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LaCommare, Katherine S.
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2011 |
The Conservation and Habitat Ecology of Antillean Manatees (Trichechus manatus manatus) in the Drowned Cayes Area, Belize, Central America.
Boston, University of Massachusetts: 1-160. 6 tabs. 21 figs. June 2011.
–ABSTRACT: The Drowned Cayes area of Belize, Central America is regionally important for the conservation of Antillean manatees in the Caribbean (Lefebvre et al. 2001; Quintana-Rizzo & Reynolds 2008). These islands are increasingly threatened by human activities such as tourism, development and population growth. The objective of this dissertation is to evaluate manatee habitat use and status in this area. The 5 specific objectives are to examine manatee (1) distribution in the Drowned Cayes, (2) use of seagrass beds and forage selection, (3) resting habitat use and selection (4) response to disturbance, and (5) trends in abundance and to suggest a method for monitoring manatees and other sirenians. The principal findings are that manatees utilize all habitat types within the area to meet a variety of their physiological and behavioral requirements. Some habitat types like seagrass beds and resting holes are clearly important components to the overall seascape. Manatees selectively forage on Halodule wrightii. Resting holes and seagrass beds that are adjacent to each other are a particularly important habitat configuration. Manatee habitat use seems to be resilient to mangrove removal, but foraging resources may not. Number of manatees sighted per scan over the duration of this study does not appear to have changed, but our method would not be able to detect a slight decline in abundance. Our survey protocol--point-based scan sampling from a small boat platform--is a relatively inexpensive, effective and repeatable method for monitoring sirenian population trends. By identifying important habitat types, foraging resources and resting areas, this research provides information that wildlife managers can use to promote watercraft guidelines and guide development decisions.
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LaCommare, Katherine S.; Brault, Solange; Self-Sullivan, Caryn; Hines, Ellen M.
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2012 |
Trend detection in a boat-based method for monitoring sirenians: Antillean manatee case study.
Biological Conservation 152: 169-177. 2 tabs. 4 figs. DOI: 10.1016/j.biocon.2012.02.021. Aug. 2012.
–ABSTRACT: Accurate monitoring is a critical step in evaluating the conservation and management needs of endangered species. We evaluated a low cost, effective survey method for monitoring West Indian manatees (Trichechus manatus manatus) in Belize, Central America. The objectives for this paper are (1) to evaluate a count-based population index derived from a boat-based survey method, (2) to examine trends in manatee abundance in the Drowned Cayes area, (3) to conduct a power analysis to explore our ability to detect a trend and the ramifications of survey structure on trend detection. We used a generalized linear model to evaluate the impact of environmental conditions on sighting probability and to determine whether the number of manatees observed per 20-min scan changed from 2001 to 2007. We used simulations to determine statistical power – the ability to detect potential declines of 10%, 25% or 50% over 15 years and for various sampling regimes. The number of manatees sighted per scan was not affected by sighting conditions. There was no change in the mean number of manatees sighted per scan from 2001 to 2007. Our ability to detect a trend ranged from 9% to 100% depending on the level of decline, scan duration, number of points surveyed and number of surveys. This survey protocol is a practical and repeatable way to examine population trends of sirenians in similar habitats around the world.
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Bibliography and Index of the Sirenia and Desmostylia 