European Shag - Gulosus aristotelis

European shag (Gulosus aristotelis) are a species of cormorant, smaller and slimmer in size than great cormorants (Phalacrocorax carbo). Adult breeding plumage consists of an all black body with a blue/green-ish gloss, a small crest on the head, and bright yellow gap at the start of their slim beak (fig. 1) (Svensson et al, 2020). They can sometimes be seen standing on rocks with their wings spread wide, drying out. Shags nest in areas such as rocky coastlines and cliff ledges, in loose colonies. Their diet mainly consists of small fish such as sandeels. Shags typically live to around 12 years old, breeding at 4 years, but the oldest Shag ringing record to date was found to be 29 years, 10 months and 25 days old (Svensson et al, 2020; Harris et al, 2024).

Population & Distribution:
At least 22% of the global european shag breeding population is hosted by Britain and Ireland, alongside around 38% of the global population of subspecies aristotelis. Approximately 65% of the Britain and Ireland population can be found in Scotland (fig. 2) (Burnell et al, 2023; Harris et al, 2024). Shags are common along the east coast throughout the year. Breeding has been recorded at various sites including Longhaven, Bullers of Buchan, Forvie, Findon, Newtonhill, and Fowlsheugh (fig. 3). The species has been recorded at other locations along the coast including Fraserburgh Harbour,  Scotstown Head, Peterhead, Boddam, and Aberdeen Harbour where they will rest or roost (North East Scotland Bird Reports).

Conservation Status:
Shags are an Amber listed species (Stanbury et al, 2024). During the latest seabird census Seabird Counts 2015-21 it was found that the shag population in Scotland had declined by 22% since the previous census Seabird 2000 in 1998-2002 (Burnell et al, 2023).

Shag Ringing Project - East Coast:
Shags are ringed in many areas along the east of the UK and around islands such as Shetland, Orkney, the Isle of May and the Farne islands. The shags are colour ringed, a white, blue, green, red, or yellow ring with a three letter unique code (fig. 4). Along the East Grampian Coast they are ringed at cliff sites such as Bullers of Buchan where they breed every year (UKCEH, n.d.). The shags will utilise many sites along the East Grampian Coast as resting and roosting sites as well, including Fraserburgh harbour, Boddam, and Aberdeen harbour. From colour ringing data we know that the same individuals will return to the same breeding, resting, and/or roosting sites up the East Coast. Any rings sighted should be reported to shags@ceh.ac.uk.

Factors Impacting European Shags:
Shags are impacted by a number of factors. Adult survival rates have been linked to climate change with rising sea surface temperatures changing prey distribution, and extreme weather events (with strong winds and high rainfall) causing large-scale mortality. Shag plumage is only partially waterproof and requires time out of water to dry off, but this makes them particularly vulnerable to foraging and roosting in rough stormy weather. Extreme weather events can also have an impact upon more exposed breeding colonies, withpotential high failure rates (Frederiksen et al, 2008; Newell et al, 2015; Burthe et al, 2014). There were huge shag wrecks in Scotland in autumn/winter 2023 with an estimated 80% population reduction on the East coast. With more frequent extreme weather events annually, shag populations may struggle to recover long-term.

Shags are impacted by plastic pollution, incorporating plastic and other anthropogenic (human) debris into their nests. It was found that 25% of nests monitored contained anthropogenic debris such as plastic, and two adult shags entangled at nests when they were surveyed. Higher amounts of plastic debris were recorded at colonies closer to humans (O'Hanlon et al, 2021).

Highly Pathogenic Avian Influenza (HPAI) has caused low mortality in shags as of November 2022 (Tremlett et al, 2024).

Report any sightings to BirdTrack, or NESBReC via the link below.