Cetacean sigthings in North Sea

Original provider: Marijke N. de Boer Dataset credits: Marijke N. de Boer Abstract: Minke whales and other marine mammals were recorded in the central North Sea in an area characterised by frontal features and high productivity northeast of the Dogger Bank (4677 km2). Survey efforts were carried out from 28 March to 2 July 2007, at a finer scale than in earlier studies in the region, using 2 vessels as platforms of opportunity and a dedicated line- transect survey vessel following distance sampling methods. The high density of whales indicated that this offshore bank slope is an important spring habitat for minke whales in the North Sea. In total, 77 sightings of minke whales comprising 130 individuals were recorded. The peak density of minke whales was estimated to be 0.029 whales km–2 (minimum estimate, 95% CI: 0.012 to 0.070) in May. During peak abundance, the minke whales temporarily congregated in the area, suggesting that the whales were taking advantage of the local spring abundance of sandeels. The density found was higher than previous studies have suggested for the central North Sea. The results correspond to recent observations of minke whale redistribution within the North Sea, and these may be related to a decline in sandeel availability elsewhere in the North Sea. Offshore banks that aggregate prey may therefore become increasingly important feeding habitats for minke whales and other top predators in the North Sea. The observed habitat preference of minke whales along this offshore bank appeared to be similar to that observed in coastal areas, and this suggests some degree of generality regarding the preference for this type of habitat. Purpose: As part of a geophysical seismic survey, marine mammals observations were carried out from three vessels: one seismic vessel, one supply vessel operating well ahead from the seismic vessel. The third vessel, MV ‘Andfjord’, carried out a dedicated Line Transect (LT) survey (23 April to 17 May). The LT vessel was surveying at distances of ≥20 km away from the geophysical vessel and followed predetermined line transects placed randomly in a zigzag pattern in the central (German) part of the survey area.