"A 3-year population monitoring program was put in place for a study area within SK2 Central covering 16,092 km2 using fecal DNA based capture–recapture methods to estimate population sizes and population rate of change."
Boreal caribou populations were listed as threatened under the Species at Risk Act in 2003 and a national recovery strategy was developed by Environment and Climate Change Canada in 2012. At the time, there had been no population assessment of Saskatchewan’s Boreal Plain (SK2) caribou conservation unit and it was assessed “as likely as not” to be self-sustaining, based on a high level of disturbance resulting in only 57% undisturbed habitat. A threshold of 65% undisturbed habitat is expected to provide a 60% probability of population persistence.
The large size of SK2 (109,717 km2 ) made range assessment and range planning difficult, so in 2015, three smaller caribou administration units within SK2 were delineated: SK2 East, SK2 Central, and SK2 West. The SK2 Central area covers 36,052 km2 . Saskatchewan committed to assess caribou population status, and in 2017, the province initiated a 3-year population monitoring program for the SK2 Central in a study area covering 16,092 km2 . Fecal-DNA based capture–recapture methods were used to estimate population sizes and population rate of change from 2017-2019.
The results for the population analysis show a significant decline in both female and male caribou numbers in the SK2 Central study area from 2017-2019 and since 2007 when assessed for the smaller Prince Albert Greater Ecosystem (PAGE) area. The SK2 Central results for females show a statistically non-significant increase from 2017 to 2018 (lambda = 1.2) followed by a significant decrease between 2018 and 2019 (lambda = 0.7), with the decrease largely accounted for by the low survival rate (55%).
Population size estimates for females were 103 in 2017, and 89 in 2019. For the males, a steady decline in abundance was observed over the 3 years (lambda = 0.66) with population size estimates of 78 in 2017, and 36 in 2019 for the study area. The total population estimate is 125 (112-160) animals for 2019 in the study area.
The results for the PAGE area over the 2017 to 2019 period are comparable, although the population is approximately 60% the size of that of the SK2 Central study area; demographic trends are less clear due to lower precision in the estimates. Population size estimates for females were 63 in 2017, and 50 in 2019 and estimates for males were 50 in 2017, and 27 in 2019.
The PAGE results for the 2007 to (2017-2019) time period points to a long-term loss rate of females, averaging around 7.5% per year (lambda = 0.927) and for males around 1.5% per year (lambda = 0.984). The MARK RD analysis indicates the loss rate for both sexes in recent years is much higher, around 30% per year (lambda = 0.71). The population size estimates for females were 137 in 2007, and 50 in 2019 and for males, estimates were 39 in 2007, and 27 in 2019.
Caribou in the SK2 Central study area are generally found in the remaining large, relatively intact areas with suitable habitat (Priadka et al. 2019, McFarlane et al. 2021). The remaining habitat areas are largely disconnected and the short and long term declining population trend clearly indicates that they are not sufficient to maintain a self-sustaining caribou population. Additional efforts to reduce the human-caused disturbance footprint should be made, as identified in the Range Plan for Woodland Caribou in Saskatchewan, Boreal Plain Ecozone – SK2 Central Caribou Administration Unit