Procedural Guideline No . 4 – 5 Using photographic identification techniques for assessing bottlenose dolphin ( Tursiops truncatus ) abundance and behaviour

Cetacean populations are increasingly being managed to support regional and international conservation policies. However, effective management requires information on relevant population data, particularly knowledge of abundance and changes in abundance over time, which necessitate long-term monitoring programs. Within the European Union (EU), where populations are protected under the EU Habitats Directive, population assessments will form a key part of the monitoring programmes established for Special Areas of Conservation (SAC). These results must categorise the condition of the site, or population of interest, as either favourable or unfavourable and, if unfavourable, determine whether it is declining, recovering or showing no change (Council of the European Communities, 1992). However, a common problem in the study of cetacean populations is that not all the animals are detected during surveys, and complete enumeration of population size is often not possible. Therefore monitoring programs will typically require field-based approaches for obtaining samples from the population, coupled with statistical approaches for using these samples to estimate abundance and trends. For example, the application of mark-recapture models to photo-identification data to produce estimates of population size and trends. Recognition of individuals has long been acknowledged as central to the study of animal behaviour and ecology (reviewed in Würsig & Jefferson 1990). Techniques that facilitate our ability to recognise individual animals have markedly increased our knowledge of the biology and behaviour of many taxa (e.g. Hammond et al. 1990a; Palsboll et al. 1997). Photographic identification techniques make use of naturally occurring, unique markings enabling identification of individual animals. Commencing with several concurrent studies in the early 1970s (refer to Würsig & Jefferson 1990), identification of individual cetaceans by exploiting these natural markings has become a standard tool for studying marine mammal populations of interest. Moreover, the validity of photo-identification based on natural markings has been confirmed by double-tagging studies in which artificial tags were used as a positive control (e.g. Irvine et al. 1982; Scott et al. 1990). Photographic identification is a flexible technique that can be modified to accommodate both the study species characteristics (e.g. behaviour, individually-identifiable features) and survey type. Boat-based surveys are the most practical approach for studying groups of small cetaceans. This platform allows both a high degree of search effort and manoeuvrability. These two factors are critical not only for locating highly mobile, wide-ranging cetacean species, but also for maintaining a slow, parallel boat course around schools. Typically, small motor vessels are favoured for photo-ID work, as they facilitate positioning the boat to accommodate photos perpendicular to the focal animal’s body axis, and provide the low-angle photography necessary for high quality, identifiable dorsal fin photos (Würsig & Jefferson 1990).