Integrating <scp>3D</scp> models with morphometric measurements to improve volumetric estimates in marine mammals

Hirtle, Nathan O.; Stepanuk, Julia E. F.; Heywood, Eleanor I.; Christiansen, Fredrik; Thorne, Lesley H.

doi:10.1111/2041-210x.13962

Cited by 8 publications

(8 citation statements)

References 75 publications

(114 reference statements)

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“…However, it is possible to use UAVs to estimate the 2D body size of fully-aquatic species such as cetaceans (Gray et al, 2019), whale sharks (Whitehead et al, 2022) and corals (Levy et al, 2018). It is also possible to estimate body volume in cetaceans by creating a 3D model of the study species and scaling the model to different individuals using 2D body size estimates (Hirtle et al, 2022). Such methods present alternatives to our pipeline for some fully-aquatic species.…”

Section: Discussionmentioning

confidence: 99%

“…We manually located each seal within each orthomosaic. Any seals in the water were counted but their volumes were not estimated as it is currently only possible to estimate the volume of seals on land (but alternative methods and techniques have emerged that may contribute in this context: Chirayath & Earle, 2016; Chirayath & Li, 2019; Hirtle et al, 2022).…”

Section: Methodsmentioning

confidence: 99%

“…CC-BY-NC-ND 4.0 International license perpetuity. It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in seals on land (but alternative methods and techniques have emerged that may contribute in this context:Chirayath & Earle, 2016; Chirayath & Li, 2019;Hirtle et al, 2022).…”

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confidence: 99%

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An unmanned aerial vehicle pipeline to estimate body volume at scale for ecological monitoring

Stone,

Davis

2023

Preprint

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Demographic data are essential to construct mechanistic models to understand how populations change over time and in response to global threats like climate change. Existing demographic data are either lacking or insufficient for many species, particularly those that are challenging to study, such as marine mammals. A pipeline for collecting accurate demographic data to construct robust demographic models at scale would fill this knowledge gap for many species, including marine mammals like pinnipeds (seals, sea lions, and walruses).We introduce a non-invasive pipeline to estimate the 3D body size (volume) of species that will allow monitoring at high spatial and temporal scales. Our pipeline integrates 3D structure-from-motion photogrammetry data collected via planned flight missions using off-the-shelf, multirotor unmanned aerial vehicles (UAVs). We apply and validate this pipeline on the grey sealHalichoerus grypus, a marine species that spends much of its time at sea but is predictably observable during its annual breeding season. We investigate the optimal ground sampling distance (GSD) for surveys by calculating the success rates and accuracy of volume estimates of individuals at different elevations.We establish an optimal GSD of 0.8 cm px-1for animals similar in size to UK grey seals (∼1.4 - 2.5 m length), making our pipeline reproducible and applicable to a broad range of organisms. Volume estimates were accurate and could be made for up to 68% of hauled-out seals in the study areas. Finally, we highlight six key traits that make a species well-suited to estimating body volume following this pipeline. Good candidates include large reptiles like crocodiles, large mammals such as hippopotamus, and shrubs or bushes in deserts and Mediterranean habitats.Our pipeline accurately estimates individual body volume of marine macrovertebrates in a time-and cost-effective manner whilst minimising disturbance. Whilst the approach is applied to pinnipeds here, the pipeline is adaptable to many different taxa that are otherwise challenging to study. Our proposed approach therefore opens up previously inaccessible areas of the Tree of Life to demographic studies, which will improve our ability to protect and conserve these species into the future.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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An unmanned aerial vehicle pipeline to estimate body volume at scale for ecological monitoring

Stone,

Davis

2023

Preprint

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“…Drone-based photogrammetric studies have assessed the body length of killer whales (Orcinus orca) [119], sperm whales (Physeter macrocephalus) [91], and several species from the family Balaenopteridae [24,25,84,[116][117][118]140], as well as other parameters such as the dorsal surface area [26,44,81,112] or total body volume [72,82,[85][86][87][88]90,96], which have been used to estimate the body condition. Photogrammetric studies assessing body volume and body condition have been widely applied for baleen whale species [23,26,27,44,60,72,[81][82][83][85][86][87][88]90,112,141] and medium and large odontocetes [61,62,96,[120][121][122]. However, they have also been shown to be feasible and reliable for smaller marine mammals such as dolphins [63,126], porpoises…”

Section: Photogrammetrymentioning

confidence: 99%

Unmanned Aerial Vehicles (UAVs) in Marine Mammal Research: A Review of Current Applications and Challenges

Álvarez-González,

Suarez-Bregua,

Pierce

et al. 2023

Drones

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Research on the ecology and biology of marine mammal populations is necessary to understand ecosystem dynamics and to support conservation management. Emerging monitoring tools and instruments offer the opportunity to obtain such information in an affordable and effective way. In recent years, unmanned aerial vehicles (UAVs) have become an important tool in the study of marine mammals. Here, we reviewed 169 research articles using UAVs to study marine mammals, published up until December 2022. The goals of these studies included estimating the number of individuals in populations and groups via photo-identification, determining biometrics and body condition through photogrammetry, collecting blow samples, and studying behavioural patterns. UAVs can be a valuable, non-invasive, and useful tool for a wide range of applications in marine mammal research. However, it is important to consider some limitations of this technology, mainly associated with autonomy, resistance to the marine environment, and data processing time, which could probably be overcome in the near future.

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“…It is also important to note that while BAI yields low measurement uncertainty with high precision for capturing differences in body condition amongst individuals (Bierlich et al, 2021a), BAI does not capture body condition change in the vertical plane of the body, which also contributes to energy storage (Lockyer et al, 1985). Imagery of animals rolling on their side throughout the season could be incorporated into a volumetric model (Christiansen et al, 2020b;Hirtle et al, 2022) to help determine whether changes in the horizontal and vertical plane are consistent across reproductive classes, and such a model could also be used to estimate body mass (Christiansen et al, 2019).…”

Section: Caveats and Considerationsmentioning

confidence: 99%

Seasonal gain in body condition of foraging humpback whales along the Western Antarctic Peninsula

et al. 2022

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Most baleen whales are capital breeders that use stored energy acquired on foraging grounds to finance the costs of migration and reproduction on breeding grounds. Body condition reflects past foraging success and can act as a proxy for individual fitness. Hence, monitoring the seasonal gain in body condition of baleen whales while on the foraging grounds can inform how marine mammals support the costs of migration, growth, and reproduction, as well as the nutritional health of the overall population. Here, we use photogrammetry from drone-based imagery to examine how the body condition of humpback whales (Megaptera novaeangliae) changed over the foraging season (November to June) along the Western Antarctic Peninsula (WAP) from 2017 to 2019. This population (IWC stock G) is recovering from past whaling and is growing rapidly, providing an opportunity to study how whales store energy in a prey-rich environment. We used a body area index (BAI) to estimate changes in body condition and applied a Bayesian approach to incorporate measurement uncertainty associated with different drone types used for data collection. We used biopsy samples to determine sex and pregnancy status, and a length-based maturity classification to assign reproductive classes (n = 228; calves = 31, juveniles = 82, lactating females = 31, mature males = 12, mature unknown sex = 56, non-pregnant females = 12, pregnant females = 3, pregnant & lactating females = 1). Average BAI increased linearly over the feeding season for each reproductive class. Lactating females had lower BAI compared to other mature whales late in the season, reflecting the high energetic costs of nursing a calf. Mature males and non-pregnant females had the highest BAI values. Calves and juvenile whales exhibited an increase in BAI but not structural size (body length) over the feeding season. The body length of lactating mothers was positively correlated with the body length of their calves, but no relationship was observed between the BAI of mothers and their calves. Our study establishes a baseline for seasonal changes in the body condition for this humpback whale population, which can help monitor future impacts of disturbance and climate change.

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Integrating 3D models with morphometric measurements to improve volumetric estimates in marine mammals

Cited by 8 publications

References 75 publications

An unmanned aerial vehicle pipeline to estimate body volume at scale for ecological monitoring

An unmanned aerial vehicle pipeline to estimate body volume at scale for ecological monitoring

Unmanned Aerial Vehicles (UAVs) in Marine Mammal Research: A Review of Current Applications and Challenges

Seasonal gain in body condition of foraging humpback whales along the Western Antarctic Peninsula

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