Abstract:
Peninsular bighorn sheep (Ovis canadensis nelsoni) are found exclusively in
Southern California and Baja Mexico. They are federally endangered due to
multiple threats, including introduced infectious disease. From 1981 to 2017,
we conducted surveillance for 16 pathogens and estimated population sizes,
adult survival, and lamb survival. We used mixed effects regression models to
assess disease patterns at the individual and population levels. Pathogen infection/
exposure prevalence varied both spatially and temporally. Our findings
indicate that the primary predictor of individual pathogen infection/exposure
was the region in which an animal was captured, implying that transmission
is driven by local ecological or behavioral factors. Higher Mycoplasma
ovipneumoniae seropositivity was associated with lower lamb survival, consistent
with lambs having high rates of pneumonia-associated mortality, which
may be slowing population recovery. There was no association between
M. ovipneumoniae and adult survival. Adult survival was positively associated
with population size and parainfluenza-3 virus seroprevalence in the same
year, and orf virus seroprevalence in the previous year. Peninsular bighorn
sheep are recovering from small population sizes in a habitat of environmental extremes, compounded by infectious disease. Our research can help inform
future pathogen surveillance and population monitoring for the long-term
conservation of this population.
