Using photography to determine sex in pilot whales ( Globicephala melas ) is not possible: Males and females have similar dorsal fins

Photo-identification is used to study populations, movements and social structure (e.g., Bigg et al. 1987, Ottensmeyer and Whitehead 2003, Oremus et al. 2007). All of these analyses are more informative if the sexes of the identified individuals are known. In a few ideal cases the identification photograph itself contains a strong indicator of sex. For instance the great sexual dimorphism in the size and shape of the dorsal fin in adult killer whales (Orcinus orca) allows sex to be determined together with individual identity from photographs (Bigg et al. 1987). Long-finned pilot whales (Globicephala melas) are delphinids, almost entirely black or dark colored. They present three lighter areas of skin, varying from cream to white: the saddle patch, located posterior to the dorsal fin; the postorbital eye blaze, located above the eyes; and an anchor shaped patch on the throat area, extending ventrally (Sergeant 1962). Adult size length can reach up to 4.72 m for females and 6.10 m for males (Sergeant 1962). The sexual dimorphism of the species is also present in the size of the dorsal fin. Because dorsal fin size increases isometrically with body length, adult males have bigger dorsal fins than females (Bloch et al. 1993). It has also been suggested that dorsal fin shape differs between the sexes, with males showing a thicker edge, a more rounded contour and a more rounded tip (Sergeant 1962). Shape can be analyzed using digital photography and shape analysis methods, such as the elliptical Fourier descriptor analysis (Kuhl and Giardina 1982). This method has been widely used to describe shape in different taxa, such as petals of Japanese primrose (Primula sieboldii) (Yoshioka et al. 2004), roots of Japanese radish (Raphanus sativus L.) (Iwata et al. 1998), wings of mosquitoes (Ritera culicidae) (Rohlf and Archie 1984), fish otoliths (Reig-Bolano et al. 2010), and dorsal fins of bottlenose dolphins (Tursiops truncatus) (Rowe and Dawson 2009). This method also has the advantage of analyzing shape independently of size (Kuhl and Giardina 1982). The population of pilot whales that summers off Cape Breton, Canada, has been the subject of study since 1998 (Ottensmeyer and Whitehead 2003). Individual pilot whales have been identified using photo-identification, based on the number and location of mark points in their dorsal fins (Auger-Methe and Whitehead 2007). Saddle patch color and density were also found to be useful when identifying individual pilot whales. Although, given the high number of individual pilot whales identified in this population, the amount of photographic data collected each year,