Population Health of California Fishers

The range of the fisher (Martes pennati), a mid-sized carnivore which once inhabited a large proportion of North America's temperate forests, has contracted significantly in comparison to historical accounts. Much of this contraction is believed to stem from anthropogenic influences; however, the specific mechanisms or interactions with infectious or non-infectious agents for this species are not known. Understanding the dynamics of wildlife populations requires the knowledge of many factors that influence health, mortality and reproduction. One requirement is to understand the baseline parameters of health for a species.;In Chapter 1, I conducted an extensive literature review of the pathogens and parasites for the genus Martes, of which the fisher is a member, as well as review and discussion of conservation and management techniques, directions and future aims for the genus. Due to the lack of health knowledge for fishers, and the genus in general, much of the information is an amalgam of known health threats within the genus extrapolated from examples from phylogenetically related species. The chapter provides the first extensive table of all known pathogens and parasites of Martes and potential transmission routes for each example. It also highlights collection techniques for relevant biological samples to test for health parameters, and disinfection protocols for field equipment commonly used for Martes.;Rapid diagnostic tests (RDT) for exposure to or infection with pathogens are readily available for small animal veterinarians to use on domestic animals, and the option of using such tests to rapidly screen wildlife is inviting to researchers in the field. In Chapter 2, I tested the effectiveness of RDT in comparison to standard gold standard tests to determine if fishers were actively infected with parvoviruses or had been exposed to Anaplasma phagocytophilum. I compared a parvovirus RDT to a molecular gold standard test, and an RDT to detect exposure to A. phagocytophilum to a gold standard serological test to see if the results for each pathogen were in agreement. I determined that these tests were not in agreement and that these two RDT were not viable options for wildlife field researchers looking to screen individuals for potentially infectious agents that can compromise an individual's or a populations health.;In Chapter 3, I investigated the emerging threat of exposure and poisoning of fishers from anticoagulant rodenticide (AR) toxicants. This previously undocumented threat is emerging in fisher-occupied California forests and likely stems from the illegal use of these toxicants at illegal marijuana cultivations sites on public, tribal and community lands. I found a 79% prevalence of exposure for California's fisher populations to AR. Specifically, I reported second generation AR were the dominant class of AR in fishers. I documented several mortalities directly attributed to toxicosis from AR. I described the first neonatal or milk transfer of AR to a fisher kit. Through spatial analysis, I was not able to detect any spatial patterns, thus signifying that this toxicant threat is most likely widespread within the fisher's current range in California. This chapter was a foundational study to highlight this novel threat to fishers throughout their range in California.;Finally, in Chapter 4, I described mortality factors for 128 fishers in California collected over a six-year period. I found that predation was the leading cause of death for fishers, followed by disease, human-caused factors and vehicular strikes. I found moderate agreement between field-based suspected cause of death and necropsy-confirmed determinations. I determined that males were more likely to die of disease over predation when compared to females. Furthermore, the year 2009 was more likely to have mortalities due to disease, which likely reflected the canine distemper virus epizootic that occurred in fishers that year. This chapter provides a comprehensive look at mortality factors for fishers in California to aid wildlife managers and agencies of the main mortality threats that affect fishers in California.