PHOTO-IDENTIFICATION AT ASSOCIACIÓ CETÀCEA
Associació Cetàcea carries out the Photo-identification Project: Whales and dolphins along the Catalan coast since 2014. The main goal of the project is to study the dolphin and whale populations off the Catalan coast, by using photo-identification techniques. Cetacean sighting surveys have been carried out in the central Catalan coast, using working methods that allow us to take photographs of the animals, as well as collect both environmental data and
data about the species. Data and photographs of 4 different species of cetaceans have been collected so far: bottlenose dolphin, striped dolphin, Risso’s dolphin and fin whale. We have developed a strict selection method, that allows us to select only those photographs with enough quality to ensure the identification of every photographed individual. Thanks to a team of volunteers we are now developing photo-identification catalogues for some of the sighted species.
BRIEF OVERVIEW OF THE PHOTO-IDENTIFICATION’S HISTORY
Photo-identification is a research method based on the use of photographs to identify every individual of a population thanks to their natural markings. The first researchers who realised that it was possible to recognise the different individuals thanks to specific characteristics where, on the one hand David K. Caldwell, who determined in 1955 that it was possible to study free bottlenose dolphins (Tursiops truncatus)
distinguishing the different individuals from each other (Caldwell, 1955). On the other hand the researchers William E. Schevill and Richard H. Backus proved that it was possible to recognise humpback whale (Megaptera novaeangliae) individuals. Despite these findings, it was not until the 1970s that these technique was used in the study of the cetacean populations. By that time, different scientists started using and adapting it to study mainly 4 species of toothed whales: the killer whale (Orcinus orca), Indo-Pacific humpback dolphin (Sousa chinensis), the bottlenose dolphin and the spinner dolphin (Stenella longirostris) and 2 species of baleen whales: the southern right whale (Eubalaena australis) and the humpback whale (Würsig and Jefferson, 1990 & Mann et al., 2000). These authors realised that it was possible to study whales in a less invasive manner by using photo-identification techniques:
“Serious science can be done without dead whales” – Roger Payne, 1983
This new approach allowed researchers to develop new types of long-term studies, that allowed the individual identification of the animals and the expansion of the knowledge about the studied species. These studies required the development of new working techniques, which where developed by scientists such as Roger and Katy Payne for the southern right whale, Michael Bigg for the killer whale, James Darling and Deborah Glockner for the humpback whale or Bernd Würsig and Randall Wells for the bottlenose dolphin.
MATERIALS AND OBSERVATION PLATFORMS
The material used in photo-identification studies will vary depending on the observation platform and this will be different depending on the studied species or population. There are mainly three observation platforms used in photo-identification studies:
- Observation from the coast: This kind of observation platforms are used to study mainly those cetacean species or populations that live close to the coast or that come so close to the shore that can be photographed from land. In general, such observation platforms are appropriate for species that can be seen at less than 500 metres from the shore, but only if the platform is not located not higher than 15 metres above the sea level (Würsig and Jefferson, 1990 & Mann et al., 2000).
These are rather cheap studies, which have a quite important limitation for those species that can be identified by their dorsal fin, because is rather difficult to take photographs of both sides of the fin, because the animals usually move along the coast, showing only one side of the body to the researcher. This platform has been used in studies about bottlenose dolphins, Indo-Pacific humpback dolphins or spinner dolphins among other species (Würsig and Jefferson, 1990).
- Observation from airplanes: Airplaines are mainly used to study those species of great cetaceans, in which photo-identification characteristics are located on the dorsal part of their body (excluding the dorsal fin) or on their head. Some examples are the right whales (Eubalaena sp.) or the bowhead whale (Balaena mysticetus). The technique consists in flying at 200 m or less while looking for cetaceans and circle them at a lower altitude when sighted (Payne, 1987). These studies allow the researchers to cover a great area of study in a small ammount of time. However, the biggest disadvantage is the high economic cost of such studies. In addition the noise of the airplanes may be potentially disturbing for the animals.
Observation from boats: This probably is the method used by most research groups all over the world, because it allows the researchers to stay very close to the studied groups and to remain for long periods of time with them. For this reason, there are very clear regulations concerning the navigation with cetaceans, in order to reduce the disturbance caused by the presence of the research vessel (Würsig and Jefferson, 1990). Small and manoeuvrable boats are a better option for these studies in order to adapt the navigation to the movements of the animals.
Besides the observation platform, not much material is needed to carry out photo-identification studies, although it should be adapted to the observation spot. It mainly consists on data sheets, on which all the environmental data and information about the sightings should be written down, binoculars to facilitate the detection of cetaceans, a GPS in order to collect all the geographical information about the sightings, and, obviously, a camera. In order to obtain high quality photographs, which will facilitate the recognition of individuals, scientists recommend the use of SLR 35 mm cameras, equipped with auto-focus and multi-shot technologies. Because the lenses of such cameras can be changed, they allow a better adaptation to all observation platforms explained above. Thus, telephoto lenses (of up to 1000 mm of focal length) are mainly used in shore-based studies, while in studies carried out from airplanes or boats researchers mainly use variable length lenses about 80 to 300 mm, up to a maximum of 300 mm (Würsig and Jefferson, 1990).
CHARACTERISTICS OF THE PHOTO-IDENTIFICATION MARKS
Although morfological traits used to diferentiate individuals may vary between species, some requirements have to be met by all of them.
Stability: All the individual marks used have to be stable in time. That means that the characteristics have to remain constant along the years, in order to facilitate the individual recognition in comming years. The presence of the marks used in every species is rather stable and this fact allowed the researchers to report resightings of individuals many years appart: up to 34 years in the killer whale (Durban and Deecke, 2011) or up to 14 yeras in southern right whales (Perkins et al., 1984).
Singularity: The marks of every individual must be unique to allow researchers to differentiate them from each other. Although it is not possible to ensure that a characteristic is unique, it is universally accepted that the more complex a mark is, more information is associated to it, and thus the more improbable is to repeat the exact same pattern (Hammond 1986).
Same resighting probability. It is very important that all the photo-identified individuals have the same resighting probability in population studies, above all those which try to estimate its abundance (Hammond, 1986 & Würsig and Jefferson, 1990). That means, that every individual should have the exact same probability to be identified in coming years (if captured on a photographs), thanks to its natural marks.
In addition to the characteristics mentioned above, natural marks us for photo-identification should be located in a place, which should be easily spotted from outside the water. Thus, most of the marks are located on the dorsal part of the body of the animals, because most cetaceans regularly show their dorsal parts when they surface. However, marks located in ventral parts are also used for some species (Mann et al., 2000):
- Callosities: They are areas of hardened, raised skin on the head of the animals. It is believed that they are related to facial hair and they are located in the same areas where humans have facial hair. That is, above the eyes, behind the nostrils, along the lip and on the “chin” (Payne, 1987 & Perrin et al., 2009). Their shape, position and number are unique for every individual, and their general pattern remains stable over the years (Payne, 1987). They are mainly used in right whales.
- Fluke: It is used in species such as the sperm whale (Physeter macrocephalus) or the humpback whale, which raise their flukes out of the water before a deep dive. In the first example, researchers use the shape of the fluke and the notches and scars on its trailing edge, (Arnborn, 1987; Dufault and Whitehead, 1995 & Mann et al., 2000), whereas in the second example, researchers also use the coloration pattern of the ventral side of the fluke, which is unique for every individual (Darling et al., 1983; Perkins et al., 1984; Perry et al., 1990 & Mann et al., 2000).
- Dorsal fin: It probably is the part of the body, which is easily seen out of the water when a cetacean surfaces, thus it is used in the photo-identification of many species of toothed whales and some species of baleen whales. The most stable marks are its shape and the nicks and notches on its posterior edge, which do not regenerate and are visible during the whole life of the animal (Würsig and Würsig, 1977; Bigg, 1982 & Lockyer and Morris, 1990). It is very important to have photographs of each side of every animal. The dorsal fin is mainly used in the photo-identification of bottlenose dolphins and killer whales, although it has also been used in other species such as pilot whales (Globicephala sp.) or fin whales (Balaenoptera physalus) among others.
- Scars: All the scars on the body of any individual may be used as secondary photo-identification marks, because they usually heal quicker and thus they are not so stable (Lockyer and Morris, 1990). Those marks can have a natural or an anthropogenic origin and they have been used in the photo-identification of bottlenose dolphins, killer whales, Risso’s dolphins (Grampus griseus) or fin whales among other species (Agler et al., 1990; Bigg et al, 1990; Würsig and Jefferson, 1990 & Hartmann et al, 2008).
- Coloration patterns: The coloration of different structures has been used as a primary or secondary photo-identification feature for many cetacean species. In some cases, as for example in the striped dolphin (Stenella coeruleoalba), the fin whale or the blue whale (Balaenoptera musculus), the general coloration pattern has been used. In other cases, however, scientists use the coloration of concrete structures such as the saddle-patch –white patch just behind the dorsal fin– of killer whales and pilot whales or the fluke’s ventral coloration pattern of the humpback whale (Bigg, 1982; Darling et al., 1983; Baird and Stacey 1988; Agler et al., 1990; Bigg et al., 1990; Auger-Méthé and Whitehead, 2007 & Maglio et al., 2010).
En totes les espècies en que es pugui utilitzar més d’una marca, ja sigui de forma primària o secundària, és recomanable fer ús de totes les marques possibles, ja que d’aquesta manera s’augmenta la informació per a la identificació d’un individu, facilitant-ne el seu reconeixement
USES OF PHOTO-IDENTIFICATION
Photo-identification was initially developed as a technique to study the biology of cetacean populations and species, but other studies about the population structure or even the migratory patterns of some species were developed already from the beginning (Mann et al., 2000). Nowadays photo-identification is used in wide variety of studies such as those focussed on life cycle, group structure, geographical characteristics, population structure or population size estimates (Bigg, 1982; Hammond, 1986; Shane et al., 1986; Würsig and Jefferson, 1990; Mann et al., 2000; Calambokidis et al., 2001; Grellier et al., 2003; Parsons, 2005 & Perrin et al., 2009).
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