Abstract
In the early 1990s, the high bycatch of harbour porpoise in gillnet fisheries in the North and Celtic Seas prompted researchers from Range States to develop a project to survey these waters with the aim of obtaining the first comprehensive estimates of abundance of harbour porpoise. As a result, the first large-scale line transect (distance) sampling survey for cetaceans (Small Cetaceans in European Atlantic Waters and the North Sea, known as SCANS) was conducted in summer 1994 (Hammond et al. 2002). SCANS generated abundance estimates for harbour porpoise that allowed bycatch (and other anthropogenic pressures) to be assessed in a population context. Abundance was also estimated for white-beaked dolphin and minke whale in the North Sea.
SCANS 1994 was envisaged to be the first in a series of large-scale, long-term surveys with an approximately decadal frequency. Accordingly, a second survey covering all European Atlantic shelf waters was conducted in 2005 (SCANSII 2008; Hammond et al. 2013), supplemented by a survey in offshore waters in 2007 (CODA 2009). A third survey, SCANS-III, followed in 2016 (Hammond et al. 2021) covering the same area as SCANS-II and CODA combined but excluding waters to the south and west of Ireland, which were surveyed by the ObSERVE project in 2015 and 2016 (Rogan et al. 2018).
The motivation for ongoing surveys continues to be providing robust estimates of abundance to allow an assessment of anthropogenic pressures, such as bycatch. Moreover, there is a need to provide information on distribution and abundance of cetaceans required by Range States to report on Favourable Conservation Status under the Habitats Directive and on Good Environmental Status (GES) under the Marine Strategy Framework Directive (MSFD) (or National equivalent). This information is also needed for impact assessments of offshore industries, especially renewable energy. The Habitats Directive and MSFD have a reporting cycle of six years, and a fourth survey was thus planned for the early 2020s.
A primary aim of SCANS-IV was to provide robust large-scale estimates of cetacean abundance to inform the upcoming MSFD assessment of GES in European Atlantic waters in 2024. Some surveys generating robust estimates of abundance have been conducted since the SCANS-II/CODA surveys in 2005/2007, as detailed in Geelhoed et al. (2022), but these do not provide comprehensive estimates of abundance for multiple species over the whole of European Atlantic waters.
This report summarises design-based estimates of abundance for those cetacean species for which sufficient data were obtained during SCANS-IV: harbour porpoise (Phocoena phocoena), bottlenose dolphin (Tursiops truncatus), Risso’s dolphin (Grampus griseus), white-beaked dolphin (Lagenorhynchus albirostris), white-sided dolphin (Lagenorhynchus acutus), short-beaked common dolphin (Delphinus delphis), striped dolphin (Stenella coeruleoalba), long-finned pilot whale (Globicephala melas), beaked whales (all species combined; Cuvier’s beaked whale (Ziphius cavirostris), Sowerby’s beaked whale (Mesoplodon bidens) and unidentified beaked whale), fin whale (Balaenoptera physalus) and minke whale (Balaenoptera acutorostrata).