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Alligators Dying in Florida Lake Date Posted: August 25, 2000 The Brunswick Field Office is working with several Federal and State partners to help identify causes of wildlife mortalities in Floridaﾒs Central Lakes. Many of Floridaﾒs lakes were used as muck farms, where areas of the lakes were dyked and drained, and the organic-rich sediments used for crops. Often, several crop rotations were produced each year, with pesticides being applied for each rotation. Many of these lakes, particularly Lake Apopka and Lake Griffin, were considered to have extremely poor water quality and were eutrophic (contained excess nutrients that promote algae growth which, in turn, decreases oxygen levels) as a result of fertilizers that were applied to the farm fields. The water management district for these lakes has bought these farms in an attempt to improve water quality. The farms were to be returned to wetlands, and used as a filter for nutrients and other contaminants. Much of this work has already been instituted, and in the past few years, since the ﾑrestorationﾒ work began on Lake Griffin, more than 300 adult alligators have died. So far this year, nearly 100 alligators have died. Alligator deaths on Lake Griffin seems to occur in cycles, peaking in early spring as water temperatures increase, and in late fall, as temperatures drop. Just before dying, sick alligators will not or cannot move (i.e., to avoid capture) and some tremors were observed in one captured sick alligator. Other animals possibly affected include turtles and wading birds. There are several theories as to why the alligators are dying, including the possibility of phytotoxins (substances that cause decreased growth or death in plants). The composition of algae in Lake Griffin appears to have shifted since the restoration occurred; however, no algaltoxins (substances that cause decreased growth or death in algae) have yet been identified. Organochlorine pesticides are also some concern, given the farming practices around the lake and the bird mortality seen on Lake Apopka last year from a similar restoration project. Tissue samples from alligators, as well as birds, reptiles, insects, fish, and mammals, have been collected and will be analyzed for organochlorine pesticide and metal residues.
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