title: Influence of Manatees' Diving on Their Risk of Collision with Watercraft.
abstract: Watercraft pose a threat to endangered Florida manatees (Trichechus manatus latirostris). Mortality from watercraft collisions has adversely impacted the manatee population's growth rate, therefore reducing this threat is an important management goal. To assess factors that contribute to the risk of watercraft strikes to manatees, we studied the diving behavior of nine manatees carrying GPS tags and time-depth recorders in Tampa Bay, Florida, during winters 2002-2006. We applied a Bayesian formulation of generalized linear mixed models to depth data to model the probability (Pt) that manatees would be no deeper than 1.25 m from the water's surface as a function of behavioral and habitat covariates. Manatees above this threshold were considered to be within striking depth of a watercraft. Seventy-eight percent of depth records (individual range 62-86%) were within striking depth (mean = 1.09 m, max = 16.20 m), illustrating how vulnerable manatees are to strikes. In some circumstances manatees made consecutive dives to the bottom while traveling, even in areas >14 m, possibly to conserve energy. This is the first documentation of potential cost-efficient diving behavior in manatees. Manatees were at higher risk of being within striking depth in shallow water (<0.91 m), over seagrass, at night, and while stationary or moving slowly; they were less likely to be within striking depth when ≤50 m from a charted waterway. In shallow water the probability of a manatee being within striking depth was 0.96 (CI = 0.93-0.98) and decreased as water depth increased. The probability was greater over seagrass (Pt = 0.96, CI = 0.93-0.98) than over other substrates (Pt = 0.73, CI = 0.58-0.84). Quantitative approaches to assessing risk can improve the effectiveness of manatee conservation measures by helping identify areas for protection.
authors.affiliation: Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Ave. SE, St. Petersburg, FL, 33710, United States of America.
authors.forename: Holly H
authors.initials: HH
authors.lastname: Edwards
authors.affiliation: Southeast Ecological Science Center, U.S. Geological Survey, 7920 NW 71st Street, Gainesville, FL, 32653, United States of America.
authors.forename: Julien
authors.initials: J
authors.lastname: Martin
authors.affiliation: Wildlife Research Laboratory, Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 1105 SW Williston Road, Gainesville, FL, 32601, United States of America.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Deutsch
authors.affiliation: Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Ave. SE, St. Petersburg, FL, 33710, United States of America.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Muller
authors.affiliation: Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Ave. SE, St. Petersburg, FL, 33710, United States of America.
authors.forename: Stacie M
authors.initials: SM
authors.lastname: Koslovsky
authors.affiliation: Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Ave. SE, St. Petersburg, FL, 33710, United States of America.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Smith
authors.affiliation: Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Ave. SE, St. Petersburg, FL, 33710, United States of America.
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Barlas
mesh_terms: D000059:Accidents / Q000706:statistics & numerical data*; D000818:Animals; D001499:Bayes Theorem; D001522:Behavior, Animal; D004242:Diving; D005431:Florida; D008962:Models, Theoretical; D012767:Ships; D020457:Trichechus manatus / Q000502:physiology* / Q000523:psychology; D014947:Wounds and Injuries / Q000662:veterinary*