Pacific Marten Occupancy Study on the Olympic Peninsula 2022–2023

Hubl, Dylan; Happe, Patricia; Howell, Betsy; Long, Robert; MacKay, Paula; Wirsing, Aaron

Pacific marten (Martes caurina) populations began to decline along the US west coast at the turn of the twentieth century due to deforestation and increased mortality rates linked to unregulated trapping for their pelts and the use of poisons targeting larger carnivores. The population of martens on Washington’s Olympic Peninsula once occupied forests from the coast to the high elevation tree line. However, owing to anthropogenic pressures, the population has suffered an extreme contraction in its range and is thought to only occupy high elevation forests. Multiple surveys targeting forest carnivores, and specifically martens, since 1991 have yielded very few marten detections. Indeed, between 1968 and 2022, there had been only 25 verified marten detections on the Olympic Peninsula. Furthermore, researchers have a poor understanding of the population’s genetic health as only a single recent (2008) sample was available for recent genetic analyses. Here, we implemented a marten occupancy study using a novel technology— automated scent dispensers—which allowed us to conduct surveys through the winter, when mustelids are most likely to be detected, in high elevation forests that would otherwise be inaccessible due to snow and rugged terrain. These automated scent dispensers have proven effective at detecting martens in the Olympics and elsewhere but had not been deployed on a large scale in this region. We also paired passive hair snare devices with the automated scent dispensers, opportunistically collected scat samples, and deployed transects of hair snare devices in sample units in which martens were recently detected. We used a stratified random sampling design and a geographically extensive sampling frame to survey 67 sites in Olympic National Park and Olympic National Forest. We detected martens in only five of the surveyed sample units, further suggesting the limited presence of martens on the Peninsula and precluding our ability to conduct a full occupancy analysis. We collected 41 hair samples and 24 scat samples which we have sent to the US Forest Service National Genomics Center for Wildlife and Fish Conservation for species identification and microsatellite analysis. Finally, we recommend that 1) future surveys focus on high-elevation locations and on the collection of genetic samples to help guide future management actions, 2) managers begin the petitioning process to have the Olympic marten population listed as threatened or endangered at the federal and state level, and 3) direct management actions should be considered, such as a population augmentation, to increase the population abundance and distribution within the national park and national forest.