2017-10-26 / Nature

Osprey Newest Threat to Koi Ponds

By Charles Avenengo

(Photo by Liz Renshaw) (Photo by Liz Renshaw) In August 2002, I wrote an article about a thief raiding a koi pond. The culprit turned out to be a species of colonial bird called a black-crowned night-heron. A local wildlife photographer was able to capture a photo of the offender inaction, stalking the fish, therefore offering definitive proof that a night-heron was indeed the culprit.

The night-heron has long been a predator to backyard koi ponds. But it’s not the only one. Across the country, there are other types of hunters that raid backyard ponds, including herons, egrets, kingfishers, raccoons, mink and of course, “Mittens” and “Tabby,” the household cats.

Now, you can add osprey to the list of thieves.

Last summer, I saw an osprey return to its nest, clutching a large orange-reddish fish. At the time, I was perplexed as to what type of fish it was. It wasn’t until the Broadway Street Fair two weeks ago when I spoke to local wildlife photographer Liz Renshaw at her photography sales tent that I was able to connect the dots. On display, Renshaw had a photo of an osprey flying off with an orange fish in its talons. She said the fish in the photo was a large koi.

Newport Mayor Harry Winthrop said that osprey have been a problem for his koi pond. He also saw Renshaw’s photo and wondered if the osprey in the photo was making off with one of his koi. “Osprey would land on my neighbor’s garage roof and wait until we left,” he said, adding that they then raided his pond.

The fish-loving raptors have steadily grown their numbers on Aquidneck Island over the past 15 years, after an absence of more than half a century. This year, there were at least a dozen osprey nests on the island. Multiply the adults at these nests with their offspring, and that becomes a significant amount of fish needed for their daily catch. And now, this includes koi.

Despite these osprey-koi interactions, “Osprey’s are really not on the radar yet,” said Marc Domina of Domina’s Agway in Portsmouth. “I know they are around. However, mink is the biggest predator on the island.”

But there are ways to combat the pillaging. One is with the use of a cave in the pond, where the fish can hide under a protective ledge when a predator is lurking. This is a solution Winthrop used, and some of his koi now weigh more than 10 pounds, which is too big for an osprey to capture. The largest prey for an osprey has been measured at less than three pounds.

Koi in ornamental ponds can pay off as a long-term investment because koi can live for decades. In 1977, a koi fish died in Japan at age 226!

The trick is learning how to keep those lurking predators at bay.

World’s Most Expensive Pet

Ornamental fish are big business. The United Nation’s Food and Agricultural Organization reports that exports globally are more than $1 billion. The United States is the leading consumer, with over $300 million in ornamental fish imported annually. This includes the backyard koi, rock stars of the ornamental fish industry.

Koi are carp. Rising from their humble beginnings in Asian rice paddies, Japanese farmers began to selectively breed the fish, with the result being the colorful variants of white, black, orange and red that we have today. It was early in the 20th century that the fish began to appear and were subsequently raised in the European and North American markets. Koi are now considered the world’s most expensive pets. In October 2015, a prized koi in Japan sold at auction for 44 million yen, or $387,000.

The largest known koi currently is a giant in England named “Big Girl” that weighs an incredible 91 pounds. While ornamental carp generally become more valuable as they grow larger, collectors look for a number of additional factors, including body shape, pure coloration and pattern.

Naturalist Charles Avenengo has been chasing Aquidneck Island wildlife for more than 40 years.

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