Effective stewardship of Florida's coast requires, in part, detailed characterizations of ecological components of the marine system. Characterization of one component, manatees (Trichechus manatus latirostris), involves mapping its distribution and abundance and identifying features of the landscape that are intimately associated with its life history. In this study, we developed a raster-based spatial model that transformed radiotelemetry point data to surfaces illustrating the areas manatees visited frequently for relatively long periods, called ''places,'' and areas visited frequently for short periods, called ''movement corridors.'' This work involved (1) simulating manatee movement paths between sequential telemetry points using a cost surface based on manatee bathymetric preferences that were derived from empirical associations between telemetry locations and water depth, (2) distributing movement time to cells that were crossed by the simulated movement path, and (3) extracting cells from the movement-path map that qualified as places and those that qualified as corridors. Movement characteristics of wild and rehabilitated animals were similar. Movement rates of males were significantly greater than those of either females with calves or females without calves. Mean number of visits per cell and mean time per visit for the three adult classes were not significantly different. Males had the smallest mean patch size for places, and females without calves had the largest but fewest places. Based on qualitative evaluations by field biologists, we concluded that the model performed well in estimating places. The locations of movement corridors were less certain, although reasonable, given that manatee spatial cognition was considered sufficient to permit directed movement between places.

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 (x̄= 79, n= 29 flights) than in non‐winter (x̄= 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.

ABSTRACT:Stranding networks, in which carcasses are recovered and sent to diagnostic laboratories for necropsy and determination of cause of death, have been developed to monitor the health of marine mammal and bird populations. These programs typically accumulate comprehensive, long-term datasets on causes of death that can be used to identify important sources of mortality or changes in mortality patterns that lead to management actions. However, the utility of these data in determining cause-specific mortality rates has not been explored. We present a maximum likelihood-based approach that partitions total mortality rate, estimated by independent sources, into cause-specific mortality rates. We also demonstrate how variance estimates are derived for these rates. We present examples of the method using mortality data for California sea otters (Enhydra lutris nereis) and Florida manatees (Trichechus manatus latirostris).

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