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Using opportunistic photo-identifications to detect a population decline of killer whales (Orcinus orca) in British and Irish waters

Published online by Cambridge University Press:  04 September 2013

Suzanne Beck
Affiliation:
Marine Biodiversity Research Group, Galway—Mayo Institute of Technology Dublin Road, Galway, Ireland
Andrew D. Foote
Affiliation:
Center for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Øster Volgade 5-7, DK-1350 Copenhagen K, Denmark
Sandra Kötter
Affiliation:
Hebridean Whale and Dolphin Trust, 28 Main Street, Tobermory, Isle of Mull, PA75 6NU, UK
Olivia Harries*
Affiliation:
Hebridean Whale and Dolphin Trust, 28 Main Street, Tobermory, Isle of Mull, PA75 6NU, UK
Laura Mandleberg
Affiliation:
Hebridean Whale and Dolphin Trust, 28 Main Street, Tobermory, Isle of Mull, PA75 6NU, UK
Peter T. Stevick
Affiliation:
Hebridean Whale and Dolphin Trust, 28 Main Street, Tobermory, Isle of Mull, PA75 6NU, UK
Pádraig Whooley
Affiliation:
Irish Whale and Dolphin Group, Dereen, Rossmore, Clonakilty, Co. Cork, Ireland
John W. Durban
Affiliation:
Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 8901 La Jolla Shores Drive, La Jolla, CA 92037, USA
*
Correspondence should be addressed to: O. Harries, Hebridean Whale and Dolphin Trust, 28 Main Street, Tobermory, Isle of Mull, PA75 6NU, UK email: [email protected]

Abstract

An assemblage of killer whales that has been sighted in waters off the west coast of the British Isles and Ireland has previously been shown to be isolated from other North Atlantic killer whale communities based on association patterns. By applying a Bayesian formulation of the Jolly–Seber mark-recapture model to the photo-identification data compiled from opportunistic photographic encounters with this population of killer whales, we show that such sparse and opportunistically-collected data can still be valuable in estimating population dynamics of small, wide-ranging groups. Good quality photo-identification data was collected from 32 encounters over 19 years. Despite a cumulative total of 77 identifications from these encounters, just ten individuals were identified and the remaining 67 identifications were re-sights of these ten animals. There was no detected recruitment through births during the study and, as a result, the population appears to be in a slight decline. The demography of the population was highly skewed towards older individuals and had an unusually high ratio of adult males, and we suggest that demographic stochasticity due to a small population size may be further impacting the population growth rate. We recommend that this population be managed as a separate conservation unit from neighbouring killer whale populations.

Type
Research Article
Copyright
Copyright © Marine Biological Association of the United Kingdom 2013 

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