REPRODUCTION IN FEMALE MANATEES OBSERVED IN SARASOTA BAY, FLORIDA

Resightings of recognizable individual Florida manatees, Trichechus manatus latirostris , in Sarasota Bay provided information on life history and reproductive parameters. These parameters have been documented at winter aggregation sites, but few data existed for Florida's west coast at non-winter sites. Life history data are needed to estimate annual reproduction and survival rates and construct population models for manatees along west central Florida. Observations of 113 recognizable manatees of known sex sighted between 1993 and 1997 indicated a 1: 1 sex ratio. Fifty-three females produced at least 55 calves during five years of observation. Two large, presumably sexually mature females were never observed with calves in over five years of monitoring. Not surprisingly, several reproductive parameters matched those measured in previous studies at winter sites with a mean of 1.8 seasons of calf dependence, 2.2 seasons between births, and age of sexual maturity at 3–4 yr. Birth rates, fecundity, and proportions of females with calves varied only slightly among investigations.     

OBSERVATIONS OF FLORIDA MANATEES(TRICHECHUS MANATUS LATIROSTRIS) AROUND SELECTED POWER PLANTS IN WINTER

Sixty-four aerial surveys were flown during cold, winter weather between December 1982 and February 1772 to provide an index of trends in abundance of the Florida manatee ( Trichechus manatus latirostris )around five Florida Power & Light Company (FPL) plants. The surveys documented high winter use of warm-water discharges at four of the plants (Canaveral, Riviera. Port Everglades, and Fort Myers). The total number of manatees sighted at the five primary plants surveyed during a single survey ranged from 6 to 765 manatees (= 330 ± 45 manatees per survey): thus, up to 41% of the total Florida manatee minimum population of 1.850 animals may be found on cold days at FPL plants. The number of calves sighted at the plants during winter has decreased; similarly, for three consecutive years (winter 1989–1970 through winter 1991–1992), the percentage of the manatees that are calves sighted at the plants has decreased. Although data from the surveys of FPL plants do not necessarily reflect what may be happening with manatees located elsewhere in Florida, a possible reduction in calf numbers, coupled with increasing numbers of dead calves being documented by scientists involved in manatee carcass salvage work, is cause for concern in this slow-reproducing, endangered species.     

HABITAT SELECTION BY MANATEES IN SARASOTA BAY, FLORIDA

Habitat selection by Florida manatees ( Trichechus manatus latirostris ) is influenced by, among other things, availability of food, thermal, and freshwater resources. However, habitat selection by females with dependent calves may differ from that of other demographic groups with regard to the relative importance of these factors. Additional factors that may influence habitat selection for females with dependent calves include ambient noise, strong currents, or increased foraging requirements. We examined distributional data for manatees from aerial surveys of the coastal waters near Sarasota, Florida, between 1994 and 2004 to determine whether habitat selection by groups of manatees that included calves differed from that of other groups. We characterized groups according to their location within seven habitat types. Enclosed bays not traversed by the Intracoastal Waterway had the highest proportions of groups with calves. Groups with calves used a No Entry refuge (from which almost all human use is barred) to a greater extent than did other groups. Overall, groups with calves exhibited significantly different habitat selection from groups without calves ( P < 0.001, χ²= 43.0, df = 6), but this was not consistent across seasons. During the winter and spring, thermal requirements influenced manatees to such an extent that all demographic groups selected habitat similarly.     

MORBILLIVIRUS INFECTION IN MANATEES

The first evidence of exposure of free-ranging Florida manatees ( Trichechus manatees latirostris ) to a morbillivirus is reported. Blood samples were collected from 148 Florida manatees between 1977 and 1994. The sample included manatees that were under rehabilitation (n = 97), free-ranging (n = 40) and fresh necropsy specimens (n = 11). Serum from six animals (4%) neutralized porpoise and dolphin morbilliviruses to a higher titer than any other member of the Morbillivirus genus. Antibodies were not detected in sera from 12 free-ranging Antillean manatees ( T. manatus manatus ) from Guyana sampled in 1992 or from 12 hand-reared Amazonian manatees ( T. inunguis ) sampled in 1984. Immunoprecipitation studies using radio-labelled canine distemper virus protein and serum from Florida manatees showed precipitation of the nucleo-capsid (N) protein. The combination of low antibody titers and absence of clinical disease suggest that the Florida manatee is a dead-end host. Sporadic infection may occur following contact with another species in which infection is enzootic. Morbillivirus could, either by fatal infection or more insidious effects on the immune system or reproduction, pose a problem to this already threatened species.     

DISTRIBUTION PATTERNS OF INDIVIDUALLY IDENTIFIABLE WEST INDIAN MANATEES (TRICHECHUS MANATUS) IN FLORIDA

Photographs of distinctively scarred manatees ( Trichechus manatus ) were taken at aggregation sites throughout Florida and assembled into a catalog for identifying individuals. Resightings of known manatees in different years or at different locations enabled us to document site fidelity and long-distance movements. Of the 891 individuals included in the catalog as of August 1986, 470 (53%) were resighted at least once. We documented 219 cases of seasonal returns to specific aggregation sites and 98 instances of movements between areas. Movements in excess of 820 km were documented for individuals on the east coast of Florida. Rapid movements south during early winter, as well as northerly spring movements, verify a seasonal migration pattern for many individuals along Florida's east coast. The wide-ranging migratory habits of manatees in Florida must be considered if meaningful management strategies are to be developed and implemented.     

AN EPIZOOTIC OF FLORIDA MANATEES ASSOCIATED WITH A DINOFLAGELLATE BLOOM

Over a 10-wk period in early 1982, 39 Florida manatees ( Trichechus manatus latirostris ) were found dead in the lower Caloosahatchee River and nearby waters of southwestern Florida. Two were killed by boats. The remainder showed no evidence of trauma. Lesions indicative of infectious agents were not identified, and bacteriological and contaminant residue findings were unremarkable. Nonspecific lesions of congestion and hemorrhage were identified in brain tissue. Numerous reports were also received of manatee morbidity. Some distressed manatees showed no biochemical lesions in clinical analyses of blood samples and recovered quickly. Timing of manatee illnesses coincided with fish and double-crested cormorant ( Phalacrocorax auritus ) mortality and morbidity. A widespread bloom of the dinoflagellate red tide organism ( Gymnodinium breve ) also coincided with these incidents. G. breve produces potent neurotoxins (brevetoxins). Circumstantial evidence links these events, and possible routes of exposure may include ingestion of filter-feeding ascidians. Ecological conditions that magnified the extent of the epizootic included an early dispersal of manatees into the area from a nearby winter aggregation site and unusually high salinities that facilitated the inshore spread of the red tide bloom. Management responses to future episodes of red tide in manatee areas are suggested.     

SIMULATED VESSEL APPROACHES ELICIT DIFFERENTIAL RESPONSES FROM MANATEES

One of the most pressing concerns associated with conservation of the endangered Florida manatee is mortality and serious injury due to collisions with watercraft. Watercraft collisions are the leading identified cause of manatee mortality, averaging 25% and reaching 31% of deaths each year. The successful establishment and management of protected areas depend upon the acquisition of data assessing how manatees use different habitats, and identification of environmental characteristics influencing manatee behavior and habitat selection. Acoustic playback experiments were conducted to assess the behavioral responses of manatees to watercraft approaches. Playback stimuli made from prerecorded watercraft approaches were constructed to simulate a vessel approach to approximately 10 m in sea grass habitats. Stimulus categories were (1) silent control, (2) approach with outboard at idle speed, (3) vessel approach at planning speed, and (4) fast personal watercraft approach. Analyses of swim speed, changes in behavioral state, and respiration rate indicate that the animals responded differentially to the playback categories. The most pronounced responses, relative to the controls, were elicited by personal watercraft. Quantitative documentation of response during playbacks provides data that may be used as the basis for future models to predict the impact of specific human activities on manatees and other marine mammal populations.     

Description of the Oocysts of Two New Species of Eimeria (Apicomplexa: Eimerüdae) from the Florida Manatee, Trichechus manatus (Sirenia: Trichechidae)

Two new species of Eimeria (Apicomplexa: Eimerüdae) are described from the feces of the Florida manatee, Trichechus manatus latirostrts (Sirenia: Trichechidae). Oocysts of Eimeria manatus n. sp. are spherical to subsphencal, 11.8 × 10.7 (10.5–13.5 × 9.0–13.5) μ m , with a smooth, thin, bilayered wall; shape index (length/width) 1.1 (1.0–1.3). Micropyle and oocyst residuum absent; polar granule(s) usually present. Sporocysts are ovoid, 8.6 × 5.1 (8.0–9.5 × 5.0–5.5) μm, with thin, membrane–like walls and a knoblike Stieda body; shape index 1.7 (1.4–1.8). Sporozoites elongate, each with a large posterior refractile body. The sporocyst residuum consists of a small cluster or row of few to many small granules. Oocysts of Eimeria nodulosa n. sp. are spherical to subspherical, 15.6 × 14.7 (14.5–17.5 × 13.0–16.0) μm, with a distinctly bilayered wall; shape index 1.1 (1.0–1.2). Unsporulated and freshly sporulated oocysts often possess large, knob–like structures on the external surface of the oocyst wall that support a thin membrane or filament. Micropyle, oocyst residuum and polar granule absent. Sporocysts are ovoid, 10.6 × 5.9 (9.5–12.0 × 5.0–6.5) μm, with a smooth, thin wall and knob–like Stieda body; shape index 1.8 (1.5–2.1). Sporozoites granular and elongate, each with a large posterior refractile body. The sporocyst residuum consists of a loose aggregate or scattered mass of moderately sized granules.     

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.     

Methods and models to determine perinatal status of Florida manatee carcasses

Differences in perinatal mortality can be indicators of differences in physiology, behavior, toxicology, population dynamics, and ecology of species and individuals. Extensive data collected under the Florida Manatee Carcass Recovery Program provide important information about manatee perinatal mortality. However, early age at death can be difficult to determine for often highly decomposed carcasses. Here, I provide quantitative methods to identify perinatal status for manatee carcasses. First, perinatal and nonperinatal mortality were defined based on physiological indicators. After review of necropsy reports, specific length classes became clear indicators of perinatal status: carcasses <82‐cm long were always perinatal, and carcasses >160‐cm long were always nonperinatal. Using data from carcasses 82–160 cm long of known perinatal status, Bayesian models quantify the relationship among age at death, carcass length, and carcass recovery month. The models predict the perinatal status of carcass 82–160 cm long when physiological indicators are unavailable. Overall, perinatal status could be determined for 98.2% of carcasses collected from 1978 to 2005. Initial examination of the fraction of perinatal mortalities within the entire carcass sample reveals interesting spatial and temporal patterns that warrant further analyses.     

DETERMINATION OF MANATEE POPULATION TRENDS ALONG THE ATLANTIC COAST OF FLORIDA USING A BAYESIAN APPROACH WITH TEMPERATURE-ADJUSTED AERIAL SURVEY DATA

In many animal population survey studies, the construction of a stochastic model provides an effective way to capture underlying biological characteristics that contribute to the overall variation in the data. In this paper we develop a stochastic model to assess the population trend and abundance of the Florida manatee, Trichechus manatus latirostris , along the Atlantic coast of the state, using aerial survey data collected at winter aggregation sites between 1982 and 2001. This model accounts for the method by which the manatees were counted, their movements between surveys, and the behavior of the total population over time. The data suggest an overall increase in the population from 1982 to 1989 of around 5%–7%, a reduction in growth or a leveling off (0%–4% annual growth) from 1990 to 1993, and then an increase again of around 3%–6% since 1994. In winter 2001–2002 (the most recent survey season for which analyses were done), we estimated the adult manatee population along the east coast of Florida to be 1,607 individuals (range = 1,353–1,972; 95% credible interval). Our estimate of manatee abundance corresponds well with maximum counts (approximately 1,600 manatees) produced during synoptic aerial surveys under optimal conditions. Our calculations of trends correspond well with mark and recapture analyses of trends in survival of adult manatees along the east coast through the early 1990s. Our population trend estimates since that time are more optimistic than those generated by mark-recapture models.     

LONG-TERM TRENDS IN ABUNDANCE AND DISTRIBUTION OF MANATEES (TRICHECHUS MANATUS) IN THE NORTHERN BANANA RIVER, BREVARD COUNTY, FLORIDA

Four aerial survey projects were conducted between 1977 and 1986 to determine the abundance, density and distribution of West Indian manatees (Trichechus manatus), in the northern Banana River, Kennedy Space Center, Florida. Manatee density and distribution within selected portions of the 78.5 km² study area were determined. Peak numbers of manatees occurred in spring of each year. The maximum counts increased from 56 in 1978 to 297 in 1986. Manatee abundance was lowest in the winter of each year. Mean density per flight increased from 0.52 manatees/km2 in 1977–78 to 2.73/km² in 1984–86. This increase may reflect increases in the east coast population or shifts in the population distribution. Distributional changes were observed in the study area through time, with a lower percentage of manatees occurring in industrial areas and a correspondingly higher percentage of manatees in nonindustrial areas by 1985.     

TRENDS IN MANATEE (TRICHECHUS MANATUS LATIROSTRIS) COUNTS AND HABITAT USE IN TAMPA BAY, 1987–1994: IMPLICATIONS FOR CONSERVATION

Aerial surveys ( n = 88) were used to document locations and count sightings of manatees ( Trichechus manatus latirostris ) in the inshore waters of Tampa Bay, Florida, between November 1987 and May 1994. We made 5,358 sightings of manatees in 1,958 groups. Calves represented 8% of the manatees sighted. Counts were significantly higher in winter ( = 79, n = 29 flights) than in non-winter ( = 46, n = 47) months. Counts of manatees in winter increased significantly during the study, but warm-season counts did not. Regression models demonstrated a relationship between counts and environmental factors. Year-round counts were related to air temperatures and seasons, with highest counts in winter. However, in the winter season, counts were significantly correlated only with wind speed, not air temperature. Yearround counts were predicted to be curvilinear with highest counts at 15°C average air temperature. Areas used differed with season: in cold weather, 76% of all sightings occurred in zones with warm-water sources. High-use areas were identified for summer months. Spatial filter analysis was used to compare manatee density in high-use areas between two two-year time periods. The data indicate that (1) manatee use of Tampa Bay was high and increasing in winter, (2) there are particular zones of the bay where conservation of manatees and habitat should be a priority, and (3) sufficient information has been collected for management agencies to develop and implement manatee protection plans.     

Behavioral response of manatees to variations in environmental sound levels

Florida manatees (Trichechus manatus latirostris) inhabit coastal regions because they feed on the aquatic vegetation that grows in shallow waters, which are the same areas where human activities are greatest. Noise produced from anthropogenic and natural sources has the potential to affect these animals by eliciting responses ranging from mild behavioral changes to extreme aversion. Sound levels were calculated from recordings made throughout behavioral observation periods. An information theoretic approach was used to investigate the relationship between behavior patterns and sound level. Results indicated that elevated sound levels affect manatee activity and are a function of behavioral state. The proportion of time manatees spent feeding and milling changed in response to sound level. When ambient sound levels were highest, more time was spent in the directed, goal‐oriented behavior of feeding, whereas less time was spent engaged in undirected behavior such as milling. This work illustrates how shifts in activity of individual manatees may be useful parameters for identifying impacts of noise on manatees and might inform population level effects.     

SURVIVAL ESTIMATES FOR FLORIDA MANATEES FROM THE PHOTO-IDENTIFICATION OF INDIVIDUALS

We estimated adult survival probabilities for the endangered Florida manatee ( Trichechus manatus latirostris ) in four regional populations using photoidentification data and open-population capture-recapture statistical models. The mean annual adult survival probability over the most recent 10-yr period of available estimates was as follows: Northwest - 0.956 (SE 0.007), Upper St. Johns River - 0.960 (0.011), Atlantic Coast - 0.937 (0.008), and Southwest - 0.908 (0.019). Estimates of temporal variance independent of sampling error, calculated from the survival estimates, indicated constant survival in the Upper St. Johns River, true temporal variability in the Northwest and Atlantic Coast, and large sampling variability obscuring estimates for the Southwest. Calf and subadult survival probabilities were estimated for the Upper St. Johns River from the only available data for known-aged individuals: 0.810 (95% CI 0.727–0.873) for 1st year calves, 0.915 (0.827–0.960) for 2nd year calves, and 0.969 (0.946–0.982) for manatee 3 yr or older. These estimates of survival probabilities and temporal variance, in conjunction with estimates of reproduction probabilities from photoidentification data can be used to model manatee population dynamics, estimate population growth rates, and provide an integrated measure of regional status.     

INFLUENCE OF POWER PLANTS AND OTHER WARM-WATER REFUGES ON FLORIDA MANATEES

Because of limited tolerance to cold, most Florida manatees survive cold winter periods by aggregating at warm‐water discharges from power plants and natural springs in central and northern Florida. Many power plants used by manatees may soon be retired. When this occurs, some people assume manatees will move to warmer areas in southern Florida; others fear they will stay near retired plants and sustain high levels of cold‐related deaths causing a decline in abundance. To assess these possibilities, we examine warm‐water habitats, population structure and movement, cold‐related deaths, and information on possible historical manatee distribution. Winter water temperatures even in southernmost Florida periodically fall below manatee tolerance levels. To survive such periods, manatees use two types of warm‐water refuges: warm‐water discharges, and passive thermal basins that cool slowly, thereby temporarily retaining warm temperatures. During the coldest periods, perhaps 60% of all manatees use 10 power plants and 15% use four natural springs; most others use thermal basins in southern Florida. Site fidelity to these refuges appears to be the principal factor segregating manatees into at least four subpopulations. Since 1986, rates of cold‐related deaths in southernmost Florida (10.0%) have exceeded those in areas with natural springs in central and northern Florida (8.8%). Our findings suggest that warm‐water springs in northern Florida offer better winter habitat than thermal basins in southern Florida and are better able to support large numbers of manatees. Although evidence is scant, we suggest that manatees historically overwintered principally at northern springs, but that Pre‐Columbian and European hunting restricted their winter range to southernmost Florida by the early 1900s. We also suggest that southernmost Florida may not be able to sustain a large influx of displaced of manatees in the absence of power plants, and that warm‐water springs in northern Florida should be considered the most important source of natural warm‐water habitat.     

FORENSIC METHODS FOR CHARACTERIZING WATERCRAFT FROM WATERCRAFT-INDUCED WOUNDS ON THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

Watercraft-related mortality represents 1,253 (24.9%) of 5,033 Florida manatee ( Trichechus manatus latirostris ) deaths recorded between 1 January 1979 and 31 December 2004. Wound patterns generated by collisions with watercraft are diagnostic. Sets of cuts and scrapes that are roughly equidistant and perpendicular to the direction of vessel travel are consistent with lacerations made by propeller blades. From these lesions, estimates of propeller diameter, pitch, rotation, and direction of travel may be obtained. Considerable overlap of propeller sizes and pitches on different size vessels, common use of counter rotation propellers, and numerous other complicating factors may confound efforts to accurately predict vessel size and type from propeller wounds. Of the more than one million watercraft registered in Florida, 98% are ≤12.2 m (40 ft), yet watercraft 5.3–36.6 m (17.5–120 ft) are known to have killed manatees. Analysis of a 5-yr subset of mortality data suggests that a disproportionate number of propeller-caused watercraft-related mortalities could be attributed to propeller diameters ≥43.2 cm (17 in.), inferring that these were caused by watercraft ≥12.2 m (40 ft).     

ACCURACY OF AGE DETERMINATION IN THE GREY SEAL HALICHOERUS GRYPUS OF EASTERN CANADA

The ages of 82 grey seals of known age from 1 to 10 yr were determined from growth layer groups in the cementum, readily seen in longitudinal sections 150 μm thick viewed under transmitted light. The sample of teeth was read five times in a series of blind replicates.
With only one reading, an accuracy of 84% was achieved. This increased to 93% on the basis of three readings but improved only marginally to 94% when all five readings were considered. Accuracy was best in the middle range of ages (3–6 yr) which are the critical years for estimating age-specific reproductive rates in population models.     

INTERSPECIFIC AND INTRASPECIFIC MORPHOLOGICAL VARIATION IN MANATEES (SIRENIA: TRICHECHUS)

The three living species of Trichechus are clearly defined and well exemplify the degree of variability and taxonomic value of morphological characters in a well-understood mammalian genus. Statistical analysis of the largest sample of manatee skulls yet studied has allowed us to identify small suites of characters that effectively distinguish these species. The two subspecies of T. manatus proposed by Hatt (1934) can likewise be distinguished, and their use as taxonomic categories seems justified. This suggests that the cool winters of the northern Gulf Coast, on the one hand, and the deep water and strong currents of the Straits of Florida, on the other, are effective barriers to gene flow between Florida and Antillean manatees. Alleged taxonomic distinctions within T. senegalensis , however, have no demonstrated basis. No significant sexual dimorphism was detected in skulls of any of the species. Many interspecific differences can be correlated with feeding ecology, but others remain unexplained. Features of tooth crown morphology are among the most constant characters examined, but some osteological characters are equally good. T. manatas and T. senegalensis (which are phenetically the most similar) also seem to share a more recent common ancestor than either does with T. inunguis. However, the three species probably separated from each other at nearly the same time. T. inunguis has since become the most derived species, while T. senegalensis has changed the least.     

DISTRIBUTION AND INNERVATION OF FACIAL BRISTLES AND HAIRS IN THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

The distribution and anatomy of sirenian perioral bristles (modified vibrissae) and facial hairs are of interest because of their use during feeding and tactile exploration. In the present study we have identified six fields of perioral bristles on the face of the Florida manatee (T. manatus latirostris), four (U1-U4) on each side of the upper lips and oral cavity, and two (L1-L2) on each side of the lower lip pad, inside the oral cavity and rostral to the horny mandibular pad. Each field has a characteristic location, number of bristles, and range of bristle length and diameter. There is a mean of 110 (± 19) bristles per side, with no left-right differences. Branches of the infraorbital nerve innervate the bases of the largest bristles (U2 group) on the upper bristle pad, and the inferior alveolar nerve supplies the bristles of the lower bristle pad. The dorsal and ventral buccal branches of the facial nerve innervate the superficial facial musculature, which is likely to be involved in bristle eversion and other movements which constitute feeding behavior. Hair is denser in the facial region than on the remainder of the body. Within the face, hair is denser on the oral disk than on the supradisk. The oral disk contains bristle-like hair, whereas the supradisk region possesses hair that is similar in length and diameter to that on the postcranial body. The mean total of bristles and hairs per face was 1,942. Means for the subregions were 220 (± 39) bristles on the perioral bristle pads, 601 (± 115) bristlelike hairs in the oral disk region, 710 (± 229) typical hairs in the supradisk region, and 411 (± 108) typical hairs on the chin. There were no significant differences between left and right side counts. Facial hair density was inversely correlated with facial area and body size. These data provide new information on the anatomical basis of the exceptional orofacial activities characteristic of manatees during feeding and tactile exploration.