Invasions of harp seals<i>Phoca groenlandica</i>Erxleben to coastal waters of nor way in 1995: Ecological and demographic implications

Nilssen, Kjell Tormod; Haug, Tore; Øritsland, Torger; Lindblom, Lotta; Kjellqwist, Sten Anders

doi:10.1080/00364827.1998.10413693

Cited by 19 publications

(12 citation statements)

References 17 publications

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“…This estimate correlates well with the timing of observed mass migrations of harp seals from the Barents Sea south along the coasts of Norway and into the North Sea in the winter of 1987-1988 (Haug & Nilssen, 1995). The migration event is widely believed to have introduced PDV to the previously unexposed European harbour seals (Haug & Nilssen, 1995;Nilssen et al, 1998;Dietz et al, 1989a,b;Härkönen et al, 2006), and was presumably caused by the collapse of the Barents Sea capelin (Mallotus villosus) and herring (Clupea harengus) stocks (Haug & Nilssen, 1995).…”

Section: A Winter Origin Of the 1988 And 2002 Pdv Strainssupporting

confidence: 77%

“…PDV antibodies were not detected in harbour seals in these waters prior to the 1988 outbreak, and the proportion of the European population carrying antibodies declined steadily after each outbreak, dropping from more than 50% in 2003 to less than 10% in 2007 (Bodewes et al, 2013;Ludes-Wehrmeister et al, 2016;Pomeroy et al, 2005). It has been hypothesized that the unusual mass migration of harp seals in the winter and spring 1987/1988 lead to the introduction of the virus to the European harbour seals in 1988 (Haug & Nilssen, 1995;Nilssen et al, 1998), but the exact timing of these events have never been investigated, and a vector for the 2002 epidemic has not been proposed. Moreover, while the long-distance transmission events of PDV among harbour seal colonies was initially suggested to be aided by the less susceptible and more mobile grey seal (Haliocherus grypus) (Härkönen et al, 2006;McConnell et al, 1999) more recent tagging data indicate that while harbour seals are, in general, philopatric, individual seals occasionally undertake long-distance movements (Dietz et al, 2013;Reijnders et al, 2010;Tougaard et al 2008;Aarts et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Phylogenomic insights to the origin and spread of phocine distemper virus in European harbour seals in 1988 and 2002

Stokholm

Härkönen²,

Hårding³

et al. 2019

Dis. Aquat. Org.

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The 1988 and 2002 Phocine Distemper Virus (PDV) outbreaks in European harbour seals (Phoca vitulina) are among the largest mass mortality events recorded in marine mammals. Despite its large impact on harbour seal population numbers, and three decades of studies, many questions regarding the spread and temporal origin of PDV remain unanswered. Here, we sequenced and analysed 7,123 base pairs of the PDV genome, including the coding and non-coding regions of the entire P, M, F and H genes in tissues from 44 harbour seals to shed new light on the origin and spread of PDV in 1988 and 2002. The phylogenetic analyses trace the origin of the PDV strain causing the 1988 outbreak to between May 1987 and April 1988, while the origin of the strain causing the 2002 outbreak can be traced back to between June 2001 and May 2002. The analyses further point to several independent introductions of PDV in 1988, possibly linked to a southward mass immigration of harp seals in the winter and spring of 1987-1988. The vector for the 2002 outbreak is unknown, but the epidemiological analyses suggest that the subsequent spread of PDV from the epicentre in Kattegat, Denmark, to haul-out sites in the North Sea through several independent introductions.

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Section: A Winter Origin Of the 1988 And 2002 Pdv Strainssupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Phylogenomic insights to the origin and spread of phocine distemper virus in European harbour seals in 1988 and 2002

Stokholm

Härkönen²,

Hårding³

et al. 2019

Dis. Aquat. Org.

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“…Despite the fluctuations in stock dynamics of prey species (inferred from previous diet studies), it appears that harp seal food availability has improved in the Barents Sea during the 1990s, compared to the late 1980s. Nilssen et al (1998) reported a smaller harp seal invasion in 1995; nevertheless, the body condition observed for seals in 1995 was higher than in 2006 and 2011. The current analyses suggest stable or even improved condition of harp seals for the period 1997−2001, a period which was characterised by high abundance of pelagic fish and low abundance of krill (Gjøsaeter et al 2009a).…”

Section: Discussionmentioning

confidence: 87%

Functional relationship between harp seal body condition and available prey in the Barents Sea

Øigård¹,

Lindstrøm²,

Haug³

et al. 2013

Mar. Ecol. Prog. Ser.

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The Barents Sea ecosystem has undergone substantial ecological fluctuations over the past 40 yr, including large variations in the abundance of capelin Mallotus villosus, herring Clupea harrengus, krill Thysanoessa sp. and Meganyctiphanes norvegica, polar cod Boreo gadus saida, and Atlantic cod Gadus morhua. There is evidence to suggest that harp seals Pagophilus groenlandicus have responded to these changes. The current study analysed the relationships between harp seal body condition, environmental variables and the biomass of major harp seal prey. Harp seal body condition was estimated from samples taken in the southeastern Barents Sea during spring from 1992 to 2011. Body condition of juveniles and adults varied between years, improving from 1992 until 2001 and later deteriorating, with weakest condition in 2011. We investigated covariates that might explain such interannual variation. Significant relationships were found between harp seal blubber thickness and prey abundances. High abundances of capelin, polar cod and Atlantic cod had a negative impact on condition, whereas high abundance of krill had a positive impact. Environmental covariates did not improve the models, probably because these were strongly correlated with prey abundance. We also found a correlation between pup production and blubber thickness, indicating that observed declines in pup production may be associated with decreased body condition of the seals. We further show that competitive interactions in the food web (e.g. competition between harp seals and some of their prey for shared resources, such as krill) may result in unexpected negative predator-prey relationships. This has implications for predator breeding success and population dynamics.

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“…Most of the entangled seals were juveniles and most were in poor body condition (Øritsland, 1990). The ‘invasion’ of harp seals is thought to have resulted from a collapse of capelin stocks in the Barents Sea that was caused by fisheries and predation by herring (Nillsen et al ., 1998). Few of the harp seal pups born from 1986 to 1988 survived to sexual maturity (Kjelliqwist, Huag & Øritsland, 1995).…”

Section: Pinnipeds and Nutritional Stressmentioning

confidence: 99%

The decline of Steller sea lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesis

2003

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1. The decline of Steller sea lions Eumetopias jubatus in the Gulf of Alaska and Aleutian Islands between the late 1970s and 1990s may have been related to reduced availability of suitable prey. Many studies have shown that pinnipeds and other mammals suffering from nutritional stress typically exhibit reduced body size, reduced productivity, high mortality of pups and juveniles, altered blood chemistry and specific behavioural modifications. Morphometric measurements of Steller sea lions through the 1970s and 1980sin Alaska indicate reduced body size. Reduced numbers of pups born and an apparent increase in juvenile mortality rates also appear to be nutritionally based. Blood chemistry analyses have further shown that Steller sea lions in the Gulf of Alaska and Aleutian Islands area exhibited signs of an acute phase reaction, or immune reaction, in response to unidentified physical and/or environmental stress. Behavioural studies during the 1990s have not noted any changes that are indicative of an overall shortage in the quantity of prey available to lactating female sea lions. 3. The data collected in Alaska are consistent with the hypothesis that Steller sea lions in the declining regions were nutritionally compromised because of the relative quality of prey available to them (chronic nutritional stress), rather than because of the overall quantity of fish per se (acute nutritional stress). This is further supported by captive studies that indicate the overall quality of prey that has been available to Steller sea lions in the declining population could compromise the health of Steller sea lions and hinder their recovery.

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Invasions of harp sealsPhoca groenlandicaErxleben to coastal waters of nor way in 1995: Ecological and demographic implications

Cited by 19 publications

References 17 publications

Phylogenomic insights to the origin and spread of phocine distemper virus in European harbour seals in 1988 and 2002

Phylogenomic insights to the origin and spread of phocine distemper virus in European harbour seals in 1988 and 2002

Functional relationship between harp seal body condition and available prey in the Barents Sea

The decline of Steller sea lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesis

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