Although the UK has only a relatively small section of the North Atlantic Ocean, these waters have very diverse topography, habitats and food resources. Thus, we have a large diversity of cetaceans – whales, dolphins and porpoises. Some 28 species of cetacean have been recorded here, of which 11 appear regularly. The greatest diversity occurs off the continental shelf, particularly in waters to the north and west of Scotland and in the southwest.

Cetaceans as a group have a long history of direct exploitation by humans and continue to be impacted both directly and indirectly by a range of human activities. As a result, all species are protected by various international conventions and agreements.

Cetaceans are very mobile, and some range widely including regular seasonal migrations. This means that most of the animals found in UK waters are part of much larger and more widespread biological populations. Also, the number of individuals present at any one time may be only a small proportion of those that make use of UK waters at some point during their lives. We based our assessment for this report on expert judgement, using mainly the 2007 Favourable Conservation Status (FCS) assessments of all cetacean species occurring in UK waters. The assessments used a baseline of the Cetacean Atlas and/or data from the large-scale dedicated surveys undertaken in 1994, which generated information on summer distribution and abundance estimates for a range of species. We supplemented these with data collected in 2005 during SCANS II, and with additional survey work undertaken in 2007 off the continental shelf, as well as continued collection of strandings and by-catch data and assessments of bottlenose dolphins in nearshore Special Areas of Conservation (SACs). The judgements also took into account the approach used for the OSPAR Quality Status Report 2010 assessments. The final status assessments were therefore a combination of the FCS and OSPAR approaches, using OSPAR terminology for the final condition statement.

The FCS assessment was considered favourable for the five species that are most abundant in UK waters. (This paragraph is a summary of the Article 17 report required under the EU Habitats Directive, hence the term ‘favourable’ here.) The status of a further six species was unknown due to a lack of suitable abundance estimates. The remaining 17 species are considered rare or vagrant and therefore we could not assess their conservation status in UK waters.

Overall, cetaceans as a group are considered to be in good condition in both the Northern North Sea and Southern North Sea; although we cannot assess them with a high degree of certainty. Cetaceans are considered to be in poor condition in the Eastern Channel, and in moderate condition in the Western Channel and Celtic Sea, the Irish Sea and the Minches and Western Scotland waters. The status of cetaceans is unknown in the Scottish Continental Shelf area and offshore waters north and west of Scotland. Sitebased assessment of certain SACs, designated specifically for bottlenose dolphins, suggest that these populations are stable. With the possible exception of the inshore populations of bottlenose dolphins, it should be noted that for most cetacean populations it is not appropriate to report on status for individual regions since most populations cross these boundaries and, data collection is of insufficient resolution to allow such an assessment.

Direct mortality through by-catch in fishing gears remains the most important human impact on cetaceans in UK waters, predominantly affecting harbour porpoise and common dolphins. Nevertheless, by-catch has declined in the Northern North Sea, the Southern North Sea, and the Irish Sea due to a decline in static net fishing. Historic by-catch probably contributed to the current low densities of harbour porpoise in the Eastern Channel. The number of cetaceans caught accidentally appears to have remained stable in the Western Channel and Celtic Sea. By-catch seems less of a problem in Scottish waters compared to other areas of the UK. However, the entanglement of minke whales in nets is recognised as an issue in the Minches.

Cetaceans are particularly vulnerable to persistent organic pollutants, such as polychlorinated biphenyls (PCBs) and flame retardants, which can affect development, growth and reproduction and can increase vulnerability to infection. In the early 1990s there were high concentrations of pollutants in the tissues of several species of cetacean in UK waters, but more recently the concentration levels seem to be declining.

The impact of climate change on cetaceans remains poorly understood. It is extremely difficult to separate changes in abundance or distribution as a result of short-term regional variability in the prey resource from changes due to longer-term environmental change. The direct impact of any future climate change on cetaceans in UK waters is only likely to be observed in those species for which the UK represents the edge of their range, such as white-beaked dolphins. Cetaceans may, however, be impacted indirectly through changes in prey distribution and greater susceptibility to disease and contaminants. In addition to the current monitoring of designated sites, a strategic monitoring and surveillance programme will be essential to meet the requirements of the EU Habitats Directive and the Marine Strategy Framework Directive. As cetaceans are so mobile and range so widely, the work will need a fully international approach.

A better understanding of the abundance and distribution patterns of cetaceans, including any seasonal variation, as well as basic life history parameters such as growth rates, age at sexual maturity, reproductive rates and mortality, would help determine the magnitude of any impacts on populations and also potentially aid industry in reducing the risk of impacts.

Although the UK’s by-catch monitoring scheme is recognised as one of the best in Europe, there is a need for further monitoring of static-net fisheries where cetacean by-catch is greatest. This will inform possible management measures, which will need to be implemented at a European rather than national level. Work will need to continue on assessing the effectiveness of acoustic deterrent devices in fisheries. We also need more information about the potential impacts on cetaceans of other anthropogenic activities that generate noise in different sea areas and under different environmental conditions. The possible synergistic effects of chronic exposure of cetaceans to various environmental pollutants also require further consideration.

Finally, we need to develop the frameworks and methods for assessing conservation status, review the thresholds above which change can realistically be detected, and set the baselines for future assessments.