Laser photogrammetry to determine dorsal fin size in a population of bottlenose dolphins from Doubtful Sound, New Zealand
Lucy E. Rowe A B and Stephen M. Dawson AA Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand.
B Corresponding author. Email: rowelucy@gmail.com
Australian Journal of Zoology 56(4) 239-248 https://doi.org/10.1071/ZO08051
Submitted: 31 May 2008 Accepted: 1 December 2008 Published: 22 December 2008
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.
Acknowledgements
This project was funded by the New Zealand Whale and Dolphin Trust. We thank past members of the University of Otago Marine Mammal Research Group who gathered the sex data used in this paper and Rohan Currey for his support in the field and for providing valuable feedback on an early draft of this manuscript. Brian Niven provided statistical advice and David Fletcher helped us with the Bayesian analysis of dorsal fin height and base length. Comments from reviewers improved our manuscript.
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Appendix 1. Code of the Bayesian hierarchical model conducted in WinBUGS (ver. 1.4) that fitted a linear relationship between dorsal fin height and dorsal fin base length separately for male and female bottlenose dolphins from Doubtful Sound
model {
for (i in 1:n1f) {
for (j in 1:n2f) {
yxf[i,j,1] ~ dnorm(Xf[i],tauyf)
yxf[i,j,2] ~ dnorm(Yf[i],tauxf)
}
Yf[i] ~ dnorm(EYf[i],tauef)
EYf[i] < –af+bf*Xf[i]
Xf[i] ~ dnorm(0,0.0001)
af ~ dnorm(0,0.0001)
bf ~ dnorm(0,0.0001)
tauyf < –1/(syf*syf)
tauxf < –1/(sxf*sxf)
tauef < –1/(sef*sef)
syf ~ dunif(0,1000)
sxf ~ dunif(0,1000)
sef ~ dunif(0,1000)
for (i in 1:n1 m) {
for (j in 1:n2 m) {
yxm[i,j,1] ~ dnorm(Xm[i],tauym)
yxm[i,j,2] ~ dnorm(Ym[i],tauxm)
}
Ym[i] ~ dnorm(EYm[i],tauem)
EYm[i] < –am+bm*Xm[i]
Xm[i] ~ dnorm(0,0.0001)
}
am ~ dnorm(0,0.0001)
bm ~ dnorm(0,0.0001)
tauym < –1/(sym*sym)
tauxm < –1/(sxm*sxm)
tauem < –1/(sem*sem)
sym ~ dunif(0,1000)
sxm ~ dunif(0,1000)
sem ~ dunif(0,1000)
ad < –am – af
bd < –bm – bf
}
