Dicromantispa interrupta

Dicromantispa interrupta
Mantisfly

Thursday, October 1, 2009

Orange Lake Fish Kill

Lynn and I rendezvoused at Heagy Burry Park on the south side of Orange Lake for a late afternoon canoe paddle. We headed out straight into the wind for a couple of miles NNE along the open path through dense submerged macrophytes to the edge of the big lake’s open water. She had told me about gobs o' ‘gators on the south side of the lake up in the weed cuts and airboat trails, and I had never canoed around in that part of the lake.

As we pulled away from the boat ramp we noticed a few dozen dead, rotting fish floating in the weeds just off the boat path. Most were a foot or more in length and torpedo-shaped, so I expected them to be bowfin (Amia calva) and/or gar (Lepisosteus spp.) because local anglers often catch and then deliberately kill them, and throw them back in the water. Why do they kill them? When I was a boy, my older fishing fellows insisted that we kill rough fish because that would make room for more eatin’ fish in the lake for us to catch. Sheesh! Anyway, when we pulled over to examine them I was shocked to see they were chain pickerel (Esox niger) instead! We saw one that was easily 18 inches in length, but it sank out of sight when we tried to maneuver it for photography. This other one was only about 14 inches long:


A very few of the dead fish were sunfishes (Centrarchidae), I saw a largemouth bass (Micropterus salmoides) and an unidentified bream (Lepomis sp.), but there were no dead gar or bowfin. The great majority of the dead fish were chain pickerel, a delicious fish that anglers readily keep. Pickerel are among the most finicky of our Peninsular Florida fishes, needing cleaner water and more dissolved oxygen than sunfishes. Could the killer instead be nocturnal dissolved oxygen deficits? Orange Lake and the other large lakes in the Orange Creek Basin are hypereutrophic and have frequent blooms of blue-green algae (Cyanobacteria), dominated by Cylindrospermopsis raciborskii (http://tinyurl.com/ybby3x5). The new satellite images of Orange Lake on Google Earth clearly show a massive algae bloom in January 2008, possibly from “cylindro:”


How about that? A huge algae bloom in mid-winter! Do you think the bloom might extend all the way to Heagy Burry boat ramp by late September? (Or was its photosignature simply not picked up by the next image?) As I have noted before, the lake’s enormous submerged macrophyte biomass also depresses nocturnal oxygen levels. Between macrophytes in the shallows and cylindro in deep waters, there could be a huge deficit of dissolved oxygen just before dawn on a hot summer day like the one we had a few days ago. That could kill a sensitive taxon like Esox, which could be likened to a canary taken into a mine to warn miners of bad air.

Or was the kill caused by a toxin? Cylindro produces cylindrospermopsin, which in sufficient quantities results in closure of public lake beaches in Indiana (http://tinyurl.com/y99uof8). The Indiana group also pointed out that cylindro is positively related to elevated dissolved phosphorus levels, which Orange Lake certainly has. This toxin has been implicated in deaths of mice, cattle, shellfish, fish, horses, sheep, dogs, birds, bats and muskrats (http://tinyurl.com/y85hftl). In humans it has caused skin rash, fever, hay fever-like symptoms, hepatoenteritis and toxic hepatitis (http://tinyurl.com/y85hftl).

Or was the fish kill a result of too much toxin and too little oxygen working in synergy?

Moving right along…

We ran across a couple of patches of yellow water lily, Nymphaea mexicana. I had never seen it before, and I’ve been on a LOT of Florida’s freshwaters taking inventory of plants and such, and was therefore certain it was an exotic. But no, the Center for Aquatic and Invasive Weeds (http://aquat1.ifas.ufl.edu/node/289) lists it as a native of Florida. How could I have missed this plant after all these years of wandering around Florida’s aquatic ecosystems? Egad! Having fewer petals, it is not as showy as its sister species, white water lily (N. odorata), but it does also have a very pleasant fragrance:


At that we turned around and headed slowly for the ramp with the wind at our backs, reaching shore as the sun was setting and a three-quarter moon rising higher. A group of black vultures was coming back to the ramp too, for the snag roosts there. It was a good ending to a fine early fall day.

3 comments:

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  2. What can we do to reduce fish kill or bring the water back to the lake. It is drying up again. Ideas?

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  3. In the first place, the lake needs more rain. But even so, Orange Lake has several sinkholes that drain directly into the Floridan Aquifer. With so many people, farms, and industries pumping water from the aquifer, there is good reason to believe that the lake may not return to its former levels. Only time will tell. We can all do our part by using less water, however. For instance, stop the wasteful practice of irrigating lawns with potable water, and instead allow nature to re-vegetate lawns with native wildflowers, shrubs and trees. Stop the use of overhead irrigation on crops, and require farms instead to use drip irrigation and similar low-evaporation systems.

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