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Ursula Siebert - One of the best experts on this subject based on the ideXlab platform.
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Assessing Seal carcasses potentially subjected to Grey Seal predation.
Scientific reports, 2021Co-Authors: Abbo Van Neer, Stephanie Gross, Tina Kesselring, Miguel L. Grilo, Eva Ludes-wehrmeister, Giulia Roncon, Ursula SiebertAbstract:In order to conduct an objective evaluation of potential ecological effects of Grey Seal predation on marine mammals, it is essential to establish a broad knowledge base helping in the thorough identification of such cases during post-mortem examination. The aim of this work is to report and discuss outcomes resulting from a retrospective evaluation of harbour (Phoca vitulina) and Grey Seal (Halichoerus grypus) stranding and necropsy data (n = 3274). In addition, the results are compared to a recent case of definite Grey Seal predation from Germany as well as reports from other countries. Carcasses potentially subjected to Grey Seal predation show severe lacerations with a circular pattern leaving a smooth, linear and cut-like wound margin. Large parts of skin and underlying tissue are detached from the body and loss of blubber is common. Occurrence frequencies of encountered lesions are presented and a list of parameters to be used for the assessment of similar cases as well as a complementary decision tree are suggested. With the proposed parameters, categories and tools, a baseline can be built in order to facilitate the standardised recognition of predation cases during post-mortem examinations of Seals between groups working with populations across several geographic ranges.
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Assessing harbour porpoise carcasses potentially subjected to Grey Seal predation.
Scientific reports, 2020Co-Authors: Abbo Van Neer, Stephanie Gross, Tina Kesselring, Miguel L. Grilo, Eva Ludes-wehrmeister, Giulia Roncon, Ursula SiebertAbstract:As a follow-up on the data presented for Seals, we herein report and discuss outcomes resulting from a retrospective evaluation of harbour porpoise stranding and necropsy data from Schleswig-Holstein, Germany (n = 4463) to enable an objective evaluation of potential ecological effects of Grey Seal predation on porpoises. Results are compared to a recent case of definite Grey Seal predation as well as to reports from other countries. Porpoise carcasses potentially subject to Grey Seal predation show severe lacerations, with large parts of skin and underlying tissue being detached from the body. Loss of blubber tissue is common. Based on the occurrence frequencies of encountered lesions, a list of parameters as well as a complementary decision tree are suggested to be used for future assessments. The results shown add to an increasingly standardised assessment protocol of suspected Grey Seal predation cases making respective results comparable between different areas and countries. The usage of a standardised protocol may increase the awareness of Grey Seal predation and the reporting of such cases. By this, differences in the predation and feeding patterns as well as the potential ecological relevance of this behaviour may be elucidated.
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Male Grey Seal commits fatal sexual interaction with adult female harbour Seals in the German Wadden Sea
Scientific Reports, 2020Co-Authors: Simon Rohner, Stephanie Gross, Peter Wohlsein, Amir Abdulmawjood, Kirsten Hülskötter, Madeleine Plötz, Jutta Verspohl, Ludwig Haas, Ursula SiebertAbstract:Males of several Seal species are known to show aggressive copulating behaviour, which can lead to injuries to or suffocation of females. In the North Sea, Grey Seal predation on harbour Seals including sexual harassment is documented and represents violent interspecific interaction. In this case series, we report pathological and molecular/genetic findings of 11 adult female harbour Seals which were found dead in Schleswig–Holstein, Germany, within 41 days. Several organs of all animals showed haemorrhages and high loads of bacteria, indicating their septic spread. All females were pregnant or had recently been pregnant. Abortion was confirmed in three cases. Lacerations were seen in the uterus and vagina in six cases, in which histology of three individuals revealed severe suppurative inflammation with intralesional spermatozoa. Molecular analysis of vaginal swabs and paraffin-embedded samples of the vagina identified Grey Seal DNA, suggesting violent interspecific sexual interaction with fatal outcome due to septicaemia. This is the first report of female harbour Seals dying after coercive copulation by a male Grey Seal in the Wadden Sea.
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EG-Seals Grey Seal surveys in the Wadden Sea and Helgoland in 2019-2020 : Less disturbance?
2020Co-Authors: Sophie Brasseur, Anders Galatius, Ursula Siebert, Armin Jeß, Peter Körber, Jonas Teilmann, F. Carius, B. Diederichs, Jessica Schop, C. Bie ThostesenAbstract:The Wadden Sea areas in Denmark, Germany and the Netherlands were surveyed for Grey Seals (Halichoerus grypus) during the pupping season (November 2019 –January 2020) and during the moulting period (March-April 2020) by means of coordinated aerial surveys and in the case of Helgoland, by land based counts. These surveys provide data on the changes in Grey Seal occupancy of the area and changes in the local breeding population. In part, the Grey Seals observed in the Wadden Sea during the moult may breed in the UK where the largest part of the greater North Sea population are observed (~100.000 individuals).
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Pathological findings in North Sea and Baltic Grey Seal and harbour Seal intestines associated with acanthocephalan infections.
Diseases of aquatic organisms, 2020Co-Authors: Jan Lakemeyer, Peter Wohlsein, Kristina Lehnert, Benno Woelfing, Iwona Pawliczka, Martin Silts, Michael Dähne, Vivica Von Vietinghoff, Ursula SiebertAbstract:Grey Seals Halichoerus grypus and harbour Seals Phoca vitulina are common Seal species in the North and Baltic seas and final hosts of Corynosoma acanthocephalans. C. strumosum and C. magdaleni infect the small intestines of both Seal species. In contrast to harbour Seals, Baltic Grey Seals in the past have regularly displayed severe C. semerme infections in the caecum and colon, with associated tunica muscularis hypertrophy, inflammation and ulcerations as part of the Baltic Seal disease complex (BSDC). Pathogenesis and correlation of acanthocephalan infections with these lesions are still unknown. This study describes the intestinal pathology and parasitic distribution in each Seal species. Grey Seal (n = 83) and harbour Seal (n = 1156) intestines of all age groups and sexes, collected in Poland, Germany and Estonia from 1998 to 2017, were investigated. Most harbour Seals came from the North Sea, whereas Grey Seals were predominantly derived from the Baltic Sea. Both species featured mild to moderate small intestinal infections. Grey Seals showed colonic infections not found in harbour Seals and featured a chronic erosive to ulcerative, eosinophilic or lympho-plasmacytic colitis with tunica muscularis hypertrophy, indicating still prevailing clinical signs of the BSDC. Harbour Seals displayed granulomatous, eosinophilic, lympho-plasmacytic or catarrhal enteritis. The prevalence of acanthocephalan infections in harbour Seals increased from 2012 onwards. Furthermore, significant associations between acanthocephalan infection and the presence of intestinal inflammation were found for both Seal species. This study suggests that the level of acanthocephalan infection and associated lesions are suitable Seal population health indicators, with the colon being a specific target organ for Baltic Grey Seal health monitoring.
Kimberley A Bennett - One of the best experts on this subject based on the ideXlab platform.
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predicting consequences of pop induced disruption of blubber glucose uptake mass gain rate and thyroid hormone levels for weaning mass in Grey Seal pups
Environment International, 2021Co-Authors: Kimberley A Bennett, Simon Moss, Kelly J Robinson, Georges Scholl, Cathy Debier, Jeanpierre Thome, Gauthier Eppe, Holly C Armstrong, Alexandra Tranganida, Ailsa J HallAbstract:Persistent organic pollutants (POPs) are endocrine disruptors that alter adipose tissue development, regulation and function. Top marine predators are particularly vulnerable because they possess large fat stores that accumulate POPs. However, links between endocrine or adipose tissue function disruption and whole animal energetics have rarely been investigated. We predicted the impact of alterations to blubber metabolic characteristics and circulating thyroid hormone (TH) levels associated with polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) on suckling mass gain and weaning mass in wild Grey Seal pups. Glucose uptake by inner blubber was a strong predictor of whole animal mass gain rate, which in turn, resulted in heavier weaning mass. Weaning mass was predicted to increase by 3.7 ± 1.59 (sem) %, through increased mass gain rate, in the absence of the previously reported suppressive effect of dioxin-like PCB (DL-PCBs) on blubber glucose uptake. PBDEs were, conversely, associated with faster mass gain. Alleviation of this effect was predicted to reduce weaning mass by 6.02 ± 1.86% (sem). To better predict POPs effects on energy balance, it is crucial to determine if and how PBDEs promote mass gain in Grey Seal pups. Weaning mass was negatively related to total T3 (TT3) levels. A 20% (range = 9.3-31.7%) reduction in TT3 by DL-PCBs partially overcame the effect of DL-PCB -mediated reduction in blubber glucose uptake. Overall, DL-PCBs were thus predicted to reduce weaning mass by 1.86 ± 1.60%. Organohalogen impacts on whole-animal energy balance in Grey Seal pups appear to partially offset each other through opposing effects on different mechanisms. POP effects were generally minor, but the largest POP-induced reductions in weaning mass were predicted to occur in pups that were already small. Since weaning mass is positively related to first-year survival, POPs may disproportionately affect smaller individuals, and could continue to have population-level impacts even when levels are relatively low compared to historical values. Our findings show how in vitro experiments combined with measurements in vivo can help elucidate mechanisms that underpin energy balance regulation and help to quantify the magnitude of disruptive effects by contaminants and other stressors in wildlife.
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investigating decadal changes in persistent organic pollutants in scottish Grey Seal pups
Aquatic Conservation-marine and Freshwater Ecosystems, 2019Co-Authors: Kelly J Robinson, Alisa J Hall, Georges Scholl, Cathy Debier, Jeanpierre Thome, Gauthier Eppe, Catherine Adam, Kimberley A BennettAbstract:Persistent organic pollutants (POPs) remain a risk to marine ecosystem health. POPs accumulate in fat tissue and are biomagnified up through food webs, generating high concentrations in apex predators, including marine mammals. Seals are thus often cited as sentinels of marine environment POP levels. Measuring changes across decadal timescales in these animals is key to understanding the effectiveness of regulations controlling POPs, predicting health, population, and ecosystem level impacts, and informing conservation and management strategies. Information on recent changes in legacy POPs in Seals is relatively sparse, however, and datasets are not always continuous in the absence of dedicated POP monitoring programmes. Here, POP concentrations in the blubber of weaned Grey Seal pups from the Isle of May, Scotland, were compared between studies investigating POP impacts on survival and energy balance in 2002, and in 2015–17. By 2017, the total dioxin‐like polychlorinated biphenyls (ΣDL‐CBs) and the total non‐dioxin‐like polychlorinated biphenyls (ΣNDL‐CBs) had decreased to ~75% of 2002 levels. The organochlorine pesticides (OCPs), dichlorodiphenyltrichoroethane (ΣDDT), dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyldichoroethane (DDD), and some CB congeners, did not fall over the 15‐year period; however, the power to detect small changes at low concentrations was limited. High DDE and a lack of change in DDD are likely to reflect the low excretion of DDT metabolites, rather than recent exposure. The limited change in many POPs over 15 years suggest that risks remain for energy balance, endocrine status, and immune function in Grey Seal pups, with contingent effects on conservation and management objectives for this species. These data highlight the need for long‐term datasets and parity in sampling and analytical methods to evaluate continuing impacts of POPs in Grey Seals and on marine ecosystems more widely.
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effects of handling regime and sex on changes in cortisol thyroid hormones and body mass in fasting Grey Seal pups
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2012Co-Authors: Kimberley A Bennett, Simon Moss, Paddy P Pomeroy, John R Speakman, M A FedakAbstract:article i nfo Survival of Seal pups may be affected by their ability to respond appropriately to stress. Chronic stress can adversely affect secretion of cortisol and thyroid hormones, which contribute to the control of fuel utilisation. Repeated handling could disrupt the endocrine response to stress and/or negatively impact upon mass changes during fasting. Here we investigated the effects of handling regime on cortisol and thyroid hormone levels, and body mass changes, in fasting male and female Grey Seal pups (Halichoerus grypus). Females had higher thyroid hormone levels than males throughout fasting and showed a reduction in cortisol midway through the fast that was not seen in males. This may reflect sex-specific fuel allocation or development. Neither handling frequency nor cumulative contact time affected plasma cortisol or thyroid hormone levels, the rate of increase in cortisol over the first five minutes of physical contact or the pattern of mass loss during fasting in either sex. The endocrine response to stress and the control of energy balance in Grey Seal pups appear to be robust to repeated, short periods of handling. Our results suggest that routine handling should have no additional impact on these animals than general disturbance caused by researchers moving around the colony.
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effects of mass and body composition on fasting fuel utilisation in Grey Seal pups halichoerus grypus fabricius an experimental study using supplementary feeding
The Journal of Experimental Biology, 2007Co-Authors: Kimberley A Bennett, Simon Moss, Paddy P Pomeroy, John R Speakman, M A FedakAbstract:This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in Grey Seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86-99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of Grey Seal pups.
M A Fedak - One of the best experts on this subject based on the ideXlab platform.
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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
PLOS ONE, 2012Co-Authors: Lars Boehme, Mike O. Hammill, M A Fedak, Dave Thompson, Don Bowen, Garry B. StensonAbstract: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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effects of handling regime and sex on changes in cortisol thyroid hormones and body mass in fasting Grey Seal pups
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2012Co-Authors: Kimberley A Bennett, Simon Moss, Paddy P Pomeroy, John R Speakman, M A FedakAbstract:article i nfo Survival of Seal pups may be affected by their ability to respond appropriately to stress. Chronic stress can adversely affect secretion of cortisol and thyroid hormones, which contribute to the control of fuel utilisation. Repeated handling could disrupt the endocrine response to stress and/or negatively impact upon mass changes during fasting. Here we investigated the effects of handling regime on cortisol and thyroid hormone levels, and body mass changes, in fasting male and female Grey Seal pups (Halichoerus grypus). Females had higher thyroid hormone levels than males throughout fasting and showed a reduction in cortisol midway through the fast that was not seen in males. This may reflect sex-specific fuel allocation or development. Neither handling frequency nor cumulative contact time affected plasma cortisol or thyroid hormone levels, the rate of increase in cortisol over the first five minutes of physical contact or the pattern of mass loss during fasting in either sex. The endocrine response to stress and the control of energy balance in Grey Seal pups appear to be robust to repeated, short periods of handling. Our results suggest that routine handling should have no additional impact on these animals than general disturbance caused by researchers moving around the colony.
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effects of mass and body composition on fasting fuel utilisation in Grey Seal pups halichoerus grypus fabricius an experimental study using supplementary feeding
The Journal of Experimental Biology, 2007Co-Authors: Kimberley A Bennett, Simon Moss, Paddy P Pomeroy, John R Speakman, M A FedakAbstract:This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in Grey Seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86-99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of Grey Seal pups.
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status and conservation of the Grey Seal halichœrus grypus in france
Biological Conservation, 2005Co-Authors: Cecile Vincent, M A Fedak, Bernie J Mcconnell, L Meynier, C Saintjean, Vincent RidouxAbstract:Abstract We investigated the status of the Grey Seal in the Molene archipelago, western Brittany, where a Marine National Park is planned. We combined regular censuses, photo-identification and satellite telemetry to investigate trends in Grey Seal abundance, site fidelity, individual movements and haulout site use. Individual movements and seasonal variations in abundance suggest that the Seals used the Molene archipelago alternatively with other haulout sites of the South-west British Isles during their annual cycle. Nine out of 16 Seals fitted with Satellite Relay Data Loggers (SRDLs) moved to the Isles of Scilly, English Cornwall, Wales or the Channel islands. On average the Seals spent 85% of their time Near Haulout, 56.8% of which in the Molene archipelago. Overall the Seals spent 66% of their tracking time within the boundaries of the Marine National Park. From 1997 to 2000 in the Molene archipelago, we observed a peak in number during the moulting season (mean = 49.8 Seals) and a lower abundance during the breeding season (mean = 38.3 Seals). The sex ratio was strongly skewed towards males during the moult (between 3.1 and 5.3–1), and was close to 1:1 during the summer. Inter-annual site fidelity outside the breeding season was very high, varying from 70% to 95% of identified Seals, suggesting that the observed movements constitute rotations rather than random dispersion. From 1991/1994 to 1997/2000, the mean number of Seals counted at haulout sites increased by 7%, close to the rates of increase observed in the core population of the British Isles at the same period. The Marine National Park may be too restricted for the overall conservation of the population but management plans should be aimed at preserving the characteristics of the habitat for the Grey Seal.
D. J. Boness - One of the best experts on this subject based on the ideXlab platform.
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The rate of fertilization in male mating tactics of the polygynous Grey Seal.
Molecular ecology, 2004Co-Authors: Damian C. Lidgard, D. J. Boness, W. D. Bowen, Jim I. Mcmillan, Robert C. FleischerAbstract:Studies using molecular markers have shown that some Grey Seal males may be gaining success through exhibiting alternative mating tactics. We estimated the probability of fertilization success of Grey Seal males exhibiting the primary tactic of female defence and one alternative tactic of mating with departing females on Sable Island, Nova Scotia, Canada, during the breeding seasons of 1997-2002. Although the fertilization rate of the primary tactic (27-43%) was greater than that of the alternative tactic (10-12%), these low rates indicate the potential fitness value of alternative mating tactics in this size-dimorphic pinniped species.
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Mother-pup vocal recognition in the Grey Seal (Halichoerus grypus) of Sable Island, Nova Scotia, Canada
Journal of Zoology, 2000Co-Authors: Samantha Mcculloch, D. J. BonessAbstract:Parental recognition of offspring would be expected to evolve among densely populated species in which parental investment is large, and separations of the mother±pup pair are frequent. Although otariids present a well-developed system of mutual vocal recognition, evidence in phocids is weak. Furthermore, allo-suckling is prevalent in some species and may re¯ect confusion over the identity of pups. The vocalizations of Grey Seal Halichoerus grypus pups have been found to be stereotyped and individually distinctive on the Isle of May, Scotland. However, playback experiments showed that mothers fail to discriminate between the vocalizations of their pup and a non-®lial pup. Moreover, widespread allosuckling was observed. In contrast, Grey Seals on Sable Island, Nova Scotia, a population reproductively isolated from that of the Isle of May, show very little allo-suckling. This may re¯ect the presence of a recognition system that does not seem to be present on the Isle of May. During the 1999 breeding season on Sable Island, vocalizations of Grey Seal pups were recorded and playback experiments carried out to determine whether female Grey Seals respond differently to the playback of vocalizations of their own pup, a familiar pup and an unfamiliar pup. Grey Seal mothers were found to make signi®cantly more head turns and body movements towards the loudspeaker during the playback of their own pup call than during the playback of a familiar or unfamiliar pup call. In addition, there was no evidence of an effect of pup age. This suggests that female Grey Seals can discriminate between pup calls using the stereotyped and individually distinctive vocalizations of their pup, and that different selective pressures may be in operation between the Sable Island and Isle of May colonies.
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Mother–pup vocal recognition in the Grey Seal (Halichoerus grypus) of Sable Island, Nova Scotia, Canada
Journal of Zoology, 2000Co-Authors: Samantha Mcculloch, D. J. BonessAbstract:Parental recognition of offspring would be expected to evolve among densely populated species in which parental investment is large, and separations of the mother–pup pair are frequent. Although otariids present a well-developed system of mutual vocal recognition, evidence in phocids is weak. Furthermore, allo-suckling is prevalent in some species and may reflect confusion over the identity of pups. The vocalizations of Grey Seal Halichoerus grypus pups have been found to be stereotyped and individually distinctive on the Isle of May, Scotland. However, playback experiments showed that mothers fail to discriminate between the vocalizations of their pup and a non-filial pup. Moreover, widespread allo-suckling was observed. In contrast, Grey Seals on Sable Island, Nova Scotia, a population reproductively isolated from that of the Isle of May, show very little allo-suckling. This may reflect the presence of a recognition system that does not seem to be present on the Isle of May. During the 1999 breeding season on Sable Island, vocalizations of Grey Seal pups were recorded and playback experiments carried out to determine whether female Grey Seals respond differently to the playback of vocalizations of their own pup, a familiar pup and an unfamiliar pup. Grey Seal mothers were found to make significantly more head turns and body movements towards the loudspeaker during the playback of their own pup call than during the playback of a familiar or unfamiliar pup call. In addition, there was no evidence of an effect of pup age. This suggests that female Grey Seals can discriminate between pup calls using the stereotyped and individually distinctive vocalizations of their pup, and that different selective pressures may be in operation between the Sable Island and Isle of May colonies.
Mike O. Hammill - One of the best experts on this subject based on the ideXlab platform.
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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
PLOS ONE, 2012Co-Authors: Lars Boehme, Mike O. Hammill, M A Fedak, Dave Thompson, Don Bowen, Garry B. StensonAbstract: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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Winter foraging by a top predator, the Grey Seal Halichoerus grypus, in relation to the distribution of prey
Marine Ecology Progress Series, 2012Co-Authors: Valerie Harvey, Mike O. Hammill, Douglas P. Swain, Greg A. Breed, Christian Lydersen, Kit M. KovacsAbstract:Identifying foraging areas of individuals and correlating them with potential food resources allows for a better understanding of predator-prey relationships. Herein, we examine whether Grey Seal movements were associated with overwintering concentrations of several com- mercial fish species in the Cabot Strait, Atlantic Canada, using data from satellite transmitters deployed on Grey Seals (between 1993 and 2005) and winter bottom-trawl survey data (1994 to 1997). The distribution of searching effort by male Grey Seals varied throughout the winter. In early winter, males concentrated their movements around St. Paul's Island. In late winter, they were found to the southeast of this area, where females also occurred. The fish community dif- fered between apparent foraging and non-foraging areas. Densities of small plaice, hake and red- fish, large herring and cod of all sizes were relatively high in the male Grey Seal foraging zones; female foraging zones were characterized by higher densities of small plaice and redfish and large cod. Areas where Grey Seal foraging was not concentrated were characterized by high densities of medium and large redfish as well as large turbot and witch flounder. Diet samples are needed to determine whether Grey Seals are feeding on the fish groups that distinguish foraging from non- foraging areas or alternatively on other prey that occur in the same areas.
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covariation between Grey Seal halichoerus grypus abundance and natural mortality of cod gadus morhua in the southern gulf of st lawrence
Canadian Journal of Fisheries and Aquatic Sciences, 2005Co-Authors: G A Chouinard, Mike O. Hammill, Douglas P. Swain, G A PoirierAbstract:More than 10 years after the collapse of Atlantic cod (Gadus morhua) fisheries in Canada, the role of increased Seal populations in the decline and lack of recovery of the stocks continues to be discussed. Using removals and abundance indices from synthetic populations, we found that sequential population analysis can uncover trends in natural mortality. We used this approach to examine variation in natural mortality (M) of southern Gulf of St. Lawrence cod. M increased from the late 1970s to the mid-1990s but declined slightly recently. Results were consistent with previous work indicating that M increased in the 1980s. Changes in estimated M for this cod stock matched fluctuations in Grey Seal (Halichoerus grypus) abundance. The increase in Grey Seal abundance from the late 1970s to the mid-1990s corresponded with the increase in estimated M of cod over this time period. The correspondence between Seal abundance and M of cod supports the hypothesis that Seal predation may be a cause of increased M. Howe...
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Pup production and population trends of the Grey Seal (Halichoerus grypus) in the Gulf of St. Lawrence
Canadian Journal of Fisheries and Aquatic Sciences, 1998Co-Authors: Mike O. Hammill, Garry B. Stenson, Ransom A. Myers, W T StoboAbstract:Grey Seal (Halichoerus grypus) pup production of the Gulf of St. Lawrence component of the Northwest Atlantic Grey Seal population was determined for the 1984-1986 and 1989-1990 periods using mark-...
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Consumption of cod by the Northwest Atlantic Grey Seal in Eastern Canada
Developments in Marine Biology, 1995Co-Authors: Mike O. Hammill, M.s. Ryg, B. MohnAbstract:Abstract The Northwest Atlantic Grey Seal is perceived by fishermen as having a negative impact on commercial fish stocks, particularly Atlantic cod. Both the Sable Island and Gulf of St. Lawrence components of this population have increased substantially over the past several decades, such that total population size in eastern Canada in 1993 was estimated at about 140,000 animals. Estimated total consumption of cod by Grey Seals is estimated to have increased from
