Trends in Counts of Florida Manatees at Winter Aggregation Sites

Garrott, Robert A.; Ackerman, Bruce B.; Cary, John R.; Heisey, Dennis M.; Reynolds, John E.; Rose, Paul; Wilcox, J. Ross

doi:10.2307/3809677

Cited by 22 publications

(27 citation statements)

References 10 publications

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“…Furthermore, the population size cannot be directly estimated because of environmental, survey-related, and manatee behavior-related factors . Trend analyses of temperature-adjusted aerial survey counts show promise for providing insight to general patterns of population growth in some regions, although the estimated rates of change in counts may not be an accurate reflection of actual population rates (Garrott et al, 1994;Craig et al, 1997;Eberhardt et al, 1999). Strip-transect aerial survey methods have been applied to estimate the number of manatees in the Banana River during the warm season, and could be used to detect a 5% annual rate of change in <4 years with power ≥0.75 (Miller et al, 1998).…”

Section: North America United Statesmentioning

confidence: 99%

Status and Biogeography of the West Indian Manatee

Lefebvre¹,

Marmontel²,

Reid³

et al. 2001

Biogeography of the West Indies

109

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We review historical and recent information on the distribution, status, and habitat associations of the West Indian manatee, Trichechus manatus, summarize threats to its continued survival, and discuss some biogeographical patterns of trichechids. Historical accounts indicate that manatees were once more common and that hunting has been responsible for declining numbers throughout much of their range. Small numbers occur throughout the Greater Antilles, where opportunistic taking by fishermen is a major source of mortality. Populations in Haiti, the Dominican Republic, and Jamaica are particularly vulnerable. Manatees have not been documented to occur in the Lesser Antilles since the 18th century, except for rare sightings in the Virgin Islands. Manatee sightings in the Bahamas are also rare; however, a recent dispersal from the northwest coast of Florida to the Bahamas has been documented. Manatees are relatively abundant in Belize compared with other countries of Central America. They persist in some of the large river systems of South America: the Río Magdalena in Colombia, Río Orinoco in Venezuela, and probably the Río Mearim in Brazil. They are absent or scarce along most of the South American coast, except in the extensive coastal wetlands of Guyana and Suriname. At present, there are only three regions in Mexico where manatees are still commonly found. Manatees are widely distributed on both coasts of Florida, and some venture westward along the Gulf coast and northward along the Atlantic coast of the southeastern United States, primarily during the warm season. Heated industrial effluents along both coasts have influenced manatee distribution and migratory patterns in the United States. Illegal killing continues to threaten the survival of manatees in many countries. Despite protective measures to regulate boating activity, collision with boats is still the major cause of human-related manatee mortality in Florida. Habitat alteration is a growing concern in all countries.Manatees in the Greater Antilles and Central and South America belong to the same subspecies, T. manatus manatus. However, results of recent genetic analysis indicate greater similarity between the Florida manatee, T. manatus latirostris, and manatees in the Dominican Republic and Puerto Rico, than between the latter and manatees in South America. The highest genetic diversity is found along the northern coast of South America, at the core of the species' range; marginal populations (in Florida, Mexico, and Brazil) were each found to be monomorphic (only one haplotype apiece) although distinct from one another. Salinity, temperature, water depth, currents, shelter from wave action, and availability of vegetation are important determining factors of manatee distribution. The association of T. manatus with freshwater sources is a highly consistent pattern. Throughout most of their range, manatees appear to prefer rivers and estuaries to marine habitats. The Amazonian species, T. inunguis, may be restricted to the Amazon River because of in...

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Section: North America United Statesmentioning

confidence: 99%

Status and Biogeography of the West Indian Manatee

Lefebvre¹,

Marmontel²,

Reid³

et al. 2001

Biogeography of the West Indies

109

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“…2). Counts at aggregation areas along the Atlantic coast also have increased, but with indications of decreasing rates of population growth since the late 1980s (Garrott et al 1994). Boat speed zones for manatee protection have only recently been implemented beyond the limited areas of the discharge canals, and regulations at winter aggregation sites have not been as well enforced as at Crystal River or Blue Spring.…”

Section: Manatee Aggregations and The Focal Study Areasmentioning

confidence: 99%

Estimates of Annual Survival Probabilities for Adult Florida Manatees (Trichechus manatus latirostris)

Langtimm¹,

O’Shea²,

Pradel³

et al. 1998

Ecology

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Abstract. The population dynamics of large, long-lived mammals are particularly sensitive to changes in adult survival. Understanding factors affecting survival patterns is therefore critical for developing and testing theories of population dynamics and for developing management strategies aimed at preventing declines or extinction in such taxa. Few studies have used modern analytical approaches for analyzing variation and testing hypotheses about survival probabilities in large mammals. This paper reports a detailed analysis of annual adult survival in the Florida manatee (Trichechus manatus latirostris), an endangered marine mammal, based on a mark-recapture approach. Natural and boatinflicted scars distinctively "marked" individual manatees that were cataloged in a computer-based photographic system. Photo-documented resightings provided "recaptures." Using open population models, annual adult-survival probabilities were estimated for manatees observed in winter in three areas of Florida: Blue Spring, Crystal River, and the Atlantic coast. After using goodness-of-fit tests in Program RELEASE to search for violations of the assumptions of mark-recapture analysis, survival and sighting probabilities were modeled under several different biological hypotheses with Program SURGE. Estimates of mean annual probability of sighting varied from 0.948 for Blue Spring to 0.737 for Crystal River and 0.507 for the Atlantic coast. At Crystal River and Blue Spring, annual survival probabilities were best estimated as constant over the study period at 0.96 (95% ci = 0.951-0.975 and 0.900-0.985, respectively). On the Atlantic coast, where manatees are impacted more by human activities, annual survival probabilities had a significantly lower mean estimate of 0.91 (95% ci = 0.887-0.926) and varied unpredictably over the study period. For each study area, survival did not differ between sexes and was independent of relative adult age. The high constant adult-survival probabilities estimated for manatees in the Blue Spring and Crystal River areas were consistent with current mammalian life history theory and other empirical data available for large, long-lived mammals. Adult survival probabilities in these areas appeared high enough to maintain growing populations if other traits such as reproductive rates and juvenile survival were also sufficiently high. Lower and variable survival rates on the Atlantic coast are cause for concern.

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“…Belize, Caribbean coast of Mexico, Puerto Rico; Lefebvre et al 2000, Morales-Vela et al 2000 or where obligatory seasonal clustering occurs due to manatees' inability to tolerate low temperatures (i.e. Florida; Garrott et al 1994, Craig & Reynolds 2004) have been reliably surveyed. In the present study, we examined the effectiveness of using side-scan sonar as an alternative method to detect and survey manatees in the wild.…”

Section: Introductionmentioning

confidence: 99%

Detection of free-ranging West Indian manatees Trichechus manatus using side-scan sonar

Gonzalez‐Socoloske

Olivera‐Gómez²,

Ford³

2009

Endang. Species. Res.

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Turbid and tannin-stained waterways are difficult habitats to study and present problems with respect to the management of aquatic fauna, and especially of endangered and cryptic animals such as manatees Trichechus spp. Linnaeus. Throughout much of the range of the extant trichechid species (T. inunguis, T. manatus, and T. senegalensis), the scientific approaches that are used successfully to document the status of the Florida subspecies (T. m. latirostris) are not feasible, due either to constraints associated with habitat or to the high costs involved. We examined the use of side-scan sonar as a novel way to acoustically detect free-ranging West Indian manatees (T. m. latirostris and T. m. manatus), and evaluated the effectiveness of the technology under various environmental conditions. Blind transects, where one observer only looked at the sonar, were conducted in Mexico and Florida to confirm that manatees could be detected and to determine a preliminary manatee detection rate for the sonar unit. Quality sonar images were produced under most environmental conditions examined, provided that ambient water movement was low. Manatees were successfully detected laterally up to 18 m, and the best acoustic images were produced when the animals were stationary and oriented parallel to the boat. Preliminary detection was 81 and 93% in Florida and Mexico, respectively. We conclude that over limited areas, and under certain environmental conditions, side-scan sonar is a cost-effective option to accurately detect manatees and provide important information for conservation decisions. Like all survey techniques, it has limitations, but its unique advantages will be a welcomed alternative to aerial surveys and visual boat surveys of opaque waterways.

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Trends in Counts of Florida Manatees at Winter Aggregation Sites

Cited by 22 publications

References 10 publications

Status and Biogeography of the West Indian Manatee

Status and Biogeography of the West Indian Manatee

Estimates of Annual Survival Probabilities for Adult Florida Manatees (Trichechus manatus latirostris)

Detection of free-ranging West Indian manatees Trichechus manatus using side-scan sonar

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