Summer diet of European Shags Phalacrocorax aristotelis desmarestii in southern Mallorca
https://doi.org/10.61350/sbj.26.8
* Correspondence author: jaalcover@imedea.uib-csic.es
1 Institut Mediterrani d'Estudis Avançats (CSIC-UIB), c/o Miquel Marquès, 21, 07190 Esporles, Balearic Islands, Spain;
2 SKUA Gabinet d'Estudis Ambientals SLP, Cr Arxiduc Lluis Salvador 5, entresol, esq., 07004 Palma, Balearic Islands, Spain;
3 Institut de Ciències del Mar (CSIC), Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalonia, Spain.
Analysis of pellets of European Shags Phalacrocorax aristotelis desmarestii collected at a non-breeding roost site in southern Mallorca identified 36 species of fish prey, belonging to 27 genera and to 16 families. This diversity is higher than in the diet of P. a. aristotelis in the Atlantic, and higher than in the previous literature for P. a. desmarestii in the Mediterranean. European Shags in southern Mallorca foraged mainly on fishes with a mean estimated length of 11.6 cm (84.1% ranging from 6.1-15.0 cm in estimated length), most being pelagic species (59.6%). The most important fish in numerical frequency (43.9%) and estimated biomass (37.2%) was the Bogue Boops boops (Sparidae). This species has not been reported in European Shag diet in the Atlantic, and its importance was low in other Ph. a. desmarestii populations studied. The second most frequent prey was sand smelt Atherina (15%), but its contribution to biomass was low (1.4% of estimated biomass) because of its small size, as has been reported from other Mediterranean locations. The occurence of Scorpaenidae (10.7% by frequency, 17.4% of estimated biomass) was higher than in previous studies of Ph. a. desmarestii. Scorpaenids have not been found in the diet of Ph. a. aristotelis. Sandeels (Ammodytidae), a key prey for Ph. a. aristotelis in the Atlantic, were very scarce in this study, as in other recent Mediterranean studies. The relative abundance of species anatomically well protected against predation, such as scorpaenids and trachinids, and the diversity of prey probably reflects the scarcity or absence of other preferred prey. This study reflects the opportunistic behaviour of European Shags in the Mediterranean Sea, foraging on fish with very different ecological requirements, in an environment that is poor but diverse.
The European Shag Phalacrocorax aristotelis is distributed along the coasts of the Western Palaearctic with three subspecies recognised: Ph. a. aristotelis, with
66-73,000 pairs breeding along Atlantic coasts from the Kola Peninsula in Russia to southern Portugal (Wanless & Harris 2004); Ph. a. riggenbachi in south-western Morocco; and Ph. a. desmarestii, which is endemic to the Mediterranean, from the Iberian Peninsula to the Black Sea, with an overall breeding population estimated at between 3,000 (Velando & Munilla 2008) and 10,000 (Muntaner & Mayol 2007) pairs. Ph. a. riggenbachi and Ph .a. desmarestii are morphologically smaller than the nominal subspecies, having a smaller crest, and a brighter yellow coloration at the basis of the bill. However, differences between the subspecies are slight, and their taxonomic separation has not been evaluated genetically.
The European Shag is a coastal feeding seabird, showing a strong preference for rocky coasts and small islands with clear, shallow waters over sandy or rocky seabeds (del Hoyo et al. 1992). Birds mainly feed on fish, with a few species dominating the diet, and within a foraging range of up to 20 km around their breeding and roosting sites (Wanless et al. 1991; Velando 1997). Although almost exclusively piscivorous, small numbers of polychaetes, cephalopods, other molluscs and small benthic crustaceans have been reported in the diet (e.g. Barrett et al. 1990; Velando & Freire 1999; Hillersøy 2011). Prey-items taken can differ spatially, even between neighbouring colonies (Velando & Freire 1999), or seasonally, between the breeding season and the rest of the year (Lilliendahl & Solmundsson 2006), depending on availability, suggesting opportunistic foraging behaviour (Barrett 1991).
There is abundant literature on the diet of Atlantic/North European Shags. With exception of the northernmost latitudes where gadoids are often their main prey (Barrett et al. 1990; Hillersøy 2011), different species of sandeels (Ammodytidae) are usually, but not always (Fortin et al. 2013), the main food source for Ph. a. aristotelis (Steven 1933; Lack 1945; Lumsden & Haddow 1946; Snow 1960; Pearson 1968; Harris & Wanless 1991, 1993; Velando & Freire 1999; Furness & Tasker 2000; Pennington et al. 2004; Lilliendahl & Solmundsson 2006). However, fewer dietary studies have been performed in the Mediterranean Sea, where the diet seems to be much more varied, especially during the breeding season, with some fish families such as Atherinidae, Labridae, Sparidae or Gobiidae playing an important role as prey items (Araujo et al. 1977; Guyot 1985; Morat 2007; Cosolo et al. 2011; Morat et al. 2011).
The Balearic Islands hold one of the most important populations of Ph. a. desmarestii (hereafter 'Mediterranean Shag'). Censuses carried out on Menorca, Eivissa and Formentera in 2005, and on Mallorca and Cabrera in 2006, estimated their populations at 1,800 breeding pairs, 95% of the Spanish population for this subspecies, and 18% of its world population (after Muntaner & Mayol 2007); a further census in 2006 and 2007 estimated 2,017 breeding pairs (Álvarez & Velando 2007). It has been suggested that the Balearic Islands could be a source region for individuals dispersing to other areas (García et al. 2011). Despite the importance of this area, the only information on their diet in the Balearic Islands comes from stomach contents analysis of eight specimens, with 16 individual fish identified, and several prawns (Araujo et al. 1977). Shags regurgitate pellets containing fish bones, otoliths and scales, small invertebrates, marine vegetation and even small stones. Although several authors (Ainley et al. 1981; Duffy & Laurenson 1983; Johnstone et al. 1990) estimated that pellets were regurgitated at least once a day, Russell et al. (1995) obtained a mean production of one pellet every four days for birds in the wild. Here, we present diet data inferred from an analysis of pellets from Mediterranean Shags collected on an islet off southern Mallorca (Balearic Islands). This information contributes to our knowledge of the diet of this species in the Mediterranean Sea.
We would like to express our gratitude to Dr Daniel Oro, Dr Alejandro Martínez- Abraín and Dr Damià Jaume for valuable comments, and to Silvia Pérez and Itzíar Álvarez for their help and useful technical recommendations. This paper is included as a colateral research in the DGICYT Research Projects CGL2012-38089 and MINECO Research Project CTM2010-19701. Dr. Victor M. Tuset has a contract JAE-DOC (CSIC) co-funded by the European Social Foundation. Finally, we thank Dr David Grémillet and an anonymous reviewer for their useful comments and improvements, and Martin Heubeck and Andy Webb for their editorial improvements.
http://www.cmima.csic.es/aforo/index.jsp
Centre Mediterrani d'Investigacions Marines i Ambientals CMIMA-CSIC (Barcelona),Condor 83: 120-131. [Crossref]
. Feeding ecology of marine Cormorants in southwestern North America.Phalacrocorax aristotelis in the Cantabrian Sea, northern Spain, during the breeding season. Seabird 20: 22-30.
. The diet of ShagsEl CormorÁn moñudo en España y Gibraltar. Población en 2006-2007 y método de censo. SEO/BirdLife, Madrid.
.Naturalia Hispanica 12: 1-94.
. Las rapaces y aves marinas del archipiélago de Cabrera.Phalacrocorax aristotelis L.) as potential samplers of juvenile saithe (Pollachius virens (L.)) stocks in northern Norway. Sarsia 76: 153-156. [Crossref]
. Shags (Phalacrocorax aristotelis and Cormorants P. carbo in Norway and possible implications for gadoid stock recruitment. Marine Ecology Progress Series 66: 205-218. [Crossref]
. Diets of ShagsPhalacrocorax aristotelis. Seabird 9: 3-10.
. Notes on the eggs and chicks of North Norwegian ShagsSupplementi di Richerche Biologia della Selvaggina 26: 197-230.
Techniques for assessing cormorant diet and food intake: towards a consensus view.Biología Marina. Ariel Editions, Barcelona.
.Phalacrocorax aristotelis desmarestii between the breeding and post-breeding seasons in the upper Adriatic Sea. Bird Study 58: 461-472.
. Dietary changes of Mediterranean Shags [Crossref]. Handbook of the Birds of the World. Vol. 1. Lynx Editions, Barcelona.
Condor 85: 305-307.
. Pellets of Cape Cormorants as indicators of diet.Rostocker Meeresbiologische Beiträge 18: 30-62.
. Studies on the ichthyofauna of the coastal waters of Ibiza (Balearic Islands, Spain).Phalacrocorax aristotelis in Mor Braz, France. Aquatic Living Resources 26: 179-185. [Crossref]
.The demography and ecology of the European shag FishBase. World Wide Web electronic publication.Ornis Scandinavica 16: 305-313. [Crossref]
. The food requirements and ecological relationships of a seabird community in North Norway.Marine Ecology Progress Series 202: 253-264. [Crossref]
. Seabird-fishery interactions: quantifying the sensitivity of seabirds to reductions in sandeel abundance, and identification of key areas for sensitive seabirds in the North Sea.Es Busqueret 24: 5-8.
. El Corbmarí.Phalacrocorax carbo and Shags Phalacrocorax aristotelis: benthic or pelagic feeding? Ibis 140: 113-119. [Crossref]
. Flexible foraging techniques in breeding CormorantsPhalacrocorax aristotelis en Corse. In: Oiseaux marins nicheurs du Midi et de la Corse: 70-76. Annales du C.R.O.P. No. 2, Aix-en-Provence.
. La reproduction du Cormoran huppéAmmodytes marinus in the diet of the Shag Phalacrocorax aristotelis. Ornis Scandinavica 22: 375-382. [Crossref]
. The importance of the lesser sandeelPhalacrocorax aristotelis during the chick-rearing period assessed by three methods. Bird Study 40: 135-139. [Crossref]
. The diet of ShagsPhalacrocorax aristotelis) at Sklinna, Central Norway, and possible relationship between reproduction and abundance of year class 1-saithe in the diet'. Masters Thesis, Norwegian University of Life Sciences.
. 'Annual variation in the diet of the European Shag (Phalacrocorax aristotelis. Bird Study 37: 5-11. [Crossref]
. The usefulness of pellets for assessing the diet of adult ShagsPhalacrocorax carbo) and Shag (P. aristotelis). Journal of Animal Ecology 14: 12-16. [Crossref]
. The ecology of closely related species with special reference to Cormorant (Atherina boyeri Risso, 1810 (Pisces: Atherinidae) in the Mesolongi and Etolikon lagoons (W. Greece). Fisheries Research 62: 89-96. [Crossref]
. Age, growth and mortality ofPhalacrocorax aristotelis and great cormorants P. carbo in Iceland. Marine Biology 149: 979-990. [Crossref]
. Feeding ecology of sympatric European shagsScientia Marina 70: 147-152. [Crossref]
. A web-based environment from shape analysis of fish otoliths. The AFORO database.Guida all'identificazione dei Pesci Marini d'Europa e del Mediterraneo. Il Castello Editore, Milan.
.Phalacrocorax aristotelis) in the Clyde sea area. Journal of Animal Ecology 15: 35-42. [Crossref]
. The food of the shag (Naga. ICLARM Quarterly 20: 66-68.
. Length-Weight relationship of fishes and cephalopods from the Balearic Islands (Western Mediterranean).Régime alimentaire de la population de cormoran huppé de Méditerranée (Phalacrocorax aristotelis desmarestii) de Riou. Centre d'Océanologie de Marseille (CEEP-DIMAR), Marseille.
.Phalacrocorax aristotelis desmarestii, its ecological significance and interaction with local fisheries in the Riou Archipelago (Marseille, France). Life and Environment 61: 77-86.
. Diet of the Mediterreanean European shag,Fisheries Research 62: 89-96. [Crossref]
. Weight-length relationships of littoral to lower slope fishes from the western Mediterranean.Pla Balear de Maneig de la Gavina Roja, Larus audouinii i del Corbmarí, Phalacrocorax aristotelis. Sèries: Plans d'Espècies catalogades. Quaderns de Natura. Govern de les Illes Balears.
.Lipophrys trigloides (Pisces, Blenniidae) at the Spanish Mediterranean coast. Miscellania Zoológica 17: 189-197.
. Nocturnal activity of a blennyJournal of Animal Ecology 37: 53-102. [Crossref]
. The feeding biology of sea-bird species breeding on the Farne Islands, Northumberland.The Birds of Shetland. Christopher Helm, London.
.Fauna e Flora del Mediterraneo. Franco Muzzio Editore, Padua.
.Phalacrocorax aristotelis. Seabird 17: 44-49.
. Factors affecting the production of pellets by ShagsPhalacrocorax aristotelis on the island of Lundy, Bristol Channel. Ibis 102: 554-575. [Crossref]
. The breeding biology of the ShagJournal of the Marine Biological Association of the United Kingdom 19: 277-292.
. The food consumed by Shags and Cormorants around shores of Cornwall (England).Scientia Marina 72 (S1): 198 pp. [Crossref]
. Otolith Atlas for the Western Mediterranean, North and Central Atlantic.. The UNEP Large Marine Ecosystem Report. A Perspective on Changing Conditions in the LMEs of the World's Regional Seas. UNEP Regional Seas Report and Studies. No. 182.
Phalacrocorax aristotelis) en las Islas Cíes y Ons'. PhD Thesis, University of Vigo.
. 'Ecología y comportamiento del cormorÁn moñudo (Marine Ecology Progress Series 188: 225-236. [Crossref]
. Intercolony and seasonal differences in the breeding diet of European shags on the Galician coast (NW Spain).Plan de Conservación del CormorÁn Moñudo en el Parque Nacional de las Islas AtlÁnticas. University of Vigo.
.Phalacrocorax aristotelis Shag. BWP Update 1: 3-13.
.Phalacrocorax aristotelis. In: Mitchell, P. I., Newton, S. F., Ratcliffe, N. & Dunn, T. E. (eds.) Seabird Populations of Britain and Ireland: 146-159. Poyser, London.
. European ShagICES Journal of Marine Science 55: 1141-1151. [Crossref]
. Summer sandeel consumption by seabirds breeding in the Firth of Forth, south-east Scotland.Phalacrocorax aristotelis during chick rearing. Ibis 133: 30-36. [Crossref]
. Foraging range and feeding locations of Shags