Does interspecific competition drive patterns of habitat use and relative density in harbour porpoises?
Determining the drivers that are responsible for the fine-scale distribution of cetacean species is fundamental to understand better how they respond to changes in their environment. We utilized information theoretic approach to carry out a comprehensive investigation of the key environmental and anthropogenic correlates of habitat use and relative density of harbour porpoises. In all, 273 daily boat surveys over a period of 38 months, between April 2014 and November 2017, were spent in the field monitoring 9417 km along the coastal and shelf waters of Northwest Spain. Throughout this period, there were 70 encounters with harbour porpoises and 712 encounters with common bottlenose dolphins. The observed unequal use of available habitat indicates that harbour porpoises present a fine-scale pattern of habitat selection along the study area, which is likely related to the variation in oceanographic variables and human disturbance mainly caused by marine traffic and fisheries. While differences in habitat use between harbour porpoises and bottlenose dolphins were observed, interspecific competition with bottlenose dolphins (as competitive exclusion hypotheses) did not appear to play an important role in the distribution and relative density of harbour porpoises. These findings highlight the importance of considering both environmental and anthropogenic variables in ecological studies, in addition to highlighting the importance of using a multi-species ecology approach in research and conservation management planning.
Field observations carried out during this work are part of a long-term study supported by funding from the Bottlenose Dolphin Research Institute (BDRI). We would like to thank Niki Karagouni, Victoria Hope, and Oriol Giralt Paradell who generously gave their time to help with field and laboratory work. Many thanks are also extended to the BDRI students and volunteers who assisted with fieldwork and data transcription. Authors thank the valuable comments of Daniel E. Crocker and three anonymous reviewers which helped to improve the quality of the manuscript. Data collection complies with the current laws of Spain, the country in which it was performed.
BDL and SM conceived, designed, and executed this study. BDL analysed the data and wrote the manuscript, and SM provided editorial advice.
This research did not receive any specific Grant from funding agencies in the public, commercial, or not-for-profit sectors.
Compliance with ethical standards
Conflict of interest
The authors of this study declare that they have no conflict of interest.
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