Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population

1. Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. 2. We investigated whether variation in age and sex-specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. 3. To estimate annual survival probabilities we applied capture-recapture models to photo-identification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multi-state models to estimate sex-specific survival, and age-models to estimate calf survival. 4. We found strong support for an in...