Some characteristics of narwhal, Monodon monoceros, diving behaviour in Baffin Bay

Abstract

Dive data were collected from nine narwhals, Monodon monoceros, instrumented with satellite-linked dive recorders in northwest Greenland in August–September 1993 and 1994. Data were collected for periods ranging from a few weeks to 9 months. The narwhals made daily dives to depths of more than 500 m and frequently dived to 1000 m or more. However, most of the time spent below the surface was in the water column at depths of between 8 and 52 m. For two males that were tracked from September through November the maximum dive depth increased steadily through time. There were no consistent differences in the duration of dives or the number of dives to depths > 8 m during four 6-h periods that were monitored. There were significant differences in dive rates (number of dives per hour) between the large males, the small male, and the females. More than half of the dives lasted less than 5 min and few lasted more than 20 min. These relatively short dive times suggest that narwhals do not exceed their aerobic dive limit. The average time spent in the upper 5 m of the water column was 39.3% (SD = 13.5%; n = 632) for seven whales combined. Speed of vertical movements increased significantly from 1 m∙s−1 for 100-m dives to more than 2 m∙s−1 for dives deeper than 900 m. A female accompanied by a calf had dive parameters and surfacing times that were identical with those of the other females.