The Grass carp one of the four Asian carp species has reportedly entered the great freshwater lakes of Michigan, Erie, and Ontario. The invasion of Grass carp poses a serious threat to the lake's aquatic environment, reveals a scientific study.
Grass carp is an herbivorous fish found in freshwaters which can weigh a maximum of 90 pounds. It is not a naturally occurring fish in United States and Europe.
Why Were Grass Carp Cultivated In America?
The Grass carp was first cultivated in early 1960s in the United States to control growth of weed in the waterways. Some escaped through the system and went north, gradually settling down in the Great Lakes. This is not the first time the invasive fish has been spotted in the great lakes.
What Threat Do They Pose?
Bighead Grass carp and Silver Grass carp are most feared in the aquatic ecosystem as they feed on microscopic plants and animals in huge quantities. Grass carp as a species is considered to be the most invasive of all fishes and they pose a threat to other fishes in the lakes. Why? As Grass carps "aggressively outcompete" native fish for food and are capable of eventually overtaking the particular aquatic ecosystem.
A report has been prepared by American and Canadian experts with help from Fisheries and Oceans Canada, the U.S. Fish and Wildlife Services, and the Great Lakes Fisheries Commission, which states that nine out of 10 Grass carp caught between 2013 and 2016, were found to be fertile. It is believed that the fertile fish were not born in the Great Lakes and eventually made their way into Canada.
"Grass carp have been in the Great Lakes for ... probably 30 years or even more but they've been sterile, lately ... we've been seeing recurring incidents of fertile grass carp in the Great Lakes. They're not supposed to be fertile," said Mark Gaden from Great Lakes Fishery Commission.
They are known to reside the freshwater lakes for quite some time "humming in the background." Most of these fishes were sterile, thus the question of invasion and risk to the ecosystem never arose.
However, in recent years, the concern has been growing as more and more fertile Grass carps are being captured. Grass carps reared in hatcheries in some states have to be sterile before they are released into water.
"Right now, the sterile fish outnumber the fertile fish. This isn't game over, but we are finding more of these fertile fish," said Becky Cudmore, primary author of the study.
How To Control The Growth
The study's analysis points out that Grass carp will eventually become "established" in the lakes of Erie, Huron, Michigan, and Ontario in 10 years unless serious action is taken. To reach an established population, the species has to reproduce over multiple generations.
Several options like strict laws regarding bringing Grass carp in the region, along with prevention of release of fertile fish, may help control the alarming situation. Also, nets can be used to block the fish's course to spawning areas during the time of reproduction.
"Our assessment is saying that yes, they were showing up before, but now they're starting the invasion process. They have arrived. Now is the time to act," noted Cudmore.