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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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Hagihara, Rie; Jones, Rhondda E.; Grech, Alana; Lanyon, Janet M.; Sheppard, James K..; Marsh, Helene D.
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2014 |
Improving population estimates by quantifying diving and surfacing patterns: A dugong example.
Marine Mammal Science 30(1): 348-366. 3 tabs. 3 figs. DOI: 10.1111/mms.12041. January 2014.
–ABSTRACT: Diving animals are available for detection from above the water when environmental conditions are favorable and the animals are near the surface. The number of animals that are unavailable for detection needs to be estimated to obtain unbiased population estimates. The current availability correction factors used in aerial surveys for the dugong (Dugong dugon) allow for variation in environmental conditions but use the average time dugongs spend near the surface (i.e., constant availability corrections). To improve availability estimates, we examined location and dive data from nine dugongs fitted with satellite telemetry units and time-depth recorders (TDRs) in eastern Australia. The effects of water depth, tidal conditions, and habitat types on dugong surfacing time were examined using generalized linear mixed models (GLMMs). We found that availability for detection differed with water depth, and depth-specific availability estimates were often lower than the constant estimates. The habitat effect was less influential, and there was no tidal effect. The number of dugongs estimated using depth-specific availabilities were higher than those obtained using constant availabilities across water depth. Hence, information on water depth can refine availability estimates and subsequent abundance estimates from dugong aerial surveys. The methodology may be applicable to other aquatic wildlife.
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Marsh, Helene; Grayson, Jillian; Grech, Alana; Hagihara, Rie; Sobtzick, Susan
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2015 |
Re-evaluation of the sustainability of a marine mammal harvest by indigenous people using several lines of evidence.
Biological Conservation 192:324-330. 1 table. 3 figures. DOI: 10.1016/j.biocon.2015.10.007. December 2015.
–ABSTRACT- People in 114 countries have consumed meat and other products from similar to 87 species of marine mammals since 1990. Nonetheless, assessment of the sustainability of most harvests is very difficult because information on the target populations and harvest numbers is inadequate. Dugongs have been harvested by the indigenous peoples of Torres Strait between Australia and Papua New Guinea, for at least 4000 years; the harvest has been substantial for at least the last 400-500 years. We use several lines of evidence to re-evaluate the sustainability of this harvest in the absence of robust data on the absolute size of this dugong population or the harvest. The evidence suggests that the harvest is sustainable. Dugong relative density was significantly higher in 2013 than in any other survey year and their Area of Occupancy has trended slightly upward since 1987. The proportion of calves in 2013 was the highest recorded. Genetic diversity is high. Dugongs are caught in only 5.0% of the 5268 km(2) of very high dugong density habitat as the result of the controls on the harvest and socio-economic factors. Nonetheless, many in the wider Australian community disapprove of this harvest and demand that hunting be banned. Enhancing culturally-appropriate spatial controls may be a more practical approach to managing this harvest than a more data-demanding Total Allowable Catch approach and may also be appropriate for some other indigenous harvests of marine mammals.
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Bibliography and Index of the Sirenia and Desmostylia 