Spatial and temporal distribution of cetaceans in the mid-Atlantic waters around the Azores

Abstract

Cetaceans living in offshore waters are under increasing pressure from anthropogenic activities. Yet, due to the lack of survey effort, relatively little is known about the demography or ecology of these populations. Spatial and temporal distribution of cetaceans in mid-Atlantic waters were investigated using a long term dataset collected from boat surveys and land-based observations around the Azores. From 1999 to 2009, 7307 cetacean schools were sighted during 271,717 km of survey effort. In 4944 h of land-based observations, 2,968 cetacean groups were detected. Twenty-four species were recorded: seven baleen whales, six beaked whales, eight dolphin species, Physeter macrocephalus, Kogia breviceps and Kogia sima. Overall, Delphinus delphis was the most frequently sighted species, but its encounter rate decreased in June–November, coinciding with the presence of Stenella frontalis in the region. Tursiops truncatus, P. macrocephalus and Grampus griseus were frequently encountered year-round, whereas large baleen whales showed a distinct peak in encounter rates in March–May. Mesoplodonts were fairly common and appear to be present throughout the year. These findings fill in a significant gap in the knowledge of cetaceans occurring in a poorly studied region of the North Atlantic, providing much needed data to inform management initiatives.

Key words:

• Cetaceans
• spatial and temporal distribution
• mid-Atlantic waters
• sighting surveys

Acknowledgements

We are grateful to the skippers, crew members, students and volunteers that helped us throughout this study, and to Antero Soares for the land-based data. We acknowledge the collaboration of all the observers, captains, crew members and shipowners of tuna vessels of the Azorean Fisheries Observer Programme (POPA). We acknowledge two anonymous reviewers for their comments on an early draft of the paper. This work was supported by FEDER funds, through the Competitiveness Factors Operational Programme – COMPETE, by national funds, through FCT – Foundation for Science and Technology, under projects CETAMARH (POCTI/BSE/38991/01) and TRACE (PTDC/MAR/74071/2006), and by regional funds, through DRCT/SRCTE, under project MAPCET (M2.1.2/F/012/2011). We thank the Azorean Regional Government for funding POPA, the Shipowners Proprietors and the Association of the Tuna Canning Industries for their support to the programme. MAS was supported by an FCT postdoctoral grant (SFRH/BPD/29841/2006), and IC and RP were supported by doctoral grants SFRH/BD/41192/2007 and SFRH/BD/32520/2006. IMAR-DOP/UAç is the R&D Unit #531 and part of the Associated Laboratory #9 (ISR), funded through the pluri-annual and programmatic funding schemes of FCT-MCTES and DRCT-Azores.

Editorial responsibility: Rus Hoelzel