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Chapter One: General Introduction
1.6. Principal methodological tools used in this study
1.6.1. Photo-identification
Individual identification has a long history in the study of animal ecology; for example,
the use of coloured bands to follow the movement of birds (Lockley & Russell 1953).
In cetaceans, the first method utilised to identify individual animals was based on
“discovery marks” that were shot by the whalers into the blubber of whales and
recovered later when the animals were killed and flensed (Brown 1978). In the 1970s,
biologists started to use natural marks to recognise individuals, notably using
photographs of scars on and the shape of dolphins’ dorsal fins (e.g., Würsig & Würsig
1977).
Since then, identification of individual whales and dolphins by using photographs of
natural markings (e.g., trailing edge and pigmentation of humpback whales’ flukes, or
head callosities of right whales) has been a key component to all long-term and
reasonably detailed studies of cetacean social organisation (e.g., Bigg et al. 1990).
This technique has now been applied to more than 30 species of cetaceans (Mann
2000). Photo-identification can provide a wide range of information, including
movements and association patterns, population size and dynamics (e.g., Wells
1986, Smolker & Richards 1992, Rossbach & Herzing 1998, Wilson et al. 1999, Parra
et al. 2006). In long-term studies, it can also provide information on basic life history
parameters (Würsig & Jefferson 1990, Wells 2003) and in combination with other
information such as group composition, it has the potential to provide a model of
social systems (Whitehead 1997). See Whitehead et al. (2000) for a review on photoidentification
techniques.
For this thesis, photo-identification techniques was used on spinner dolphins
(Chapter 2) and rough-toothed dolphins (Chapter 6) to investigate various aspects of
their social organisation, including community size, pattern of residency and rate of
inter-change.
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