Reasons for Dead Fish Known but Duck Deaths Remain a Mystery

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by Elaine Marranzano – 

The discovery of five dead ducks and dozens of dead fish floating on the water’s surface have the public speculating that something may be amiss at the Tarrytown Lakes.

Nicole Carles found the ducks one morning last month in the lakes parking lot, dead, but not obviously injured. Someone else reported the dead “sunnies,” or sunfish, floating white-eyed along the shoreline of the larger, lower lake.

“Does anyone know if an animal would kill for fun like this? Or is it human?” asked Carles on Facebook about the ducks. “I am so sad.”

Speculation on Facebook was robust. They could have been poisoned, killed by unleashed dogs, attacked by rival Canada geese or swans, or perhaps killed by a semiaquatic mink.

Wanting to solve the mystery, Tarrytown Village Administrator Richard Slingerland, wearing rubber gloves and carrying a plastic grocery bag, walked around the lakes hoping to retrieve a duck carcass – a task perhaps not included in his job description. The New York State Department of Environmental Conservation (DEC) was ready to do a duck autopsy or, at the very least, test the creature for the presence of chemicals or lethal toxins. But by the time Slingerland came around looking for bodies, none were to be found. So, we are left only with speculation about what killed the ducks. But first some facts.

The Cornell Laboratory of Ornithology identified the dead duck in a photograph as a possible mallard, the most abundant duck in North America. The Tarrytown Lakes Committee thinks the ducks were possibly juvenile mergansers who live on the island and very often arrive this time of year. Regardless of breed, ducks in general face plenty of dangers, including those posed by humans.

Ducks in parks can become quite tame and accustomed to being hand-fed by visitors. This can be bad for their health. In 2016, 20 ducks in Canada died after eating bread and other human junk food. Full of bread, but unable to process carbohydrates, the ducks died of starvation. Don’t feed ducks bread.

If the deaths of the Tarrytown ducks were caused by a natural predator, such as a coyote, raccoon or weasel, a mink is as good of a guess as any. Weasel-like creatures, such as minks and ermine, can snap a duck’s neck without leaving a mark anywhere else on the body. And they sometimes kill just for the fun it, not bothering to eat their prey. We will never know for sure what killed these ducks, but the dead fish are less of a mystery.

“These little guys ‘bought the farm’ over the winter due to lack of oxygen under the ice,” said John Tucci, president of Everblue Lakes, contracted by Tarrytown to look after the health of the lower lake where the skate shack used to be.

According to Tucci, the territorial little sunfish don’t like to leave their chosen corner of the lake even if that means suffocating due to lack of oxygen.

“The lower lake had a huge, untreated algae bloom late last year that choked off the oxygen in some areas,” said Cathy Ruhland, chairperson of the Tarrytown Lakes Committee. “White eyes indicate the fish had been dead for a long time, probably on the bottom of the lake. Decomposition results in them floating to the top.”

The lower lake is maintained by members of Tarrytown’s Water Department who are “properly licensed,” according to Slingerland, to administer copper sulfate, a treatment for algae. Improperly used, copper sulfate can be toxic to fish, but there is nothing to indicate that was the case. The lower lake has not been treated with copper sulfate since last July and, according to the Water Department, the DEC tested the water last month and found nothing suspicious.

“If this had been a chemical poisoning, all types of fish and waterfowl would have died,” said Ruhland. “I don’t have a lot of concern that the deaths of the ducks and the fish are related.”

Facebook users also questioned the safety of the dye used in the upper lake as an algae retardant. Not to worry.

“The dye is organic and harmless,” said Tucci. “You could make blue cupcakes out of it.”

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