Habitat use and abundance of striped dolphins in the western Mediterranean Sea prior to the morbillivirus epizootic resurgence

Abstract

International audienceAlthough the striped dolphin Stenella coeruleoalba has a world status of Least Concern, a recent IUCN Red List assessment has proposed that the Mediterranean population be listed as Vulnerable and stresses the need for an estimate of abundance and distribution. While substantial efforts have been made to study cetaceans in regions of the western Mediterranean Sea (WM), we have little knowledge of their large-scale distribution and interaction with oceanographic features at various scales. We conducted 18 basin-wide surveys from ferry platforms within the WM from early September 2006 to late July 2007 and used spatial modelling to investigate the distribution, abundance and habitat use of striped dolphins. Most striped dolphins were sighted north of the Balearic Islands, where they are closely associated with the counter-clockwise circulation defined by negative absolute dynamic topography. In the Algerian basin, dolphins were mostly found in recent Atlantic water mass. Densities of striped dolphins were also related to high gradients of sea surface temperature and high chlorophyll concentrations. Moreover, we found similar results (1) when the northern and southern data sets were pooled and (2) in the northern area only, where the majority of sightings occurred. These relationships suggest that dolphins were found in dynamic and productive areas generated by mesoscale processes which could create favourable foraging conditions. Despite our relatively small data set, dolphins were found year-round. We estimated the number of striped dolphins in the area between 3° and 6° E to have been 38 600 (95% CI: 25 900 to 53 900) before the resurgence of the morbillivirus epizootic in summer 2007. This is considerably more than the estimate from the 1991 WM survey, which reported a 43% lower abundance, probably affected by the 1990 epizootic. Platforms of opportunity are therefore relevant not only to assess animal ecology but also to monitor population in a given area. Such interanual monitoring is especially important to detect and quantify the response of animal populations, in terms of distribution and density, to environmental stresses

Abundance, activity and critical habitat of the striped dolphinStenella coeruleoalbain the Gulf of Taranto (northern Ionian Sea, central Mediterranean Sea)

“…The overall density value estimated for S. coeruleoalba in the present study (0.97 specimens/km 2 ) is the highest among those reported for both the eastern (Bearzi, Bonizzoni, Agazzi, & Gonzalvo, ; Panigada et al, ; Santostasi, Bonizzoni, Bearzi, Lavinia, & Olivier, ) and western Mediterranean regions (Cotté et al, ; Forcada et al, ; Forcada & Hammond, ; Forcada, Notarbartolo di Sciara, & Fabbri, ; Gannier, ; Gómez de Segura, Crespo, Pedraza, Hammond, & Raga, ; Gómez de Segura, Hammond, Cañadas, & Raga, ; Lauriano, Panigada, Cannieri, Zeichen, & Notarbartolo di Sciara, ; Panigada et al, ; Panigada, Burt, Lauriano, Pierantonio, & Donovan, ; Panigada, Lauriano, Burt, Pierantonio, & Donovan, ). However, in these latter studies, much larger areas were considered and different observation platforms and estimation methods were used, thus caution is required in any further comparative considerations.…”

“…Unfortunately, knowledge about the presence and distribution of cetaceans as well as their behaviour patterns in the Mediterranean Sea is still patchy, and that available refers mostly to the western regions (Notarbartolo di Sciara & Birkun, 2010;Pace, Tizzi, & Mussi, 2015). Concerning the striped dolphin Stenella coeruleoalba (Meyen, 1833), the available information reports the species as the most abundant cetacean distributed both inshore and offshore with a decreasing west to east trend in abundance (Aguilar, 2000;Cañadas, Sagarminaga, & García-Tiscar, 2002;Cotté, Guinet, Taupier-Letage, & Petiau, 2010;Forcada, Aguilar, Hammond, Pastor, & Aguilar, 1994;Gannier, 1999Gannier, , 2005Gaspari, Azzellino, Airoldi, & Hoelzel, 2007).…”

Estimating cetacean density and abundance in the Central and Western Mediterranean Sea through aerial surveys: Implications for management

“…In terms of striped dolphins, it does appear that the present boundaries of the Sanctuary do not incorporate all of the high density striped dolphin areas (e.g. Cotté et al, 2010;Bauer et al, 2015;Lauriano et al, 2010;Panigada et al, 2011).…”

“…Gannier, 1999) while seasonal movements are currently hypothesized but not supported by comprehensive evidence (e.g. Cotté et al, 2010). For fin whales, long to short distance movements have been reported for the Mediterranean (e.g.…”

Facilitating fishing decisions in an artificial reef area off southern Portugal: a case study using generalized additive models

“…However, despite being flexible and efficient, back-fitting of GAM with a linear smoothers presents some drawbacks concerning model selection and inference (Wood and Augustin, 2002). In fisheries as well as other disciplines, GAM have been utilized in diverse studies on abundance and distributions of cetaceans (Forney, 2000;Williams et al, 2006;Cott e et al, 2010), fish species (Maravelias, 1997;Leathwick et al, 2005;Wang et al, 2009), trophic relationships (Litzow and Ciannelli, 2007), and other areas of research (e.g. Bigelow et al, 1999;Underwood, 2009;Casini et al, 2010).…”