Thousands of fish dead in Ellis Harbor; culprit is temperature fluctuations

CEDAR RAPIDS — The Iowa Department of Natural Resources fielded a series of calls last week after dead fish were found floating in Cedar Rapids’ Ellis Harbor.

Chris Mack, a fisheries biologist with the DNR who responds to fish kill events, said it was a naturally occurring event that killed “thousands” of gizzard shad.

He said the DNR does not have a specific number of how many fish were killed because the kill was not caused by a chemical spill.

The culprit for the kill, which was first reported by KCRG-TV9, was Eastern Iowa’s temperature fluctuations in late February and early March. Warm temperatures allowed the fish to spawn and be more mobile. When colder temperatures moved in, the fish were “shocked” and died, Mack said.

Mack said Ellis Harbor is a “wintering hole” for the gizzard shad, so many of them stay in the harbor during the cold months. He said with more fish in the harbor’s smaller area, it could have stressed them and contributed to some of the deaths as well.

A gizzard shad is essentially a “bigger minnow,” Mack said, and is used for baiting bigger fish.

The fish species is a member of the herring family and is a native fish to fresh and brackish waters. Mack said Eastern Iowa is in the shad’s northern range and they are usually found in more southern states.

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An annual occurrence

The gizzard shad is an inherently “weaker” fish that are sensitive to temperature changes, Mack said, so these natural fish kills happen nearly every spring when the weather tips back and forth between warmer and cooler temperatures.

Mack, who said the first call to the DNR to report the kill was last Friday, estimated that additional fish will likely die with the spring weather fluctuations still underway.

“With the warmup, it will probably stress out a few more fish, and there's been a little continual die-off, which is pretty typical for this time of year,” he said.

Mack said shads are used as bait for catfish, so Iowa fishers are taking advantage of the free bait available at the harbor. He said other animals, like turtles and pelicans, also will eat them, so the DNR will not remove the dead fish.

Although gizzard shad fish kills are common in the springtime, Mack said the population will bounce back easily.

“They're out there in very high quantities and so when you get a die off like that, it's really not affecting the population,” he said. “They're not a game fish that people go out and catch.

“They basically have no cost or value, as far as fish kills go,” he added. “And being a natural kill, we wouldn't assess it anyway, because there's no one to charge for it. Mother Nature doesn’t cut us a check.”

However, Mack said Iowans should call the DNR if they believe they’ve spotted a fish kill.

It is “extremely natural and extremely common for this to happen at this time of year,” he said. “I would encourage people to report when they do see dead fish. … By people telling us about kills, it’s a good way to make sure that we don't miss them.”

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

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Comments: olivia.cohen@thegazette.com