Occurrence of killer whales in Scottish inshore waters: temporal and spatial patterns relative to the distribution of declining harbour seal populations

Bolt, Harriet E.; Harvey, Paul V.; Mandleberg, Laura; Foote, Andrew D.

doi:10.1002/aqc.1030

Cited by 31 publications

(27 citation statements)

References 24 publications

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“…A similar decline has been observed in Scottish waters: harbour seals Phoca vitulina in Shetland and Orkney declined by 40% between 2000 and 2006 (Lonergan et al 2007). Harbour seals are a preferred prey of killer whales in the northeastern Pacific (Ford et al 1998, Saulitis et al 2000, Dahlheim & White 2010, and predation on harbour seals has also been reported from killer whales around Shetland and Orkney (Weir 2002, Bolt et al 2009). …”

Section: Introductionmentioning

confidence: 58%

“…While predation by killer whales could be an important factor in the decline in harbour seals off northern Scotland (Bolt et al 2009), assessing the impact of killer whale predation requires precise information on abundance, distribution, diet and population identity of local killer whales. Killer whales have been sighted regularly in Shetland waters since the 1970s (Evans 1988, Weir 2002.…”

Section: Introductionmentioning

confidence: 99%

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Vocal behaviour and feeding ecology of killer whales Orcinus orca around Shetland, UK

Deecke¹,

Nykänen²,

Foote³

et al. 2011

Aquat. Biol.

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Killer whales Orcinus orca are sighted regularly off Shetland, UK, but little is known about their numbers, diet and population identity. We aimed to relate vocal behaviour to diet of killer whales around Shetland in order to investigate population structure and differences in feeding strategies. Fieldwork was conducted in the summers of 2008 and 2009. We located killer whales through a sightings network and shore-based scans and collected photo-ID data, behavioural information, feeding data and acoustic recordings from a small boat. The majority of encounters (n = 14) were of small groups (1 to 15 individuals) travelling close to shore and feeding on marine mammals. Two encounters were with large groups (20+ individuals) feeding on herring Clupea harengus farther offshore. Seal-hunting groups vocalised rarely, producing pulsed calls, echolocation clicks and whistles almost exclusively when surface-active or milling after a kill. Herring-eating groups were largely silent during one encounter, but very vocal during the other. Analysis of pulsed calls identified 6 stereotyped call types for seal-hunting groups and 7 for herring-eating groups. No call types were shared between both kinds of groups. The vocal behaviour of seal-hunting groups showed striking parallels to that of Pacific marine mammal specialists and presumably evolved to decrease detection by acoustically sensitive prey. One call type produced by Shetland herring-eating killer whales matched a vocalisation that a previous study had described from Iceland and identified as a possible herding call that may function to concentrate herring during feeding. These findings point to behavioural and dietary specialisation among Shetland killer whales, which should be taken into account when making management decisions affecting these animals. Aquat Biol 13: 79-88, 2011

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Section: Introductionmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Vocal behaviour and feeding ecology of killer whales Orcinus orca around Shetland, UK

Deecke¹,

Nykänen²,

Foote³

et al. 2011

Aquat. Biol.

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“…As above, there is likely to be a seasonal bias in opportunistic encounters. The occurrence of killer whales in this area is highly correlated with the harbor seal pupping season (Bolt et al 2009) and observed predation events, group follows and collected prey remains suggest that the killer whales photo-identified in this area are predating frequently upon seals (Foote unpublished data).…”

Section: Study Sites and Data Collectionmentioning

confidence: 93%

“…There are no published studies using data on identified individuals from any other region of the Northeast Atlantic. Therefore, although it is known that killer whales are regularly seen feeding around trawlers in the northern North Sea (Luque et al 2006), predating seals around the Northern Isles (Bolt et al 2009) and feeding on herring around Iceland (Simon et al 2007), we know nothing of the relationship among these groups of killer whales and movement among these sites.…”

Section: Introductionmentioning

confidence: 96%

Movement, site fidelity and connectivity in a top marine predator, the killer whale

Foote

Stevick²

2009

Evol Ecol

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Movement, site fidelity and connectivity have important consequences for the evolution of population structure and therefore the conservation and management of a species. In this study photographs of naturally marked killer whales collected from sites across the Northeast Atlantic are used to estimate fidelity to sampling locations and movement between locations, expressed as transition probabilities, pt, using maximum likelihood methods. High transition probabilities suggest there is high inter-annual site fidelity to all locations, and large-scale movement between the spawning and wintering grounds of both Norwegian and Iceland stocks of Atlantic herring. There was no evidence of movement between the Norwegian herring grounds and Icelandic herring grounds, or between the mackerel fishing grounds and the herring fishing grounds. Thus the movement of predictable and abundant prey resources can lead to intrinsic isolation in this species We also find movement between the Northern Isles, Scotland and East Iceland. An association network indicates that killer whales predating seals around the Northern Isles, Scotland are linked to the community of killer whales that follow the Icelandic summer-spawning herring. This adds support to existing evidence of a broad niche width in some populations.

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“…Our study is the first successful application of a forensic DNA technique in the marine environment and could be extended to identify other marine aggressors (Bolt et al 2009, Estes et al 2009), including cases involving persons mutilated at sea (Sweet & Shutler 1999). Fig.…”

Section: Discussionmentioning

confidence: 96%

Detection of grey seal Halichoerus grypus DNA in attack wounds on stranded harbour porpoises Phocoena phocoena

Bleijswijk¹,

Begeman²,

Witte³

et al. 2014

Mar. Ecol. Prog. Ser.

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DNA was analysed from external wounds on 3 dead harbour porpoises Phocoena phocoena that were stranded in the Netherlands. Puncture wounds as well as the edges of large open wounds were sampled with sterile cotton swabs. With specific primers that target the mtDNA control region of grey seal Halichoerus grypus, a 196 bp DNA fragment was amplified from 4 puncture wounds. Sequencing of the fragments confirmed the presence of grey seal DNA in the puncture wounds. DNA sequences differed between the cases, implying that 3 individual grey seals were involved. As 8 control swabs from intact skin and the transport bag as well as 6 swabs from open wounds on the same harbour porpoises were all negative, contamination with environmental DNA is considered unlikely. The results provide a link between strandings of mutilated harbour porpoises and recent observations of grey seals attacking harbour porpoises. Ours is the first study to use forensic techniques to identify DNA in bite marks from carcasses recovered from the marine environment. This approach can be extended to identify other marine aggressors, including cases involving persons mutilated at sea.

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Occurrence of killer whales in Scottish inshore waters: temporal and spatial patterns relative to the distribution of declining harbour seal populations

Abstract: 2. There was a strong seasonal peak in sightings around Shetland during June-July, coinciding with the harbour seal pupping season. 5. These findings are discussed in terms of potential impacts upon local declining harbour seal populations and future research requirements.

Cited by 31 publications

References 24 publications

Vocal behaviour and feeding ecology of killer whales Orcinus orca around Shetland, UK

Vocal behaviour and feeding ecology of killer whales Orcinus orca around Shetland, UK

Movement, site fidelity and connectivity in a top marine predator, the killer whale

Detection of grey seal Halichoerus grypus DNA in attack wounds on stranded harbour porpoises Phocoena phocoena

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