Seasonal distribution and concentration of four baleen whale species in the St. Lawrence Estuary based on 22 years of DFO observation data

Abstract

The Estuary and the Gulf of St. Lawrence are feeding grounds for several North Atlantic whales, including minke, humpback, endangered blue whales and fin whales which are designated by COSEWIC as Special Concern. The St. Lawrence is an important shipping route and vessel strikes are an important source of mortality for these species. The development of efficient protection measures requires knowledge about their spatial and temporal distribution. Observations of these species collected during aerial and boat surveys conducted between 1995 to 2017 were used to produce maps presenting raw sightings, relative densities from kernel analyses and predicted relative probability of occurrence from spatial distribution modelling. The latter allowed a more complete use of the data available, while reducing biases linked to survey coverage, and the resulting maps are considered to be the best representation of spatial distribution of the four baleen whales in the Estuary. The models predict a higher probability of fin, humpback and minke whale occurrence at the head of the Laurentian Channel. A higher probability of blue, fin and humpback whale occurrence is also predicted along the slopes of the Laurentian Channel, while a higher probability of minke whale occurrence is predicted along the shallow water slopes near the 20 m isobath. Finally, a higher probability of blue whale occurrence is also predicted in the deeper waters of the Laurentian Channel between Les Escoumins and Forestville. These maps highlight potentially important zones to be considered when defining management plans aiming to reduce risks of vessel strikes.