TY - JOUR
T1 - Inferring dolphin population status
T2 - using unoccupied aerial systems to quantify age-structure
AU - Vivier, F.
AU - Andrés, C.
AU - Gonzalvo, J.
AU - Fertitta, K.
AU - van Aswegen, M.
AU - Foroughirad, V.
AU - Mann, J.
AU - McEntee, M.
AU - Wells, R. S.
AU - Bejder, L.
N1 - Publisher Copyright:
© 2024 Zoological Society of London.
PY - 2025/4
Y1 - 2025/4
N2 - 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.
AB - 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.
KW - age-length growth curve
KW - age-structure
KW - bottlenose dolphin
KW - conservation
KW - critically endangered
KW - population monitoring
KW - UAS-photogrammetry
UR - https://www.scopus.com/pages/publications/105004077958
U2 - 10.1111/acv.12978
DO - 10.1111/acv.12978
M3 - Journal article
AN - SCOPUS:105004077958
SN - 1367-9430
VL - 28
SP - 262
EP - 276
JO - Animal Conservation
JF - Animal Conservation
IS - 2
ER -