Research Document - 2016/052
Definition and characterisation of the St. Lawrence Estuary beluga (Delphinapterus leucas) habitat following an ecosystemic approach
By Mosnier, A., Larocque, R., Lebeuf, M., Gosselin, J.-F., Dubé, S., Lapointe, V., Lesage, V., Lefaivre, D., Senneville, S., Chion, C.
Abstract
Within Fisheries and Oceans Canada (DFO), the ecosystem approach is considered as a tool for operational planning, project implementation and preparation of advisory reports. In response to this strategic direction, the science division of DFO is committed to implement the ecosystem approach in its activities as Ecosystem Research Initiatives (ERI) in each of the six administrative regions of DFO. In the Quebec region, two pilot projects were set up, one targeting forage species responsible for the presence of blue whales (Balaenoptera musculus) in the St. Lawrence estuary and the other aiming to define and characterize the habitat of the St. Lawrence beluga (Delphinapterus leucas). Issued from this last topic, this document is also a contribution to the knowledge needed to protect this population considered as endangered. First, it presents a review of data describing the use of the different regions by belugas, the physical, chemical and biological characteristics of the habitat, the recent diet composition of beluga, as well as threats that may affect beluga or its habitat and jeopardize the recovery of this population. Based on the integration of environmental data available, the ecosystem approach is then applied through several modeling exercises aiming to explain the occurrence and density variations of belugas detected during systematic aerial surveys and to look for possible characteristics common to the most used areas. The results show that in summer, belugas can be found in almost the entire St. Lawrence estuary in a network of 36 concentration areas between which they are likely to move in the same day. These concentration areas can be assembled into three groups with specific characteristics linked to the probability of sandlance (Ammodytes americanus) occurrence, the hardness of the sediment, the speed and variability of surface water current and the probability of occurrence of oceanographic structures such as gyres or fronts. The models show no significant relationships between changes in occurrence and density of belugas and environmental variables available and do not allow recommending simple indicators of the habitat quality. However, the synthesis map produced by the analysis of 35 aerial surveys completed from 1990 to 2009 may be a useful tool for management, although it will be important to carefully consider the dynamic nature of the belugas distribution. The application of the ecosystem approach requires detailed data on a large number of variables, however, several important variables such as the distribution of potential prey, salinity and temperature were not available with the coverage and the spatial or temporal resolution required for this study. This knowledge is needed to identify habitat characteristics fulfilling the essential biological functions and to identify activities or phenomena that may cause degradation of these characteristics and affect the recovery of St. Lawrence beluga population.
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