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Research Document 2022/012

Seasonal occurrence and spatial distribution of four species of baleen whales vulnerable to ship strikes in the Saguenay–St. Lawrence Marine Park (Quebec, Canada)

By Martins, C.C.A., Turgeon, S., Michaud, R., and Ménard, N.

Abstract

Information on seasonal occurrence and fine scale spatial distribution of baleen whales is essential to design effective conservation measures. Given the intensity of navigation activities which overlap with whale habitat, the Saguenay–St. Lawrence Marine Park area is considered a high risk area for vessel collision with cetaceans. Management measures to reduce the risk of collision and minimize disturbance were included in the Marine Activities in the Saguenay–St. Lawrence Marine Park Regulations which regulate the activities of commercial and recreational boats in the park. Additionally, voluntary protection measures in and around the marine park were implemented in 2013 in collaboration with the shipping industry with the aim to minimize the risk of ship strikes with baleen whales and the impact of noise for the St. Lawrence Estuary beluga whales.

Datasets from different monitoring programmes were analyzed in order to characterize baleen whale occurrence and spatial distribution within the marine park and its surrounding waters. The modelling approach, applied to both line-transect and point-sampling databases, allowed us to identify areas of high predicted relative density of four baleen whale species: minke (Balaenoptera acutorostrata), fin (Balaenoptera physalus), blue (Balaenoptera musculus) and humpback whales (Megaptera novaeangliae). The use of spatial and fixed environmental variables allowed us to map the whale density over the space providing valuable information on each species distribution within the study area.

Overall, the potential core habitat of minke, fin and humpback whales was located within the 100 and 200 m isobaths, which includes the head of the Laurentian Channel, and its northern and southern submarine slopes. Blue whales’ predicted core habitat was in the area downstream of the 200 m isobath in the center of the Laurentian Channel.

Using the combined datasets, the whale presence/absence analysis indicates that these four species use the area at least from early May to late October, with a main period of occurrence from early June to late September. Point sampling modelling results indicate that the occurrence of minke, humpback, and blue whales peaked from late July to early August, while fin whale relative abundance increased until the end of September. Relative abundance has fluctuated over the years for these species, and further analyses are required in order to understand the underlying mechanisms guiding the dynamics of this ecosystem.

These aggregated results provide valuable information for science-based cetacean habitat conservation. Furthermore, they provide support to evaluate the needs of adapting and developing new measures to reduce the risk and severity of whale collision with all boat categories within the Saguenay–St. Lawrence Marine Park and its surrounding waters.

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