unexpectedly for a long‐lived organism, adult survival varied among colonies. We explored potential causes of this differential survival by (1) measuring egg volume as a proxy of food availability and parental condition; (2) building a specific longline bycatch risk map for the species; and (3) assessing the distribution patterns of breeding birds from the three study colonies via GPS tracking. Egg volume was very similar between colonies over time, suggesting that environmental variability related to habitat foraging suitability was not the main cause of differential survival. On the other hand, differences in foraging movements among individuals from the three colonies expose them to differential mortality risk, which likely influenced the observed differences in adult survival. The overlap of information obtained by the generation of specific bycatch risk maps, the quantification of population demographic parameters, and the foraging spatial analysis should inform managers about differential sensitivity to the anthropogenic impact at mesoscale level and guide decisions depending on the spatial configuration of local populations. The approach would apply and should be considered in any species where foraging distribution is colony‐specific and mortality risk varies spatially.