Written by Fabien Vivier
We are pleased to announce a new publication in Animal Conservation entitled:
Inferring dolphin population status: using unoccupied aerial systems to quantify age-structure.
Abstract: Assessing trends in population abundance and demographics is crucial for managing long-lived and slow-reproducing species. Obtaining demographic data, and age-structure information, is challenging, notably for cetaceans. To address this, we combined Unoccupied Aerial System (UAS; drone) photogrammetry data with long-term (>20 years) photo identification data to assess the age-structure of the critically endangered sub-population of common bottlenose dolphins (Tursiops truncatus) of the Gulf of Ambracia, Greece. We compared our findings with two extensively studied non-endangered bottlenose dolphin populations (T. aduncus in Shark Bay, Australia, and T. truncatus in Sarasota Bay, USA). Using a log-linear model, we estimated the total body lengths (TL) of 160 known-aged dolphins between 2021 and 2023 from blowhole-to-dorsal-fin distance (BHDF) measurements collected during surfacing. Subsequently, we tested four growth models to establish an age-length growth curve. We assessed the sub-population's age-structure using three methods: (1) UAS-derived TL estimates, (2) age-length growth curve and (3) long-term monitoring data (i.e. actual age-structure). UAS-measured TL (247.6 ± 32.2 cm) and UAS-estimated TL (246.0 ± 34.7 cm) of the Greek sub-population showed no differences. The Richards Growth model suggested an asymptotic length of 258.5 cm. In Greece, resulting age-structure estimates across the three methods revealed no significant differences (P > 0.1). The Gulf of Ambracia and Shark Bay populations shared similar age-structures, while Sarasota had higher proportions of 2–10 year-olds and lower proportions of 10+ year-olds. All populations had a comparable proportion of 0–2 year-olds (~14%), indicating a similar reproductive rate. Our findings suggest stability in the Greek sub-population; however, additional monitoring of reproductive parameters is essential before concluding its status. We demonstrated the effectiveness of UAS-photogrammetry in rapidly quantifying population age-structure, including scenarios with limited or no demographic data. This technique shows promise for enhancing precision, timeliness, cost-effectiveness and efficiency in population monitoring and informing timely conservation management decisions.
Using drones, we were able to quickly quantify the age-structure of the critically endangered bottlenose dolphin population in the Gulf of Ambracia, Greece, in a few days compared to long-term data. Our study highlights the accuracy of drone-photogrammetry (i.e., imagery) as a rapid and reliable tool for quantifying and monitoring the status of wild dolphin populations.
With this method, we may be able to quickly monitor the age-structure of free-ranging dolphin populations. This information can facilitate the detection of early signs of population changes, such as a decrease in the number of calves, and provide important insights for timely management decisions
Collaborators: We thank our funders (the Office of Naval Research, NOAA-PIFSC, Dolphin Quest, Costas M Lemos Foundation, OceanCare, Georgetown University, National Science Foundation, and Charles and Margery Barancik Foundation) and our partners (Ionian Dolphin Project from Tethys Research Institute, Sarasota Dolphin Research Program and the Shark Bay Dolphin Research Project) for their collaboration.
Full citation details: Vivier, F., Andrés, C., Gonzalvo, J., Fertitta, K., van Aswegen, M., Foroughirad, V., Mann, J., McEntee, M., Wells, R.S. and Bejder, L. (2024), Inferring dolphin population status: using unoccupied aerial systems to quantify age-structure. Anim. Conserv.. https://doi.org/10.1111/acv.12978