Feasibility and applications of non-invasive laser photogrammetry on free-ranging coastal dolphins

Morphometric data plays a pivotal role in understanding key life history traits to elucidate biological, ecological and evolutionary processes. Obtaining morphometric data from free-ranging cetaceans is difficult, as traditional methods rely on either post-mortem or highly invasive techniques. The present study evaluated the feasibility of remote laser photogrammetry as a non-invasive technique to obtain morphometric data on free-ranging coastal dolphins. First, simulation models and post-mortem specimens were used to investigate potential sources of measurement error and quantify their influence on the accuracy and precision of the morphometric data. These sources include horizontal angle, distance, and body curvature. Second, to demonstrate the potential applications of this technique, laser photogrammetry measurements were obtained during boat-based photo identification surveys on Indo-Pacific bottlenose dolphins (Tursiops aduncus) from Western Australia (Bunbury, Shark Bay and Mandurah). Laser-derived, blowhole-to-dorsal fin (BH-DF) measurements were obtained from individuals of known ages in Bunbury (N=103) and Shark Bay (N=76), in addition to individuals in Mandurah (N=28). Our laser-derived measurement data facilitated the development of population growth curves in conjunction with longitudinal demographic data from Bunbury (~10 years) and Shark Bay (~33 years). These growth curves characterise not only the relationship between age and length, but also the significant morphological differences between these geographically-isolated populations. This study demonstrates the value of remote laser photogrammetry as an effective tool to investigate individual and population-based growth and life-history parameters. This non-invasive technique will provide unique opportunities to better understand the ecological, demographic and life-history characteristics of a population and so better inform conservation management strategies for free-ranging cetacean populations

Bellwethers of change: population modelling of North Pacific humpback whales from 2002 through 2021 reveals shift from recovery to climate response

For the 40 years after the end of commercial whaling in 1976, humpback whale populations in the North Pacific Ocean exhibited a prolonged period of recovery. Using mark–recapture methods on the largest individual photo-identification dataset ever assembled for a cetacean, we estimated annual ocean-basin-wide abundance for the species from 2002 through 2021. Trends in annual estimates describe strong post-whaling era population recovery from 16 875 (± 5955) in 2002 to a peak abundance estimate of 33 488 (± 4455) in 2012. An apparent 20% decline from 2012 to 2021, 33 488 (± 4455) to 26 662 (± 4192), suggests the population abruptly reached carrying capacity due to loss of prey resources. This was particularly evident for humpback whales wintering in Hawai‘i, where, by 2021, estimated abundance had declined by 34% from a peak in 2013, down to abundance levels previously seen in 2006, and contrasted to an absence of decline in Mainland Mexico breeding humpbacks. The strongest marine heatwave recorded globally to date during the 2014–2016 period appeared to have altered the course of species recovery, with enduring effects. Extending this time series will allow humpback whales to serve as an indicator species for the ecosystem in the face of a changing climate