Issues and opportunities associated with using manatee mortality data to evaluate the effectiveness of manatee protection efforts in Florida

Protection zones to reduce risks to Florida manatees Trichechus manatus latirostris associated with boat operation have been in place since the 1990s or earlier in most areas considered important for the species. Despite the relatively long period of time protections have been in place, evaluating the effectiveness of these efforts has proven to be difficult. This paper discusses manatee mortality data, which is one of the most long-term sources of data available for analysis, and some of the difficulties associated with using these data to evaluate effectiveness. It then explores the concept of using differences in rates of change in mortality during three 10 yr periods as an evaluation metric. Rates were calculated for the state of Florida as a whole and for Treatment and No Treatment groups, with the Treatment group including all counties where comprehensive protection zones have been established. The only rates of change that were statistically different from one another were for boat-related deaths, both statewide and for the Treatment group, between the 1981-1990 and 2001-2010 periods. Statewide, the average rate of increase fell from 11.2 to 1.0% yr(-1), while, within the Treatment group, the rate fell from 12.4 to 1.2% yr(-1). These results provide evidence that protection efforts have likely helped to reduce boat-related mortality risks; however, the analysis does not account for some uncertainties associated with the mortality data, and the confidence intervals are fairly wide. Additional research and analyses should be pursued to account for these issues and also to consider risks related to non-lethal manatee-boat collisions.