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Hagihara, Rie; Jones, Rhondda E.; Sheppard, James K.; Hodgson, Amanda J.; Marsh, Helene D.
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2011 |
Minimizing errors in the analysis of dive recordings from shallow-diving animals.
Journal of Experimental Marine Biology and Ecology 399(2): 173-181. 1 table. 5 figs. DOI: 10.1016/j.jembe.2011.01.001 April 2011.
–ABSTRACT: Knowledge of the diving behaviour of aquatic animals expanded considerably with the invention of time–depth recorders (TDRs) in the 1960s. The large volume of data acquired from TDRs can be analyzed using dive analysis software, however, the application of the software has received relatively little attention. We present an empirical procedure to select optimum values that are critical to obtaining reliable results: the zero-offset correction (ZOC) and the dive threshold. We used dive data from shallow-diving coastal dugongs (Dugong dugon) and visual observations from an independent study to develop and test a procedure that minimizes errors in characterizing dives. We initially corrected the surface level using custom software. We then determined the optimum values for each parameter by classifying dives identified by an open-source dive analysis software into Plausible and Implausible dives based on the duration of dives. The Plausible dives were further classified as Unrecognized dives if they were not identified by the software but were of realistic dive duration. The comparison of these dive types indicated that a ZOC of 1 m and a dive threshold of 0.75 m were the optimum values for our dugong data as they gave the largest number of Plausible dives and smaller numbers of other dive types. Frequency distributions of dive durations from TDRs and independent visual observations supported the selection. Our procedure could be applied to other shallow-diving animals such as coastal dolphins and turtles.
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Hodgson, Amanda J.
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2011 |
Marine Mammals. Chap. 8 in: Ronald A. Loughland & Khaled A. Al-Abdulkader (eds.), Marine Atlas. Western Arabian Gulf.
Kingdom of Saudi Arabia, A Saudi Aramco Environmental Protection Publication, 242-263. ISBN: 978-0-9776600-8-7.
–Dugongs, 250-251.
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Hodgson, Amanda J.; Kelly, Natalie; Peel, David
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2013 |
Unmanned aerial vehicles (UAVs) for surveying marine fauna: A dugong case study.
PLoS ONE 8(11): e79556. 15 pp. 5 figs. DOI:10.1371/journal.pone.0079556. Nov. 4, 2013.
–ABSTRACT: Aerial surveys of marine mammals are routinely conducted to assess and monitor species' habitat use and population status. In Australia, dugongs (Dugong dugon) are regularly surveyed and long-term datasets have formed the basis for defining habitat of high conservation value and risk assessments of human impacts. Unmanned aerial vehicles (UAVs) may facilitate more accurate, human-risk free, and cheaper aerial surveys. We undertook the first Australian UAV survey trial in Shark Bay, Western Australia. We conducted seven flights of the ScanEagle UAV, mounted with a digital SLR camera payload. During each flight, ten transects covering a 1.3 km2 area frequently used by dugongs, were flown at 500, 750 and 1000 ft. Image (photograph) capture was controlled via the Ground Control Station and the capture rate was scheduled to achieve a prescribed 10% overlap between images along transect lines. Images were manually reviewed post hoc for animals and scored according to sun glitter, Beaufort sea state and turbidity. We captured 6243 images, 627 containing dugongs. We also identified whales, dolphins, turtles and a range of other fauna. Of all possible dugong sightings, 95% (CI = 90%, 98%) were subjectively classed as 'certain' (unmistakably dugongs). Neither our dugong sighting rate, nor our ability to identify dugongs with certainty, was affected by UAV altitude. Turbidity was the only environmental variable significantly affecting the dugong sighting rate. Our results suggest that UAV systems may not be limited by sea state conditions in the same manner as sightings from manned surveys. The overlap between images proved valuable for detecting animals that were masked by sun glitter in the corners of images, and identifying animals initially captured at awkward body angles. This initial trial of a basic camera system has successfully demonstrated that the ScanEagle UAV has great potential as a tool for marine mammal aerial surveys.
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Maire, Frederic; Mejias, Luis; Hodgson, Amanda J.; Duclos, Gwenael
(detail)
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2013 |
Detection of dugongs from unmanned aerial vehicles.
2013 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS): pp. 2750-2756. 5 tabs. 5 figs. DOI:10.1109/IROS.2013.6696745. Nov. 2013.
–ABSTRACT: Monitoring and estimation of marine populations is of paramount importance for the conservation and management of sea species. Regular surveys are used to this purpose followed often by a manual counting process. This paper proposes an algorithm for automatic detection of dugongs from imagery taken in aerial surveys. Our algorithm exploits the fact that dugongs are rare in most images, therefore we determine regions of interest partially based on color rarity. This simple observation makes the system robust to changes in illumination. We also show that by applying the extended-maxima transform on red-ratio images, submerged dugongs with very fuzzy edges can be detected. Performance figures obtained here are promising in terms of degree of confidence in the detection of marine species, but more importantly our approach represents a significant step in automating this type of surveys.
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Bibliography and Index of the Sirenia and Desmostylia 