Slowing down wolves to protect boreal caribou populations: a spatial simulation model of linear feature restoration

Abstract

In Canada, boreal caribou (Rangifer tarandus caribou) are declining in numbers, in part due to increased predation by wolves (Canis lupus). One management option to reduce wolf–caribou interactions and thus protect caribou is to remove man‐made linear features (LFs), structures such as roads, trails, and cut lines, which are used by wolves as traveling paths. Linear features increase wolf traveling speed and could additionally facilitate wolf entry into caribou habitat. Our goal was to quantify the expected effect of LF removal on caribou mortality and investigate whether this LF restoration could be a sufficient measure to stop caribou declines. We simulated the effects of LF restoration on caribou adult and calf survival in spatially explicit wolf–caribou encounter models. The models were parameterized using Global Positioning System (GPS) data, hidden Markov models (HMMs), and information from the published literature. Complete LF restoration decreased wolf traveling speed and thus reduced caribou mortality. The proportional reduction in adult caribou mortality ranged from 10 to 25% of its original value, and the proportional reduction in calf mortality ranged from 8 to 23%, depending on caribou density, number of wolf packs, kill probability given an encounter, and detection distance of wolves for caribou. Building on the model output, we used empirical caribou data to calculate the effects of reduced mortalities on the finite rate of annual population change, normalλ. Assuming that 25% or less of calf mortality was wolf‐related, normalλ stayed below one, that is, populations kept declining, even with complete LF restoration. With 50% of calf mortality due to wolves, caribou populations stopped declining (λ≥1) if adult and calf mortality were reduced by at least 19 to 24%. However, these values were not achieved in a majority of the parameter combinations in our study, not even with complete LF restoration. Given that LF restoration as a single measure is unlikely to stop boreal caribou populations from declining, we used a case example to illustrate how LF restoration could make a small contribution in a portfolio of short‐term and long‐term management options to reduce wolf predation on caribou.

Management‐mediated predation rate in the caribou–moose–wolf system: spatial configuration of logging activities matters

“…First, we considered that an encounter occurred when a prey was within a 1km radius of a wolf, a distance within the detection range reported for wolves (Mech and Boitani 2003). This distance was also used in previous studies (DeMars et al 2016, Spangenberg et al 2019 and was similar to distances of 1.5 km chosen by Muhly et al (2010) and of 1.3 km considered by Whittington et al (2011). When both caribou and moose were within the detectable distance, wolves chose moose over caribou every time (Mech and Boitani 2003).…”

Multispecies modelling reveals potential for habitat restoration to re‐establish boreal vertebrate community dynamics

“…To date, the majority of studies assessing the potential impacts of seismic line restoration on caribou have been simulation‐based (e.g. Serrouya et al., 2020; Spangenberg et al., 2019; Yemshanov et al., 2019), and empirical assessments of restoration effectiveness remain rare (but see Tattersall et al., 2020a).…”

Habitat loss on seasonal migratory range imperils an endangered ungulate

“…Enhanced restoration of degraded seasonal ranges could also, over time, mitigate the current conservation challenge of habitat degradation (e.g. Ray, 2015; Spangenberg et al., 2019). Avoiding further extirpation of migratory caribou will only be possible if the full suite of landscape and habitat requirements for this species are affectively conserved in all seasonal ranges.…”

“…Moreover, early seral forage promoted by cutblocks enhances forage availability for moose and deer, leading to increases in primary prey abundance and subsequently, predator population growth (Seip, 1992; Serrouya, McLellan, Boutin, Seip, & Nielsen, 2011). Simultaneously, linear disturbances increase predator efficiency at searching for, encountering, and killing caribou (Spangenberg et al., 2019; Whittington et al., 2011). In response, caribou attempt to avoid anthropogenic disturbances, leading to indirect habitat loss, and yet are still often unsuccessful at predator avoidance.…”