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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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Martin, Julien; Sabatier, Quentin; Gowan, Timothy A.; Giraud, Christophe; Gurarie, Eliezer; Calleson, Charles Scott; Ortega-Ortiz, Joel G.; Deutsch, Charles J.; Rycyk, Athena M.; Koslovsky, Stacie M.
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2015 |
A quantitative framework for investigating risk of deadly collisions between marine wildlife and boats.
Methods in Ecology and Evolution 7: 42-50. 3 figs. DOI: 10.1111/2041-210X.12447. Published online Nov. 12, 2015.
–ABSTRACT: 1. Speed regulations of watercraft in protected areas are designed to reduce lethal collisions with wildlife but can have economic consequences. We present a quantitative framework for investigating the risk of deadly collisions between boats and wildlife.
2. We apply encounter rate theory to demonstrate how marine mammal–boat encounter rate can be used to predict the expected number of deaths associated with management scenarios. We illustrate our approach with management scenarios for two endangered species: the Florida manatee Trichechus manatus latirostris and the North Atlantic right whale Eubalaena glacialis. We used a Monte Carlo simulation approach to demonstrate the uncertainty that is associated with our estimate of relative mortality.
3. We show that encounter rate increased with vessel speed but that the expected number of encounters varies depending on the boating activities considered. For instance, in a scenario involving manatees and boating activities such as water skiing, the expected number of encounters in a given area (in a fixed time interval) increased with vessel speed. In another scenario in which a vessel made a transit of fixed length, the expected number of encounters decreases slightly with boat speed. In both cases, the expected number of encounters increased with distanced travelled by the boat. For whales, we found a slight reduction (˜0·1%) in the number of encounters under a scenario where speed is unregulated; this reduction, however, is negligible, and overall expected relative mortality was ˜30% lower under the scenario with speed regulation. The probability of avoidance by the animal or vessel was set to 0 because of lack of data, but we explored the importance of this parameter on the model predictions. In fact, expected relative mortality under speed regulations decreases even further when the probability of avoidance is a decreasing function of vessel speed.
4. By applying encounter rate theory to the case of boat collisions with marine mammals, we gained new insights about encounter processes between wildlife and watercraft. Our work emphasizes the importance of considering uncertainty when estimating wildlife mortality. Finally, our findings are relevant to other systems and ecological processes involving the encounter between moving agents.
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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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Bibliography and Index of the Sirenia and Desmostylia 