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Lynn W. Lefebvre

Publications and source records attributed to Lynn W. Lefebvre.

9 recordsLinked to original sources
USGS2017

Manatee grazing impacts on a mixed species seagrass bed

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 13x13 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.

Marine Ecology Progress Series↗
USGS2014

Historical records, sources, and spatial trends of PCBs along the Rhône River (France).

Despite bans on PCB use since 1975 (open systems) and 1987 (closed systems), concentrations of PCBs in riverine fish in France continue to exceed regulatory levels. We present historical records of PCB concentrations in sediment cores from eight sites on the Rhône River, from Lake Geneva to the Mediterranean Sea. Maximum PCB concentrations (sum of seven indicator PCBs) increase downstream, from 11.50 μg/kg at the most upstream site to 417.1 μg/kg at the most downstream site. At some sites peak concentrations occur in sediment deposited as recently as the 2000s. Hierarchical clustering (five clusters) identified differences in PCB congener profiles within and between sites. Exponential models fit to decadal time windows indicate that rapid reductions in concentrations during about 1990-2000 have slowed, and that it might be decades before target concentrations in sediment that correspond to regulatory thresholds in fish will be reached at some sites.

Chemosphere↗
USGS2001

Manatees in the Gulf of Mexico

The endangered Florida manatee (Trichechus manatus latirostris) inhabits rivers and estuaries along both coasts of Florida and, to a lesser extent, adjacent states (Figure 1). Since 1990, documented sightings of manatees outside of Florida have been increasing. This increase in sightings probably represents northward shifts in manatee distribution made possible by man-made sources of warm water (i.e., industrial effluents), as well as a decade of relatively warm winters. The most likely source of emigrants on the Gulf coast is the population of manatees that overwinter in the headwaters of the Crystal and Homosassa Rivers, Citrus County, FL. This group of manatees has undergone a steady increase in numbers, (approximately 7% per year from 1977-1991; Eberhardt and O’Shea 1995). Some emigrants may also come from the Tampa-Ft. Myers region, where human impacts on habitat are greater. Manatees are intelligent, long-lived mammals that appear to adapt readily to new environments and situations. However, manatees have relatively low metabolic rates, and cold winter temperatures restrict their northern distribution.

Florida↗
USGS2001

Florida manatees: Perspectives on populations, pain, and protection

This overview has three related objectives. First, it provides simple documentation, descriptive summaries, and anecdotal accounts that demonstrate the extent to which maiming, and likely pain and suffering, occur in wild manatees as a result of strikes by boats. The chapter calls attention to the issues wounding raises for policy makers and managers involved with implementing boat speed zones, particularly in regard to existing laws and emerging ethical points of view. The authors suggest that considerations related to wounding should also be embraced in developing boat speed zone and sanctuary decisions, and that this issue adds a strong dimension that can override debate about manatee population trends. The strength of the science behind the latter is often misunderstood, leading to unnecessary controversy. Therefore, the second major objective is to provide a simple primer on concepts and uncertainties in manatee population biology for manatee veterinarians, rehabilitators, and biomedical specialists. Although these specialists may have little training in population ecology, they are on the front lines in manatee rescue and treatment efforts, and are often asked by the media to comment on questions related to manatee population trends. This primer is generally restricted to review of information in the published literature or widely accessible management documents. Finally, the authors submit their viewpoint that issues surrounding uncertainty in manatee population biology may be “red herrings” that detract from implementation of management actions. As humanity enters an era of growing ethical concerns for animal welfare, the degree of maiming and injury to manatees by boats will become unacceptable. Indeed, long-standing statutes that have been overdue in their application are cited to justify manatee speed zones and sanctuaries.

Florida↗
USGS1995

Florida manatees

The endangered Florida manatee ( Trichechus manatus latirostris ) is a survivor. It is one of only three living species of manatees which, along with their closest living relative, the dugong ( Dugong dugon ), make up the Order Sirenia. This taxonomic distinctiveness reflects their evolutionary and genetic uniqueness. Sirenians are the only herbivorous marine mammals; manatees feed on seagrasses; freshwater plants, including nuisance species such as hydrilla and water hyacinth; and even some shoreline vegetation. Because manatees depend on marine, estuarine, and freshwater ecosystems, our efforts to protect them necessitate protection of aquatic resources.

Book chapter↗
USGS1990

Simulation of cotton rat population dynamics and response to rodenticide applications in Florida sugarcane

Alternative deterministic simulation models were compared to test the management consequences of present uncertainty about the degree of density dependence involved in cotton rat population cycles in southern Florida sugarcane fields. Efficacy of rodenticide applied in different months was explored under six different scenarios of density dependence and independence in two population parameters: fecundity and juvenile survival. Output from the six models differed considerably in the number of rats produced, but was remarkably consistent in the most effective months to apply rodenticide. Since models without density-dependent fecundity were inherently unstable and an inverse relationship between fecundity and population size is apparent in field data, such a population-growth mechanism seems possible in Florida sugarcane fields. The model in which fecundity was density-dependent at all times produced rat densities closest to field data. Output from this model was most sensitive to changes in the amount litter size declines as population size increases. Field tests are necessary to validate the general agreement among the models about the most effective months to apply rodenticide.

Florida↗
USGS1989

Relationship of roof rat population indices with damage to sugarcane

Roof rats ( Rattus rattus ) cause substantial damage to sugarcane in South Florida (Samol 1972; Lefebvre et al. 1978, 1985). Accurate estimates of roof rat populations in sugarcane fields would be useful for determining when to to treat a field to control roof rats and for assessing the efficacy of control. However, previous studies have indicated that roof rats exhibit trap shyness, which makes capture-recapture population estimates difficult (Lefebvre et al. 1978, 1985; Holler et al., 1981). Until trapping methods are sufficiently improved to allow accurate population estimates, indices of population size that relate to damage need to be developed. The objectives of our study were to examine the relationship of several indices of roof rat populations to the percentage of sugarcane stalks damaged at harvest; to determine which population index would be most useful for sugarcane growers; and to report on a test of several types of live traps for roof rats.

Wildlife Society Bulletin↗