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Harvey, J. W.; Harr, Kendal E.; Murphy, D.; Walsh, Michael T.; Nolan, E. C.; Bonde, Robert K.; Pate, M. G.; Deutsch, Charles J.; Edwards, Holly H.; Clapp, W. L.
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2009 |
Hematology of healthy Florida manatees (Trichechus manatus).
Veter. Clin. Pathol. 38(2): 183-193.
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Martin, Julien; Royle, J. Andrew; Mackenzie, Darryl I.; Edwards, Holly H.; Kery, Marc; Gardner, Beth
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2011 |
Accounting for non-independent detection when estimating abundance of organisms with a Bayesian approach.
Methods in Ecology and Evolution 2: 595-601. 1 tab. DOI: 10.1111/j.2041-210X.2011.00113.x.
–ABSTRACT:
1. Binomial mixture models use repeated count data to estimate abundance. They are becoming increasingly popular because they provide a simple and cost-effective way to account for imperfect detection. However, these models assume that individuals are detected independently of each other. This assumption may often be violated in the field. For instance, manatees (Trichechus manatus latirostris) may surface in turbid water (i.e. become available for detection during aerial surveys) in a correlated manner (i.e. in groups). However, correlated behaviour, affecting the non-independence of individual detections, may also be relevant in other systems (e.g. correlated patterns of singing in birds and amphibians).
2. We extend binomial mixture models to account for correlated behaviour and therefore to account for non-independent detection of individuals. We simulated correlated behaviour using beta-binomial random variables. Our approach can be used to simultaneously estimate abundance, detection probability and a correlation parameter.
3. Fitting binomial mixture models to data that followed a beta-binomial distribution resulted in an overestimation of abundance even for moderate levels of correlation. In contrast, the beta-binomial mixture model performed considerably better in our simulation scenarios. We also present a goodness-of-fit procedure to evaluate the fit of beta-binomial mixture models.
4. We illustrate our approach by fitting both binomial and beta-binomial mixture models to aerial survey data of manatees in Florida. We found that the binomial mixture model did not fit the data, whereas there was no evidence of lack of fit for the beta-binomial mixture model. This example helps illustrate the importance of using simulations and assessing goodness-of-fit when analysing ecological data with N-mixture models. Indeed, both the simulations and the goodness-of-fit procedure highlighted the limitations of the standard binomial mixture model for aerial manatee surveys.
5. Overestimation of abundance by binomial mixture models owing to non-independent detections is problematic for ecological studies, but also for conservation. For example, in the case of endangered species, it could lead to inappropriate management decisions, such as downlisting. These issues will be increasingly relevant as more ecologists apply flexible N-mixture models to ecological data.
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Martin, Julien; Edwards, Holly H.; Burgess, Matthew A.; Percival, H. Franklin; Fagan, Daniel E.; Gardner, Beth E.; Ortega-Ortiz, Joel G.; Ifju, Peter G.; Evers, Brandon S.; Rambo, Thomas J.
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2012 |
Estimating distribution of hidden objects with drones: from tennis balls to manatees.
PLoS One 7(6):e38882. 8 pp. 7 figs. DOI: 10.1371/journal.pone.0038882. June 25, 2012.
–ABSTRACT: Unmanned aerial vehicles (UAV), or drones, have been used widely in military applications, but more recently civilian applications have emerged (e.g., wildlife population monitoring, traffic monitoring, law enforcement, oil and gas pipeline threat detection). UAV can have several advantages over manned aircraft for wildlife surveys, including reduced ecological footprint, increased safety, and the ability to collect high-resolution geo-referenced imagery that can document the presence of species without the use of a human observer. We illustrate how geo-referenced data collected with UAV technology in combination with recently developed statistical models can improve our ability to estimate the distribution of organisms. To demonstrate the efficacy of this methodology, we conducted an experiment in which tennis balls were used as surrogates of organisms to be surveyed. We used a UAV to collect images of an experimental field with a known number of tennis balls, each of which had a certain probability of being hidden. We then applied spatially explicit occupancy models to estimate the number of balls and created precise distribution maps. We conducted three consecutive surveys over the experimental field and estimated the total number of balls to be 328 (95%CI: 312, 348). The true number was 329 balls, but simple counts based on the UAV pictures would have led to a total maximum count of 284. The distribution of the balls in the field followed a simulated environmental gradient. We also were able to accurately estimate the relationship between the gradient and the distribution of balls. Our experiment demonstrates how this technology can be used to create precise distribution maps in which discrete regions of the study area are assigned a probability of presence of an object. Finally, we discuss the applicability and relevance of this experimental study to the case study of Florida manatee distribution at power plants.
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Stith, Bradley M.; Slone, D. H.; De Wit, Martine; Edwards, Holly H.; Langtimm, Catherine A.; Swain, E. D.; Soderqvist, L. E.; Reid, James P.
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2012 |
Passive thermal refugia provided warm water for Florida manatees during the severe winter of 2009-2010.
Marine Ecology Progress Series 462: 287-301. DOI:10.3354/meps09732. Aug. 21, 2012.
–ABSTRACT: Haloclines induced by freshwater inflow over tidal water have been identified as an important mechanism for maintaining warm water in passive thermal refugia (PTR) used by Florida manatees Trichechus manatus latirostris during winter in extreme southwestern Florida. Record-setting cold during winter 2009-2010 resulted in an unprecedented number of manatee deaths, adding to concerns that PTR may provide inadequate thermal protection during severe cold periods. Hydrological data from 2009-2010 indicate that 2 canal systems in the Ten Thousand Islands (TTI) region acted as PTR and maintained warm bottom-water temperatures, even during severe and prolonged cold periods. Aerial survey counts of live and dead manatees in TTI during the winter of 2009-2010 suggest that these PTR were effective at preventing mass mortality from hypothermia, in contrast to the nearby Everglades region, which lacks similar artificial PTR and showed high manatee carcass counts. Hydrological data from winter 2008-2009 confirmed earlier findings that without haloclines these artificial PTR may become ineffective as warm-water sites. Tidal pumping of groundwater appears to provide additional heat to bottom water during low tide cycles, but the associated thermal inversion is not observed unless salinity stratification is present. The finding that halocline-driven PTR can maintain warm water even under extreme winter conditions suggests that they may have significant potential as warm-water sites. However, availability and conflicting uses of freshwater and other management issues may make halocline-driven PTR unreliable or difficult to manage during winter.
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Edwards, Holly H.
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2013 |
Potential impacts of climate change on warmwater megafauna: the Florida manatee example (Trichechus manatus latirostris).
Climatic Change 121(4): 727-738. DOI: 10.1007/s10584-013-0921-2. Dec. 2013.
–ABSTRACT: Most discussions of impacts of Climate Change have focused on species from temperate or polar regions. Impacts to species inhabiting warm climates are often believed to be small relative to those of species living in cooler climates. However, it is evident that some tropical/sub-tropical species, including some marine megafauna, may face potentially serious consequences from a changing climate. For example, larger, warmer oceans may appear to benefit marine wildlife species like cold-sensitive Florida manatees; however, findings regarding the impact of global climate change (GCC) on estuaries and nearshore areas of Florida indicate that predicted impacts of climate change may be detrimental to endangered manatees. An examination of how projected impacts of climate change will affect threats to manatees and their habitat indicates that threats may be exacerbated. The most significant threats to the Florida manatee population, such as cold-stress, watercraft collisions, and harmful algal blooms, likely will increase. Habitat is likely to be degraded under future climate scenarios. Alterations to Florida's marine environment are ongoing, yet current manatee management plans do not consider the impacts of climate change. The ability of manatees to adapt to change will be influenced by the speed of change and the degree to which human activity impedes or alters it. To minimize impacts to species we must recognize the influence GCC may have on populations, and begin to identify and implement ways to slow or reverse negative impacts arising from it.
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Edwards, Holly H.; Stone, Suzanne B. P.; Hines, Ellen M.; Gomez, Nicole Auil; Winning, Birgit E.
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2014 |
Documenting manatee (Trichechus manatus manatus) presence at Turneffe Atoll, Belize, Central America and its conservation significance.
Caribbean Jour. Sci. 48(1): 71-75. 1 fig.
–ABSTRACT: Belize in Central America supports one of the largest populations of endangered Antillean manatees in the Caribbean. In 2012, a country–wide survey resulted in the highest count ever recorded (507 manatees). Manatee use of atolls has only been documented at Turneffe Atoll in Belize. Manatees in Belize, including those that use Turneffe, have been shown to be impacted by human activities including habitat degradation, entanglement in fishing gear, poaching, and watercraft. The atoll itself faces threats to its diversity and productivity. In 2002, the Oceanic Society began monitoring manatees on Turneffe to document numbers, distribution, and seasonality of use to facilitate the atoll's designation as a protected area. Since 2002, 52 sightings of manatees have been recorded at Turneffe, including cow/calf pairs, indicating it is an important part of the resource network used by the manatees. Protecting the atoll should be a priority for all working to protect manatees and Belize's natural resources.
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Martin, Julien; Edwards, Holly H.; Bled, Florent; Fonnesbeck, Christopher J.; Dupuis, Jérôme A.; Gardner, Beth; Koslovsky, Stacie M.; Aven, Allen M.; Ward-Geiger, Leslie I.; Carmichael, Ruth H.; Fagan, Daniel E.; Ross, Monica A.; Reinert, Thomas R.
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2014 |
Estimating upper bounds for occupancy and number of manatees in areas potentially affected by oil from the Deepwater Horizon oil spill.
PLoS ONE 9(3): e91683. 6pp. 1 tab. 2 figs. DOI: 10.1371/journal.pone.0091683. Mar. 26, 2014.
–ABSTRACT: The explosion of the Deepwater Horizon drilling platform created the largest marine oil spill in U.S. history. As part of the Natural Resource Damage Assessment process, we applied an innovative modeling approach to obtain upper estimates for occupancy and for number of manatees in areas potentially affected by the oil spill. Our data consisted of aerial survey counts in waters of the Florida Panhandle, Alabama and Mississippi. Our method, which uses a Bayesian approach, allows for the propagation of uncertainty associated with estimates from empirical data and from the published literature. We illustrate that it is possible to derive estimates of occupancy rate and upper estimates of the number of manatees present at the time of sampling, even when no manatees were observed in our sampled plots during surveys. We estimated that fewer than 2.4% of potentially affected manatee habitat in our Florida study area may have been occupied by manatees. The upper estimate for the number of manatees present in potentially impacted areas (within our study area) was estimated with our model to be 74 (95% CI 46 to 107). This upper estimate for the number of manatees was conditioned on the upper 95% CI value of the occupancy rate. In other words, based on our estimates, it is highly probable that there were 107 or fewer manatees in our study area during the time of our surveys. Because our analyses apply to habitats considered likely manatee habitats, our inference is restricted to these sites and to the time frame of our surveys. Given that manatees may be hard to see during aerial surveys, it was important to account for imperfect detection. The approach that we described can be useful for determining the best allocation of resources for monitoring and conservation.
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Martin, Julien; Edwards, Holly H.; Fonnesbeck, Christopher J.; Koslovsky, Stacie M.; Harmak, Craig W.; Dane, Teri M.
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2015 |
Combining information for monitoring at large spatial scales: First statewide abundance estimate of the Florida manatee.
Biological Conservation 186: 44-51. 4 figs. DOI: 10.1016/j.biocon.2015.02.029 June 2015.
–ABSTRACT: Monitoring abundance and distribution of organisms over large landscapes can be difficult. Because of challenges associated with logistics and data analyses uncorrected counts are often used as a proxy for abundance. We present the first statewide estimate of abundance for Florida manatees (Trichechus manatus latirostris) using an innovative approach that combines multiple sources of information. We used a combination of a double-observer protocol, repeated passes, and collection of detailed diving behavior data to account for imperfect detection of animals. Our estimate of manatee abundance was 6350 (95%CI: 5310–7390). Specifically, we estimated 2790 (95%CI: 2160–3540) manatees on the west coast (2011), and 3560 (95%CI: 2850–4410) on the east coast (2012). Unlike uncorrected counts conducted since 1991, our estimation method considered two major sources of error: spatial variation in distribution and imperfect detection. The Florida manatee is listed as endangered, but its status is currently under review; the present study may become important for the review process. Interestingly, we estimated that 70% (95%CI: 60–80%) of manatees on the east coast of Florida were aggregated in one county during our survey. Our study illustrates the value of combining information from multiple sources to monitor abundance at large scales. Integration of information can reduce cost, facilitate the use of data obtained from new technologies to increase accuracy, and contribute to encouraging coordination among survey teams from different organizations nationally or internationally. Finally, we discuss the applicability of our work to other conservation applications (e.g., risk assessment) and to other systems.
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Edwards, Holly H.; Ackerman, Bruce B.; eds.
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2016 |
Aerial surveys of manatee distribution in Florida, 1984-2004.
Florida Fish & Wildlife Conservation Commission, Fish & Wildlife Research Institute, Technical Report TR-19: 1-273. Illus. https://indd.adobe.com/view/a647c953-8fa5-404c-bf57-bbc49d9040ee.
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Edwards, Holly H.; Martin, Julien; Deutsch, Charles J.; Muller, R. G.; Koslovsky, Stacie M.; Smith, A. J.; Barlas, M. E.
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2016 |
Influence of manatees' diving on their risk of collision with watercraft.
PLOS One 11(4): e0151450. https://doi.org/10.1371/journal.pone.0151450. 2 tabs. 5 figs. Apr. 6, 2016.
–ABSTRACT: Watercraft pose a threat to endangered Florida manatees (Trichechus manatus latirostris). Mortality from watercraft collisions has adversely impacted the manatee population's growth rate, therefore reducing this threat is an important management goal. To assess factors that contribute to the risk of watercraft strikes to manatees, we studied the diving behavior of nine manatees carrying GPS tags and time–depth recorders in Tampa Bay, Florida, during winters 2002–2006. We applied a Bayesian formulation of generalized linear mixed models to depth data to model the probability (Pt) that manatees would be no deeper than 1.25 m from the water's surface as a function of behavioral and habitat covariates. Manatees above this threshold were considered to be within striking depth of a watercraft. Seventy-eight percent of depth records (individual range 62–86%) were within striking depth (mean = 1.09 m, max = 16.20 m), illustrating how vulnerable manatees are to strikes. In some circumstances manatees made consecutive dives to the bottom while traveling, even in areas >14 m, possibly to conserve energy. This is the first documentation of potential cost-efficient diving behavior in manatees. Manatees were at higher risk of being within striking depth in shallow water (<0.91 m), over seagrass, at night, and while stationary or moving slowly; they were less likely to be within striking depth when ?50 m from a charted waterway. In shallow water the probability of a manatee being within striking depth was 0.96 (CI = 0.93–0.98) and decreased as water depth increased. The probability was greater over seagrass (Pt = 0.96, CI = 0.93–0.98) than over other substrates (Pt = 0.73, CI = 0.58–0.84). Quantitative approaches to assessing risk can improve the effectiveness of manatee conservation measures by helping identify areas for protection.
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Marsh, Helene D.; Arraut, Eduardo Moraes; Keith Diagne, Lucy; Edwards, Holly H.; Marmontel, Miriam
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2017 |
Impact of climate change and loss of habitat on sirenians. Chap. 19 in: Andy Butterworth (ed.), Marine mammal welfare: human induced change in the marine environment and its impacts on marine mammal welfare.
Springer International Publishing: Animal Welfare Series, Vol. 17: 333-357. DOI: https://doi.org/10.1007/978-3-319-46994-2. June 20, 2017.
–ABSTRACT: Although the impacts of climate change on the welfare of individual manatees and dugongs are still uncertain, the effects are likely to be through indirect interactions between meteorological and biotic factors and the human responses to climate change. We divided the potential impacts into (1) those that will potentially affect sirenians directly including temperature increases, sea-level rise, increased intensity of extreme weather events and changes in rainfall patterns and (2) indirect impacts that are likely to cause harm through habitat loss and change and the increase in the likelihood of harmful algal blooms and disease outbreaks. The habitat modification accompanying sea-level rise is likely to decrease the welfare of sirenians including increased mortality. Many species of tropical seagrasses live close to their thermal limits and will have to up-regulate their stress-response systems to tolerate the sublethal temperature increases caused by climate change. The capacity of seagrass species to evoke such responses is uncertain, as are the effects of elevated carbon dioxide on such acclimation responses. The increase in the intensity of extreme weather events associated with climate change is likely to decrease the welfare of sirenians through increased mortality from strandings, as well as habitat loss and change. These effects are likely to increase the exposure of sirenians to disease and their vulnerability to predators, including human hunters. Climate-related hazards will also exacerbate other stressors, especially for people living in poverty. Thus the risks to sirenians from climate change are likely to be greatest for small populations of dugongs and manatees occurring in low-income countries. The African manatee will be particularly vulnerable because of the high levels of human poverty throughout most of its range resulting in competition for resources, including protein from manatee meat.
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Udell, Bradley J.; Martin, Julien; Fletcher, Robert J., Jr.; Bonneau, Mathieu; Edwards, Holly H.; Gowan, Timothy A.; Hardy, Stacie K.; Gurarie, Eliezer; Calleson, Charles S.; Deutsch, Charles J.
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2019 |
Integrating encounter theory with decision analysis to evaluate collision risk and determine optimal protection zones for wildlife.
Jour. Applied Ecology 56(5): 1050-1062. https://doi.org/10.1111/1365-2664.13290 May 2019.
–ABSTRACT: Better understanding human–wildlife interactions and their links with management can help improve the design of wildlife protection zones. One example is the problem of wildlife collisions with vehicles or human-built structures (e.g., power lines, wind farms). In fact, collisions between marine wildlife and watercraft are among the major threats faced by several endangered species of marine mammals. Natural resource managers are therefore interested in finding cost-effective solutions to mitigate these threats.
We combined abundance estimators with encounter rate theory to estimate relative lethal collision risk of the Florida manatee (Trichechus manatus latirostris) from watercraft. We first modelled seasonal abundance of watercraft and manatees using a Bayesian analysis of aerial survey count data. We then modelled relative lethal collision risk in space and across seasons. Finally, we applied decision analysis and Linear Integer Programming to determine the optimal design of speed zones in terms of relative risk to manatees and costs to waterway users. We used a Pareto efficient frontier approach to evaluate the performance of alternative zones, which included additional practical considerations (e.g., spatial aggregation of speed zones) in relation to the optimal zone configurations.
Under the various relationships for probability of death given strike speed that we considered, the current speed zones reduced the relative lethal collision risk by an average of 51.5% to 70.0% compared to the scenario in which all speed regulations were removed (i.e., the no-protection scenario). We identified optimal zones and near-optimal zones with additional management considerations that improved upon the current zones in terms of cost or relative risk.
Policy implications. Our analytical framework combines encounter rate theory and decision analysis to quantify the effectiveness of speed zones in protecting manatees while accounting for uncertainty. Our approach can be used to optimize the design of protection zones intended to reduce conflicts between human waterborne activity and marine mammals. This framework could be extended to address many other problems of human–wildlife interactions, such as the optimal placement of wind farms to minimize collisions with wildlife or the optimal allocation of ranger effort to mitigate poaching threats.
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Bibliography and Index of the Sirenia and Desmostylia 