Our final objective is to identify the specific geographic locations(s) in the TNMPA, if any, that were preferentially and recurrently used by belugas during the July aggregation period, and by doing find more so, provide a tool that could be used by regulators for assessing developments, setting terms and conditions for activities

that are proposed by industry, and evaluating changes in the location of preferred areas. The results we present are timely given recent renewed interest by the hydrocarbon industry in the Beaufort/Mackenzie region (AANDC, 2012) and Canada’s legal requirement to design and undertake monitoring programs in the TNMPA (Loseto et al., 2010, Canada Gazette, 2010 and Beaufort Sea Partnership, 2014). In addition, knowledge of beluga critical habitats and the ways in which they have used them in the past may also help us in the future to predict how belugas have or will respond to climate change or other factors that alter habitat (Laidre et al., 2008). Systematic aerial surveys were conducted over six summers between late June and early August, 1977–1985, and in late July 1992, to monitor the distribution and relative abundance of belugas in all four bays (subareas) of the Mackenzie Estuary (Niaqunnaq Bay, East Mackenzie Bay,

West Mackenzie Bay and Kugmallit Bay), including portions of the estuary that would eventually become the TNMPA in 2010. A total of 169 subarea surveys were attempted or completed during this period. The same

systematic transect lines were flown in all survey years in the 1970s and 1980s (Fig. 2), with transects spaced at intervals of 3.2 km, except in West Mackenzie Bay where they were spaced at 4.8 km. Nutlin-3a cost A strip-transect method was used (Caughley, 1977) in all surveys, with a strip width of 1.6 km (800 m per side), except in L-NAME HCl 1992 when the strip width was 400 m per side (Harwood et al., 1996). This provided survey coverage of 50% in the 1970s and 1980s (33% in West Mackenzie), and 29% and 15% in July 1992, respectively. Survey altitude was 305 m during all surveys, which was measured with the aircraft’s altimeter, and adjusted by the pilots during the surveys as necessary. Target ground speed was 200 km/h. Sighting coordinates were calculated using ArcGIS, using start and end-coordinates for each transect, and elapsed time. Mean ground speed for all surveys pooled was 188 km/h (SD 54.2). Primary search positions were equipped with bubble windows in 1984, 1985 and 1992, for enhanced visibility under the aircraft, close to the flight path. Surveys were flown in Cessna 185 on wheels (1970s) and in de Havilland Twin Otters (1980s and 1992). Survey conditions were assessed and recorded by observers at the beginning and end of each transect, and were summarized in the database for each subarea survey, by transect line. The usual flying time was 6–8 h per day. Observers rested during ferrying flights, refuelling stops, and when flying between transects.