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A simple laser photogrammetry technique for measuring Hector's dolphins ( Cephalorhynchus hectori ) in the field
Author(s) -
Webster Trudi,
Dawson Steve,
Slooten Elisabeth
Publication year - 2010
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/j.1748-7692.2009.00326.x
Subject(s) - allometry , photogrammetry , fin , dorsal fin , population , laser scanning , fish fin , measure (data warehouse) , laser , mathematics , biology , dorsum , remote sensing , geography , anatomy , optics , physics , ecology , computer science , engineering , medicine , mechanical engineering , database , fishery , environmental health , fish <actinopterygii>
The ability to measure and age individuals within a population has many important applications, for example, for examining growth and determining size class. We developed a simple photogrammetric system using two parallel lasers and a digital camera, in order to measure dorsal fin dimensions of free‐ranging Hector's dolphins. Laser dots were projected onto the fin, providing scale, thus allowing measurement as well as simultaneous photo‐ID of 34 individuals from fin nicks and other marks. Multiple measurements (≥5) were available for six individuals; these resulted in mean CVs of 3.71% for fin length and 3.76% for fin height. Errors due to variations in angle and measurement were quantified via photography of a fiberglass Hector's dolphin model. Allometric measurements and age data were collated from 233 autopsied Hector's dolphins. Using these data, fin length was found to be a better predictor of total length (females r 2 = 0.732, males r 2 = 0.678) than fin height. Gompertz age/length growth curves were fitted to these individuals. Linear regressions were used to estimate total length for 34 individuals from laser‐metrically estimated fin base length. Individuals were then assigned one of three age categories. This system shows promise as a noninvasive way of measuring individuals, while allowing simultaneous photographic identification.