Predator Reduction Background
The British Columbia Caribou Recovery Program is considering a five-year re-approval for the continuation of predator reduction to support the recovery of the Columbia North, Central Selkirks, Hart Ranges, Itcha-Ilgachuz, Graham, Tweedsmuir-Entiako, Pink Mountain, Chinchaga, and South Peace[1] caribou herds, recommencing in the winter of 2021-2022. This would include wolf reduction in support of all the aforementioned herds, and cougar reduction specifically in the Central Selkirks, Columbia North, and Itcha-Ilgachuz herds. Additionally, a new predator reduction program is being proposed for the North Cariboo Mountains herd, to commence in the winter of 2021-2022 for an initial 5-year program approval. These caribou herds cannot afford delays that could jeopardize ongoing recovery efforts that could ultimately lead to a decline in levels at which recovery would not be possible.
Background
British Columbia (B.C.) is home to 54 herds of woodland caribou (Rangifer tarandus caribou). Despite significant investments in managing many of these herds, caribou populations have become threatened in the past three decades, going from approximately 40,000 animals decades ago to 15,500 currently.
The reasons for caribou population declines are complex and differ somewhat across the province. However, scientific evidence indicates that the leading cause of declines is facilitated by a phenomenon known as “apparent competition”, mediated by habitat disturbance. In this process, habitat alteration leads to increased abundance of moose/deer/elk (aka. primary prey species) that benefit from early-seral forest conditions (i.e., young forests) and become the main prey of wolves. While primary prey species do not compete directly with caribou, their increased abundance support higher wolf populations in caribou ranges that historically had low densities of primary prey and predators. As a result of these changes to predator-prey dynamics, habitat alteration from natural resource development is the main factor leading to unsustainable predation rates towards caribou. Although landscape-scale habitat management is needed to support self-sustaining caribou populations, it may be decades before the benefits of such measures are realized. Direct management (i.e., reduction) of predators has the most rapid effect as a short-term, emergency action. If primary prey is also managed while habitat recovers and is protected, the need for wolf reduction will diminish over time.
Predator reduction to support caribou recovery has been occurring in B.C. since 2015. The reduction efforts were expanded into new caribou herds in 2019 with an initial two-year approval. Since the expansion of predator reduction in 2019, there have been 399 wolves removed from the Central Selkirks, Hart Ranges, Itcha-Ilgachuz, Graham, and Tweedsmuir-Entiako herds, and 21 cougars removed from the Central Selkirks and Columbia North herds. During that two-year period, an additional 312 wolves were removed from Columbia North, Chinchaga, Pink Mountain, and South Peace herds (these programs were approved separately prior to 2019). Early monitoring efforts suggest several of these herds have responded positively to predator reduction, however, further treatment and monitoring are required to fully measure the caribou population response.
Wolves
Wolves are the primary predator of caribou in BC and increased wolf abundance is linked with declining caribou populations through the apparent competition process. With greater abundance of primary prey species resulting from habitat alterations that created younger forests, wolf populations grew to levels beyond what would be expected in a natural system (undisturbed by industrial impacts). Wolf predation towards caribou can be further exacerbated by linear features associated with resource development, which increase wolves’ hunting efficiency and access into caribou habitat. The interaction between caribou, wolf, and primary prey populations can be managed to the benefit of caribou by managing primary prey populations and habitat while directly reducing wolf populations.
For threatened caribou populations, reducing the density of wolves in caribou habitat is the quickest and most effective short-term management tool to reverse declining caribou population trends. For example, the Central Group of Southern Mountain Caribou (South Peace herds) were declining by approximately 15% annually prior to the implementation of wolf reduction, but since initiating wolf reduction treatment[2] in 2015 the overall population has increased in size by approximately 81% (13% annually).
Cougars
Although wolves are the most common predator of caribou, cougars can also contribute significantly to caribou mortality, specifically in B.C.’s southern herds. Multiple occurrences of cougar predation on adult caribou has been confirmed in the Central Selkirks, Columbia North, and Itcha-Ilgachuz herds. Cougars are often a habitual predator and can develop a proclivity for specific prey species, such as caribou. For small, declining caribou populations, even one specialist cougar can have a significant impact on a small population. For example, a single cougar was confirmed to have killed four caribou in the Columbia North herd in a span of a few weeks. With steeply declining populations in these southern herds, targeted removal (i.e., removing only those cougars known or suspected to kill caribou) within caribou habitat is likely to provide a substantial benefit to the herds.
Continuation of Predator Reduction for 13 Caribou Herds
Predation by wolves is the proximate cause of most declining woodland caribou herds in B.C., often resulting in reduced herd sizes, poor calf recruitment, and high rates of adult mortality. Without a continued effort to reduce the loss of caribou to predation by wolves (and cougars in some cases), recovery is unlikely. The Province is recommending continued wolf reduction in the thirteen aforementioned herds, as well as cougar reduction in the Central Selkirks, Columbia North, and Itcha-Ilgachuz based on the following factors:
- In the absence of wolf reduction, wolf densities will exceed the recommended threshold of three wolves per 1000 km2 (Recovery Strategy for the Woodland Caribou, Southern Mountain population in Canada, 2014) within the herds’ critical habitat;
- Ongoing monitoring indicates that predation is the main cause of mortality and the proximate reason for recent population declines; and
- These herds have the highest likelihood for recovery or are the highest priority for recovery based on current population numbers.
New Wolf Reduction Program for North Cariboo Mountains Herd
The North Cariboo Mountains herd is declining rapidly. Estimated at 215 caribou in 2016, the herd had declined to 145 caribou by 2020. The North Cariboo Mountains herd would be an extension of the Hart Ranges treatment area. The expansion of wolf reduction into this new treatment area would be of low operational cost but could contribute significantly to the recovery of the herd.
Approach
To continue to support the recovery of these caribou herds, a high rate of wolf removal (>80%) must be achieved to meet wolf density objectives annually. To ensure wolf density targets are met, a combination of radio collaring and aerial shooting from helicopters is used. The deployment of radio collars supports aerial field crews to locate packs to ensure that all members of a pack are lethally removed. Aerial removal is the preferred method as it is considered the most effective and humane method to thoroughly reduce wolf populations with no risk of by-catch. Monitoring is carried out to ensure safety, efficacy, and the humane treatment of animals consistent with the current guidelines for euthanasia of wildlife in field conditions.
Implementation during the winter season is necessary, as snow cover is required for tracking and locating wolves. Ground-based trapping and hunting alone are not sufficiently effective but may be supplemental to aerial reduction efforts under some circumstances. Wolf reduction programs typically cost between $100,000–$275,000 per herd annually.
Cougar reduction also occurs during the winter but is ground-based. Cougars cannot be effectively reduced using aerial methods as they are not typically encountered in open areas, and their escape strategy is to retreat to cover or climb into a tree where they cannot be seen from aircraft. Experienced hound handlers will be contracted to target cougar within the specified treatment areas.
Adaptive Management
An adaptive management approach will be utilized to monitor how caribou, primary prey, and predator populations respond to predator reduction. The predator reduction programs may be adapted based on population responses and should occur in conjunction with other short- and long-term recovery measures. Predator reduction alone will not recover caribou herds to self-sustaining populations and is not proposed as the sole recovery action but is being considered as an immediate conservation measure while habitat management (i.e., protection and restoration) and other long-term measures, such as primary prey management, are identified and implemented. Enacting multiple management actions concurrently is the most effective means of reaching and maintaining self-sustaining caribou population in the long-term.
[1] Includes Kennedy Siding, Moberly, Narraway, Scott East, and Quintette herds
[2] In combination with other short-term measures, such as maternal penning and supplemental feeding.
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We encouraged respondents to review the following content prior to completing the survey. The content provides a robust explanation on the predator reduction program.
