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Stith, Bradley M.; Reid, James P.; Langtimm, Catherine A.; Swain, Eric D.; Doyle, Terry J.; Slone, Daniel H.; Decker, Jeremy D.; Soderqvist, Lars E.
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2011 |
Temperature inverted haloclines provide winter warm-water refugia for manatees in southwest Florida.
Estuaries & Coasts 34(1): 106-119. 2 tabs. 11 figs. DOI 10.1007/s12237-010-9286-1 Published online April 21, 2010.
–ABSTRACT: Florida manatees (Trichechus manatus latirostris) overwintering in the Ten Thousand Islands and western Everglades have no access to power plants or major artesian springs that provide warm-water refugia in other parts of Florida. Instead, hundreds of manatees aggregate at artificial canals, basins, and natural deep water sites that act as passive thermal refugia (PTR). Monitoring at two canal sites revealed temperature inverted haloclines, which provided warm salty bottom layers that generally remained above temperatures considered adverse for manatees. At the largest PTR, the warmer bottom layer disappeared unless significant salt stratification was maintained by upstream freshwater inflow over a persistent tidal wedge. A detailed three-dimensional hydrology model showed that salinity stratification inhibited vertical convection induced by atmospheric cooling. Management or creation of temperature inverted haloclines may be a feasible and desirable option for resource managers to provide passive thermal refugia for manatees and other temperature sensitive aquatic species.
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Haase, Catherine G.; Fletcher, Robert J., Jr.; Slone, Daniel H.; Reid, James P.; Butler, Susan M.
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2017 |
Landscape complementation revealed through bipartite networks: an example with the Florida manatee.
Landscape Ecology 32(10): 1999-2014. 2 tabs. 5 figs. + supplemental materials. doi:10.1007/s10980-017-0560-5. Oct. 2017.
–ABSTRACT: Context -- Landscape complementation, or how landscapes that contain two or more non-substitutable and spatially separated resources facilitate resource use, is critical for many populations. Implicit to the problem of landscape complementation is the movement of individuals to access multiple resources. Conventional measures of complementation, such as habitat area or distance between habitats, do not consider the spatial configuration of resources or how landscape features impede movement.
Objectives -- We advanced a bipartite network approach to capture the spatial configuration and connectivity of two habitat types and contrasted this framework to conventional approaches in a habitat selection model.
Methods -- Using satellite-telemetry of the Florida manatee (Trichechus manatus latirostris), a marine mammal that relies on two distinct, spatially separate habitats for foraging and thermoregulating, we parameterized and compared mixed conditional logistic models with covariates describing classic habitat selection metrics, conventional measures of landscape complementation, and bipartite network metrics.
Results -- The models best supported included habitat area, resistance distance between habitats, and the bipartite network metric eigenvector centrality. The connectivity between habitats and the spatial configuration of one habitat type relative to other types better described habitat selection than conventional measures of landscape complementation alone. The type of habitat, i.e. seagrass or thermal refuge, influenced both the direction and magnitude of the response.
Conclusions -- Landscape complementation is an important predictor of selection and thus classic complementation measures are not sufficient in describing the process. Formalization of complementation with bipartite network can therefore reveal effects potentially missed with conventional measures.
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Lefebvre, Lynn W.; Provancha, Jane A.; Slone, Daniel H.; Kenworthy, W. Judson
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2017 |
Manatee grazing impacts on a mixed species seagrass bed.
Marine Ecology Progress Series 564: 29-45. 2 tabs. 9 figs. doi:10.3354/meps11986. Jan. 2016.
–ABSTRACT: The endangered manatee Trichechus manatus is one of few large grazers in seagrass systems. To assess the long-term impacts of repeated grazing on seagrasses, we selected a study site within Kennedy Space Center in the northern Banana River, Brevard County, Florida, that was typically grazed by large numbers of manatees in spring. Two 13 × 13 m manatee exclosures and 2 paired open plots of equal size were established at the study site in October 1990. Shoot counts, biomass, and species composition of the co-dominant seagrass species, Syringodium filiforme and Halodule wrightii, were sampled 3 times per year in all 4 plots between October 1990 and October 1994. We used a Bayesian modelling approach, accounting for the influence of depth, to detect treatment (exclosed vs. open) effects. S. filiforme shoot counts, total biomass, and frequency of occurrence significantly increased in the exclosures. By July 1993, mean biomass values in the exclosures (167 g dry wt m?²) greatly exceeded those in the open plots (28 g dry wt m?²). H. wrightii decreased in the exclosures by 1994. Initially, both S. filiforme and H. wrightii responded positively to release from manatee grazing pressure. As S. filiforme continued to become denser in the exclosures, it gradually replaced H. wrightii. Our findings may be helpful to biologists and managers interested in predicting seagrass recovery and manatee carrying capacity of repeatedly grazed seagrass beds in areas of special significance to manatees and seagrass conservation.
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Slone, Daniel H.; Butler, Susan M.; Reid, James P.; Haase, Catherine G.
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2017 |
Timing of warm water refuge use in Crystal River National Wildlife Refuge by manatees -- results and insights from Global Positioning System telemetry data.
U.S. Geological Survey Open-File Report 2017–1146: 1-17. 1 tab. 11 figs. doi:10.3133/ofr20171146.
–ABSTRACT: Managers at the U.S. Fish and Wildlife Service Crystal River National Wildlife Refuge (CRNWR) desire to update their management plan regarding the operation of select springs including Three Sisters Springs. They wish to refine existing parameters used to predict the presence of federally threatened Trichechus manatus latirostris (Florida manatee) in the springs and thereby improve their manatee management options. The U.S. Geological Survey Sirenia Project has been tracking manatees in the CRNWR area since 2006 with floating Global Positioning System (GPS) satellite-monitored telemetry tags. Analyzing movements of these tagged manatees will provide valuable insight into their habitat use patterns.
A total of 136 GPS telemetry bouts were available for this project, representing 730,009 locations generated from 40 manatees tagged in the Gulf of Mexico north of Tampa, Florida. Dates from October through March were included to correspond to the times that cold ambient temperatures were expected, thus requiring a need for manatee thermoregulation and a physiologic need for warm water. Water level (tide) and water temperatures were obtained for the study from Salt River, Crystal River mouth, Bagley Cove, Kings Bay mouth, and Magnolia Spring. Polygons were drawn to subdivide the manatee locations into areas around the most-used springs (Three Sisters/Idiots Delight, House/Hunter/Jurassic, Magnolia and King), Kings Bay, Crystal/Salt Rivers and the Gulf of Mexico.
Manatees were found in the Crystal or Salt Rivers or in the Gulf of Mexico when ambient temperatures were warmer (>20 °C), while they were found in or near the springs (especially Three Sisters Springs) at colder ambient water temperatures. There was a trend of manatees entering springs early in the morning and leaving in the afternoon. There was a strong association of manatee movements in and out of the Three Sisters/Idiots Delight polygon with tide cycles: manatees were more likely to enter the Three Sisters/Idiots Delight polygon on an incoming tide, and leave the polygon on an outgoing tide. Both movement directions were associated with midtide. Future analysis will incorporate human activity and a finer spatial scale, including movements between Three Sisters Springs and Idiots Delight and nearby canals.
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Littles, Chanda J.; Bonde, Robert K.; Butler, Susan M.; Jacoby, Charles A.; Notestein, Skye K.; Reid, James P.; Slone, Daniel H.; Frazer, Thomas K.
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2019 |
Coastal habitat change and marine megafauna behavior: Florida manatees encountering reduced food provisions in a prominent winter refuge.
Endangered Species Research 38: 29-43. 3 tabs. 6 figs. DOI: https://doi.org/10.3354/esr00933 Jan. 24, 2019.
–ABSTRACT: A decline in submerged aquatic vegetation (SAV) within Florida's spring-fed, thermal refuges raises questions about how these systems support winter foraging of Florida manatees Trichechus manatus latirostris. We analyzed telemetry data for 12 manatees over 7 years to assess their use of Kings Bay, a winter refuge with diminished SAV. After accounting for the effect of water temperature, we hypothesized that the number of trips out of Kings Bay would increase and the time wintering manatees spent in Kings Bay would decrease. Trips out of and into Kings Bay also were compared to assess potential influences on exiting or entering. There were no detectable differences in the number of trips out of the bay or overall time manatees spent in Kings Bay across winters. The percentage of time water temperatures were below 20oC was the single best predictor of increased time spent in Kings Bay. Trips out of Kings Bay were more likely to occur after 12:00 h and during a high but ebbing tide, compared to trips into the bay. Nine manatees tracked for longer than 75 days in winter spent 7–57% of their time in the Gulf of Mexico, and 3 of these manatees spent 7–65% of the winter >80 km from the mouth of Kings Bay. Results suggest the low amount of SAV in Kings Bay does not obviate its use by manatees, though there are likely tradeoffs for manatees regularly foraging elsewhere. Accounting for movements of Florida manatees through a network of habitats may improve management strategies and facilitate desirable conservation outcomes.
Note correction on website: "February 22, 2019: Substantial changes were made throughout the article after publication: to the text, Tables 1 & 2, and Fig. 4 (see .pdf 'Original text with edits')."
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Haase, Catherine G.; Fletcher, Robert J., Jr.; Slone, Daniel H.; Reid, James P.; Butler, Susan M.
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2020 |
Traveling to thermal refuges during stressful temperatures leads to foraging constraints in a central-place forager.
Jour. Mammalogy 101(1): 271-280. 1 tab. 3 figs. + online supplementary data. doi:10.1093/jmammal/gyz197 Feb. 2020 (publ. online Dec. 13, 2019).
–ABSTRACT: Central-place foragers can be constrained by the distance between habitats. When an organism relies on a central place for thermal refuge, the distance to food resources can potentially constrain foraging behavior. We investigated the effect of distance between thermal refuges and forage patches of the cold-intolerant marine mammal, the Florida manatee (Trichechus manatus latirostris), on foraging duration. We tested the alternative hypotheses of time minimization and energy maximization as a response to distance between habitats. We also determined if manatees mitigate foraging constraints with increased visits to closer thermal refuges. We used hidden Markov models to assign discrete behaviors from movement parameters as a function of water temperature and assessed the influence of distance on foraging duration in water temperatures above (> 20°C) and below (? 20°C) the lower critical limit of the thermoneutral zone of manatees. We found that with increased distance, manatees decreased foraging duration in cold water temperature and increased foraging duration in warmer temperatures. We also found that manatees returned to closer thermal refuges more often. Our results suggest that the spatial relationship of thermal and forage habitats can impact behavioral decisions regarding foraging. Addressing foraging behavior questions while considering thermoregulatory behavior implicates the importance of understanding changing environments on animal behavior, particularly in the face of current global change.
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Bibliography and Index of the Sirenia and Desmostylia 