# Fisher (Pekania pennanti) Populations Exhibit Regional Differences in Cause‐Specific Mortality but Not Survival Rates

## TL;DR

Fishers in western regions face more predation and toxicant exposure, while eastern fishers are more affected by hunting, but survival rates are similar across regions.

## Contribution

This study identifies regional differences in cause-specific mortality but not survival rates between western and eastern fisher populations.

## Key findings

- Western fishers experience higher mortality from predation and toxicants compared to eastern fishers.
- Eastern fishers have higher mortality due to legal harvest.
- Survival rates for male and female fishers are similar across regions despite differences in mortality causes.

## Abstract

Mortality causes and survival rates often vary between the geographically disparate populations of a species. Fishers (
Pekania pennanti
) are a mesocarnivore inhabiting forested areas across Canada and the United States of America. Due to their economic and ecological value, fishers have become the focus of many management and conservation efforts. However, a clear understanding of influential demographic parameters and pressures exerted on disparate populations is necessary for such discussions. We conducted a literature review of peer‐reviewed studies investigating fisher cause‐specific mortalities and survival to (a) synthesize the current available knowledge, (b) assess differences in cause‐specific mortalities and the sex‐specific adult survival rates between western fisher populations (i.e., populations from California, Oregon, Washington, or British Columbia) and eastern fisher populations (i.e., elsewhere in their distribution), and (c) identify potential gaps in the literature. We identified 26 studies between 1994–2024 describing cause‐specific mortality (n = 4), survival rates (n = 15 studies), or both (n = 7), with 20 studies assessing western fisher populations. There were significant differences between the cause‐specific mortalities for fishers in the eastern and western populations. Western fishers had higher mortality from predation and lethal toxicant exposure, while eastern fishers had higher mortality from legal harvest. Survival rates of males and females were not significantly different between the eastern and western populations; however, we found that male survival rates in the western populations varied considerably between studies. The geographic concentration of recent research presents a lack of information regarding the species outside of western populations, which may hinder management efforts throughout their range.

Western fisher populations have been the focus of many recent studies and exhibit differences in cause‐specific mortalities but not in survival rates when compared to eastern fisher populations. Western fisher mortalities were dominated by predator attacks while eastern fisher mortalities were dominated by harvest.