John E. Reynolds

Florida Manatees, Warm-Water Refuges, and an Uncertain Future

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 withdrawals for human use threaten natural springs. This article examines possible effects on manatees from losing major warm-water refuges and alternative management actions. Because of manatee site-fidelity patterns, plant retirements may increase cold-stress-related deaths and significantly decrease manatee abundance. A forward-looking management strategy is urgently needed before decisions are made to retire plants now used by large numbers of manatees. Possible management alternatives include: gradually weaning manatees off plant outfalls, maintaining the flow of springs now used by manatees, enhancing access to suitable warm-water springs now little used or unused by manatees, constructing new non-industry dependent warm-water refuges, and creating new thermal basins to retain warm-water pockets able to support overwintering manatees.

Estimation of Detection Probability in Manatee Aerial Surveys at a Winter Aggregation Site

Abstract Estimating components of detection probability is crucial to improving the design of aerial surveys for wildlife populations, and this is especially true for species of marine mammals that are threatened or endangered. To evaluate the probability that Florida manatees (Trichechus manatus latirostris) will be detected by observers during aerial surveys, we conducted 6 series of survey flights, during mornings and afternoons on 14–16 consecutive days over the Tampa Electric Companys (TECO) Big Bend power plant discharge canal in Tampa Bay, Florida, USA (winter 2000 through 2003). Our objective was to understand how our ability to detect manatees at a winter aggregation site affects aerial survey counts, so that we may improve techniques for estimating manatee population size. We estimated the probability that manatees would be present at the warm-water discharge of the plant during winter cold fronts and estimated the overall detection probability of manatees present at the plant and the 2 components that make up the probability of detection (the probability of being available and the probability of being detected given they are available). We used telemetry tags and marker flags (n = 15) to facilitate capture–recapture analyses. The probability that marked manatees would be at the plant varied from 48% to 68% across flight series and was inversely related to the ambient water temperature. Based on sightings of marked animals, estimates of the overall probability of detecting a manatee ranged from 45% to 69% across flight series (x̄ = 58%, n = 6). The probability that a manatee would be available to an observer ranged from 73% to 94% across flight series (x̄ = 83%) but was constant among years (83%, 81%, and 78%; x̄ = 81%). The probability that an available manatee would be detected by an aerial observer was variable across flight series (55–95%) and years (73%, 86%, and 66%, x̄ = 73%). Independent estimates of the probability that a manatee would be available to the observer on one pass were obtained from time–depth data loggers and ranged from 5% to 33% (x̄ = 19%, SE = 3.7%), and the probability that a manatee would be available during ≥1 of 10 passes ranged from 41% to 98% (x̄ = 88%, 95% confidence bounds 0.71–0.95). We adjusted survey counts using measures of detectability. Although corrected counts presented here are site-specific, adjusting counts based on detection probability will greatly improve reliability of population estimates from all aerial surveys. Special sampling to estimate components of detection probability should be built into all aerial surveys to ensure that reliable and unbiased information on species abundance is used to evaluate wildlife populations.

Comparison of lipids in selected tissues of the Florida manatee (Order Sirenia) and bottlenose dolphin (Order Cetacea; Suborder Odontoceti).

The position, porosity and oil-filled nature of the zygomatic process of the squamosal bone (ZPSB) of the Florida manatee, Trichechus manatus latirostris, suggest that it may have a similar sound conduction function to that of the intramandibular fat body (IMFB) of the bottlenose dolphin, Tursiops truncatus, and other odontocetes. To examine this possibility we determined the lipid composition of the ZPSB and adipose tissue from the dorsal part of the head region of the Florida manatee, and compared it to that of the dolphin IMFB and melon (another fatty area implicated in sound conduction in odontocetes). Lipids from manatee ZPSB and from adipose tissue were composed almost entirely of triacylglycerols. The most abundant fatty acids of the ZPSB were 18:1, 16:0, 14:0 and 16:1. The major fatty acids of the adipose tissue in the head were the four mentioned above, along with 12:0 and 18:0. Manatee samples did not contain isovaleric acid (iso-5:0), which was found in the bottlenose dolphin IMFB and melon, and has been related to sound conduction in dolphins and some other odontocetes. Thus, if manatee tissues are capable of sound conduction, and this process does occur through the ZPSB, a somewhat different suite of lipid components must support this function.

Reproductive Biology of South American Manatees

The order Sirenia includes the only mammals that are both fully aquatic and herbivorous. The members of this order possess adaptations for both their habitat and their diet. For example, the large fusiform body is almost hairless; external appendages such as the hind limbs and external ear pinnae are absent; the pectoral flippers are reduced and paddlelike; and the tail is modified into a large paddle (manatees) or deeply notched flukes (dugongs) to facilitate locomotion through an aquatic medium. Pachyostotic (swollen) and osteosclerotic (very hard and solid) bones play a role in buoyancy regulation. A peculiar mode of tooth replacement (with an indeterminate number of molars in manatees), presence of horny plates in the mouth, ventral deflection of the rostrum (most pronounced in Dugong), the size, proportions, and structure of the digestive tract, and hindgut fermentation are all adaptations for herbivory. Fossil evidence suggests that sirenians were derived from primitive terrestrial herbivores early in the Tertiary (Reinhart 1971), and biochemical analysis of proteins points to a common origin with elephants and hyraxes (Kleinschmidt et al. 1986).

Aligning conservation and research priorities for proactive species and habitat management: the case of dugongs Dugong dugon in Johor, Malaysia

Conservation efforts use scientific data to provide an adaptive framework wherein habitat and wildlife sustainability can co-exist with human activities. Good science informs decision-makers and facilitates the development of successful conservation approaches. However, conservation concerns for the dugong Dugong dugon in South-east Asia are sufficiently urgent that action must be taken quickly, even though science has not provided complete answers to critical questions. In Johor, Malaysia, aerial surveys were conducted to assess dugong numbers, dugong high-use areas and overlap of dugong sightings with areas of seagrass. Dugong distribution included existing marine parks and locations where known conservation threats exist. We conclude that the Johor islands may represent a significant congregation site for dugongs in Peninsular Malaysia, with as many as 20 dugongs recorded in a single day. The existence of a marine park where the dugong sightings were most prominent is encouraging but only 38% of those sightings fell within the boundaries of the park. Anthropogenic threats need to be assessed and addressed prior to complex development activities such as dredging and coastal reclamation for tourism development in this critical area. We use this case to explore the concept of advancing species conservation through focused research and management, particularly where uncertainties exist because data are scarce.

Winter Habitat Preferences for Florida Manatees and Vulnerability to Cold

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 refuges has created four relatively discrete Florida manatee subpopulations. Using statewide winter counts of manatees from 1999 to 2011, we provide the first attempt to quantify the proportion of animals using the three principal refuge types (power plants, springs, and passive thermal basins) statewide and for each subpopulation. Statewide across all years, 48.5% of all manatees were counted at power plant outfalls, 17.5% at natural springs, and 34.9 % at passive thermal basins or sites with no known warm-water features. Atlantic Coast and Southwest Florida subpopulations comprised 82.2% of all manatees counted (45.6% and 36.6%, respectively) with each subpopulation relying principally on power plants (66.6% and 47.4%, respectively). The upper St. Johns River and Northwest Florida subpopulations comprised 17.8% of all manatees counted with almost all animals relying entirely on springs (99.2% and 88.6% of those subpopulations, respectively). A record high count of 5,076 manatees in January 2010 revealed minimum sizes for the four subpopulations of: 230 manatees in the upper St. Johns River; 2,548 on the Atlantic Coast; 645 in Northwest Florida; and 1,774 in Southwest Florida. Based on a comparison of carcass recovery locations for 713 manatees killed by cold stress between 1999 and 2011 and the distribution of known refuges, it appears that springs offer manatees the best protection against cold stress. Long-term survival of Florida manatees will require improved efforts to enhance and protect manatee access to and use of warm-water springs as power plant outfalls are shut down.

A Hierarchical Covariate Model for Detection, Availability and Abundance of Florida Manatees at a Warm Water Aggregation Site

We constructed a Bayesian hierarchical model for estimating the population size and associated probabilities of availability and conditional detection for Florida manatees aggregating during winter, based on a series of monitoring flights over 3 years, 2001–2003. Building upon the findings of Edwards et al. (2007), our approach combines four sources of monitoring data in a single integrated modeling framework to estimate all model parameters simultaneously. Population size was modeled as a function of availability and detection, which in turn were estimated with covariate models consisting of environmental predictor variables. Previous work estimating manatee abundance from aerial surveys have either serially combined parameters estimated in separate models (Edwards et al. 2007), modeled availability and detection jointly (Craig and Reynolds 2004) or ignored detection bias altogether. Time-specific estimates of availability were high, with some variation among flight series, while estimates of conditional detection were extremely variable from one survey to the next. We obtained improved precision in our estimates of population size relative to Edwards et al. (2007). Our results emphasize the consequences of ignoring detection bias when interpreting survey counts. We hope that this research will be influential in the design of a new state-wide aerial survey monitoring program for Florida manatees.

PERMANENT GENETIC RESOURCES: Eighteen new polymorphic microsatellite markers for the endangered Florida manatee, Trichechus manatus latirostris

Here we describe 18 polymorphic microsatellite loci for Trichechus manatus latirostris (Florida manatee), isolated using a polymerase chain reaction‐based technique. The number of alleles at each locus ranged from two to four (mean = 2.5) in specimens from southwest (n = 58) and northeast (n = 58) Florida. Expected and observed heterozygosities ranged from 0.11 to 0.67 (mean = 0.35) and from 0.02 to 0.78 (mean = 0.34), respectively. Departures from Hardy–Weinberg equilibrium occurred at two loci. There was no evidence of genotypic disequilibrium for any pair of loci. For individual identification, mean random‐mating and θ‐corrected match probabilities were 9.36 × 10−7 and 1.95 × 10−6, respectively.

Differential response by manatees to playbacks of sounds simulating approaching vessels

One of the most pressing concerns associated with the endangered Florida manatee is mortality due to collisions with watercraft. Watercraft collisions are the leading identified cause of adult mortality, resulting in greater than 30% of manatee deaths each year. Reducing adult mortalities is critical to the recovery of the manatee population, as population trends are more sensitive to adult deaths than to those of other age groups. Acoustic playback experiments were conducted to assess the behavioral responses of manatees to watercraft approaches. Playback stimuli were constructed to simulate a vessel approach to approximately 10 m in seagrass habitats. Stimulus categories were (1) silent control; (2) idle outboard approach; (3) planing outboard approach; and (4) fast personal watercraft approach. These results are the first to document responses of wild manatees to playback stimuli. Analyses of swim speed, changes in behavioral state, and respiration rate indicate that the animals respond differentially to the playback categories. The most pronounced responses, relative to the controls, were elicited by the personal watercraft. Quantitative documentation of response during playbacks will provide data that may be used as the basis for future models to predict the impact of specific human activities on manatee and other marine mammal populations.