Demographic and Population Models to Assess Recovery and Status of the Endangered Florida Manatee

Science Center Objects

Population models developed by USGS are the primary decision-support tools used for status assessments, and rely on estimates of adult survival and reproduction rates from mark-recapture studies.

West Indian manatees
West Indian manatees

The Science Issue and Relevance: In January 2016, the U.S Fish and Wildlife Service (USFWS) completed its 5-yr status review of the endangered West Indian manatee and proposed that the species be reclassified to threatened status under the Endangered Species Act (ESA). A final decision will be made in 2017. USGS demography and population modelers at WARC, PWRC and The Colorado Cooperative Fish and Wildlife Research Unit, collaborated with Florida’s Fish and Wildlife Research Institute to develop the Florida manatee population viability and threats analyses that were major  scientific components of the status reviews in 2007 and 2015. In this management-support collaboration, WARC research objectives are to develop empirical-based manatee demography models that realistically describe manatee demography processes, to test hypotheses of cause and effect expected to impact survival and breeding rates, and to provide unbiased, empirical estimates of these rates to parameterize the population models. To provide USFWS with the latest scientific information prior to their final status determination, demographic estimates and the population viability and threats analyses are being revised and updated.

Methodology for Addressing the Issue: Long-term monitoring data in the Manatee Individual Photo-identification System (MIPS) developed and coordinated by WARC, is the basis for modeling vital rates. We have developed and applied new robust-design mark-recapture models to better estimate survival and breeding. One model reduces bias in breeding estimates due to possible errors in identifying a female as a successful breeder and the second reduces bias in survival estimates due to some individuals not using the monitoring sites in some years (temporary emigration). Environmental indices of red tide severity and winter cold severity have been developed and used to model and test explanatory predictions of cause and effect on survival and breeding estimates. Results are used to develop a suite of future scenarios and parameterize components of the population viability and threats analyses.

West Indian manatee with boat propeller scars
West Indian manatee with boat propeller scars

Future Steps: Regardless of the final status determination in 2017, monitoring and analyses of manatee population dynamics will be critical to management to meet full recovery under the ESA and the Marine Mammal Protection Act. Future steps include: To ensure continuity of future data and analyses, develop and implement new monitoring designs to address changing patterns of manatee use of historic warm-water monitoring sites. Continue development of new demographic models to address emerging issues, such as the impact on movement, as well as survival and breeding due to the inevitable loss of coastal power plants and artificial winter warm-water habitat. Continue to work with resource managers and population modelers to implement new demographic information into decision-support models. Provide reference baseline estimates of past annual survival, breeding and movement rates for assessments of ecosystem level research and management programs, such as the Gulf of Mexico Restoration. Results will be useful to USFWS as support science for status assessments and management actions, and will extend the body of knowledge on population dynamics and life history strategies in large, long-lived mammals. 

Related Project(s): MIPS project, Structured Decision-making Model of manatee warm-water habitat, Gulf of Mexico Restoration