DIVING BEHAVIOR OF HARBOR PORPOISES, PHOCOENA-PHOCOENA

The diving behaviour of seven free-ranging harbour porpoises (Phocoena phocoena) was examined using time-depth recorders. In total, 8167 ind ividual dives were recorded over 254 h. The longest period of data col lection from an individual was 106.1 h. Mean dive depths and durations ranged from 14 +/- 16 to 41 +/- 32 m, and from 44 +/- 37 to 103 +/- 6 7 s, respectively. The maximum recorded dive depth and duration was 22 6 m and 321 s. This performance may not represent the maximum capacity of harbour porpoises but rather the maximum depth of the study area. Individual dives had similar rates of descent and ascent, which ranged from 1.1 +/- 0.6 to 2.3 +/- 1.4 m/s, and from 0.9 +/- 0.6 to 2.1 +/- 1.4 m/s, respectively. Two porpoises with monitoring periods >2 days d emonstrated a diel pattern in their diving, making fewer, but deeper d ives at night. Comparison of the diving behaviour of harbour porpoises with data on the depth of 140 porpoises entanglements in groundfish g ill nets in the Bay of Fundy showed these seven porpoises made between 22 and 70 % of dives to depths (range 20-130 m) where the majority of entanglements were reported.