| Summary: | We develop statistical models and maximum likelihood methods for estimating bowhead whale population size from photo-identification data. We test them on simulated data, and on actual data from 1985 and 1986 photographic studies. We begin with a multinomial model that accounts for unmarked whales. Variance is estimated using the parametric bootstrap. In the cases considered, we find that our variance estimators perform similarly to previously used delta method based estimators in terms of confidence interval coverage, as long as log-normal rather than symmetric confidence intervals are used for the delta method based estimators. We develop further models to account for heterogeneity in capture probabilities (highly marked whales are more likely to be captured than moderately marked) and nonrandom sampling caused by age segregation. These models, particularly the latter, perform better than the multinomial model on simulated data that incorporate these violations of standard capturereca.
|
|---|