CHINOOK SALMON RESEARCH

Allan Kapitany of New London proudly displays a 15 pound chinook salmon
Photo by Joe Kapitany

Chinook Salmon Project

Under the auspices of the Great Lakes Fishery Commission the overall fisheries management goal established for Lake Michigan in the Fish-community Objectives (FCOs) is to restore and maintain the biological integrity of the fish community so that production of desirable fish is sustainable and ecologically efficient.  The salmonine objective specifies establishment of a diverse salmonine community capable of sustaining an annual harvest of 2.7 to 6.8 million kg, of which 20-25% is lake trout Salvelinus namaycush.

Inherent in this objective is the desire to maintain a salmonine community that has abundant levels of Chinook salmon Oncorhynchus tshawytscha (i.e., target annual yield of 3.1 million kg) sufficient to suppress alewife Alosa pseudoharengus populations but not beyond levels where predator consumption would threaten food web integrity.  The Salmonine and Planktivore Objectives are based on the understanding that large populations of exotic forage fishes, such as alewife and rainbow smelt Osmerus mordax, negatively impact recruitment of native fishes, and that controlling exotic prey fishes presents an opportunity to create new, diverse fishing opportunities.  Therefore, progress toward these objectives is evaluated by determining the relative balance between predator and prey (e.g., Chinook salmon and alewife interactions) rather than suppression of alewife through extreme top-down predation.

Chinook salmon stocking levels were highly correlated with harvest in the first two decades of stocking.  There was a disparity between stocking and harvest, even with sustained stocking rates, during the late-1980s.

Nancy Ruff with a nice Chinook taken out of Sturgeon Bay.
Photo by Bill Ruff

OTC Marking

Recruitment of naturally-produced Chinook salmon smolts has increased since their introduction in 1967. Natural reproduction has been estimated periodically throughout the period 1985-2008. Estimates in the early 1990s from oxytetracycline (OTC) studies suggested that natural recruitment accounted for 29-35% of lakewide adult stocks when stocking levels were near their highest.

For the last several years fish managers around the lake have been marking all chinook stocked from hatcheries so that hatchery fish can be distinguished from naturally reproduced fish. Fish managers have been marking most of the hatchery chinook with oxytetracycline (OTC). The OTC is mixed with food, fed to chinook fingerlings while in the hatchery. OTC is a FDA approved antibiotic used in treating fish that has the side effect of laying down a mark on bony structures, (like vertebrae) that fluoresces under ultraviolet light. By collecting a vertebrae from sport caught salmon, fish biologists can determine if the chinook was stocked or naturally reproduced.

Estimates for 2001-2003 from OTC-marked fish collected in 2004 and, more recently, estimates from the lakewide OTC evaluation starting with the 2006 year-class, indicate that natural recruitment has increased.  For the last several years naturalized recruitment of chinook salmon has remained high, at over 50 percent. The 2006 year class of Chinook was estimated to be 54 percent naturalized. The 2007 year class was estimated to be 52.8 percent naturalized. And, during the summer of 2009, we will get our first estimate of the 2008 year class.  The decline in Chinook salmon recruitment is, in part, due to stocking reductions aimed at reducing total Chinook salmon abundance to be more in alignment with prey abundance.

2009 Fishing Season

For the 2009 fishing season, Wisconsin Department of Natural Resources will again be collecting tail samples from chinook salmon as part of this study.  Unlike previous years when only 1+ chinook salmon tails were collected, this year all sizes of chinook salmon will be collected because we have fish that are 1+, 2+ and 3+ years old marked with the Oxytetracycline.

If you are fishing in a Lake Michigan contest, please consider donating a section of your chinook tail for this study.  You may also come across personnel collecting biological information at fish cleaning stations as well as chinook salmon tails for this study. Please consider giving us your chinook salmon tail so that we can continue to investigate the natural reproduction capabilities of chinook salmon in Lake Michigan.