Monitoring of grizzly bear population trends and demography using DNA mark–recapture methods in the Owikeno Lake area of British Columbia

Abstract

We used DNA sampling and mark–recapture modeling to estimate population trend(s), population size, and the demographic response of a coastal British Columbia grizzly bear population (Ursus arctos L., 1758) to low salmon escapement levels from 1998 to 2002. We contrasted the demography of three sampling areas in response to temporal and spatial variation in salmon availability. Population trend (λ) estimates suggested that salmon availability was too low in the first 2 years of the study to sustain grizzly bear populations. One of the sampling areas exhibited higher levels of salmon availability in later years of the study, leading to increased rates of addition. Apparent survival rates increased in all areas potentially as a result of increased salmon availability. Joint interpretation of λ and superpopulation estimates allowed for the assessment of whether salmon availability levels were high enough to sustain current population sizes of grizzly bears on salmon streams. This study illustrates how joint modeling of separate sampling areas can be used to assess spatial variation in population demography and population trends, as well as increase precision of estimates for individual sampling areas. It also illustrates how DNA mark–recapture can be used as a methodology to explore the effects of changes in environmental conditions on population demography and population trend of grizzly bears or of other wildlife species.