Comparison of the summer habitat of four preferential teuthophagous cetaceans in north-western Mediterranean Sea

• Main Author: Gannier, Alexandre
• Format: Article in Journal/Newspaper
• Language: French
• Published: HAL CCSD 2018
• Subjects: envir; geo; Lambda; Pennington; Western Basin; Sperm whale
• Online Access: https://hal.archives-ouvertes.fr/hal-03532608/file/bitstream_130072.pdf; https://hal.archives-ouvertes.fr/hal-03532608

International audience More than 50 squid species inhabit the Mediterranean Sea and four of the common cetacean species are preferential squid eaters. This suggests that teuthophagous cetaceans might be in competition for food and suitable habitats. Descriptive and multivariate analyses were carried out from long term dedicated survey data (1988-2012) in the north-western Mediterranean, including the northern Tyrrhenian Sea. A total of 298 on-effort sightings were obtained between 1988 and 2012, including 202 on effective effort: 157 observations of Sperm whale, 39 of Cuvier's beaked whale, 49 of Long-finned pilot whale and 53 of Risso's dolphin. Five environmental variables (depth, slope, distance-to-200m-isobath (D200), monthly chlorophyll concentration and SST) were defined for every 3x3 km cell in the western basin, as well as summer sighting rates using Pennington estimators for each individual species. Based on Kruskal-Wallis test, the observed habitats were not homogeneous for all species, excepted for SST: preferred depth was significantly distinct for each species. D200 was also distinct, with the exception of the pair Cuvier's beaked whale/pilot whale. Based on a discriminant analysis (stepwise ascending mode), four variables contributed significantly (Wilk's lambda = 0.49) to habitat description of the four species, the most important of them being the depth. Discriminant function was highly efficient to classify Cuvier's beaked whale and pilot whale habitats (respectively 84.6 % and 83.7 % success rate), but sperm whale was poorly discriminated from other species (29.6 % correct prediction). Cuvier's beaked whale and pilot whale habitats were well separated, when those of sperm whale and Risso's dolphin largely overlapped. From available results from different regions worldwide, it seems that Risso's dolphins and pilot whales are rarely abundant together in a given area, which raises the question of a possible competition between these teuthophagous delphinids. Based on published literature, these ...