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Female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

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This study investigates the female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland, using long-term relational sightings and photographic databases. Data were collected between 2008 and 2016, during 654 boat-based surveys, from two dolphin-watching vessels and a research vessel. During 1018 sightings, 4231 identifications of 184 individual dolphins were recorded. The population size was charted through direct counts of known dolphins from 2011 to 2015 (mean 142, range 131–150), with 145 extant individuals in 2015: 80 adults, 25 juveniles, and 40 calves. Excluding dependent calves, 121 individuals were sighted, of whom 98% (n = 119) were sighted in multiple years, with 64% (n = 77) sighted in all 4 years (2012–2015). Between 2008 and 2016, 37 reproductive females and 69 dependent calves were recorded. Overall, 35% (n = 13) of these females were sighted with one calf, 43% (n = 16) with two calves and 22% (n = 8) with three calves. An average of seven (range 3–10) calves were born each year. Parturition peaked in July. Weaning ages ranged from 2.0 to 4.1 (mean 2.9) years. The mean inter-birth interval ranged between 2.7 ± 0.6 and 3.5 ± 1.3 years, depending on the method used. Mean annual calving rate was 0.29 young-of-year/reproductive female/year. Average crude birth rate was 0.07 ± 0.01. Fecundity was 0.26 ± 0.03. An average 11% of newborn calves were lost before age 1. These results are generally within the lower range of values reported for similar populations and provide essential data for conservation management and global bottlenose dolphin research.

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Acknowledgements

We would like to thank the dolphin-watching tour boat operators, Geoff and Susanne Magee and Gerald and Geraldine Griffin, for their ongoing support of our work. Many thanks to Mr. Louis Keating and the staff at Kilrush Marina for sponsoring a berth for our research vessel and facilitating dolphin research surveys. Many thanks to Jeff Adams for help with FinBase. We are very grateful to all of the researchers involved—John Baker, Joanna Barker, Chantelle Barry, Sarah Blennerhassett, Florence Erbs, Aoife Foley, Elisa Keeling Hemphill, Mark Hosford, Lonneke Ijsseldijk, Emer Keaveney, Gary Kett, Stephanie Levesque, Stephanie Linehan, Michael Marrinan, Giada Maugeri, Enda McKeogh, Jamie Nicol, Paddy O’Dwyer, Victoria Odynsky, Jamie Phillips, Meadhbh Quinn, Katharina Reusch, Gary Robinson, Stefanie Rowland, Clodagh Russell, Conor Ryan, Andrew Shine, Rebecca Treacy, Kerstin Voigt and Joel Vikberg Wernström. Many thanks to Emer Rogan and Simon Ingram for biopsy sampling data. Dedicated behavioural research was carried out under licenses (nos. 109/2014, 020/2015) issued by the National Parks and Wildlife Service of the Department of Arts, Heritage, Regional, Rural and Gaeltacht Affairs.

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Authors and Affiliations

  1. Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland

    Isabel Baker, Joanne O’Brien & Simon Berrow

  2. Shannon Dolphin and Wildlife Foundation, Merchants Quay, Kilrush, County Clare, Ireland

    Isabel Baker, Joanne O’Brien & Simon Berrow

  3. Sarasota Dolphin Research Program, Chicago Zoological Society, c/o Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA

    Katherine McHugh

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  1. Isabel Baker
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Baker, I., O’Brien, J., McHugh, K. et al. Female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland. Mar Biol 165, 15 (2018). https://doi.org/10.1007/s00227-017-3265-z

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