Data from: Harvest of transboundary gray wolves from Yellowstone National Park is largely additive

Large carnivores are globally threatened due to habitat fragmentation and
loss, prey depletion, and human exploitation. Human exploitation includes
both legal and illegal hunting and trapping. Protected areas can create
refugia from hunting and trapping, however, hunting can still threaten
wide-ranging large carnivores when they leave these areas. Large carnivore
reintroductions to protected areas are often motivated to restore
ecological processes, including wolf reintroduction to Yellowstone
National Park (YNP). Determining if harvest is compensatory or additive is
essential for informed conservation strategies, as it influences the
overall impact on wolf populations and their ecosystems. If the harvest
was compensatory, then increasing harvest pressure outside YNP should not
decrease overall survival for transboundary wolves. Alternatively, if
increasing harvest was additive, then increasing harvest pressure outside
YNP should decrease overall survival for transboundary wolves. We tested
the effects of variable harvest pressure following delisting on the
survival of YNP gray wolves (Canis lupus) from 1995 to 2022. We defined
three harvest levels: no harvest, harvest with limited quotas, and
unlimited harvest. We used Cox-proportional hazards models and cumulative
incidence functions to estimate survival rates, factors affecting
survival, and cause-specific mortality between these three harvest periods
to test predictions of the additive mortality hypothesis. Most wolves that
primarily lived in YNP were harvested adjacent to the park border.
Cox-proportional hazards models revealed that mortality was highest during
years of unlimited harvest during winter outside YNP. Cause-specific
mortality analyses showed that natural mortality from other wolves and
harvest were the two leading causes of death, but that harvest mortality
had additive effects on wolf mortality. Wolf survival decreased with
increased harvest mortality, while natural mortality remained relatively
unchanged. High rates of additive harvest mortality of wolves could
negatively impact wolf survival in YNP. Harvest mortality of transboundary
wolves is additive possibly due to source-sink dynamics of uneven spatial
susceptibility of wolves to harvest mortality across protected area
borders, as well as effects of harvest on complex social dynamics of
wolves in YNP. Transboundary management of large carnivores is
challenging, yet cooperation between agencies is vital for wolf management
in and around Yellowstone National Park. Our results support the use of
small quota zones surrounding protected areas, that minimize transboundary
mortality impacts on large carnivores living primarily inside protected
areas.