Evaluation of Thermal Characteristics of Secondary Warm-Water Sites for the Florida Manatee

Abstract

While the threat of collisions with recreational watercraft continues to be a serious concern for the Florida manatee population, a growing threat in the future is likely to be the loss of available winter habitat. Manatees are at risk of illness or death in water temperatures less than 20°C. To meet their thermoregulatory needs, manatees rely on sources of warm-water habitat. Currently the majority of the population is utilizing thermal discharges at coastal power plants to stay warm during winter cold periods; however, most of these power plants are expected to close down in the next t20 to 50 years. Since 1998 the Florida Fish and Wildlife Conservation Commission (FWC) has collected time-series temperature data at various sites used by manatees in winter. The goal of my project was to evaluate the thermal characteristics of 10 suspected warm-water sites in southern Florida to assess their potential suitability as winter habitat for manatees. Sites were assessed based on how frequently they were at temperatures considered threatening to manatee health and mortality, and on how many consecutive days they remained below these threshold temperatures. Delta-T and regression analysis were also used to compare the temperature of potential warm-water sites to that of nearby ambient sites. The results of this analysis will be used to make recommendations to the FWC about which sites might provide suitable warm-water habitat and should be further investigated with more detailed monitoring efforts in the future. This information could be used to meet the agency’s long-term goal of creating a protected network of warm-water habitat throughout the state.