Fish
 
Direction of Fish Movement in Sawgrass Marsh Drydown
 

   The sawgrass marsh ecosystem is a freshwater slough in which there are long wet seasons, but the short dry seasons are very dry.  Many fish die in this drydown and the only ways they can possibly survive it are to congregate in the pools that remain all year long, or to follow the receding water.
    To test the migration of fish away from the drydown, I chose a rivulet in the sawgrass marsh with a reed directly across it.  I then counted the number of fish traveling across the reed in both directions for one hour.   Since it was hard to distinguish between the fish that swam back and forth, and those that actually left the area, the count couldn't be completely accurate.  There were also many fish that swam randomly or around in circles, chasing other fish.
    I counted 234 fish crossing the reed heading away from the drydown.  However, there were 205 fish swimming back in the direction of the drydown.  Many of these fish were probably the same ones, and it appears that the fish in the rivulet I was watching were content to stay where they were for the time being, at least not obviously moving away from the drydown.
    One possible reason for this lack of motion is that this year is much drier than normal.  Perhaps the fish were actually in a pond or channel that had stopped moving because it had dried up further down.  This could account for the random swimming and similar numbers of fish swimming in both directions. They had already found their "pond" to survive in.  Another possibility is that the large amounts of people on the boardwalk watching other animals and plants were startling the fish and disturbing their natural motions by moving, dropping things in the water, etc.
    The most prevalent fish I observed were male and female mosquito fish.  They were amusing to watch because the males often stayed near the females, and they would both chase each other around in circles, as if they were playing.
    Future experiments that could be done include watching the fish movements in future years that are wetter or drier to see if there is any obvious change in direction of movement.  One could also try to count the fish movements without including those fish that were obviously swimming in circles. The fish could be identified to discover in which direction certain species move most.
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