Summer social distribution of sperm whales (Physeter macrocephalus) in the Mediterranean Sea

Abstract

Sperm whale social distribution was investigated in the Mediterranean Sea, using data collected during summer surveys from 1997 to 2002. Variations in the size of sperm whale schools/underwater aggregations were assessed using both visual and acoustic data. Individual body lengths were estimated acoustically, using the click inter-pulse intervals. Regional comparisons were undertaken, taking the 41° parallel as a north/south boundary. In the southern region, schools of up to seven sperm whales were sighted and calves were relatively frequent. The animals ranged between 8·6 m and 13·1 m long. In the northern region, school sizes were significantly smaller, with a maximum of three whales sighted at the surface. However, the acoustic survey showed that sperm whales form loose aggregations of up to five animals in certain areas. Whales detected in the north were 12·6 m long on average, and the body size range was relatively small. This summer survey demonstrated a segregation of males, in the north, from larger schools including calves, which seemed to be confined to the southern region.

Population genetics and social organization of the sperm whale (Physeter macrocephalus) in the Azores inferred by microsatellite analyses

“…In agreement with these results, photo-identification surveys indicated site fidelity to the central group of islands over periods up to 7 years (Matthews et al 2001) and use of different groups of islands in different years by some individuals (S. Magalhães, unpublished data). Site fidelity of sperm whales has also been reported based on genetic data in the Galapagos Islands , the archipelago of the Azores (Bond 1999), Gulf of Mexico (Weller et al 2000) and Balearic Islands (Drouot et al 2004). …”

Analysis of mercury and methylmercury concentrations, and selenium:mercury molar ratios for a toxicological assessment of sperm whales (Physeter macrocephalus) in the most recent stranding event along the Adriatic coast (Southern Italy, Mediterranean Sea)

“…Genetic analysis indicates that the population is reproductively isolated while photo-identification and acoustic data have revealed little interchange with the neighboring Atlantic population (Drouot et al, 2004). While there are no estimates of overall abundance in the region, numbers seem to be in the hundreds and the Mediterranean population is thought to have considerably declined; the sperm whale is currently listed by the International Union for Conservation of Nature and Natural Resources (IUCN) as endangered, C2a(ii).…”

“…Groups stranded on coasts of the Adriatic Sea (range 3-8 individuals) are usually smaller compared to the mean size of groups stranded outside of the Mediterranean Sea (range 18-30 individuals) (Frantzis et al, 2003;Drouot et al, 2004).…”

Modelling sperm whale habitat preference: a novel approach combining transect and follow data

“…Together with the waters off Crete (Frantzis et al 2003), the Tyrrhenian Sea (e.g. Drouot et al 2004a) and, recently, the Ligurian Sea (occurrences reviewed in Notarbartolo di Sciara & Birkun 2010), the Balearic archipelago is one of the few areas in the Mediterranean Sea in which both social units and mature males are observed consistently, suggesting a possibly important role as breeding ground (Gannier et al 2002, Drouot-Dulau & Gannier 2007. Nevertheless, no long-term study has been conducted to date to specifically estimate the species distribution in this region, and thus little information exists on its space use and habitat preferences around the archipelago.…”