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We estimated sex- and age-specific apparent survival of harbor seals (Phoca vitulina richardii) born at Tugidak Island, Alaska, from 2000 to 2007 using mark-recapture models and photographs of ventral pelage markings to identify individuals. Estimates of annual apparent survival (1 - (mortality + emigration)) of females were from 0.05 to 0.10 higher than those of males and were 0.820 for weaning (~1 month) to 1 year, 0.865 for 1-3 years, and 0.929 at 3-7 years. Annual survival of males was 0.717, 0.782, and 0.879 for the same ages. Highest mortality occurred preweaning, with cumulative mortality to 4 weeks of age of 0.259, indicating this is the most vulnerable period for Tugidak harbor seals. Estimates of survival, not biased by misidentification, required that an individual had at least 2 good-quality, matching photographs in the photograph library. The number of photographs available for matching improved resighting probabilities from 0.43 for seals with 2 photographs to 0.69 for seals with 8 photographs, but this heterogeneity did not affect survival estimates. Survival estimates based on photograph-identification data were nearly identical to those based on resightings of flipper-tagged seals using mark-recapture models with a preliminary double-tag-loss estimate of 2.5% per year. Photograph identification of natural pelage markings provides a viable method for estimating vital rates of harbor seals even at large haul-outs (> 1,000 animals) and may be useful for populations of conservation concern that require low disturbance of animals or where capturing sufficient numbers of seals for artificial marking is not feasible. [ABSTRACT FROM AUTHOR]

Monitoring the dynamics and status of populations of harbor seals (Phoca vitulina richardii) requires efficient methods for estimating population parameters from mark--resight data. We used a test set of photographs from 182 individuals identified by flipper tags, scars, or unique pelage markings to test whether individuals could be identified accurately by their ventral pelage markings; to document efficiency and misidentification error rate associated with a computer-assisted photograph-matching system; and to test for bias in mark-recapture survival estimates resulting from misidentification errors. Pelage patterns of seals that were not of dark-intermediate or intermediate color phase were unique and stable from birth until 6-8 years, and from year to year as adults. The computer-assisted system greatly improved efficiency of photograph matching: 93.3% of good photographs and 69.9% of all photographs ranked 1st, and 95.2% of good photographs ranked in the top 0.3% of the ordered list for visual checking. Additional visual matching error averaged <3.0% for good photographs, and overall misidentification error rate was low at 1.8%, due to the availability of multiple photographs for matching. Inclusion of poor-quality photographs reduced ranking success by ~20% and increased additional visual matching error up to 20%. Bias in survival estimates was -7.0% for a misidentification rate of 8.8%, but was ≤1.1% for misidentification rates of <2.7%, achieved by restricting data to only good photos. Our study suggests that estimation of misidentification error rate, inclusion of only high-quality photographs, or use of models that account for misidentification error, are required to prevent bias in mark-recapture survival estimates when using data from natural-marking studies. [ABSTRACT FROM AUTHOR]