First time series of estimated humpback whale (Megaptera novaeangliae) abundance in Prince William Sound

In Prince William Sound (PWS), changes in abundance of humpback whales ( Megaptera novaeangliae ), one of PWS’s primary marine predator species, have until now been largely unknown. Using a historical dataset (1978–2009), we constructed the first time series of estimated humpback whale abundance in western PWS that is also one of the longest time series used in analyses of humpback whale mark-recapture data. Photographs from this dataset were used to “mark” and re-sight individual animals using the unique pigmentation pattern on the ventral flukes of each whale in a mark-recapture analysis. Specifically, the POPAN implementation of the Jolly-Seber mark-recapture model in program MARK was used. Estimates of probabilities of capture and survival, recruitment parameters, and total abundance over the study were obtained, leading to a time series of abundance estimates. Our results show an increase from 39 (SE = 26) to 194 (SE = 17) whales ( ≈ 500 %) over the time series. The average annual rate of increase (ROI) was 4.53 % (95 % CI 3.28–5.79 %) which is only slightly lower than the 5–7 % ROI estimated for the North Pacific. Trends in the number of whales encountered per unit effort were not consistent with abundance estimates from mark-recapture, showing that sightability changes annually.