The Mediterranean Shag (Phalacrocorax aristotelis desmarestii) with its dark, sleek appearance and distinguishing tuft of crown feathers which it sports during its winter breeding season is an endearing but reclusive coastal seabird that is endemic to the Mediterranean region. The Mediterranean Shag can be found in southern Europe and southwest Asia principally along the Mediterranean Sea coastline and, to a lesser extent, the Black Sea coast. It is one of three subspecies of the European shag (Phalacrocorax aristotelis) with a unique history and culture that contribute to the natural beauty, rich biodiversity and remarkable productivity of the region’s extraordinary coastal and marine environment.
The Mediterranean Shag is a medium to large size seabird, measuring approximately 70-80 centimetres (cm) in length with an expansive 95-110 cm wingspan. The Shag has dark feathers, pale coloured cheeks on its face, a long curved neck and a long narrow bill. This stream-lined bird is easily distinguishable by its feathered crown tuft in breeding season.
Mediterranean Shags prefer an undisturbed natural environment of rocky coasts and islands adjacent to clear water inhabited by their preferred fish and other marine mid-water and benthic prey. The Mediterranean Shags are usually never far from land and may be observed roosting on isolated rocks and boulders or along the shore of an isolated part of the coast. The Shags can also be seen swimming and diving along the coast, often alone and away from human activities.
These conditions can be found along their geographical distribution range which includes Spain, Gibraltar (UK), France, Italy, Greece, Slovenia, Croatia, Bulgaria, Albania, Ukraine, Turkey, Algeria, Libya, Tunisia and Cyprus where the entire global population of the Mediterranean Shag is estimated to be fewer than 10,000 breeding pairs.
One half of the Mediterranean Shag population breeds in the European Union (EU), especially along the coasts of Spain, Baleares, Corsica, Sardinia, the Tuscan archipelago, Lampedusa as well as Ionian Sea and Aegean Sea islands and islets. Greece hosts an estimated 1,000 to 1,200 breeding pairs which are primarily concentrated in the central and northern Aegean Sea where the largest colonies are located. The EU Andros LIFE+ Nature project area hosts approximately 178 pairs which represent 15-18% of the Greek national Mediterranean Shag population.
Significant fluctuations in the breeding success of Mediterranean Shags have been recorded from year to year in several Mediterranean colonies. These fluctuations, in addition to the reclusive nature of the Mediterranean Shags, contribute to the difficulty in assessing the global population. Experts are in agreement, however, that a decline in the Mediterranean Shag population has occurred. And although the European Shag (Phalacrocorax aristotelis) species to which the Mediterranean Shag subspecies belongs is not considered threatened at a global level by the International Union for Conservation of Nature (IUCN) in its Red List of Threatened Species in which the European Shag is listed as a species of Least Concern, the IUCN does acknowledge that the European Shag “population trend appears to be decreasing” according to its 2009 Assessment.
Foraging and Habitat:
With its expert proficiency as a foot-propelled pursuit diver, the Mediterranean Shag forages in mid-water and along the bottom of sandy and rocky seabeds. The Mediterranean Shag shows a preference for sheltered fishing grounds such as bays and channels, although it generally avoids estuaries, shallow or muddy inlets and fresh or brackish waters. The Mediterranean Shag usually forages alone when away from nesting colonies and during winter, but a dense shoal of fish may attract a small flock of Mediterranean shags in search of essential nutrition.
The Mediterranean Shag diet consists primarily of coastal fish species and marine benthic organisms. For example, in a 2011 report of a Mediterranean Shag research study conducted off the Croatian coast and in the Gulf of Trieste, post-breeding Mediterranean Shags in the Gulf preyed on fish species largely from the demersal and relatively immobile Goby (Gobiidae) family, such as the dimunitive Black Goby (Gobius niger). During the breeding season, the Shags exhibited a more varied diet including more mobile benthic-pelagic prey such as the Brown Comer (Serranus hepatus) that can be found over seagrass, sand, mud and rocks; the Peacock or Painted Wrasse (Crenilabrus tinca) that lives up to 14 years; and the schooling Big Scale Sand Smelt (Atherina boyeri). In addition, the Mediterranean Shag diet also includes other species including sandeels from the Ammodytidae family of sandlances which burrow into the gravelly sand, and, to a lesser extent, polychaetes (segmented, or bristled, worms), molluscs and small benthic crustaceans.
The Mediterranean Shag can often be seen swimming alone along the coast during the cold months of winter, during which time most tourists and residents are absent from the seashore and refrain from recreational marine activities such as boating. The bird can be distinguished from other cormorant species as it makes a slight upward movement with the upper half of its body allowing it to stretch upwards before it arches its head and neck as a prelude to diving into the water to feed on the fish or other marine prey that can be found midway in shallow coastal water or along the bottom of rocky or sandy sea beds.
Ornithologists have always stressed the important contribution of healthy seagrasses to the reproduction and population sustainability of fish and other marine organisms that are a staple food source for the Mediterranean Shag and other marine birds. In Greece, for example, Posidonia seagrass beds (Posidonia oceanica) represent an important foraging habitat for the Mediterranean Shags because the seagrass serves as an enriching habitat with plentiful food sources for the natural behaviour and protection of at least 700 animal species and 200 other plant species, including nutritionally important prey targeted by the Mediterranean Shags. In particular, Posidonia beds are especially valued as nursery grounds for a variety of fish and crustacean species that heavily rely on Posidonia for their growth, survival and reproduction.
During the winter breeding season, Mediterranean Shags form sparse colonies and nest in rocky crevices, ledges, caves within sea cliffs or between boulders. Their nesting dates vary from year to year depending on the region and its conditions. The nests, which are constructed of a variety of marine vegetation and other plant materials, are usually situated within a few metres above the high water level.
If the nests remain in good condition, they are often reused during successive seasons. The younger birds of breeding age nest later than the older, mature birds; therefore, the younger birds are left to occupy nest sites that are not as desirable or advantageous as their more mature counterparts. As a result, the younger birds experience a lower rate of breeding success. The egg-laying period varies depending on the region and can vary from year to year, but this period usually occurs during the period from January until March or early April, while in Greece, the breeding season can even last until June. Mediterranean Shags do not exhibit synchronized breeding dates among the various colonies or even among individuals within a colony. This lack of synchronisation is attributed to the different experience levels among the breeding birds, the general weather conditions in any given year as well as the variety of geographic locations of the colonies. At egg-laying, the birds usually produce a clutch of 3 eggs which are incubated for 30 days prior to hatching. The post-hatching period during which the chicks develop to a fully grown state lasts approximately 53 days, at which point the offspring are usually ready to fledge.
At the end of the breeding season, the adults as well as the juveniles disperse over a wide area, which in some cases may reach or even exceed 200 kilometres according to avian ring recoveries, whereupon the Mediterranean Shags use more remote foraging grounds. At that time, small or larger feeding and roosting groups are formed.
Current threats to Mediterranean Shags are affecting their natural ability to breed, roost and forage successfully which, in turn, impact the birds’ long term conservation status. These current threats include the following:
- Coastal development and coastal recreational activities that result in significant disturbances as well as habitat loss, fragmentation and degradation which adversely impact the birds’ foraging, roosting and breeding behaviour. Among the activities which represent some of the most serious threats to the Mediterranean Shags are tourism; the construction of ports, marinas and sea walls; uncontrolled boat anchoring; intensive marine recreational activities; livestock grazing; and sand extraction for beach regeneration which can severely damage Posidonia seagrass beds and other benthic (marine seabed) communities on which the Mediterranean Shags feed and rely for their survival;
- Intensive fishing including overfishing due to the absence of sustainable fisheries management in the Mediterranean region which results in the depletion of fish stocks and adversely impacts marine bird prey availability as well as foraging site accessibility;
- Mortality from accidental capture in fishing gear, such as gill nets, fish traps and long lines - particularly when fishing gear is permanently or semi-permanently located close to the shore near breeding colonies, moulting areas and foraging sites;
- Oil spills, marine chemical and heavy metal pollution (e.g. organochlorines, mercury, lead, selenium) and illegal tank washing that can have lethal and sub-lethal effects on adults as well as eggs through eggshell smearing;
- The predation of eggs and nestlings by Black rats (Rattus rattus) at colonies. The rats also reduce the vegetation cover thereby reducing suitable breeding habitat area;
- the introduction of invasive alien species that have impacted the quality and availability of nesting sites; and
- direct persecution, including shooting the Mediterranean Shags and chasing the birds in speed boats or other marine recreational vehicles.
The EU Andros Island LIFE+ Nature project is designed in part to improve the Mediterranean Shags’ breeding and foraging success through actions that will (i) preserve the marine productivity of key foraging sites that include the presence of Posidonia seagrass on which the Shags rely by establishing mooring buoys to eliminate boat anchoring, (ii) reduce human disturbances by elevating stakeholder and visitor awareness and (iii) increase available nesting sites within existing breeding colonies through the plantation of endemic shrubs in certain locations.
Laws and conventions related to the status and protection of the Mediterranean Shag include:
- European Union Birds Directive (Council Directive 2009/147/EC), Annex I;
- Bern Convention on the Conservation of European Wildlife and Natural Habitats, Appendix II;
- Barcelona Convention Protocol Concerning Specially Protected Areas and Biological Diversity in the Mediterranean, Annex II which provides a List of Endangered or Threatened Species;
- Bulgarian Nature Conservation Act of 1962 and 1986 national legislation (amended in 1997) relating to punitive measures for acts resulting in injuries to or the death of individuals of the species. Also, the Bulgarian Red Data Book in which the Mediterranean Shag is listed under “Threatened Species”;
- Hunting Law of Tunisia;
- Terrestrial Hunting Law of Turkey; and
- Ukrainian Red Data Book, Category II.
Contact: Constantine Alexander