Science Advisory Report 2016/030
Ecosystem Research Initiative (ERI): Integrated Advice on the Summer Habitat of the St. Lawrence Estuary Beluga (Delphinapterus leucas)
- The analyses presented in this advisory report support the critical habitat identification in the most recent recovery strategy for the St. Lawrence Estuary beluga population.
- This population is present throughout almost the entire St. Lawrence Estuary in summer, as demonstrated in systematic aerial surveys, the tracking of individuals and the tracking of groups. Analysis of data from summer aerial surveys carried out from 1990 to 2009 shows that there is a nearly continuous network of 36 concentration areas that, according to estimates, account for an average of 50% of the population. The tracking of individuals and groups shows that this distribution is dynamic, with belugas visiting more than one site in a given day.
- Based on a statistical analysis of the available environmental characteristics, the 36 concentration areas were classified into three separate groups according to the probability of sand lance being present on the sea floor, sediment hardness and the spatial and temporal variations in surface current speed and direction, which can cause gyres and fronts. These groups are divided mainly along an upstream-downstream gradient. The areas in the first group are mainly in the upper estuary, and the two other groups are mainly where the upper and marine estuaries meet.
- The spatial distribution of these three groups of concentration areas closely matches the spatial segregation of the different types of beluga herds in the St. Lawrence Estuary in summer. The first group of areas matches the sectors thought to be mainly occupied by herds of adult belugas with young. The second and third groups are thought to be occupied by a combination of herds of adults only and mixed herds.
- Statistical models show that the environmental variables currently available cannot explain the variations in beluga distribution in the estuary. These models do not show the belugas avoiding busy navigation corridors or areas with high concentrations of contaminants in sediment.
- However, the limits of these models have to be considered for their ability to explain the variations in beluga density and occurrence in the estuary in summer. Certain variables that may be important in supporting the biological functions of belugas, such as the distribution of potential prey, salinity and temperature, were not available in the required coverage or in the spatial or temporal resolution.
- Analysis performed under the ERI does not contradict the finding that belugas are generalists in terms of their diet. Data to estimate the relative importance of prey in various areas and in different seasons remain limited.
- The results cannot be used to recommend simple habitat quality indicators. However, the systematic aerial surveys currently monitor the abundance and distribution of the St. Lawrence beluga and are good indicators for the population status and habitat use in the long term, despite the fact that coverage is currently limited to summer.
- The summary map produced through analysis of the 35 summer aerial surveys carried out from 1990 to 2009 is a useful management tool. This map can be used to assess the exposure of belugas to development projects with effects in defined areas of the estuary. However, map users must take into account the fact that beluga distribution is dynamic; the animals visit more than one concentration area in any given day. Moreover, this map represents only the average summer distribution and does not take into account age groups.
- A summary map specific to calves (age 0 and 1 year) is also available, but it is based on only seven aerial photography surveys. If it is used as a management tool, the same limitations in terms of dynamic distribution as for the overall summary map must be taken into account.
This science advisory report is the result of the February 14–16, 2012 meeting on The St. Lawrence Estuary Ecosystem Research Initiative: formulation of scientific advice in support of ecosystem management. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada Science Advisory Schedule as they become available.
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