Mediterranean Shag Phalacrocorax aristotelis desmarestii

The Mediterranean Shag Phalacrocorax aristotelis desmarestii is a subspecies endemic to the Mediterranean and Black Seas. Despite their numbers are not well known experts agree that a reduction
of the population has taken place. It is a seabird species linked to the coast where it breeds in rocky areas.
The Mediterranean population of the species is included in Annex II of the Bern Convention, and thesubspecies is listed in Annex I of the Birds Directive 79/409.
The species experienced catastrophic declines in many parts of its former range due mainly to agricultural intensification (e.g. Schulz, 1985, del Hoyo et al., 1996). Its most important populations are now located in the EU, mainly within the
Iberian Peninsula. The available but incomplete figures suggest that 80-90% of the world population may be concentrated in Spain and Portugal.
This Action Plan relies largely on the results of a Workshop on the subspecies held in the Balearic Islands, on September 1999 and on replies to a specific questionnaire sent to all non-EU range states in
2001. The species is sedentary and partially dispersive, but generally philopatric. Only through adequate management at local level it would be possible to ensure the survival of all populations. Numbers and
trends of the main colonies of the species are still unknown.

Life history

Breeding
The species nests primarily in winter, however from year to year there seems to be a great difference in nesting periods (Guyot 1984). The laying dates range from November to March depending upon the region, and younger birds breed later, occupying sub-optimal nest sites and having lower breeding success. The commonest clutch size is three eggs and incubation lasts 30 days. The fledging of the chicks lasts for about 53 days.
Feeding
The subspecies feeds mainly on coastal fishes, from bottom or mid water over rocky or sandy seabeds. The Mediterranean Shag feeds mainly by pursuit-diving, and normally alone. Economically important fish seems to form a very small part of the diet.
Habitat requirements The species has a strong preference for rocky coasts and islands. It is not normally found far from land. Roost always in the seashore on rocks and stacks. During breeding period it forms sparse colonies, nesting in crevices or caves, on ledges or amongst boulders, often a few meters above the sea level. The
nest is built with a variety of vegetal materials, and is frequently reused in successive seasons.

Threats and limiting factors

Human disturbance
Mediterranean Shag is a shy bird which is severely affected by frequent visit to the colonies. (Guyot 1993). The increase of length of the tourist season and their activities close to the breeding sites, the development and the lack of effective protection of some important colonies can represent a critical threat. Birdwatching and research activities can also cause serious disturbance. These threats are not only limited at the colonies but also at roosting places.
Importance: high

Oil pollution
Incidental oil spills or illegal washing of tanks are a proved threat (Lambertini & Leonzio 1986) that can have lethal and sub-lethal effects on adults and eggs through eggshell smearing.
Importance: high

Accidental catch
Some fishing methods such as gill nets and fish traps, particularly when located permanently close to the sea shore, are responsible of the killing of a significant numbers of shags, as has been reported in
Balearic islands (Aguilar 1991).
Importance: unknown, locally high

Habitat loss
Favourable habitat (for breeding, roosting and feeding) is most often unaffected, but habitat availability for shags can locally be reduced by developments, illegal trawling, construction of ports,
marinas and sea walls, uncontrolled anchoring of yachts and sand extractions for beach regeneration. The latter can strongly affect the Posidonia beds and other benthonic communities where Mediterranean Shag
feeds.
Importance: medium - locallyhigh

Illegal prosecution
Despite legal protection, illegal prosecution of the species is still frequent in some areas.
Importance: lowPage 7

Predation by introduced mammals
It is possible that predation by rats in islets with high rodents’density would be important, but there are not enough data on the effects of predation by rats. Temporary presence of dogs may cause
serious disturbances and mortality of chicks and adults.
Importance: unknown

Chemical pollution
Levels of Hg, Se, Pb and PCBs are high in 3 studied animals, as well as contents of PCBs in two eggs reported by Lambertini & Leonzio (1986). There is no direct evidence of the impact of high
concentration of mercury and other heavy metals on the species’biology in the Mediterranean. More field data are required.
Importance: unknown

Competition with other species.
Predation and competition for nesting sites by Yellow-legged Gull is potential a problem since gull populations are increasing and many of their colonies are located close to the Shag breeding sites.
Importance: unknown

Overfishing
Depletion of fish stocks may cause the declining of entire populations.
Importance: unknown
Conservation status and recent conservation measures
The species is protected in all the member states of the European Union. Estimates of the total breeding population are incomplete and not globally updated since the 1980s