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Fish Kills: How to Turn a Negative into a Positive

by Dr. Michael L. Parsons,
The Water School, Florida Gulf Coast University

As we all know, red tide kills
fish. As dead fish decay, they release
nutrients, fueling more red tide and
causing a positive feedback loop
(i.e., a compounding problem). By
removing dead fish, a significant
nutrient source could be eliminated,
which should result in an attenuation
Holistic Focus This Summer – Hydration cells). If a red tide bloom is smaller, the environmental and
of red tide (i.e., less nutrients = less

economic impacts should also be lower. Therefore, removing
dead fish can be a mitigation tool for red tide. Additionally,
fish carcasses are currently brought to landfills where they
are treated as waste. They could be useful as a fertilizer if
composted properly. In fact, they could potentially be certified
as “organic” (the fish are wild after all) and serve as a “nutrient-
neutral” fertilizer (i.e., the nutrients in the fish came from the
Gulf, and would return to the Gulf if utilized as a land-based
fertilizer product).
In a partnership with Mote Marine Laboratory, researchers
at FGCU’s Water School recently completed a study to
measure the amounts of nutrients released by decaying fish
(it was a stinky study!) and conducted small-scale composting FGCU graduate students Andrea James and Rachael Schinbeckler
to determine if composting could destroy red tide toxins (it preparing fish for composting
can) and if a nutrient-rich product was produced suitable
for fertilizer use (it was). In conjunction with researchers in
FGCU’s Lutgert College of Business, we also demonstrated
that even moderate red tides (>100,000 cells L-1) can cause
significant economic losses (over $3 million per month in
Collier County alone), and that fish removal initiatives are an
economically feasible option ($2,000 - $6,000 per ton of fish.
In short, the data looks promising – a proactive fish
removal program may reduce red tides. Notice the operative
words used here, however: should and may. There are still some
unknowns out there. Our next steps will be to find answers
for questions like “How many Karenia cells are supported
by the nutrients released by a decaying one-pound mullet?
How about 1,000 dead mullet?” or “How much will red tide
One of the
be reduced by removing 1,000 dead mullet?”. As you can
composting
see, while we have made much progress on this front, there treatment tanks
are still critical questions that require answers before we can filled with dead
operationalize a fish removal program to mitigate red tide (and fish collected off
Clearwater Beach
create an organic fish fertilizer!).
last summer

Life in Naples | May, June, July 2022 33