Justification of Red List Category
Although this species may have a small range, it is not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The breeding population, which is confined to Europe, is estimated at 16,300-17,200 pairs, which roughly equates to 30,000-34,999 mature individuals (BirdLife International 2015).
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. The European population trend is unknown (BirdLife International 2015).
This species breeds in Iceland, Norway, Svalbard (to Norway), the Faroe Islands (to Denmark), the Scottish islands and mainland Scotland. It is a migratory species, normally wintering off the Atlantic coast of France and the Iberian Peninsulas, but juveniles can reach as far as Cape Verde, the coast of Brazil, and the Caribbean; small numbers also winter on the Grand Banks of Newfoundland (Canada) (del Hoyo et al. 1996).
This marine species avoids land during migration and winter, aggregating in winter in areas where it can scavenge from fisheries. It is a highly opportunistic feeder and thus has a hugely varied diet. Individuals regularly show specialisations in diet and feeding, sometimes with colony-specific learning. Breeding begins in May and it is loosely colonial, but highly territorial. Nesting occurs on flat ground with some vegetation cover. During this period, contact to humans is usually avoided. Most birds breed within 1 km of their birth place (del Hoyo et al. 1996).
During the breeding season, fishery discards make up more than half of the Great Skua’s diet (Furness et al. 2018); thus, directives to reduce fishery discards may result in a population decline. However, this species is thought to be resistant to this threat due to its ability to switch to other prey types (Bicknell et al. 2013). Despite this, the extent of this threat is at yet unknown, but may rapidly lead to great decreases in breeding success.
Decreases in North Sea Sandeel stocks has led to reduced prey availability in some areas of the Great Skua’s range, especially in northern Scotland, which has seen declines in Great Skua population and breeding success (Furness et al. 2018) This, however, may represent population shifts as opposed to actual declines, as colonies in south Scotland have increased over the same period (Furness et al. 2018).
Localised persecution of this species occurs in colonies in Iceland, the Faroes, northern Scotland and across Scandinavia in order to alleviate stresses to other seabirds and due to the species' aggressive behaviour towards humans during the breeding season. However, the level of persecution remains low and has declined in more recent years owing to the increased legal protection for this species.
Conservation Actions Underway
The following information refers to the species's European range only: There are currently no known significant conservation measures for this species.
Conservation Actions Proposed
The following information refers to the species's European range only: As it is not desirable to maintain current rates of fish discard, conservation measures are needed to conserve sandeel stocks in order to provide an alternative food source for this species and to avoid a switch to preying on other bird species, which may impact populations of other seabirds (Votier et al. 2004).
Text account compilers
Butchart, S., Ekstrom, J., Ashpole, J, Calvert, R.
BirdLife International (2019) Species factsheet: Catharacta skua. Downloaded from http://www.birdlife.org on 19/04/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/04/2019.