A Simple Photogrammetric Technique to Measure Sperm Whales at Sea

Abstract

Knowledge of whale length is important to ecological studies. However, photographic techniques to measure sperm whales traditionally require high vantage points or a complicated stereo system. Furthermore, these traditional techniques require an alongside approach that often prevents individual identification. For simple and fast size measurements at sea, I used a laser range finder alongside a digital camera to obtain distance to the fluke at the same time as photo-identification. The camera/lens and laser range finder were calibrated on objects of known lengths. The coefficient of variation (CV) for test objects was low (CV = 0.21%). Forty-seven individually identified sperm whales were measured repetitively on up to 12 different occasions, and the CV was lower (CV = 1.3%) than for other photogrammetric techniques (CV = 4.4%-5.1%). A regression of log fluke span to log total length from whaling and stranding data yielded an r 2 of 0.87 (CV of residuals = 6.7%). Thirty-eight female/immature sperm whales were measured in the Gulf of Mexico (median = 9.3 m, range = 7.1-12.3 m), 167 in the Gulf of California (median = 10.7 m, range = 8.4-13.1 m) and 13 bachelor males off Kaikoura, New Zealand (median = 14.2, range = 11.7-15.8 m). The results were within known sperm whale size and suggested that the population in the Gulf of Mexico was made up of smaller animals than that of the Gulf of California. This technique is easy to implement and allows the measurement of identified individuals.

Geographical variation in the body size of adult female sperm whales (Physeter macrocephalus) – an example of McNab’s resource rule?

“…Seabury's observations for the Gulf of Mexico are confirmed by a photogrammetric study in 2002/3, where 84.2% of 38 females and immatures measured were 7.5-10 m long, appreciably smaller than 167 females/ immatures measured earlier using the same technique in the Gulf of California, where 82% were 9-11.5 m long. Furthermore, a first-year non-neonate in the Gulf of Mexico measured only 3.3 m, substantially below the expected size at birth (Jaquet 2006). Sperm whales around the Ladrone (Mariana) Islands, in the Sulu Sea, Mindora Strait and around the East Indian islands were also said to be generally very small, and mostly cows with calves (Clark 1887), and whales in Indonesian waters were considered to be particularly small (D. Chatwin, pers.…”

“…Differences have also been found in social structure between female sperm whales from the eastern Pacific and North Atlantic Oceans (Whitehead et al 2012). Jaquet (2006) reports that the Gulf of Mexico whales, besides being smaller, have a different social organization, smaller group sizes and a higher incidence of some scarring types (mostly holes in and missing portions of flukes) than Gulf of California whales, while both Hembree (1980) and Fuchs (1978) refer to the small group sizes, put at three to five individuals by Fuchs (1978), of Indonesian sperm whales.…”

Cytochrome P450 isozyme protein verified in the skin of southern hemisphere humpback whales (Megaptera novaeangliae): Implications for biochemical biomarker assessment

“…Known morphological dimension of the species is used to determine unknown dimensions, by scaling. This method is cumbersome, requires complex transformations due to relative and absolute orientation of the animals (Zein, 2013), and it can be difficult to implement from small-boat research platforms alongside routine data collection (Durban and Parsons, 2006;Jaquet, 2006). Nevertheless it has been used successfully in hector's dolphins (Cephalorhynchus hectori) to measure body length (Bräger and Chong, 1999).…”

Good vibrations by the beach boys: magnitude of substrate vibrations is a reliable indicator of male grey seal size

“…1a). Distance to the male in the photograph was 190 describing how the ratio of the known length of an object in cm (SL) to the width in pixels of that object 197 in a photograph (P) changes as distance from the camera increases (D) (Jacquet, 2006). In the example 198 formula (Eq 3), at 400mm zoom, the 0.0015 was derived from the slope of the regression line and 0.0038 199 represents the intercept.…”

“…Seals cannot be handled at Donna Nook, so to determine morphological features associated with 186 RHP, we adopted a photogrammetric estimation technique similar to that used by Jacquet (2006) and 187…”