We used a case study of a coastal bottlenose dolphin population to present a framework for determining the number of individuals present and assessing the likely time scale over which trends in abundance may be determined. Such a framework is appropriate for animal species that possess natural markings sufficient for individual recognition, and may be valuable in the development and implementation of management and monitoring programs for vulnerable populations.Population abundance was estimated using mark-recapture methods applied to photoidentification data. This experiment was designed to minimize violation of method assumptions so as to allow use of the most parsimonious model for analysis. The data were examined critically to investigate mark-recapture assumptions, while analytical methods and data were selected to minimize and, where necessary, account for violations. The estimated number of animals with long-lasting marks from left and right side estimates were 73 Ϯ 12 and 80 Ϯ 11 individuals, respectively (means Ϯ 1 SE). When divided by the estimated proportion of such animals in the population (0.57 Ϯ 0.043 and 0.61 Ϯ 0.035, respectively) and averaged, weighted by inverse variance, a total population size of 129 Ϯ 15 individual animals was estimated (95% CI ϭ 110-174 animals).Data on calves observed and carcasses recovered suggest that the population could be increasing or decreasing at an annual rate of up to 5%. A power analysis, undertaken to investigate the length of monitoring program required to detect changes in population abundance at a 90% level of certainty, showed that detection of a trend could only occur following Ͼ8 yr of research effort. Biennial sampling has power similar to that of annual sampling, but savings in resources are offset by the loss of data on the reproductive histories of individuals.

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1. Monitoring spatial and temporal patterns in cetacean abundance involves a variety of approaches depending upon the target species and the resources available. As a first step, the collection of incidental sightings or strandings information aids the construction of a species list and a rough measure of status and seasonal variation in abundance. These often make use of networks of volunteer observers although the wide variation in abilities and experience means that special attention must be paid to training and to data quality control. More robust monitoring of numbers requires quantification of effort and some correction for factors that influence detectability, such as sea state. 2. The presence of cetaceans may be recorded visually, or indirectly by acoustics. Each has advantages and disadvantages, and their applicability may vary between species. The use of fixed stations tends to allow sustained monitoring at relatively low cost but coverage is limited to the immediate vicinity. For more extensive coverage, mobile platforms are necessary. Platforms of opportunity such as ferries, whale‐watching boats, etc. are often used to survey areas at low cost. These may allow repeat observations to be made over time, but with no control over where the vessel goes, it is typically not possible to sample wide areas, thus limiting abundance estimation. 3. Line transect surveys using dedicated platforms allow representative coverage of areas from which abundance estimates can be made (either using indices or absolute measures derived from density estimation). Assumptions relating to detectability and responsiveness need to be addressed and various methods (such as two‐platform surveys) have been developed to accommodate these. 4. For some cetacean species, mark‐recapture methods can be applied using photo‐identification of recognizable individuals. Again, a number of assumptions are made, particularly relating to recognizability, representativeness of sampling and capture probabilities. Capturing, on film, as many animals in the population as possible helps to reduce the problem of heterogeneity of capture probabilities. Mark‐recapture methods require at least two sampling occasions. If multiple sampling is employed, either open or closed population models can be used. 5. Measuring population change represents a particular challenge for mobile animals such as cetaceans. Changes in ranging patterns may have a large impact on abundance estimates unless very large areas are adequately covered. Power analysis is a useful method to indicate the ability of the data to detect a trend of a given magnitude. Increasingly, spatial modelling using GLMs and GAMs is being used to provide a better understanding of the biotic and hydrographic factors influencing cetacean distribution.

The ability to recognize individual animals has substantially increased our knowledge of the biology and behaviour of many taxa. However, not all species lend themselves to this approach, either because of insufficient phenotypic variation or because tag attachment is not feasible. The use of genetic markers ('tags') represents a viable alternative to traditional methods of individual recognition, as they are permanent and exist in all individuals. We tested the use of genetic markers as the primary means of identifying individuals in a study of humpback whales in the North Atlantic Ocean. Analysis of six microsatellite loci among 3,060 skin samples collected throughout this ocean allowed the unequivocal identification of individuals. Analysis of 692 'recaptures', identified by their genotype, revealed individual local and migratory movements of up to 10,000 km, limited exchange among summer feeding grounds, and mixing in winter breeding areas, and also allowed the first estimates of animal abundance based solely on genotypic data. Our study demonstrates that genetic tagging is not only feasible, but generates data (for example, on sex) that can be valuable when interpreting the results of tagging experiments.

Summary 1.The social structure of a population plays a key role in many aspects of its ecology and biology. It influences its genetic make-up, the way diseases spread through it and the way animals exploit their environment. However, the description of social structure in nonprimate animals is receiving little attention because of the difficulty in abstracting social structure from the description of association patterns between individuals. 2. Here we focus on recently developed analytical techniques that facilitate inference about social structure from association patterns. We apply them to the population of bottlenose dolphins residing along the Scottish east coast, to detect the presence of communities within this population and infer its social structure from the temporal variation in association patterns between individuals. 3. Using network analytical techniques, we show that the population is composed of two social units with restricted interactions. These two units seem to be related to known differences in the ranging pattern of individuals. By examining social structuring at different spatial scales, we confirm that the identification of these two units is the result of genuine social affiliation and is not an artefact of their spatial distribution. 4. We also show that the structure of this fission-fusion society relies principally on short-term casual acquaintances lasting a few days with a smaller proportion of associations lasting several years. These findings highlight how network analyses can be used to detect and understand the forces driving social organization of bottlenose dolphins and other social species.

Traditionally, marine resources have been managed such that controls on new developments are implemented only when harmful effects on other environmental or economic interests can be demonstrated. This approach poses particular problems for the conservation of coastal cetaceans because potential threats to their populations are diverse and likely to interact, individual threats may result from multiple sources, and the problems inherent in studying cetaceans result in considerable scientific uncertainty and low statistical power to detect any effects. Consequently, many countries are adopting integrated coastal management programs and precautionary management principles. In practice, however, issues continue to be dealt with within traditional frameworks that require demonstration of harm. Because cetaceans are long‐lived, they demand long‐term studies, and populations could decline to dangerously low levels before management action is taken. We illustrate these problems using a case study from the Moray Firth, Scotland. This inshore area will soon be designated and managed as a “special area of conservation” to protect bottlenose dolphins (  Tursiops truncatus) under the European Community's Habitats Directive. The population is small and isolated, and it faces a wide range of potential threats, but there remains considerable uncertainty over the magnitude of each threat. We combined power analysis and population viability analysis to explore the relative consequences of adopting either traditional or precautionary approaches to management. In this case, our results reaffirm the need for precautionary management. More generally, we illustrate how this approach can be used to provide a more scientific basis for determining the level of precaution required to address particular management issues in this and other marine systems.

The Mediterranean sub-population of short-beaked common dolphin is believed to have suffered a steep decline in the Mediterranean in recent years, and in 2003 it was listed as endangered in the IUCN Red List of Threatened Species. Effective conservation will depend critically on our understanding of the relationship between the species and its habitats. The Alborán Sea is believed to be the most important remaining Mediterranean habitat for this species, and thus constitutes a vital source of information for the development of conservation measures. We used spatial modelling to estimate the abundance and explore the habitat use of common dolphins in this area, examining regional, seasonal and interannual variations, as well as the influence of biological factors such as presence of calves, interspecific relationships and behaviour. From 1992 to 2004, 37 385 km of non-systematic line transects generated 738 sightings in a 19 189 km 2 study area. The point estimate of abundance was 19 428 (95% CI = 15 277 to 22 804) dolphins. Seasonal and geographical variations in abundance were detected, with higher average density in summer than in winter, and in the Western Alborán Sea than in the east Gulf of Vera, which has different physical/environmental characteristics. No overall trend in abundance was observed in the Alborán area. However, a decline was observed in the Gulf of Vera, with a summer density 3-fold lower in the period from 1996 to 2004 than in 1992 to 1995. A potential link of this decline with prey depletion due to the exponential growth of aquaculture in the area is discussed. Clear differences in habitat use were also found when examining the influence of biological factors. In particular, groups with calves and groups that were feeding preferred more coastal waters. This result could have important implications for the development of conservation measures for this species in the Mediterranean.