Correction: Challenges of implementing Mark-recapture studies on poorly marked gregarious delphinids

Hupman, Krista; Stockin, Karen A.; Pollock, Kenneth H.; Pawley, Matthew D. M.; Dwyer, Sarah; Lea, Catherine; Tezanos‐Pinto, Gabriela

doi:10.1371/journal.pone.0203356

Cited by 4 publications

(2 citation statements)

References 1 publication

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“…When using boat-based estimates, group sizes are usually estimated and later confirmed or amended by photo-identification. However, not all species are equally suited to photo-identification [60] and all individuals in a group are often not captured. Conversely, drone-based counts of small cetaceans enable all the individuals to be accurately counted and are, therefore, especially useful when studying large animal groups.…”

Section: Group Countsmentioning

confidence: 99%

Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus)

Fettermann

Fiori

Gillman

et al. 2022

Drones

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Generating accurate estimates of group sizes or behaviours of cetaceans from boat-based surveys can be challenging because much of their activity occurs below the water surface and observations are distorted by horizontal perspectives. Automated observation using drones is an emerging research tool for animal behavioural investigations. However, drone-based and boat-based survey methods have not been quantitatively compared for small, highly mobile cetaceans, such as Delphinidae. Here, we conduct paired concurrent boat-based and drone-based surveys, measuring the number of individuals in 21 groups and the behaviour within 13 groups of bottlenose dolphin (Tursiops truncatus). We additionally assessed the ability to detect behaviour events by the drone that would not be detectable from the boat. Drone-derived abundance counts detected 26.4% more individuals per group on average than boat-based counts (p = 0.003). Drone-based behaviour observations detected travelling 55.2% more frequently and association in subgroups 80.4% more frequently than boat-based observations (p < 0.001 for both comparisons). Whereas foraging was recorded 58.3% and resting 15.1% less frequently by the drone than by boat-based surveys, respectively (p = 0.014 and 0.024). A considerable number of underwater behaviours ranging from individual play activities to intra- and inter-species interactions (including those with humans) were observed from the drone that could not be detected from the boat. Our findings demonstrate that drone surveys can improve the accuracy of population counts and behavioural data for small cetaceans and the magnitude of the discrepancies between the two methods highlights the need for cautious interpretation of studies that have relied on boat-derived data.

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Section: Group Countsmentioning

confidence: 99%

Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus)

Fettermann

Fiori

Gillman

et al. 2022

Drones

View full text Add to dashboard Cite

show abstract

“…All PQ-3 images were excluded from the analysis. For highly marked dolphins, both high and medium quality images were used, while moderately marked dolphins were only confidently identifiable on PQ-1 images (see also Hupman et al, 2018). All qualifying images were used to reconstruct encounter histories for dolphins in the population, resulting in a binary dataset with "1" indicating presence and "0" indicating absence in a given year.…”

Section: Data Managementmentioning

confidence: 99%

Survival Rates and Capture Heterogeneity of Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

Ludwig

Daly²,

Levesque³

et al. 2021

Front. Mar. Sci.

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Adult survival is arguably the most important demographic parameter for long-lived species as it has a large impact on population growth, and it can be estimated for cetacean populations using natural markings and mark-recapture (MR) modelling. Here we describe a 26-year study of a genetically discrete, resident population of bottlenose dolphins in the Shannon Estuary, Ireland, conducted by an NGO using multiple platforms. We estimated survival rates (SRs) using Cormack-Jolly-Seber models and explored the effects of variable survey effort, multiple researchers, and changes in camera equipment as well as capture heterogeneity induced by changes in marks and site fidelity variation, all common issues affecting longitudinal dolphin studies. The mean adult SR was 0.94 (±0.001 SD) and thus comparable to the estimates reported for other bottlenose dolphin populations. Capture heterogeneity through variation in mark severity was confirmed, with higher capture probabilities for well-marked individuals than for poorly marked individuals and a “transience” effect being detected for less well-marked individuals with 43% only recorded once. Likewise, both SR and capture probabilities were comparatively low for individuals with low site fidelity to the Shannon Estuary, and SR of these individuals additionally decreased even further toward the end of the study, reflecting a terminal bias. This bias was attributed to non-random temporal migration, and, together with high encounter rates in Brandon Bay, supported the hypothesis of range expansion. Our results highlight the importance of consistent and geographically homogenous survey effort and support the differentiation of individuals according to their distinctiveness to avoid biased survival estimates.

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Adapting photo-identification methods to study poorly marked cetaceans: a case study for common dolphins and harbor porpoises

Elliser¹,

Linde

MacIver³

2022

Mamm Biol

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Correction: Challenges of implementing Mark-recapture studies on poorly marked gregarious delphinids

Cited by 4 publications

References 1 publication

Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus)

Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus)

Survival Rates and Capture Heterogeneity of Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

Adapting photo-identification methods to study poorly marked cetaceans: a case study for common dolphins and harbor porpoises

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