Summer Distribution and Relative Abundance of Cetaceans off the West Coast of Ireland

Abstract

From May to September 2004 a survey of cetacean distribution and relative abundance was conducted on board a 'ship of opportunity' * a vessel used as a survey platform but not chartered for this purpose * off the west coast of Ireland. In total, 508 hours of survey effort were completed, with 304.2 hours in Beaufort sea-state 3 or less. Two hundred and thirty one sightings of eight species* common dolphin Delphinus delphis (L.), Atlantic white-sided dolphin Lagenorhynchus acutus (Gray), bottlenose dolphin Tursiops truncatus (Montagu), harbour porpoise Phocoena phocoena (L.), Risso's dolphin Grampus griseus (Cuvier), pilot whale Globicephala melas (Traill), minke whale Balaenoptera acutorostrata (Lacepede) and fin whale Balaenoptera physalus (L.) * were recorded, totalling 2,933 individuals. The greatest diversity and relative abundance were recorded on the Rockall Bank where Atlantic white-sided dolphin was the most abundant species. The common dolphin was the most abundant species recorded on the continental shelf to the southwest of Ireland, while the relative abundance of cetaceans off the north coast was very low. The data suggest that cetacean species composition and relative abundance can vary greatly between adjacent marine habitat types and over relatively small geographical distances.

Summer Distribution, Relative Abundance and Encounter Rates of Cetaceans in the Mediterranean Waters off Southern Italy (Western Ionian Sea and Southern Tyrrhenian Sea)

“…However, due to variation in visibility during the survey, observations were not continuous and differed according to the run. For this reason and due to the fact that along the transect sighting could be considered an event and not a state, the relative abundance was measured using Encounter Rate (ER): i.e., numbers of sightings per hour of observation (Evans & Hammond, 2004;Wall et al, 2006). Data from the two investigated periods were compared with the Mann-Whitney (MW) test.…”

“…The cost of dedicated surveys on chartered research ves-sels is generally prohibitive in terms of carrying out regular surveys. For this reason, vessels of opportunity has been widely used for opportunistic surveying of cetaceans (Northridge et al, 1995;Pollock et al, 1997;Berrow et al, 2001;Reid et al, 2003;Evans & Hammond, 2004;O´Cadhla et al, 2004;Wall et al, 2006;. In particular, ferries allow for repetitive surveys along a fixed transect which can be conducted regularly over progressive years within a particular area of interest .…”

Using platforms of opportunity to determine the occurrence and group characteristics of orca (Orcinus orca) in the Hauraki Gulf, New Zealand

“…For example, tour vessels have been used to good effect as a research platform in studying cetaceans, including, but not limited to, studies of mother-calf interactions (Sardi et al 2005), distribution (Hauser et al 2006;Wiseman et al 2011), sightings per unit effort (Koslovsky 2008), habitat preferences (Moura et al 2012), occurrence (Dahood et al 2008;Stockin et al 2008b;Davidson et al 2014) and predation events (Visser et al 2010). However, using such PoPs places a number of limitations on the type of data which can be collected and interpreted without the introduction of biases (Hauser et al 2006;Wall et al 2006;Kiszka et al 2007;Wiseman et al 2011;Moura et al 2012).…”

“…Second, a researcher is limited by the length of time spent with a focal group and how the vessel is manoeuvred around focal individuals/groups (e.g. Wall et al 2006). Third, only animals occurring in close proximity to the vessel can be observed, which may limit species identification and group size estimation (Palacios et al 2012).…”

The distribution and habitat preference of coastally occurring minke whales (Balaenoptera acutorostrata) in the outer southern Moray Firth, northeast Scotland

“…In northwest Europe, it occurs widely along the Atlantic seaboard from Norway to France and throughout the North Sea, although less commonly in the southern North Sea and eastern Channel . In UK waters, the species is typically sighted in inshore, shelf and coastal regions less than 200 metres deep (Northridge et al 1995;Weir et al 2001;Macleod et al 2004;Wall et al 2006), but shows seasonal shifts in latitudinal abundance throughout its range (Stewart and small numbers year-round in some locations (Macleod et al 2004). …”