How Many Manatees is Enough?

In Florida, there is a sense among biologists and managers who work with manatees that they remain in a precarious position. But those of us who work on manatee conservation are often asked:  just how many manatees is enough?  It turns out that the answer is difficult to pin down because different human stakeholders have different perspectives and values on issues such as this.    For context, I am drafting this blog on Earth Day, 2017, and am more mindful than usual of the diminished status of coastal habitat in Florida.  By Earth Day, 2030, there will likely be almost 30% more people in the state than in 2015.  What will manatee habitat look like then?  I believe that diminished habitat quality and extent represent the greatest threat to manatees now and into the future.

Why is habitat so important for the species’ future?  Ecologists might well respond that there will be enough manatees when there are as many individuals as the environment can sustain (a number called carrying capacity).     Fair enough…but carrying capacity for a particular location is not a constant; it can be reduced locally due to habitat modification or loss.  Thus, to understand carrying capacity for manatees in Florida, one might logically have to design and implement measurements of habitat quality and extent that would need to be repeated several times a decade at many different locations across the state . . .  Because the coastline of Florida and Georgia (the manatee’s principal range) is approximately as long as the combined coastlines of California, Washington, and Oregon, it would be a massive and exorbitantly expensive task to estimate manatee numbers which, all the while, would be in a regular state of annual flux.  Needless to say, comprehensive empirical studies of carrying capacity have not been done, although estimates of carrying capacity based on modeling and scientific expert opinions have been attempted. 

Because of the scientific uncertainties, it is probably not possible to establish an exact number of manatees that is “enough” from an ecological perspective.  So we must turn back to values.  Some stakeholders already argue that there are far too many manatees in Florida, and some cling to the incorrect perception that the manatee is an introduced, exotic species that should not be allowed to flourish in Florida.   In extreme instances, the values behind this argument promote a belief that the existence of lots of manatees limits human activities or economic well-being, and that these interests must always prevail over nature and ecological processes on which humans and other species ultimately depend.  Paleontologists have demonstrated that manatees are native to Florida, but the belief persists among some stakeholders that Florida and Floridians would be better off with fewer or even no manatees. 

At the other end of the values, spectrum are those who suggest that humans should be stewards of the environment and of the living organisms within that environment.   At the extreme, some people would argue for as little human interference as possible with the natural world and the inhabitants thereof.  For them, it is important to let nature, not people, sort out how many manatees is enough.

For me, and most professional conservationists, the goal is to find a long-term balance that ensures the sustainability of a range of human activities, as well as of the natural world, is the goal.    I cannot say how many manatees is the right number, but the process of creating and adopting a comprehensive conservation ethic could lead us to a comfortable point that ensures a good and sustainable future for both people and nature. 

At present, the majority of the people in Florida have made adjustments in their values and behavior that have led to an increase in numbers of an iconic native Floridian: the manatee. I think that’s a good sign because the ultimate goal should be a beautiful Florida, one that supports healthy populations of both manatees and people. Let’s hope that several generations hence, that possibility is a reality.

John E. Reynolds III is the senior scientist at Mote Marine Laboratory's Manatee Research Program and the former chair of the US Marine Mammal Commission. He is the coeditor of Marine Mammal Research: Conservation beyond Crisis and the coauthor of Mysterious Manatees. His latest book, Florida Manatees: Biology, Behavior, and Conservation is available now. You can preview an excerpt here.