Journal of the Marine Biological Association of the United Kingdom, page 1 of 13. # Marine Biological Association of the United Kingdom, 2016 doi:10.1017/S0025315416001594 Temporal and spatial trends in stranding records of cetaceans on the Irish coast, 2002–2014 barry mcgovern1,2, ross m. culloch1,3, michael o’connell1 and simon berrow1,4 1Irish Whale and Dolphin Group, Merchants Quay, Kilrush, Co. Clare, Ireland, 2Namibian Dolphin Project, Waterfront, Walvis Bay, Erongo, Namibia, 3MaREI Centre, Environmental Research Institute, University College Cork, Beaufort Building, Co. Cork, Ireland, 4Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Galway, Ireland Using Irish strandings data collected between 2002 and 2014, seasonal and annual trends in the number of strandings for all strandings identified to species level (N ¼ 1480), and for the five most frequently reported species: common dolphin (25.7% of records), harbour porpoise (22.2%), long-finned pilot whale (8.8%), striped dolphin (6.9%) and bottlenose dolphin (6.9%) were investigated. With the exception of bottlenose dolphins, there was a significant linear increase in the number of strandings across years for all species and for all strandings collectively, that were identified to species-level. Only common dolphins demonstrated a significant increase in the proportion of records relative to all other strandings, which may be indicative of a real rise in the number of strandings of this species. Common dolphins and harbour porpoises showed a similar significant difference in monthly strandings, with more strandings occurring during the earlier months of the year. Significant differences in the gender of stranded animals were found in common, striped, bottlenose and Atlantic white-sided dolphins and sperm and pygmy sperm whales. Live and mass stranding events were primarily comprised of pelagic species. Most strandings occurred on the south and west coasts, with two hotspots for live and mass strandings identified. The patterns and trends identified are discussed in relation to the caveats in interpreting strandings data. Specifically to Ireland, the findings highlight the urgent need to build on the current volunteer reporting network and augment this comprehensive dataset with post- mortem examinations to better understand the cause of the trends identified. The importance of strandings data in informing conservation and management guidelines of these species’ is discussed. Keywords: Bycatch, common dolphin, harbour porpoise, mass stranding, live stranding, stranding network Submitted 20 November 2015; accepted 21 October 2016 INTRODUCTION of death is generally thought to be a result of natural occur- rences such as disease, illness, parasitism or injury (Brabyn Systematic recording of stranded cetaceans offers a cost- & McLean, 1992; Mazzuca et al., 1999). Anthropogenic effective and efficient method of collecting data on the pat- causes do account for a certain number of single strandings terns of occurrence (Siebert et al., 2006; Canning et al., and in some instances can be the primary cause of death, 2008), population structure (Mirimin et al., 2009), distribu- for example, minke whales (Balaenoptera acutorostrata)in tion (Mitchell, 1968; Norman et al., 2004), species diversity Scotland (Northridge et al., 2010) and common dolphins (Pyenson, 2011), anthropogenic threats (Panigada (Delphinus delphis) in Cornwall (Leeney et al., 2008). A live et al., 2006; D’Amico et al., 2009; Jepson et al., 2013; stranding event (LSE) occurs when an animal is found alive Allen et al., 2014), disease prevalence (Greig et al., 2005; on the shore or when post-mortem examination determined Davison et al., 2015), life history (Rogan et al., 1997; the animal(s) to have stranded alive. A mass stranding event Westgate & Read, 2007) and diet (Canning et al., 2008; (MSE) occurs when two, or more, individuals of the same Begon´a Santos et al., 2014). For many rarely sighted species species, that are not mother and calf, are found, dead or (e.g. Ziphiids), stranded individuals represent the primary alive, while coinciding both spatially and temporally (Rogan source of information on all aspects of their ecology et al., 1997; Geraci & Lounsbury, 2005). A MSE generally con- (Dalebout et al., 2002; Constantine et al., 2014). sists of pelagic, odontocete species and can range from two to A stranding event can refer to single or multiple animals hundreds of individuals (Mazzuca et al., 1999). These events that may be alive or dead when they make landfall. The generate huge interest from both scientists and the general most frequently recorded stranding events worldwide are public. The cause of MSEs are poorly understood; several sug- single dead individuals (Norman et al., 2004) and the cause gestions as to why they might occur naturally include: naviga- tional errors due to geomagnetic anomalies (Klinowska, 1985; Walker et al., 1992; Brabyn & Frew, 1994), large-scale climate Corresponding author: and oceanographic variation (Mignucci-Giannoni et al., 2000; B. McGovern Evans et al., 2005; Bradshaw et al., 2006) and as a consequence Email: [email protected] of tight social bonds (Connor, 2000), or a combination of the 1 Downloaded from http:/www.cambridge.org/core. IP address: 197.233.217.2, on 12 Dec 2016 at 11:02:50, subject to the Cambridge Core terms of use, available at http:/www.cambridge.org/core/terms. http://dx.doi.org/10.1017/S0025315416001594 2 barry mcgovern et al. above. Several anthropogenic effects have also been linked knowledge on patterns in cetacean strandings obtained from with MSEs, including fisheries interactions (Kinas, 2002; long-term datasets, whilst more locally, it will provide a Leeney et al., 2008; Allen et al., 2014), naval exercises better understanding of cetacean populations and their (Parsons et al., 2008; D’Amico et al., 2009; Jepson et al., ecology within Ireland. The study will also provide informa- 2013) and seismic surveys (Simmonds & Mayer, 1997). tion that can assist Ireland in fulfilling its legal requirements Geographic locations where clusters of strandings have under the Habitats Directive. occurred have been documented in New Zealand, (Brabyn, 1991; Brabyn & McLean, 1992), Australia (Bradshaw et al., 2006) and Hawaii (Mazzuca et al., 1999). These areas are METHODS often referred to as stranding hotspots; where two or more MSEs or three or more single strandings have occurred All records from 2002–2014 from the Republic and Northern (Brabyn, 1991). It is thought that some of these areas may Ireland in the IWDG strandings database were examined, contain oceanographic features that are indirectly influencing prior to analysis. The data prior to 2002 was omitted in strandings patterns (Bradshaw et al., 2006), such as discon- order to minimize any bias in reporting effort due to increased tinuities in the geomagnetic fields, bathymetric topography promotion of the strandings network under the ISCOPE ini- or unusual current patterns (Brabyn & McLean, 1992; tiative. The data, collated by the IWDG, consists of public Walker et al., 1992; Brabyn & Frew, 1994; Bradshaw et al., records which were submitted via the website (www.iwdg.ie) 2006). and were published in the Irish Naturalists’ Journal Irish waters are some of the most important for cetaceans (O’Connell & Berrow, 2008, 2009, 2010, 2013, 2014a, b, in Europe, with 24 species recorded to date (Reid et al., 2003; 2015). Where possible, each stranding record consists of O’Brien et al., 2009; Wall et al., 2013). All species, and their date of stranding, date of recording, location, species, resting and breeding sites, are protected by national legislation gender, length, body condition and the name of the recorder. (Wildlife Act 1976, Amended 2000). Under the EU Habitats Most (80%) of the records were submitted online or via Directive, Ireland is obliged to protect all cetacean species email and 90% of these had accompanying images, which and their habitats within the Exclusive Economic Zone, assisted in verifying species’ identity and gender. The IWDG which extends up to 200 nautical miles offshore. Further to have a network of people around the coast who are available this legislation there is a requirement to undergo surveillance to visit stranded animals and ensure relevant data are col- to ensure that all cetacean populations are maintained at a lected; between 2002 and 2014 60% of reported strandings ‘favourable conservation status’ as outlined in the conserva- were visited by members of the IWDG network. These data tion measures and management plans (EC, 2002). One of are then subject to verification and the record is then con- the more financially viable approaches for obtaining data on firmed by the IWDG prior to being uploaded onto the cetacean populations is to record information from stranded online database. Unless stated otherwise, ‘strandings’ refers animals. Strandings have been recorded in Ireland since to an event and does not take into account the number of indi- 1753, though there are historical records that date as far vidual animals stranded. back as 652 AD (Fairley, 1981), which makes the Irish strand- ings database one of the most temporally comprehensive cet- Statistical analysis acean datasets in existence (Pierce et al., 2007). Historically, records up to 1976 were collected as part of the British and Seasonal and annual trends were investigated using counts for Irish Whale Stranding Scheme coordinated by the Natural all strandings identified to species-level and for