COS 172-2 - Prioritizing hyperabundant deer management strategies to recover native ecosystem resilience and function in the Gulf Island Archipelago of Coastal British Columbia

Background/Question/Methods

The widespread loss of top predators as a result of human-wildlife conflict has disrupted ecosystem dynamics globally. Their removal triggers a trophic cascade that allows herbivores to become hyperabundant and browse vegetation unchecked. This cascading disturbance has greatly impacted the highly biodiverse and eco-cultural landscapes of the Gulf Island archipelago of Coastal British Columbia. Land dispossession by colonial governments alienated Coast Salish Peoples from their lands along with their stewardship practices and hunting of deer. Combined with the extirpation of top predators by settler communities, black-tailed deer have become hyperabundant, leading to significant declines of native plant community composition, structure, and recruitment. Evidence has suggested reducing deer densities below a threshold of 1 deer per 10 ha would allow for recovery of the understory, but there has been significant uncertainty and indecision around selecting an effective management strategy. To identify the most cost-effective strategies for different island contexts (high vs low human population density), we conducted an expert elicitation to estimate the ecological benefit, feasibility, and cost of alternative deer management strategies to allow for ecological recovery. Management objectives and strategies were determined by experts, and we followed PrOACT decision analysis steps and IDEA protocol guidelines for structured group elicitation.

Results/Conclusions

We elicited judgments from 11 experts in the ecology and management of deer. We identified 2 ecological objectives (maximize ecosystem function and minimize deer density) and 2 feasibility objectives (maximize project uptake and success). Structured group discussion identified 5 discrete strategies (Indigenous-led deer harvesting, professional contract hunting, independent licensed hunting, improve predator viability, birth control), and 4 combinations of these to form complementary strategies. Elicitation of these strategies revealed that: 1) professional contract hunting had the highest ecological benefit of all discrete strategies (~2-3x) but predominately lower feasibility than the other hunting strategies, 2) benefits were substantially higher for hunting and birth control strategies undertaken on smaller, less inhabited islands, and 3) improving predator viability and birth control had the lowest effectiveness scores accounting for both benefit and feasibility. These results will be further used in tandem with accumulated cost data and social objectives to calculate final cost-effectiveness scores and prioritize the strategies. Current benefit findings highlight that strategies undertaken may need to differ by location and that professional hunters will likely be essential to initially restore deer populations to a threshold to allow ecological recovery, although parallel cumulative threat management and restoration actions will also be needed.