Vol.:(0123456789) 1 3 Marine Biology (2018) 165:15 https://doi.org/10.1007/s00227-017-3265-z ORIGINAL PAPER Female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland Isabel Baker 1,2  · Joanne O’Brien 1,2  · Katherine McHugh 3  · Simon Berrow 1,2 Received: 21 July 2017 / Accepted: 6 November 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 Abstract 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 ves- sel. During 1018 sightings, 4231 identifcations 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 reproduc- tive 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. Introduction Bottlenose dolphins (Tursiops spp.) are found across the globe in temperate and tropical waters and in a range of habitats (Wells and Scott 1999). As a result, diferent popu- lations are subject to diferent ecological and environmental conditions and pressures. Marked variations in population dynamics, behaviour and social structure have also been reported, perhaps due to the high level of intelligence of the species (Connor et al. 2000). In light of these socio- environmental diferences between demographically dif- ferent populations, it is to be expected that the life history parameters of populations may also vary considerably. This makes it essential to establish baseline life history param- eters for specifc populations to explore species ecology and inform management. The production of reliable life history parameters is dependent on longitudinal studies with consistent continu- ous data collection (Wells 1991; Mann and Karniski 2017). Repeated sightings of identifable individuals over a long time period allows for the aggregation of individual repro- ductive histories and thus, the estimation of reproductive parameters such as birth rates, calf mortality and inter-birth intervals (Fruet et al. 2015; Tezanos-Pinto et al. 2015). For long-lived, slow-reproducing mammals like bottlenose dol- phins, these long-term datasets are essential for producing both individual- and population-level parameters for demo- graphics, patterns of reproduction and a better understanding Responsible Editor: U. Siebert. Reviewed by C. Lockyer and an undisclosed expert. * Isabel Baker Isabel.Baker@research.gmit.ie 1 Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland 2 Shannon Dolphin and Wildlife Foundation, Merchants Quay, Kilrush, County Clare, Ireland 3 Sarasota Dolphin Research Program, Chicago Zoological Society, c/o Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA