Cetaceans in the Great South Channel, 1979–1989: right whale (Eubalaena glacialis)

A continuous 11-year time-series of aerial and shipboard survey data in the Great South Channel region reveals a remarkably consistent pattern of right whale distribution, with several interesting variations. Right whales occur in the area during the spring, with a distinct peak in May. Arrival and departure dates appear to vary by a month or more between years. The distribution is concentrated in the deeper basin north of the V-shaped 100-m isobath and a thermal front which approximately parallels the isobath. Within a single year, this concentration tends to be within a relatively small area and may remain stable for days or weeks. The center of distribution changes between years, and in 1984, 1987 and 1989 was on the eastern side of the basin rather than the “typical” western side. At any one time, nearly all of the right whales may aggregate into one to several clusters of <10 km2 each. A gradual southward shift in the center of distribution can be observed as the season progresses. Single-day abundance estimates, uncorrected for animals missed while submerged, ranged up to 179 animals. There was a statistically significant long-term increase in right whale sighting rates in the region, after correcting for estimated increases in survey efficiency, of 3.8% per year. This suggests that the population might be recovering, albeit slowly, from extreme depletion. It is likely that a significant proportion of the western North Atlantic right whale population utilizes the Great South Channel region as a feeding area each spring, aggregating to exploit exceptionally dense copepod patches.