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Proportions of manatees in the Atlantic Coast and Southwest Florida subpopulations at power plants, natural springs, thermal basins, and other sites during synoptic surveys from 1999 to 2011. (Bars indicate the number of manatees counted each year over the 13-year study period; no survey was conducted in 2008.) doi:10.1371/journal.pone.0058978.g005
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To survive cold winter periods most, if not all, Florida manatees rely on warm-water refuges in the southern two-thirds of the Florida peninsula. Most refuges are either warm-water discharges from power plant and natural springs, or passive thermal basins that temporarily trap relatively warm water for a week or more. Strong fidelity to one or more...
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Most Florida manatees depend on localized warm-water refuges in the southern two-thirds of Florida to survive winter; about 60% use outfalls from 10 power plants, whereas 15% use 4 natural warm-water springs. Future availability of these refuges is in doubt; most of these power plants may be retired within the next 20 years and groundwater withdraw...
To survive cold winter periods most, if not all, Florida manatees rely on warm-water refuges in the southern two-thirds of the Florida peninsula. Most refuges are either warm-water discharges from power plant and natural springs, or passive thermal basins that temporarily trap relatively warm water for a week or more. Strong fidelity to one or more...
Citations
... The seasonal difference between autumn and spring likely results from the timing of seasonal migration relative to temperature. Our data suggest manatees departed gradually as temperature declined, remaining in the area during autumn until air temperatures were sufficiently low to force manatees to migrate to seek warm water refuge sites (Laist & Reynolds 2005, Laist et al. 2013. Human behavior may have biased these results if people were outside more on warm days, but these patterns are supported by both sighting and tagged data, suggesting that any bias is minimal. ...
Habitat selection and abundances at range margins during geographic expansion may influence movement into new areas, shaping the trajectory of climate-driven changes in species distribution. The West Indian manatee is an ideal species to study how habitat selection influences range expansion because its presence has rapidly increased during the past 2 decades in the northern Gulf of Mexico (nGoM), a region outside its historical range. We estimated the habitat selection and abundances of manatees in coastal Alabama waters along the nGoM coast using resource selection functions and N-mixture models, respectively. Warm season (May-Nov) manatee abundances were estimated at 25 and 34 manatees at any given time in coastal Alabama waters in 2010 and 2019, respectively. Manatees primarily used the Mobile-Tensaw River Delta and Dog River areas, selecting nearshore shallow water habitats proximate to submerged aquatic vegetation. Distance to boat ramps and human population density had stronger effects on opportunistic sighting data but remained important for tagged data, indicating that manatee habitat selection overlapped with humans. Temperature strongly predicted manatee sightings; most sightings occurred when temperatures were >20°C. Our data indicate that the key interacting factors likely to moderate manatee range expansion, and therefore be important to management and conservation of this species, include increased sea temperature, availability of nearshore habitat with submerged aquatic vegetation, and regional manatee population dynamics. As environmental conditions at the range margins continue to become more favorable to manatees and areas within the range core decline in quality, areas at the range margins may become increasingly important.
... Oral In addition to the clinical utility of using trapped warm air in a clinical setting, trapped air may be applied on a landscape level and could provide a warm air-refuge for Florida manatees. Currently power plant discharges are leading sources of warm water refuges for manatees in southwest Florida and along the Atlantic coast [6]. Many of these power plants are due to close due to outdated technology or high operating costs and manatees who have relied on these warm water refuges are not likely to move long distances to find other warm water sites [6]. ...
... Currently power plant discharges are leading sources of warm water refuges for manatees in southwest Florida and along the Atlantic coast [6]. Many of these power plants are due to close due to outdated technology or high operating costs and manatees who have relied on these warm water refuges are not likely to move long distances to find other warm water sites [6]. Wildlife managers have been tasked to enhance protection for other warm water sites. ...
... This would then accommodate the concerns that manatees are reluctant to move away from learned warm resources. 6 Such floating structures could also be used in natural warm water refuges to expand capacity at these sites. These structures could be designed and constructed to be used on temporary basis during extended cold events to provide sanctuary from CSS during unusual mortality events (UME) related to cold. ...
Florida manatees (Trichechus manatus latirostris) are susceptible to morbidity and mortality from cold exposure, known as Cold Stress Syndrome (CSS), when their aquatic environments measure below 20°C for extended time periods. Clinical data from a rehabilitated Florida manatee affected by CSS demonstrate how a novel nebulization therapy was used to increase the efficacy in delivering antibiotic and bronchodilation drugs resulting in clinical resolution and eventual release of a manatee with secondary pneumonia and persistent hypothermia. Treatment in the nebulization chamber over the course of several weeks also resulted in the manatee normalizing its body temperature in addition to specifically resolving the respiratory disease. Based on the resolution of the hypo-thermia, we hypothesized that the respiratory system may be an under-appreciated modality of thermoregulation in manatees. Data obtained from the rescue staff also support the concept that respiratory heat exchange plays an essential role in the thermoregulation of manatees in Florida. As a result of these clinical and anecdotal findings, a floating polyurethane portable greenhouse prototype has been constructed that will passively warm the air above the surface of the water. Preliminary findings show that a simply constructed floating greenhouse can elevate the ambient air temperature that the manatee could potentially breathe by approximately 4-5°C. Expanding this floating greenhouse concept to an environmental scale, it is possible that a warm air refuge, in contrast to a warm water refuge, can be designed and implemented to mitigate excessive morbidity and mortality due to CSS in Florida manatees. With fossil fuel powered electrical plants being phased out in Florida, this passively powered refuge can have significant conservation impacts on manatee populations.
... However, the Florida manatee and some dugong populations occur in higherlatitude regions where cold weather can exert a strong influence on movement behavior and animals have adopted behavioral thermoregulatory strategies to survive. Florida manatee reliance on warm-water habitats often restricts their winter ranges to waters surrounding artesian springs, industrial (mostly power plant) thermal effluents, or passive thermal basins (e.g., Laist et al. 2013). ...
The seemingly unhurried nature of manatees and dugongs belies their great capacity for undertaking long-distance journeys, often repeatedly in the form of round-trip seasonal migrations, but sometimes as movements independent of seasonal influence. Unique attributes
of sirenian biology that interact with features of their environment to mold patterns of movement and habitat use include herbivory, limited thermoregulatory physiology for coping with cold and, for manatees, an apparent need to ingest fresh water. Manatees and dugongs are remarkably adaptable in their large-scale movement behavior, as manifested by the considerable variation in the occurrence and extent of migrations across populations within species, and among
individuals within populations. Some populations and individuals are relatively sedentary year-round, whereas others migrate hundreds of kilometers between seasonal ranges. The environmental selective pressures driving seasonal movements vary across species, climates, and ecosystems, but are most commonly generated by predictable fluctuations in water temperature (Florida manatee, some dugong populations), rainfall (coastal populations of Antillean and
African manatees), or water level (inland populations of all 3 manatee species living in flood-pulse river systems) over the annual cycle. In each case there is a season (winter, dry, or low-water) of heightened environmental stress where the animals’ range is restricted to areas around a key limiting resource (warm water, fresh water, or deep water), and forage is therefore less available or of lower nutritional quality. Because dugongs are strictly marine and do not require
fresh water, they experience fewer seasonally imposed constraints and are less likely to migrate than manatees. Consequently, the large-scale movements of dugongs seem more stochastic; assessing the status of forage over a wide area through occasional long-distance exploratory forays may represent a behavioral adaptation to periodic extensive declines in seagrass caused by extreme weather events. The available evidence for manatees indicates strong fidelity to
seasonal or year-round ranges across years. A common finding from tracking studies is the existence of considerable variation in large-scale movement behavior among and within individuals, which should confer adaptability to environmental change in the short term and
provide the raw material for evolutionary change over the long term.
... As power plant operations become more intermittent or are replaced by cheaper and/or more energy-efficient alternatives, which are justified as a response to climate change, manatees become more at risk of death from cold stress. During statewide synoptic surveys of the Florida manatee's winter range, about half of the manatees counted have been found at these industrial warm water sites (Laist et al. 2013;Edwards pers. obs. ...
Climate change
stressors are already affecting the subtropical and tropical coastal, estuarine, and riverine habitats of sirenians with consequential changes to their ethology and behavioral ecology. Climate change
is causing temperature increases, sea level rise, changes in water chemistry
and quality
, increase in the intensity and nature of extreme weather events, and changes in rainfall patterns. These stressors are predicted to increase over the coming decades and will be exacerbated by co-stressors including harmful algal blooms, dam construction, hardening
coastlines, phasing out coastal power plants, land clearing, and human food insecurity. The cumulative impacts on all sirenian habitats will be locally variable but changes in habitat extent and continuity are likely to be widespread. Important features of some key manatee habitats such as warm water refuges, freshwater sources, and navigable migration routes
are expected to be reduced or lost. Foraging and movement behaviors
of all species will change in response to alterations in community composition of feeding habitats, and the temporary loss of such habitats resulting from the increased intensity of extreme events, including the expansion of polar vortices, marine heatwaves, tropical cyclones, floods, droughts, and harmful algal blooms. These extreme events are expected to increase sirenian mortality and reduce fecundity, local population size
, and genetic diversity. The locations of essential resources and the cues triggering the timing
of movements are expected to alter rapidly as the climate changes
. Some coastal habitats
may become unsuitable for manatees because of the salinization of sources of fresh water for
drinking
. The capacity of sirenians to alter their behavior in response to climate change
will be essential to their survival.KeywordsClimate changeDivingFeedingFood supplyHabitat changeMovementsReproductionSireniaSocial behavior
... To better understand how mesopredators establish initially, the identification and distance to source populations and the proximity to various sources of thermal refugia are critical. These include anthropogenic sources (such as power plants, Carr and Milstein, 2018), offshore/deep waters (Lamont et al., 2018), or groundwater vents/seeps (Laist et al., 2013), all of which may allow initial winter survival. Unlike shallow coastal waters that experience periodic winter storms, climate-expanding mesopredators may need thermally-stable, deeper water seagrasses initially, such as those found along western Australia, the Mediterranean Sea, and the Big Bend area of Florida (USA). ...
A warming climate is driving the poleward expansion of tropical, subtropical, and temperate plant and animal distributions. These changes have and continue to lead to the colonization of novel organisms into areas beyond their historical ranges. While the full scope of ecological impacts remains unclear, these expansions could alter density-dependent interactions, habitat occupancy patterns, and food web dynamics– similar to exotic species impacts in invaded ecosystems. Seagrasses are habitats of particular interest, given their widespread distribution and ecosystem services. While multiple recent studies report on the effects of the return of larger tropical herbivores in seagrass beds in warming subtropical waters, less is known about the addition of mid-trophic level consumers. These consumers are often key determinants of energy and nutrient transfers from basal resources to higher order predators. Here, we discuss the potential impacts of these distribution changes on temperate and subtropical seagrass communities using information derived from invasive species studies. Notably, we outline several scenarios and generate predictions about how their establishment might occur and speculate on impacts of warmer water consumers as they move poleward. We also discuss potential confounding factors of detecting changes in these consumer distributions. Following the invasive species literature, we offer a framework for generating hypotheses and predicting effects from these range-expanding organisms. Given that climates are predicted to continue to warm into the future, thus facilitating additional species expansions, our goal is to guide future research efforts and provide information for rapid dissemination and utility for this growing subdiscipline of marine ecology.
... Central place foraging: Spatial separation of resting or breeding sites from foraging areas can result in central place foraging movements (Orians and Pearson 1979), as occurs in colonial birds and otariid pinnipeds, for example (Ropert-Coudert et al. 2004;Staniland et al. 2010). The Florida manatee's reliance on warm-water habitat during cold periods (Laist et al. 2013) also generates this type of movement pattern, as individuals commute back and forth between thermal refuges and feeding grounds (e.g., seagrass beds), when ambient water temperatures fall below 20°C, to meet their thermoregulatory and energetic needs (Deutsch et al. 2003a). This general pattern of movement and refuge attendance has been documented for manatees using spring systems in north-central Florida (Bengtson 1981;Slone et al. 2017), power plant thermal discharges in central Florida (Weigle et al. 2001;Deutsch et al. 2003aDeutsch et al. , 2006Deutsch and Carlson 2007;Deutsch and Barlas 2016;Edwards et al. 2016), and passive thermal basins in south Florida (Deutsch et al. 1998;Barton 2006;Haase et al. 2017Haase et al. , 2020. ...
The coastal marine and inland freshwater environments inhabited by manatees and dugongs around the world are spatially heterogeneous and highly dynamic over a range of time scales, often aligned with predictable geophysical cycles
(tidal, diel, seasonal). Central to sirenian adaptations for meeting these varied ecological challenges is plasticity in their movement behavior
, which allows them to find and utilize resources that are key to their survival and reproduction, to escape risks posed by predators and humans, and to leave habitats that become inhospitable. The development and deployment of animal-borne GPS tags have tremendously advanced our knowledge in the domain of small spatio-temporal scales by providing highly accurate locations many times per day. The recent addition of multi-sensor biologgers is further deepening our understanding of the connections between fine-scale behavioral changes and environmental features experienced by the animal. Individual sirenians generally show strong site fidelity within a season to one or a small number of high-use core areas within their home range. Manatees and dugongs usually move at a leisurely pace within and between habitats that provide forage, shelter, thermal refuge, and (for coastal manatees) fresh water. As marathon swimmers, sirenians can sustain a cruising speed of ~2 to 4 km/h for lengthy periods, but when threatened, they can briefly sprint at speeds up to 30 km/h. A common theme across species, ecosystems, and spatio-temporal scales is that access to forage is often constrained due to environmental fluctuations, including tidal cycles
in coastal systems, seasonal
water level
cycles in flood-pulse river systems, and seasonal temperature
changes in higher-latitude regions. Sirenians negotiate trade-offs among key activities within these fluctuating environments while apparently minimizing exposure to predators and other threats through their movement behavior
. There is an increasing body of evidence suggesting that many sirenian populations predominantly forage at night, plausibly as an adaptation to reduce risk of falling victim to hunters or, possibly, boat strikes. Sexual selection has also shaped the behavioral ecology of sirenian movements, as mature males are frequently on the move in search of estrous females during the breeding season
. Mating and parturition can alter female movements and habitat selection for brief periods, but otherwise reproductive status does not appear to strongly affect female movement behavior
over large or small scales. Further research is warranted on most sirenian populations to confirm these conclusions. Continued technological and analytical advancements promise to reveal more secrets of these fascinating and cryptic creatures.KeywordsBehavioral thermoregulationBiologgerCentral place foragingDiel movementsHome rangeMovement rateSatellite trackingSeasonal rangeSex differencesSireniansSite fidelitySmall-scaleTravel corridors
... Power plants and their associated thermal discharges that were built between the 1940s and early 1970s allowed manatees to expand their winter range northward (Reynolds and Wilcox, 1994;Laist and Reynolds, 2005). Today, 66% of the Atlantic manatee population relies on power plants for thermal refuge during the winter (Laist et al., 2013). As these power plants are retired, warm water springs and passive thermal basins will become more important for manatees (Laist and Reynolds, 2005) and more animals may migrate further south to BISC. ...
In this NRCA, a selection of nine key natural resources vital to assessment of Biscayne National Park’s overall health have been identified; water quality, seagrasses, terrestrial vegetation, corals, marine invertebrates, reef fish/gamefish/sharks, sea turtles, marine mammals/American crocodiles, and birds. The condition and trend for each of these resources was evaluated using the best available science and the NPS structured resource assessment and reporting framework.
... The greatest proportion of CSS deaths occurred in large calves within the ATL region, which coincides with reports of more frequent CSS deaths within the northeastern portion of the state (O' Shea et al. 1985, Ackerman et al. 1995, Barlas et al. 2011. Colder water from south-flowing oceanic currents, fewer high-quality warm-water refuges, and variable power plant operations especially from 2010−2016 might contribute to this geographical correlation and leading COD within the region itself (Ackerman et al. 1995, Laist & Reynolds 2005, Laist et al. 2013, Runge et al. 2017. The peak in calf CSS death in 2010 correlates with 2 consecutive winters of unusually cold weather as well as a record cold wave in January of that year that resulted in the mortality of 480 manatees over the course of 89 d (NOAA 2010, Barlas et al. 2011). ...
High maternal investment and extended inter-calving intervals in Florida manatees Trichechus manatus latirostris make calf survivorship critical to overall population growth. However, detailed patterns of causes of mortality in calves have not been reported and state agency statistics report portions of perinatal mortality based on body length rather than actual cause of death (COD). The objectives of this study were to categorize COD based on necropsy data and geographical location in Florida for 1209 manatee calf carcasses (<236 cm total length) examined between January 2009 and December 2017 and to describe factors contributing to calf mortality. Results indicated COD was attributed to natural causes (47%, n = 573), cold stress syndrome (38%, n = 457), watercraft injury (13%, n = 155), or other human-related causes (2%, n = 24). Natural causes were the leading COD for small calves <151 cm, with death due to stillbirth or dystocia most frequent (48%, n = 273/573). Enteric trematodiasis contributed to a large proportion of deaths from natural causes in large calves within the southwest region of Florida, with an increasing annual trend. Brevetoxicosis contributed substantially to natural causes within the southwest region exclusively and was commonly comorbid with enteric trematodiasis. Cold stress syndrome was the leading cause of death for large calves (151-235 cm), with the Atlantic region having the highest proportion of cases. Watercraft injury was a sustained threat to large calves, especially within the southwest region. This report provides details on specific health threats and patterns of mortality among manatee calves.
... During winter, manatees in the U.S.A. depend on warm water refugia, such as natural warm springs or power plant effluents, primarily in peninsular Florida (Irvine, 1983;Deutsch et al., 2003;Laist and Reynolds, 2005). Manatee densities can be extremely high at refugia during cold periods when water temperatures are below 20 • C (Laist et al., 2013), and most manatees leave refuge sites when water temperatures rise above this thermal threshold (Deutsch et al., 2003;Cummings et al., 2014;Hieb et al., 2017). Tagging and photo-identification studies provide evidence of partial migration, with most manatees migrating at least locally. ...
... Seasonal variation in water temperatures during the time of study ranged from a daily average of ∼ 32 • C in the summer (June -August) to ∼ 16 • C in the winter (December -February) in the northern Gulf of Mexico (nGoM) and from a daily average of ∼ 32 • C in the summer to ∼ 21 • C in winter in the eastern Gulf of Mexico (Buckingham et al., 1999;. Within the study area, natural, thermal springs at the Wakulla, Homosassa, and Crystal Rivers, Florida and power plant discharge sites in Crystal River, Big Bend, and Tampa Bay, Florida provided warm-water refuge sites used by manatees (Laist and Reynolds, 2005;Laist et al., 2013). The study area includes extensive tidal river and open water systems with highly diverse habitats, such as seagrass beds in St. George Sound, Apalachicola/St. ...
Partial migration provides a mechanism for species to shift their geographic ranges into new, environmentally favorable regions but has been poorly studied as a means to alleviate effects of climate change. Populations at the edge of their geographic range are ideal to investigate how migratory behaviors may enable range expansion as adjacent areas become more climatically favorable. We determined the contribution of partial migration to the range expansion of West Indian manatees (Trichechus manatus) using GPS data from tagged individuals that migrated between the northern Gulf of Mexico (nGoM) and primary habitat in peninsular Florida. Most of these manatees migrated to the nGoM annually and exhibited high site fidelity among years. Many individuals spent cumulatively more time in the nGoM than in peninsular Florida, indicating the nGoM is a regular part of their geographic range, and they returned to peninsular Florida to meet temperature-related physiological needs for survival. Autumn migrations most frequently terminated at Crystal River, Florida, and manatees that commenced migration late in the season stopped less frequently and had more directed movements. Spring migrations most frequently terminated at Mobile Bay, Alabama, and several manatees quickly and directly migrated from Florida to nGoM stopover sites. Migrations ranged from 10 to 133 days in length, and variation in duration was primarily driven by use of stopover sites and directedness of travel. These data confirm partial migration as an important component of manatee migratory behavior that has already enabled range shifts for manatees on the U.S.A. Gulf of Mexico coast and has potential to facilitate future responses to climate change. As the most common type of migration across the animal kingdom, partial migration may provide a global mechanism for a diverse variety of species to resist the range limiting effects of climate change.
... Loss of warm-water habitat is one of the greatest threats to the Florida manatee population 33 . A goal of wildlife managers tasked with protecting manatees is to have reliable networks of warmwater habitat 7,9,34,35 . Methods for conducting surveys of aggregations have been inadequate for precisely estimating the numbers of manatees using these areas, which has made it difficult or impossible to assess changes in use of these sites over time. ...
Imperfect detection is an important problem when counting wildlife, but new technologies such as unmanned aerial systems (UAS) can help overcome this obstacle. We used data collected by a UAS and a Bayesian closed capture-mark-recapture model to estimate abundance and distribution while accounting for imperfect detection of aggregated Florida manatees (Trichechus manatus latirostris) at thermal refuges to assess use of current and new warmwater sources in winter. Our UAS hovered for 10 min and recorded 4 K video over sites in Collier County, FL. Open-source software was used to create recapture histories for 10- and 6-min time periods. Mean estimates of probability of detection for 1-min intervals at each canal varied by survey and ranged between 0.05 and 0.92. Overall, detection probability for sites varied between 0.62 and 1.00 across surveys and length of video (6 and 10 min). Abundance varied by survey and location, and estimates indicated that distribution changed over time, with use of the novel source of warmwater increasing over time. The highest cumulative estimate occurred in the coldest winter, 2018 (N = 158, CI 141–190). Methods here reduced survey costs, increased safety and obtained rigorous abundance estimates at aggregation sites previously too difficult to monitor.
