A large-scale international survey estimates that there are more than 1.5 million whales, dolphins and porpoises in the European Atlantic.
The results of the survey, which were presented at the European Cetacean Society conference in Denmark this week, was coordinated by Professor Phil Hammond and Claire Lacey from the Sea Mammal Research Unit at the University of St Andrews.
The survey is the third in a series that began in 1994 (SCANS) and continued in 2005 (SCANS-II).
The most abundant species were harbour porpoise (467,000), common dolphins (468,000) and striped dolphins (372,000), with a further 158,000 either common or striped dolphins. Numbers of other species of dolphins estimated to be present were 28,000 bottlenose dolphins, 36,000 white-beaked dolphins and 16,000 white-sided dolphins.
Deep-diving whales that feed primarily on squid in offshore waters were estimated to be 26,000 pilot whales, 14,000 sperm whales and 11,000 beaked whales of several different species. Of the filter-feeding baleen whales, 15,000 minke whales and 18,000 fin whales were estimated to be present.
The results indicate that the shift seen in harbour porpoise distribution in the North Sea from the northwest in 1994 to the south in 2005 was maintained in 2016, with highest densities found in the southwestern North Sea, and north and east of Denmark.
For harbour porpoise, white-beaked dolphin and minke whale in the North Sea, the series of abundance estimates shows no change and a stable trend in abundance over the 22 years covered by the surveys.
For the other species in the region, at least one more survey will be needed in the future before the conservation status can be assessed.
Professor Hammond, who presented the results to an international audience, said, "The results from these large-scale international surveys in the last two decades have greatly expanded our knowledge of the distribution and abundance of cetacean species in European Atlantic waters, enabling fisheries bycatch and other anthropogenic stressors to be placed in a population context and giving a strong basis for assessments of conservation status."
The survey was a collaboration among scientists in nine countries bordering the Atlantic and was supported by the governments of those countries.
Three ships and seven aircraft surveyed an area of 1.8 million square kilometres from the strait of Gibraltar in the south to Vestfjorden, Norway in the north over 6 weeks in summer 2016. Teams of observers searched along 60,000 km of transect line, recording thousands of groups of cetaceans from 19 different species.
The data were collected using sampling methods designed to allow correction for animals missed on the transect line, without which estimates of abundance would be negatively biased. This was achieved using two semi-independent teams of observers on the ships and using the “circle-back” aerial survey method, in which the aircraft flies a loop to re-survey the same piece of transect.
The new estimates of abundance will be integral to cetacean assessments undertaken for the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) quality status report and for the EU Marine Strategy Framework Directive assessments of Good Environmental Status.
The results also enable the impact of bycatch and other anthropogenic pressures on cetacean populations to be determined, fulfilling a suite of needs under the EU Habitats Directive and the Agreement on the Conservation of Small Cetaceans in the Baltic, North east Atlantic, Irish and North Seas (ASCOBANS).
Dr Santos from the Instituto Español de Oceanografía, who coordinated the Spanish ship surveys, said, "SCANS-III is a good example of how international collaboration at EU level is needed for the assessment of status and trends to inform conservation management of these wide ranging species."
Dr Gilles (University of Veterinary Medicine Hannover, Foundation) and Dr Scheidat (Wageningen Marine Research) who jointly coordinated the aerial surveys added: "The survey has been a major achievement. It would not have been possible without the large international team of observers, pilots, captains and vessel crews, who worked long and hard to make the project a success.”
Collaborating partners and institutes were:
Professor Philip Hammond, Claire Lacey, project coordinators - Sea Mammal Research Unit, University of St Andrews, UK
Dr Jonas Teilmann - Department of Bioscience, Aarhus University, Denmark
Dr Helena Herr, Dr Anita Gilles - University of Veterinary Medicine Hannover, Foundation, Germany
Professor Vincent Ridoux - University of La Rochelle, France
Dr Meike Scheidat - Wageningen Marine Research, Netherlands
Dr Nils Øien - Institute of Marine Research, Norway
Dr José Vingada - Sociedade Portuguesa de Vida Selvagem, Portugal
Dr Begoña Santos - Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, Spain
Dr Patrik Börjesson - Swedish University of Agricultural Sciences, Sweden
Dr Kelly Macleod - Joint Nature Conservation Committee, UK