Estimating Trend in Occupancy for the Southern Sierra Fisher Martes pennanti Population

Abstract

Carnivores are important elements of biodiversity, not only because of their role in transferring energy and nutrients, but also because they influence the structure of the communities where they occur. The fisher Martes pennanti is a mammalian carnivore that is associated with late-successional mixed forests in the Sierra Nevada in California, and is vulnerable to the effects of forest management. As a candidate for endangered species status, it is important to monitor its population to determine whether actions to conserve it are successful. We implemented a monitoring program to estimate change in occupancy of fishers across a 12,240-km2 area in the southern Sierra Nevada. Sample units were about 4 km apart, consisting of six enclosed, baited track-plate stations, and aligned with the national Forest Inventory and Analysis grid. We report here the results of 8 y (2002–2009) of sampling of a core set of 223 sample units. We model the combined effects of probability of detection and occupancy to estimate occupancy, persistence rates, and trend in occupancy. In combined models, we evaluated four forms of detection probability (1-group and 2-group both constant and varying by year) and nine forms of probability of occupancy (differing primarily by how occupancy and persistence vary among years). The best-fitting model assumed constant probability of occupancy, constant persistence, and two detection groups (AIC weight = 0.707). This fit the data best for the entire study area as well as two of the three distinct geographic zones therein. The one zone with a trend parameter found no significant difference from zero for that parameter. This suggests that, over the 8-y period, that there was no trend or statistically significant variations in occupancy. The overall probability of occupancy, adjusted to account for uncertain detection, was 0.367 (SE = 0.033) and estimates were lowest in the southeastern zone (0.261) and highest in the southwestern zone (0.583). Constant and positive persistence values suggested that sample units rarely changed status from occupied to unoccupied or vice versa. The small population of fishers in the southern Sierra (probably <250 individuals) does not appear to be decreasing. However, given the habitat degradation that has occurred in forests of the region, we favor continued monitoring to determine whether fisher occupancy increases as land managers implement measures to restore conditions favorable to fishers.

Impacts of Rodenticide and Insecticide Toxicants from Marijuana Cultivation Sites on Fisher Survival Rates in the Sierra National Forest, California

“…Based on long‐term carnivore monitoring data, Zielinski et al . () concluded that fishers in the southern Sierras showed stable occupancy rates over the past 8 years. Yet Spencer et al .…”

“…Yet numerous ongoing research projects agree that across the western United States, fisher population growth rates hover near zero and population expansion is not occurring (C. Thompson, USDA Forest Service, unpublished data; R. Sweitzer, University of California at Berkeley, unpublished data, Zielinski et al . ). Significant research efforts have been underway for the past 5 years, intended to document fisher ecological requirements and limiting factors as well as help identify management options for integrating fisher conservation with effective fire and fuel management (Thompson et al .…”

Seeking efficiency with carnivore survey methods: A case study with elusive martens

“…At each baited station, we randomized the 2 factors of interest: 1) bait type and 2) bait and camera height. Bait and camera height was either “high,” following protocols from prior surveys (1.4 m; e.g., Truex et al , Zielinski et al ) or low (<0.5 m; e.g., Linnell et al ). Bait type was either cat food (150‐g can of fish‐flavored wet cat food that was partially opened with >4 perforated holes) or chicken drumstick (250 g) and Gusto (long‐call olfactory lure; Gusto; Minnesota Trapline Company, Pennock, MN, USA).…”

Historical and Contemporary DNA Indicate Fisher Decline and Isolation Occurred Prior to the European Settlement of California

“…The NW and SSN populations were defined a priori based on previous research that indicated that these populations are geographically isolated due to an unoccupied 420 km gap between them [19], [27], as well as genetically isolated [23], [24]. We genotyped 127 individuals from hair samples collected in the SSN C through the U.S. Forest Service Sierra Nevada Carnivore Monitoring Program [41]. In the NW C we obtained genotypes from 148 individuals based on hair, scat, and tissue samples collected in collaboration with a number of existing research projects in the region.…”