Research Document - 2009/031

Distribution and Preliminary Abundance Estimates for Cetaceans Seen During Canada’s Marine Megafauna Survey - A Component of the 2007 TNASS

By J.W. Lawson and J-F. Gosselin

Abstract

The Canadian Department of Fisheries and Oceans (DFO) conducted a large-scale aerial survey of marine megafauna in the northwest Atlantic during the summer of 2007. This is the first systematic effort to provide coverage for much of the eastern Canadian seaboard, and the first in more than two decades to survey the continental shelf along the Labrador and Newfoundland coasts for marine mammals, sea turtles, and other species that intermittently reside near the surface. The Canadian survey is a component of the multinational Trans North Atlantic Sightings Survey (TNASS) that extends from the northeastern U.S.A. to the U.K. The Canadian survey included three initiatives that covered different geographic areas: 1) Labrador Shelf and Grand Banks, 2) Gulf of St. Lawrence and 3) Scotian Shelf. Using a deHavilland Twin Otter and two Cessna 337 Skymaster aircraft, and multiple trained observers, we flew transects at altitudes of 183 and 198 m, respectively, to gather data on the distribution and abundance of a variety of marine megafauna at the ocean surface. Using Distance-based analytical techniques, with covariates such as group size, sighting cue, depth, sea state and sea surface temperature (collected in real time from the Twin Otter), we estimated the abundance and distribution of mysticete species such as blue, fin, humpback, and minke whales, as well as large (sperm, pilot and killer whales) and small (white-beaked, common and Atlantic white-sided dolphins, and harbour porpoises) odontocetes, leatherback sea turtles, sunfish, and basking sharks. Here we present the cetacean data, uncorrected for perception and availability biases. The most abundant species was the common dolphin (54,625; 95% CI: 35,179-81,773), with lower numbers of other small cetaceans (e.g., Atlantic white-sided dolphin: 5,796; 95% CI: 2,261-13,088, and harbour porpoise: 4,955; 95% CI: 2,254-8,971). Pilot whales were the most abundant medium-sized species (5,612; 95% CI: 3,020-10,867), while there were an estimated 2,149 humpback (95% CI: 1,347-3,169), and 1,360 fin whales (95% CI: 825-2,241). These abundance estimates are negatively biased due to the lack of correction factors for availability and perception biases. Once corrected, the results will be integrated with concurrent data from other international components of the TNASS to produce the first estimate of abundance in the North Atlantic. These data will greatly improve our understanding of marine populations whose summer home ranges extend across international boundaries and improve our ability to provide advice for these species within Canada.

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