Novel data on the abundance and distribution of harbour porpoises in the North Sea, particularly in winter, are required to determine their current conservation status. A priority area for survey effort is the Dogger Bank, currently a candidate Special Area of Conservation (cSAC) under the EC Habitats Directive (Natura 2000) and part of the OSPAR network of Marine Protected Areas in the North East Atlantic Ocean. Data from the Joint Cetacean Protocol Database have indicated that the UK cSAC area is no more important for harbour porpoises than other parts of the North Sea and porpoises have therefore been removed as a qualifying feature of the site by the JNCC. However, the JCP relies on visual techniques that may be inferior to acoustic techniques for detecting porpoise presence. During November 2011, IFAW and Marine Conservation Research International conducted a visualacoustic survey in the central North Sea to investigate the presence and distribution of harbour porpoises with the aim of providing baseline data on distribution and relative abundance in a period that has traditionally received little survey effort. Over 4187 km of survey effort, 13 porpoise groups were observed with between one and six individuals (mean group size = 1.6). The acoustic detection rate was approximately 50 times higher, with 769 unique events being identified of which 561 were made on the survey trackline (19.0 detections per 100 km). There were significantly more detections in the west of the survey region than the east, with peak detections (43.7 per 100 km) in the waters to the southwest of the cSAC. These findings support growing evidence of a southward shift of harbour porpoises in the North Sea. A similar survey recently conducted by IFAW/MCR International suggests any elevation in porpoise number in the south of the North Sea is unlikely to be due to migration through the English Channel. If any recovery of porpoise numbers in the North Sea is to be secured, efforts must be made to limit potentially disturbing activities, such as those associated with the proposed development of the Hornsea Offshore (Round 3 Zone 4) Wind Farm. Sightings of other marine mammals are also presented. |
