Geographic variation in the acoustic features of whistles emitted by the striped dolphin (Stenella coeruleoalba) from the Atlantic Ocean (Azores and Canary Islands) and the Mediterranean was investigated. Ten parameters (signal duration, beginning, end, minimum and maximum frequency, the number of inflection points, of steps, of minima and maxima in the contour and the frequency range) were extracted from each whistle. Discriminant function analysis correctly classified 73% of sounds between Atlantic Ocean and Mediterranean Sea. A cline in parameters was apparent from the Azores to the Mediterranean, with a major difference between the Canaries and the Mediterranean than between Azores and Canaries. Signal duration, maximum frequency, and frequency range measured in the Mediterranean sample were significantly lower compared to those measured in the Atlantic. Modulation parameters played a considerable role in area discrimination and were the only parameters contributing to highlight the differences within the Atlantic Ocean. Results suggest that the acoustic features constrained by structural phenotype, such as whistle's frequency parameters, have a major effect on the Atlantic and Mediterranean separation while behavioral context, social, and physical environment may be among the main factors contributing to local distinctiveness of Atlantic areas. These results have potential passive acoustic monitoring applications.
The authors are grateful to International Found for Animal Welfare (IFAW) research group for its contribution. Without its support this project could not have been realized. Data collection and processing in the Azores was funded by European Regional Development Fund (FEDER) funds, through the Competitiveness Factors Operational Programme—COMPETE, and by national funds, through FCT—Foundation for Science and Technology, under projects Ecology and population structure of bottlenose dolphins and sperm whales in the Azores: assessing the relationship with habitat features (CETAMARH) (POCTI/BSE/38991/01) and Cetacean habitat associations in oceanic ecosystems: an integrated approach (TRACE) (PTDC/MAR/74071/2006). M.A.S. was supported by a FCT postdoctoral grant (SFRH/BPD/29841/2006). I.C. and R.P. were supported by FCT doctoral grants (respectively, SFRH/BD/41192/2007 and SFRH/BD/32520/2006). IMAR-DOP/UAç is the R&D Unit #531 and part of the Associated Laboratory ISR funded through the Pluri-annual and Programmatic funding schemes of Foundation for Science and Technology (FCT-MCTES) and Direcçäo Regional da Ciência e Tecnologia (DRCT)-Azores. Data collection by SECAC was funded by the U.E. LIFE program—project LIFE Inventario y designación de la Red Natura 2000 en áreas marinas del Estado español (INDEMARES) (LIFE 07/NAT/E/000732)—and the Fundación Biodiversidad, under the Spanish Ministry of Environment, Rural and Marine Affairs [project Planes de Uso y Gestión de las Zonas de Especial Conservación (ZEC) marinas de la Región macaronésica de la Red Natura 2000 en España, cuyo objetivo de declaración incluye al delfón mular (Tursiops truncatus) (ZEC-TURSIOPS)]. Many thanks also to Alice Galli for the GIS representation, Peter Tyack for his constructive suggestions, and two anonymous reviewers.
I. INTRODUCTION II. MATERIALS AND METHODS A. Study area B. Data collection C. Data analysis III. RESULTS A. Study effort B. Whistle diversity between Atlantic Ocean and Mediterranean Sea C. Whistle variation among the Azores, Canaries, and Mediterranean Sea IV. DISCUSSION