Science Advisory Report  2009/070

Advice relevant to the identification of critical habitat for St. Lawrence beluga (Delphinapterus leucas)

Summary

Several characteristics of beluga as a species and of the St. Lawrence population in particular should be considered when assessing the habitat critical for the survival and recovery of St. Lawrence beluga:

• Beluga is an Arctic species, but one population occurs in the St. Lawrence Estuary. This environment is favorable to their continued presence as a result of an upwelling of cold, mineral-rich waters, high productivity and sea ice coverage. The oceanographic processes responsible for these conditions are deemed crucial to the survival and recovery of this population;
• The population is small and has not shown recovery since the beginning of monitoring in the mid 1980's. Human-induced mortalities of a few individuals per year are likely to have a negative effect on recovery;
• Based on sampling from the 1930s, St. Lawrence beluga have a varied diet constituted mainly of fish such as capelin, herring, sand lance, rainbow smelt, lumpfish, squid, cod, flounder, tomcod, and polychaete. There are no recent data on beluga diet;
• The current range of St. Lawrence beluga is about 65% of that historically (Figure 1). At present, beluga mostly inhabit waters between Battures-aux-Loups-Marins and Rimouski/Forestville, including the Saguenay River up to Baie Ste-Marguerite;
• This population exhibits seasonal movements of limited extent. Their timing and extent are likely influenced by sea ice, predation risks, and food availability. A general movement eastward occurs during the fall and into the winter, with a proportion of the population occupying the northwestern Gulf of St. Lawrence. These movements likely aim at finding winter habitats with suitable ice cover (< 70-90% ice coverage) to minimize risks of entrapment, but where food resources are adequate. Habitats where the presence of beluga has been documented during winter include the Laurentian Channel between Tadoussac and Les Escoumins in the Estuary, and sectors of Cloridorme and Sept-Îles in the northwestern Gulf (from November to April);
• Despite the scarcity of data on distribution and habitat use for fall, winter and spring, the area comprised between Forestville/Rimouski and Pointe-des-Monts / Ste-Anne-des-Monts, as well as the northwestern Gulf of St. Lawrence should not be dismissed as habitats important for the survival and recovery of St. Lawrence beluga;
• Spring might be an important feeding period, but little is known about beluga distribution at this time. Feeding habits of the species elsewhere, and the limited diet information from St. Lawrence beluga suggest that spawning fish or other prey at locations where they are abundant in the spring may influence beluga distribution (from April to June). The exact location and characteristics of feeding habitat are largely unknown, but likely involve among others, species such as capelin, herring, and rainbow smelt;
• During summer, segregation by sex and age classes is consistently observed in many populations of this species, including St. Lawrence beluga. In the St. Lawrence, these areas include: the Upper Estuary, from Battures-aux-Loups-Marins to the Saguenay River for females with calves and juveniles (from June to October); and the northern portion of the Lower Estuary for adult males (from June to October) (Figure 2). The Upper Estuary differs mostly from the Lower Estuary by being shallower, warmer and more turbid (less saline), but the exact features attracting different sex- and age-classes to specific areas of the St. Lawrence are unknown. Nonetheless, an access to these areas for each of the classes is considered essential, at least during summer, for the survival and recovery of this population;
• Within these larger zones, there are numerous small areas where beluga occur regularly or where they spend large proportions of their time, some of which have been identified for the summer period in the St. Lawrence. These areas are interconnected via a more or less complex network of travel routes;
• The species also consistently aggregates in estuaries or river mouths during summer, sometimes in large numbers, which suggests that they are an essential part of beluga habitat, though their functions are unknown. In the St. Lawrence Estuary, river mouths where beluga currently or historically congregated during summer include Rivière-Ouelle, Saguenay River, Baie Ste-Marguerite, Manicouagan Banks (Figure 2).

Given that current distribution is small relative to that used historically, recovery of this population may be tied to use of historical habitats. Therefore, access to and integrity of historical habitat should be considered important for the survival and recovery of the population.

There is a need to understand temporal use and movement patterns of individual beluga among habitats, and to establish the key features, biological functions and relative contribution of these habitats to beluga for completing their annual cycle. It is also necessary to describe seasonal beluga diet, so that areas providing prey can be identified. All of this information will be needed to assess the implications of changes in key habitat features or a reduction in availability of key habitats on the survival and recovery of St. Lawrence beluga.

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