Distribution, social structure and habitat use of short-finned pilot whale, Globicephala macrorhynchus, in the Canary Islands

Abstract

The Canary Archipelago is considered one of the planet’s biodiversity hotspots and the short-finned pilot whale is a key species in need of conservation measures. To address a lack of knowledge, almost 2,000 day-surveys were conducted (1999-2012) resulting in 1,094 short-finned pilot whale sightings. The species was recorded year-round and distributed non-uniformly around the archipelago, with greater densities concentrated in patchy areas mainly on the leeward side of the main islands. A total of 1,320 well-marked individuals were identified, which exhibited a large degree of variability in site fidelity (from core residents to transients). Evidence of an island-associated sub-population and a transient one was found. Longitudinal data were used to infer population structure and estimate abundance, while a spatial modelling approach was used to study spatio-temporal patterns in habitat use, distribution and abundance. Spatial modelling revealed habitat preferences in areas between depths of 1000m and 1500m, and higher densities in the south-west of Tenerife and La Gomera (117 short-finned pilot whales recaptured within the two islands). Abundance of 1,980 individuals (CV = 0.33, 95% CI=1,442 – 2,324) was estimated for the entire archipelago, with higher density predicted during the summer months. Mark-recapture analysis estimated 636 resident individuals (CV = 0.028, 95% CI=602 - 671) in the southwest waters of Tenerife between 2007 and 2009. The social and temporal analyses of the behavioural relationships between pairs of individuals revealed a well-differentiated society with long-lasting and non-random social structure built of constant companions. A hierarchical social system is proposed composed of a population encompassing several clans of pilot whales, each one containing several pods. Nine long-term units were identified with a high degree of association (0.62 - 0.83). This study, the first to provide combined results on distribution, habitat use, and social structure of the species, provides essential information towards the development of recommendations for much needed conservation measures.