Arctic Network Brown Bear Monitoring Protocol Development Summary

Shults, Brad

Two statistical techniques have been predominantly used for monitoring bears in Alaska. The first approach uses capture-mark-recapture (CMR) techniques to estimate abundance and density of bears (Miller et al. 1997). This CMR approach has been used widely across Alaska and has been used for both black (Ursus americanus) and brown bears (U. arctos). The analytical techniques used for estimation are based on well developed theory (Pollock et al. 1990). A potential logistical and financial limitation of this approach is that a radio-marked sample of bears must be established and maintained to estimate probability of detecting bears, to monitor movements of bears between the marking and observation period, and ultimately to estimate abundance and density of bears. Therefore, this technique may be of limited application for large study areas where annual monitoring is of interest. Distance sampling with line transects is the second most common and rigorous method used to estimate bear density (Quang and Becker 1996). During line transect sampling, a transect is traversed and animals are observed at varying distances. The observation distances are used to model the probability of detecting animals at varying distances from the transect (i.e., detection function) with the assumption that detection of individuals on the line is perfect. This detection function is in turn used to correct raw counts of animals for detection probability and to estimate density. The assumption of perfect detection on the line has been relaxed for aerial surveys because individuals can not be observed directly beneath the aircraft (i.e., on the transect). Aerial line transect methods have been further modified for bear surveys to allow the use of covariates (e.g., habitat type)related to sightability of individual animals (Quang and Becker 1996), application in mountainous terrain where distance from lines varies with relief (Quang and Becker 1999), and the use of ancillary data (double count data from 2 observers) to further relax the assumption ofperfect detection on the transect. Like CMR techniques, line-transects have been successfully applied for bear surveys in several areas around Alaska (Becker 2003), and the sampling and analytical components of this approach are based on sound theory (Borchers et al. 2002). However, sample size needs may not be met in areas with low densities of bears and independence among observers using the double count procedure has been questioned. Therefore, an alternative technique may be useful to monitor bear populations in some areas of Alaska. The purpose of this project is to develop and implement a population monitoring protocol that has statistical validity, is cost-effective, and can be implemented across the network. Managing brown bear populations presents biological, cultural, and legal challenges for park managers. Baseline ecological data are lacking for brown bear populations in ARCN despite increasing harvest and viewing demands from the public. Brown bear abundance may be a parameter that can be estimated across the network if a logistically simpler, statistically rigorous, and cost effective estimator of brown bear abundance can be developed and implemented often (i.e., every 3-5 years in each sampling area). This technique will rely more on direct, aerial observation of bears during one sampling period which could make itmore cost-effective than the current line-transect technique used in Alaska which is more expensive and requires multiple years of effort to obtain one estimate.