ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01394

ABSTRACT: Situated on Florida’s Gulf Coast, Sarasota County provides critical habitat for manatees in the Southwest region. Prior analysis of the county’s long-term aerial survey database found increasing numbers of manatees using county waterways from 1987 to 2006. Since that study, the region has experienced rapid human population growth and development, arousing concern over high manatee mortality from threats such as red tide and watercraft collisions. We revisit the long-term database to update trends in manatee counts within the county, and analyze the factors that impact those counts. We applied a state space model to the most recent data available (2007–2020), fitting the model to each of the 3 regions of the study area: Sarasota Bay (N = 109 surveys), Lemon Bay (N = 108), and Myakka River (N = 103). Sea surface temperature was the only common covariate across all 3 models and the sole variable retained in the Myakka River model. Surveyor experience was retained in the Sarasota Bay and Lemon Bay models, although the effect was substantially more significant for the latter. In Sarasota Bay, the model’s positive time trend effect signified increased counts over the study period, while Lemon Bay and Myakka River showed more variability. The results reflect manatee population trends reported for the Southwest region remarkably well and highlight the applicability of the dataset concerning management decisions in southwest Florida, which lacks large-scale systematic aerial studies.