A Bayesian estimate of harbour seal survival using sparse photo‐identification data

Abstract

Survival rates have rarely been estimated for pinniped populations due to the constraints of obtaining unbiased sample data. In this paper, we present an approach for estimating survival probabilities from individual recognition data in the form of photographic documentation of pelage patterns. This method was applied to estimate adult (age 2+) survival for harbour seals in the Moray Firth, NE Scotland. An astronomical telescope was used to obtain digital images of individual seals, and high-quality images were used to document the annual presence or absence of individuals at a single haul-out site over a 4-year period. A total of 95 females, 10 males and 57 individuals of unknown sex were photographically documented during the study period. Survival and recapture probabilities were estimated using Jolly-Seber mark-recapture models in a Bayesian statistical framework. Computer-intensive Markov Chain Monte Carlo methods were used to estimate the probability distributions for the survival and recapture probabilities, conveying the full extent of the uncertainty resulting from unavoidably sparse observational data. The deviance information criterion was used to identify a best-fitting model that accounted for variation in the probability of capture between sexes, with constant survival. The model estimated adult survival as 0.98 (95% probability interval of 0.94-1.00) using our photo-identification data alone, and 0.97 (0.92-0.99) with the use of an informative prior distribution based on previously published estimates of harbour seal survival. This paper represents the first survival estimate for harbour seals in the UK, and the first survival estimate using photo-identification data in any species of pinniped.

Variation in breeding phenology provides insights into drivers of long-term population change in harbour seals

“…Prior to the development of Loch Fleet as a breeding site in the late 1990s [31], the Cromarty Firth had been the most accessible regional breeding site for behavioural observations and counts of mothers and pups [36,37], therefore providing the best time series of counts to investigate longterm variation in the timing of pupping. Regular counts of adults and pups were made using a telescope from shorebased vantage points during the breeding season (1 June -31 July) as described in Thompson et al [35].…”

Recognition of individual knobby sea stars Protoreaster nodosus (L., 1758) using aboral surface characteristics

“…The advancement of digital cameras has allowed photo-identification to be a promising alternative because of its efficiency in the field. However, most of the subjects so far researched on are vertebrates, such as sharks (Arzoumanian et al, 2005;Van Tienhoven et al, 2007), sea turtles (Reisser et al, 2008;Schofield et al, 2008), birds (Burghardt et al, 2004), cetaceans (Auger-Méthé andWhitehead, 2007;Auger-Méthé et al, 2010;Beekmans et al, 2005;Mazzoil et al, 2004) and seals (Hiby et al, 2007;Mackey et al, 2007). The painted crayfish Panulirus versicolor (Frisch and Hobbs, 2007) and the octopus Wunderpus photogenicus (Huffard et al, 2008) are probably the only invertebrates that have been tracked using a photo-identification method.…”

Integrated modeling of bilateral photo‐identification data in mark–recapture analyses

“…Ecologists are increasingly using mark-recapture methods to analyze photo-identification records, with numerous applications to sharks (e.g., Holmberg et al 2008), reptiles (e.g., Nair et al 2012), marine mammals (e.g., Wilson et al 1999, Calambokidis and Barlow 2004, Mackey et al 2008, and felids (e.g., Nichols 1998, Soisalo andCavalcanti 2006). When individuals are identifiable by natural or artificial marks, such experiments have the potential to provide detailed estimates of key demographic parameters such as abundance, survival, and recruitment, and are therefore extremely useful for informing management and testing ecological or evolutionary theory.…”