September 26, 2007 Edition
Conservation Corner: Chinook Salmonby Shannon Stephens
Half a continent away, seeking the stream of their birth after years in the Pacific, an amazing aquatic spawning migration is underway. The Chinook salmon are spawning. However, this fall phenomenon can be seen right here in the Nottawasaga River! Head down to the river, and you can see the end of an amazing life's journey, made by only the lucky and fittest, surviving Chinooks who will begin the next generation.
Each fall, after three years in Georgian Bay, Chinooks embark on a marathon journey up to 100 km up the Nottawasaga. Both rainbow trout and Chinook salmon go upstream into the Pine, Nottawasga and Boyne River. The Chinook are easily spotted at the Nicolston Dam fishway, near Alliston, which was installed to allow the fish access the prime spawning grounds within the Upper Nottawasaga River watershed. They eat nothing during their spawning run and rely on stored energy reserves for migration and reproductive materials.
The breeding males develop a large hooked jaw.
Their scientific name Oncorhynchus tshawytscha is derived from the Greek onkos ("hook") and rynchos (nose"). The female prepares the redd (nest) in gravel, by lying on her side and beating vigorously with her tail. Females tend to choose larger males to fertilize their 3,000 to 14,000 eggs. The male dies shortly after spawning. Afterwards, the female guards the eggs, until she too dies. The bodies of salmon float downstream, rejoining the food chain, perhaps feeding the very aquatic insects that will be eaten by their own young come spring.
The eggs need cool, clean flowing water. The eggs hatch in March. Typically, the young fry stay in the river for 3 months, and then swim down to Georgian Bay. Many Chinook die early in life due to natural predation and human changes in habitat, including siltation, low oxygen, loss of stream cover and low river flows.
Chinook were introduced in small numbers to the Great Lakes in the late 1870s for sports fishing. By the 1950s, the Lake Trout and other native fisheries had been decimated by overfishing and predation by introduced Sea Lamprey. In response, stocking of Pacific salmon increased dramatically in the 1960s and 1970s. Chinook are popular with hatcheries because they only take six months to rear, compared to the 14-16 months Coho salmon take. Stocking data, from the Great Lakes Fishery Commission, records the addition of 848 million fish between 1966 and 2001!
In Georgian Bay, the Owen Sound hatchery started stocking in 1985 and continues today. Based on mark-recapture studies, natural reproduction rose in Lake Huron; increasing from 15% in the early 1990s, to nearly 80% in 2000-2003.
In Georgian Bay about 95% of Chinook are wild, self-reproducing fish.
Salmon love to eat alewife, a small fish. Alewife are an introduced species first reported in Lake Erie in the 1930's.
Alewife populations can fluctuate dramatically. Mass die-offs of alewife have occurred, leaving tractorloads of them decaying on beaches. In the last five years, alewife populations have crashed. Without this preferred food source, mature Chinook are trimming down, reaching an average 8 pounds instead of the 13 pounds in the 1990s.
Today, a new challenge facing the Chinook and many other native fish is the Viral Hemorrhagic Septicemia (VHS).
Although fish carrying VHS are safe for humans to eat, the virus is very harmful to fish populations. Diseased fish may have pale gills and organs, bloated abdomens, bulging eyes, bleeding hemorrhages on body and organs, or may not exhibit any visible signs. VHS can spread through the water, on infected fish, or fish parts. We can all help slow the spread of VHS by not moving fish or baitfish between water bodies, and washing equipment between water bodies.