Behavioural and pathological insights into a case of active cannibalism by a grey seal (Halichoerus grypus) on Helgoland, Germany

Neer, Abbo van; Groß, Stephanie; Kesselring, Tina; Wohlsein, P.; Leitzen, Eva; Siebert, Ursula

doi:10.1016/j.seares.2019.03.004

Cited by 11 publications

(21 citation statements)

References 24 publications

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“…Carcasses were collected through the stranding network of Schleswig-Holstein, Germany 25,26 and a necropsy was performed as described in Siebert et al 26 . In contrast to seals, in German waters no case of a harbour porpoise being preyed on by a grey seal has to date been fully documented, comparable to what has been described in seals by van Neer et al 11 . In order to validate the documented wound patterns, one case of grey seal predation which was confirmed using genetic methods and was therefore labelled a "definite" case was used 8 .…”

Section: Methodssupporting

confidence: 68%

“…For seals, in the majority of cases, little to no skin is missing (skin missing in 49% of likely cases 14 ), whereas in porpoises, a considerable number of cases (81% of likely cases) have been found where skin is missing (parameter 7). Grey seals have been described to mainly target the energy rich blubber tissue of their prey 11,14 . For the elastic and robust seal skin, this is done by scraping off the blubber with the teeth.…”

Section: Discussionmentioning

confidence: 99%

“…Since the first scientific publication introducing the hypothesis that grey seals (Halichoerus grypus) utilise harbour porpoises (Phocoena phocoena) as a prey resource 1 , several publications have proven the hypothesis to be true [2][3][4][5][6][7][8] . Furthermore, it was shown that this behaviour is not restricted to specific regions but potentially occurs throughout the North Sea and beyond 9 , with not only porpoises but also harbour and grey seals being utilised as prey [10][11][12] .…”

Section: Assessing Harbour Porpoise Carcasses Potentially Subjected Tmentioning

confidence: 99%

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Assessing harbour porpoise carcasses potentially subjected to grey seal predation

Neer¹,

Groß²,

Kesselring³

et al. 2020

Sci Rep

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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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Section: Methodssupporting

confidence: 68%

Section: Discussionmentioning

confidence: 99%

Section: Assessing Harbour Porpoise Carcasses Potentially Subjected Tmentioning

confidence: 99%

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Assessing harbour porpoise carcasses potentially subjected to grey seal predation

Neer¹,

Groß²,

Kesselring³

et al. 2020

Sci Rep

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“…Septicaemia with β-haemolytic streptococci and/ or E. coli is an important cause of death of adult harbour seals from German waters, which in many cases is the result of major pathologies such as gastritis, intestinal volvulus or mastitis. Active cannibalism among grey seals, also in the North Sea, has been previously reported 39 - 42 . Predation on other marine mammals, including harbour seals, adds to this aggressive behaviour and might represent a feeding strategy 43 - 45 .…”

Section: Introductionmentioning

confidence: 87%

Male grey seal commits fatal sexual interaction with adult female harbour seals in the German Wadden Sea

Rohner

Hülskötter

Groß

et al. 2020

Sci Rep

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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 paraffinembedded 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. There are three main forms of how males sexually coerce females in animal societies: intimidation (punishment for denial of mating), harassment (increase of costs for females if they refuse to mate) and forced copulation (use of superior speed or physical strength to copulate with the female by force) 1. Sexual coercion is widely distributed among animal clades and seen in birds 2,3 , mammals 4,5 and invertebrates 6,7. Coercive behaviour of males reflects the competition for limited resources, in this case fertile females 8. It may be more common among species with polygynous mating systems 9 , including pinnipeds, where the dominance over a harem results in a substantial breeding reward for the male 10-12. Harassment and mating attempts can result in injuries to the females, such as bite wounds, mostly in the region of the face and the neck 12. Suffocation by being crushed by substantially larger males may even lead to death, as witnessed in New Zealand sea lions (Phocarctos hookeri) 13. Such aggression seen in adult male pinnipeds is usually focused on conspecifics and are mainly displayed in land breeding species like otariids and some phocids including grey seals (Halichoerus grypus) and elephant seals (Mirounga spp.) 14. Hybrids as the result of interspecific mating among sympatric species are not uncommon in the animal kingdom 15,16. Anatomical features and behavioural aspects including mate choice and reproductive competition may represent important limitations for such interspecies events 15,16. In most species, the female choice of a mating partner is considered to be a main factor to avoid hybridisation, reflecting their higher fitness and reproductive costs 16. In marine mammal polygynous mating systems though, the male dominates the mate choice, whereas the female contribution can be regarded as minor 17. Behavioural indicators for female receptivity in marine mamm...

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“…For example, an unusual dietary behaviour has been described recently on several grey seal males in the North Sea. These individuals fed on other marine mammals such as harbour seals and harbour porpoises (Phocoena phocoena) (Haelters et al 2012;Bouveroux et al 2014;Jauniaux et al 2014;van Neer et al 2015;Leopold et al 2015) or presented some case of cannibalism (Bishop et al 2016;Onoufriou et al 2016;Brownlow et al 2016;van Neer et al 2019). This particular behaviour has been hypothesized to be a consequence of (i) increased competition for food resources as grey seal population size has increased (Lotze 2005;Russell 2016) and (ii) of fishing intensity in the North Sea.…”

Section: Introductionmentioning

confidence: 99%

Habitat and resource segregation of two sympatric seals in the North Sea

Siebert

Pomeroy

Lepoint

et al. 2021

Science of The Total Environment

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Behavioural and pathological insights into a case of active cannibalism by a grey seal (Halichoerus grypus) on Helgoland, Germany

Cited by 11 publications

References 24 publications

Assessing harbour porpoise carcasses potentially subjected to grey seal predation

Assessing harbour porpoise carcasses potentially subjected to grey seal predation

Male grey seal commits fatal sexual interaction with adult female harbour seals in the German Wadden Sea

Habitat and resource segregation of two sympatric seals in the North Sea

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