The Army Corps of Engineers and the U.S. Fish and Wildlife Service released a joint report on December 23 on the possibility of Asian carp traveling past the electric barriers designed to keep them from migrating into the Great Lakes. Although the report sketched out some scenarios under which it is theoretically possible for carp to breach the barriers, it stressed that there is no evidence of any carp actually having done so.
Simulations done with scale models and caged and tethered fish indicate that it may be possible for passing barges to affect the strength of the electric field, and to possibly tow in small fish (two to four inches) in their wake, the report said. The fishes’ behavior was captured and recorded by dual-frequency identification sonar. The studies found that slow vessel speeds tend to capture and transport small fish in their wakes, while high speeds produce a reverse current, which drive the fish in the opposite direction.
The finding is described as preliminary; the report said the Corps’ Research and Development Center will undertake a further two years of testing, including more sonar studies, as part of initiatives coordinated by the Asian Carp Regional Coordinating Committee.
The report has been given wide play in local media, especially in Great Lakes communities, despite the Corps’ statement that no carp have actually crossed the barriers. The report says the closest adult carp found in the Illinois River have been 55 miles from Lake Michigan, and no small Asian carp (the size that could theoretically be dragged across the barriers in the wake of a barge) have been found closer than 131 miles from Lake Michigan.
Meanwhile, Near Lake Erie
Scientists with the U.S. Geological Survey and Bowling Green State have determined that four grass carp captured on the Sandusky River in Ohio had spent their whole lives in the river, which flows into Lake Erie. It was the first time that carp had been documented living their entire life cycle within the Great Lakes watershed.
Because the carp were fertile, scientists determined that the fish had not been introduced by stocking. Ohio had allowed the stocking of sterile grass carp since 1988.
Grass carp are on of four related carp species that a team of federal and state agencies is trying to keep out of the Great Lakes for fear they would supplant naive species and threaten the lakes’ $7 billion sport fishing industry. The carp grow fast and eat voraciously, feeding on the same plankton that sustains other species.
Bighead and silver carp are the species that cause the most concern; grass carp are not as destructive, but scientists said that where grass carp thrive, other types could also.
In support of these findings, some have called for closing the navigable waterways that connect the Great Lakes to the Mississippi River system.