Influence of seasonality on cetacean diversity, abundance, distribution and habitat use in the western Mediterranean Sea: Implications for conservation

Abstract

Abstract\ud 1. Cetaceans are key biological indicators of the status of marine waters and are protected under\ud an extensive legislative framework. Research about these highly dynamic species is challenging,\ud so seasonal cycles and patterns of distribution, especially in high sea areas, are still poorly\ud understood.\ud 2. This study contributes to improving knowledge about cetacean occurrence in largely unexplored\ud areas of medium‐latitudes in the western Mediterranean Sea. Systematic surveys were\ud conducted along a trans‐regional transect over 3 years (October 2012 to September 2015)\ud allowing consistent data collection over almost 60 000 km of effort through all seasons.\ud 3. Seasonal cetacean diversity wasinvestigated using a25km2 grid cell as a statistical unit to explore\ud patterns of abundance, distribution, and habitat use in three marine sectors (Sardinian–Balearic,\ud Bonifacio Strait, Tyrrhenian). All cetacean species regularly present in the Mediterranean basin\ud were detected, with highest occurrence in fin whale and striped dolphin, followed by bottlenose\ud dolphin and sperm whale.\ud 4. The Sardinian–Balearic sector generally showed higher species richness and diversity than the\ud Tyrrhenian, where seasonal variations were more pronounced. The study suggested seasonal\ud movements, especially for fin whale and striped dolphin, in the Sardinian–Balearic sector with\ud peaks of occurrence during spring/summer and lower numbers during winter/autumn, and also\ud delivered interesting insights to rarer pelagic species.\ud 5. The study identified areas/seasons in which the combined effect of high species diversity,\ud abundance, significance of hot spots and presence of juveniles require increasing conservation\ud effort. Results underline the important contribution of continuous monitoring in high sea areas\ud to the implementation of adaptive protection measures

An integrated approach for cetacean knowledge and conservation in the central Mediterranean Sea using research and social media data sources

“…In this way, sperm whales would be able to capitalize on the food resources (cephalopods) available in both areas by shifting between different prey targets (Gannier et al, ). The lower sperm whale relative abundance in the northern part of the study area than in the southern part (Pontine Archipelago) also seems to be consistent with recent published results showing variable encounters in the north (Arcangeli et al, ) and regular occurrences near Ponza and Ventotene islands (Mussi et al, ; Pace, ; Pace et al, ; Pace, Miragliuolo, Mariani, Vivaldi, & Mussi, ). This is also in line with sperm whale strandings, all located in the southern part of the area where deep waters are closer to the coast.…”

“…This coincides with a number of descriptions of the habitat of this species in the Mediterranean, which report a clear habitat preference for areas at least 1,000 m deep, and complex bottom topographies related to phenomena (upwelling, increased primary production, and aggregation of zooplankton) that could play a role for beaked whales’ main prey species (cephalopods) (Azzellino et al, ; Cañadas et al, ; Podestà et al, , ). Several studies demonstrated the importance of the central Tyrrhenian Sea for the species, showing long‐term site fidelity and changes in habitat selection over time (Arcangeli et al, , ; Arcangeli, Campana, Marini, & MacLeod, ; Cañadas et al, ). One of the hypotheses for these changes is related to the possible negative influence of maritime traffic (Campana et al, ).…”

Habitat suitability modeling in different sperm whale social groups

“…In the Ligurian Sea, sperm whale presence was recorded almost throughout the year (Laran and Gannier , Laran and Drouot‐Dulau ), with no suggestions of strong seasonal patterns or variations in abundance (Laran et al ). In the Sardinian‐Balearic sector, sperm whales were detected especially during summer and autumn, whereas in the central Tyrrhenian Sea the species was never detected in autumn, but it was recorded during other seasons (Arcangeli et al ).…”

“…In this study, results of environmental variables showed that depth was the most important predictor of habitat suitability for all sperm whales in the study area. Within the Mediterranean, sperm whales were principally found in waters deeper than 1,000 m to 2,500 m (Cañadas et al [Alboran Sea], Pirotta et al , Arcangeli et al [Balearic Archipelago and Sardinian‐Balearic sector], Fiori et al [Pelagos Sanctuary, Ligurian Sea]). In this study, the species tended to be sighted at water depths of 500–800 m but was also present over the 300–1,000 m contour.…”

“…A spatially bimodal distribution for the sperm whale in the western Mediterranean was proposed because of its opportunistic feeding strategy (Gannier et al , Gannier and Praca 2007), a hypothesis that was reinforced in the Pelagos Sanctuary (Azzellino et al ) and that is possibly pertinent in our study as well considering predictions outside the surveyed area. The species was sighted over the continental slope, where topographies such as canyons are considered main influences for habitat selection, and in the offshore waters, where the presence of the animals appears to be linked to the position of downwelling or upwelling water movements associated with frontal zones (Gannier and Praca , Arcangeli et al ). In this way, sperm whales would be able to capitalize on the food resources available in both areas by shifting to different prey targets (Gannier et al ).…”