That’s why the Michigan DNR killed 31,000 Atlantic salmon

HARRIETTA, Mich. – The Michigan Department of Natural Resources said fisheries personnel had to kill just over 31,000 Atlantic salmon because they were sick with bacterial kidney disease (BKD).

The disease was discovered in early April during a routine pre-stocking inspection of fish at the Harrietta State Fish Hatchery in Wexford County. Staff at Michigan State University’s Aquatic Animal Health Lab noticed signs of the disease and confirmed the presence of Renibacterium salmoninarum, the bacteria that causes BKD.

BKD is a bacterial disease known to kill trout and salmon and is thought to be the cause of the decline in Chinook salmon populations in the Great Lakes in the mid-1980s.

“The bacteria that cause bacterial kidney disease are listed as a Level 1 pathogen in the Great Lakes Model Fish Health Management Program,” said Ed Eisch, deputy chief of the DNR’s fisheries division. “Fish that test positive for Level 1 pathogens can be stocked where the pathogen is already known to exist, but only if they show no signs of the disease. This batch of fish still shows signs of active BKD and therefore cannot be stocked.”

The salmon at the Harrietta State Fish Hatchery received a 28-day course of antibiotics that was completed on May 17. However, the treatment did not completely cure the infection. After treatment, a group of fish was sent to the laboratory and internal signs of active disease were still found.

“The decision to dump these sick fish was painful, but it was clearly the right decision,” Eisch said. “The Atlantic salmon fishery is very valuable, but first and foremost we have a public responsibility to protect the water resources of the state of Michigan. Releasing fish that are known to be actively suffering from a disease outbreak would be contrary to that.”

Aaron Switzer, director of the DNR’s fish production program, said it was no surprise that the treatment was not entirely successful.

“These fish were so sick that a significant portion of them were not eating properly,” Switzer said. “This means that the antibiotic that was added to their food was not being absorbed in the amount needed to eliminate the pathogen.”

The Harrietta State Fish Hatchery is not the only DNR hatchery that raises Atlantic salmon. The Platte River State Fish Hatchery, about 15 miles west of Traverse City, has raised salmon. These fish were considered healthy and were stocked at four locations:

• Torch Lake received 15,883 fish.

• The Au Sable River in Oscoda and the Thunder Bay River in Alpena each received 25,000 fish.

• Lexington Harbor in Lake Huron received 40,000 fish.

The St. Marys River near Sault Ste. Marie will receive nearly 27,000 fish.

The DNR releases 20 to 30 million fish into Michigan’s public waters each year.

Michigan’s fish hatchery system is getting infrastructure updates to address a backlog of maintenance. Some of the upgrades will improve biosecurity, which should help protect fish from diseases like BKD.

For more information about fish and aquatic diseases, see Michigan.gov/FishHealthFor more information on the DNR’s fish production program, fish hatcheries and weirs, visit Michigan.gov/Breedinggrounds.