Abundance and distribution of harbour porpoisesPhocoena phocoena in selected areas of the western Baltic and the North sea

Abstract

An aerial survey of harbour porpoises,Phocoena phocoena, was conducted in June–July 1992 in the western Baltic (Bay of Kiel, the Great Belt, Little Belt, an area north of Fyn) and a coastal area in the North Sea off the island of Sylt. Survey procedures and statistical analysis were identical to those of a similar survey in 1991 and survey results from the two years were compared. The highest density of porpoises was found in the North Sea area, whereas the Bay of Kiel and the Little Belt had low densities. The Great Belt and the area north of Fyn had intermediate densities and the area north of Fyn had a density similar to that found in the same area in 1991. The distribution of the perpendicular sighting distance from the surveys in 1991 and 1992 was identical in locality and dispersal, but gave rise to different estimates of effective search widths. Pod sizes for the 1992 survey were smaller than pod sizes estimated from boat surveys, but were within the range of those for the 1991 aerial survey.