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ESR 9:1-11 (2009)  -  DOI:

Trends in counts of manatees Trichechus manatus latirostris from 1987 to 2006 in waters of Sarasota County, Florida, USA

Kerri M. Scolardi1,4, Lori H. Schwacke2, Jessica K. Koelsch3, John E. Reynolds III1,*, Teresa J. Kessenich1,5, Jay M. Sprinkel1, Janet G. Gannon1,6

1Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236, USA
2National Oceanographic and Atmospheric Administration, 219 Fort Johnson Rd., Charleston, South Carolina 29412, USA
3The Ocean Conservancy, 449 Central Ave, Suite 200, St. Petersburg, Florida 33701, USA
4Present address: 514 N Weber St., Colorado Springs, Colorado 80903, USA
5Present address: Southwest Florida Water Management District, Sarasota Service Office, 6750 Fruitville Road, Sarasota, Florida 34240–9711, USA
6Present address: Bowdoin College, Biology Department, Bowdoin College, 6500 College Station, Brunswick, Maine 04011, USA
*Corresponding author. Email:

ABSTRACT: To demonstrate the utility of distributional surveys for assessing relative abundance and trends in counts for a discrete area of coastline, aerial survey data from Sarasota County, Florida, USA, were analyzed for the years 1987 to 2006. The study area was divided into 3 regions: the Sarasota Bay Region (SBR; N = 353 surveys), Lemon Bay (N = 368), and the Myakka River (N = 209). Manatee counts varied significantly across seasons (p < 0.0001) for all 3 regions. Manatees within Sarasota County utilized open bays primarily in the warmer months. Such usage may have been influenced by resource availability. Conversely, usage of the Myakka River peaked in winter months when manatees seek warm-water refugia such as Warm Mineral Spring. Marginal means for yearly counts within Lemon Bay and the SBR increased significantly, beginning midway through the survey period (1996) until the early 2000s. In contrast, mean yearly counts within the Myakka River decreased over this time period. After record lows in 2003 for Lemon Bay and the Myakka River, and a considerable decline in 2004 for the SBR, mean yearly counts for all 3 regions showed an increasing trend over the remaining 2 yr of the study. Greater protection of manatee habitat and availability of forage coincided with the increase in numbers of manatees using Sarasota County waters during the 1990s, and the subsequent decline in numbers may be indicative of the increase in mortality in recent years due to watercraft collisions and severe red tide events.

KEY WORDS: Florida manatee · Trichechus manatus latirostris · Aerial survey · Seasonal distribution · Abundance · Sarasota County · Manatee refuge · Conservation

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Cite this article as: Scolardi KM, Schwacke LH, Koelsch JK, Reynolds JE III, Kessenich TJ, Sprinkel JM, Gannon JG (2009) Trends in counts of manatees Trichechus manatus latirostris from 1987 to 2006 in waters of Sarasota County, Florida, USA. Endang Species Res 9:1-11.

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