One of the most endangered marine mammals in the coastal areas of the United States is Florida manatee (Trichechus manatus latirostris). The Florida manatee population has been increasing and decreasing since 1991 along the east and west coast of Florida, respectively, and has a present population of about 6,250. However, the populations had been dramatically fluctuated due to various anthropogenic factors. Causes of manatee deaths can be broken down into five categories: watercrafts, crushed/drown by flood gate or canal lock, entanglement, perinatal, and other natural factors (such as disease and natural catastrophe). Unfortunately, three among these five categories are associated with human. Hence, we aimed to estimate and compare anthropogenic and natural catastrophic effects on the manatee population dynamics. We conducted a literature review to obtain the basic demographic data and then developed a stage-structure population dynamics model of Florida manatee during this summer. We then used the data from Florida Fish and Wildlife Conservation Commission synoptic surveys to calculate average mortality rates of those for four scenarios including baseline, anthropogenic threats, cold stress, and oil spill. We simulated each scenario with the average effects from each of their mortality rates for 20 years.
Results/Conclusions
When comparing all four scenarios based on our results, the leading factors affecting the manatee population are cold stress followed by human factors and oil damage. The population size stayed stable around 4900 without any disturbance. While the model ran with a probability of cold stress occurring 35% of the time based on the temperature averages in Florida for the past 10 years, the population decreased 24% from 4900 to 3750. When the probability of another oil spill occurring was approximated at a 10% chance, the population dropped about 1% from 4900 to 4850. Because the human disturbance was constant in Florida with a 90% chance of occurring, the population decreased 7% from 4900 to 4550. Even though the Florida manatee was reclassified from an endangered to a threatened species under the federal Endangered Species Act in early 2017, the long-term monitoring and effective protection are still need to ensure an increasing population.