Laser photogrammetry reveals variation in growth and early survival in free-ranging bottlenose dolphins

Growth and body condition can be used as indices of health and fitness, but are difficult to collect for populations of conservation concern where individuals cannot be captured. We incorporated a laser photogrammetry system into boat-based photo-identification surveys that underpin individual-based studies of cetacean populations. These data were integrated with >25years of observations from a temperate bottlenose dolphin population in Scotland to investigate the influence of sex on growth patterns, effects of birth order on calf size and the longer term consequences of variation in early growth. Field measurements of the distance from the blowhole to the dorsal fin were made in multiple years from 87 dolphins that had been followed from birth, ranging in age from newborn to 26years. These estimates were validated against direct measurements of 12 individuals that had previously been captured and released in Florida and two study individuals that subsequently stranded. Using relationships derived from other stranded individuals, age-specific body lengths were used to produce growth curves that were based entirely on remote observations. Multilevel regression growth curve analyses suggested males and females showed similar patterns of growth, unlike bottlenose dolphins in sub-tropical areas, and growth was best described by a Richards' growth curve. Newborn length was unrelated to sex; however, females' first calves were shorter than subsequent calves. Sample sizes remain small, yet there was evidence of fitness consequences of variation in calf length; calves that died in their first winter were significantly shorter than those that survived. The incorporation of this simple-to-use and inexpensive method into individual-based photo-identification studies provides new opportunities to non-invasively investigate drivers of variation in growth and the demographic consequences of variation in early growth in cetaceans from protected populations.