Asian Carps Successfully Reproducing in Great Lakes, Posing a Threat to Native Fish

A latest U.S. Geological Survey study reveals that the Asian carps have reproduced successfully in the Great Lakes watershed, which could increase the threat to native fish population.

The new U.S. Geologically survey study was conducted on four grass carp - a species of Asian Carp - that were taken from the Sandusky River, Ohio. Researchers found that the fish are a result of natural reproduction within the Lake Erie basin. The fish was captured in October 2012 by a commercial angler.

The invasive species that were brought to the U.S. to control the growth of aquatic plants in 1960s, now pose a threat to the native fish populations and simultaneously prove to be detrimental to the survival of ducks, geese and other large aquatic birds. Grass carps were initially introduced for the aquatic plants that degrade areas crucial for spawning and early development of native fish, according to USGS.

After analyzing the grass carp captured in 2012, researchers determined that the fishes were a year old and had the capacity to become spawning adults. These fishes yield crucial information as the bones in the head called otoliths provide a history of the chemistry of water the fish inhabited during its lifetime. The scientists said that the grass carp studied had lived their entire lives in the Sandusky watershed. They ruled-out the possibility of the fish origination from a fish farm after comparing the otoliths of the captured fish with those of the pond fish.

The scientists are confident that the grass carp are a result of natural reproduction as the Sandusky watershed consists of naturally occurring high strontium to calcium ratio. The same strontium to calcium ratios were detected in the otoliths of fish  that are invading the Sandusky River. Apart from the high strontium to calcium ratio, the grass carp are also helped by the  river's natural fluctuations that are caused by rainfall.

"These findings are significant because they confirm recent USGS research indicating that shorter rivers, like the Sandusky, are potential spawning sites for grass carp and other Asian carps as well," said USGS scientist Duane Chapman. "The study may also provide resource managers an opportunity to address the spread of grass carp before it becomes problematic."

Since grass carp managed to successfully reproduce in the Great Lakes, it is possible for other Asian carp species such as silver, bighead and black carp to reproduce there as their spawning and development requirement is similar to that of the grass carp.

Bighead and silvercarpos remain a major concern in the Mississippi River Basin. Scientists are concerned that they may soon make their way into the Great Lakes Basin.

The findings were published in the Journal of Great Lakes Research.