Commercial fisheries, inter‐colony competition and sea depth affect foraging location of breeding Scopoli's Shearwaters Calonectris diomedea

Abstract

The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra‐specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra‐specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long‐distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at‐sea distribution and habitat preference of a seabird inhabiting the over‐exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.

Olfactory-cued navigation in shearwaters: linking movement patterns to mechanisms

“…Scopoli’s shearwater Calonectris diomedea (Cd), Cory’s shearwater C. borealis (Cb) and Cape Verde shearwater C. edwardsii (Ce) are three closely related Procellaridae species breeding in the Mediterranean, North Atlantic Ocean, and Central Atlantic Ocean, respectively. These burrowing seabird species generally feed on pelagic fish, cephalopods and crustaceans 26 , but also fishery discards 27 . Birds were tagged using different data-loggers, all recording GPS-positions every 10 minutes.…”

Home range and foraging habitat preference of Scopoli's shearwater Calonectris diomedea during the early chick‐rearing phase in the eastern Mediterranean

“…5d). SSC fishing activity around the fishing grounds provides feeding opportunities to Scopoli's shearwater, primarily during the discarding process as shown also by Cecere et al (2015). Additionally, it should be mentioned that a small number of Italian and Greek trawlers operate in the international (e) is the semivariogram based on the Pearson residuals of the final GAM.…”

“…coastal zones of the western Peloponnese and southeastern Zakynthos) compared to the relevant findings of Karris (2014), revealed a substantial degree of fidelity to specific feeding grounds, thus ensuring their importance for the conservation of the species. This persistent use of the same feeding grounds may be explained by the fact that these areas: 1) constitute continental and insular shelves where resources are highly predictable (Weimerskirch 2007), and 2) are distant from other known colonies of shearwater species with common diet habits, resulting in low interspecific and intraspecific competition and, as a consequence, optimization of foraging success, as Cecere et al (2015) argued for the shearwater colonies of Linosa Island and Tremiti Archipelago in Italy.…”

“…Minimum distances from the coastline and the Strofades colony were estimated using the 'near' proximity tool, which forms part of ESRI's ArcGIS toolboxes (ESRI 2007). Parameters such as SST, CHL, depth and distance from coastline are considered important due to the influence on marine species such as small pelagic fish (Agostini and Bakun 2002, Giannoulaki et al 2011, Cecere et al 2015, which mainly affect the foraging pattern of Scopoli's shearwaters (Sarà 1993). Also, SLA varies with ocean processes such as gyres, meanders and eddies that enhance productivity and often function as physical barriers differentiating the distribution of species (Larnicol et al 2002).…”

“…In the Mediterranean, studies on the foraging ecology of Scopoli's shearwaters describing their breeding range, feeding areas, movements and habitat use have focused on the colonies in the western and central part of the basin (Vaughan 1980, Massa and Lo Valvo 1986, Louzao et al 2009, Arcos et al 2012, Grémillet et al 2014, Cecere et al 2015. These areas constitute the most productive part compared to the eastern Mediterranean Basin (Turley et al 2000, Lazzari et al 2012, which is a contrasting ecological regime characterized by low concentrations of annual primary productivity (C 116-126 g m -2 year -1 ) (Bosc et al 2004) and annual chlorophyll concentration (chl-a 0.13-0.27 mg m -3 ) (Gotsis-Skretas et al 1999).…”