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EVALUATION OF A COMPUTER-ASSISTED PHOTOGRAPH-MATCHING SYSTEM TO MONITOR NATURALLY MARKED HARBOR SEALS AT TUGIDAK ISLAND, ALASKA.
- Source :
-
Journal of Mammalogy . Oct2008, Vol. 89 Issue 5, p1201-1211. 11p. 1 Color Photograph, 1 Black and White Photograph, 2 Charts, 2 Graphs. - Publication Year :
- 2008
-
Abstract
- 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]
Details
- Language :
- English
- ISSN :
- 00222372
- Volume :
- 89
- Issue :
- 5
- Database :
- Academic Search Index
- Journal :
- Journal of Mammalogy
- Publication Type :
- Academic Journal
- Accession number :
- 34881905
- Full Text :
- https://doi.org/10.1644/07-MAMM-A-151.1