Research Document - 2012/157

Distribution, densities, and annual occurrence of individual blue whales (Balaenoptera musculus) in the Gulf of St. Lawrence, Canada from 1980-2008

By C. Ramp and R. Sears

Abstract

This document describes the distribution of individually identified blue whales (Balaenoptera musculus) in the Gulf of St. Lawrence (GSL), Canada. Data were collected by the Mingan Island Cetacean Study (MICS) from 1980 to 2008. The aim of this project was to provide additional information for designating blue whale critical habitat as required under the Canadian Species at Risk Act. Data from photo-identification surveys yielding over 13,000 blue whale sightings were used to identify the distribution and densities of blue whales in the north-western section of the GSL. Surveys focused on the area west of 63ºW and included opportunistic sightings from collaborators. Daily first sightings of individually identified blue whales were used to calculate encounter rates and sightings per unit of effort in each region. The largest concentrations of blue whales were found in the lower St. Lawrence Estuary, around the eastern tip of the Gaspé Peninsula, along the north shore of the Jacques-Cartier Passage, and in the waters adjacent to Sept-Îles. Several changes in blue whale distribution were observed over the course of the study period. A major shift occurred in 1992/1993, when blue whales abandoned the Jacque-Cartier Passage. The GSL is a major summer feeding ground for blue whales and they occur predominantly along the productive coasts. In general, blue whales can be observed almost anywhere in the north-western GSL. In some areas, for example along the north shore of the Gaspé Peninsula, blue whales seem to pass through on their way to and from the lower St. Lawrence Estuary. The areas with highest blue whale densities and longest residency times included the north shore of the lower St. Lawrence Estuary and the eastern tip of the Gaspé Peninsula between Rivière-au-Renard and Percé. The northern banks of the Jacques-Cartier passage were important in the years prior to 1994. Although blue whales come mainly to the GSL to feed in summer, they can occur year-round. The number of sightings tended to increase throughout the summer season, peaking in late August and early September; however, regional differences were apparent. The first peak in sightings occurred in June/July when blue whales were observed off of the Gaspé Peninsula, while sightings in the lower Estuary drove the main peak in August/September. A total of 402 blue whales have been identified in the GSL since 1980 and a maximum of 32% of these were sighted in any given year. Blue whales were observed an average of only two days per season (occurrence), with an average occupancy of 22 days. The low numbers of re-sightings within years suggest that blue whales in the GSL are highly mobile.

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