Laser photogrammetry to determine dorsal fin size in a population of bottlenose dolphins from Doubtful Sound, New Zealand

Abstract

Laser photogrammetry (also known as laser-metrics) can provide valuable morphological data but the measurement error associated with the technique has not been quantified. Here laser-metrics were used to measure the dorsal fins of an entire resident population of bottlenose dolphins (Tursiops truncatus) from Doubtful Sound, New Zealand. Dorsal fin base length, height and surface area were measured from dorsal fin photographs. Sources of measurement error were estimated by repeatedly measuring multiple photographs of dorsal fins of known individuals. Measurement error accounted for less than 6% of the total variation in dorsal fin base length and height, indicating that the technique was repeatable. Adults were the only age-class to express sexual dimorphism, with males significantly larger than females in all measurements. The relationship between dorsal fin height and base length was significantly different between male and female adults: dorsal fins of males were proportionately taller. Laser photogrammetry is an inexpensive and non-invasive measurement technique that can provide valuable size data when used in conjunction with routine dorsal fin photo-identification studies.