From the River to the Sea
In Our Waters – Part I by James Craig
It’s early spring in 2021, and juvenile salmon and trout are stirring in hundreds of rivers and streams that flow into the Salish Sea. Young fish prepare to go to sea, while eggs incubate and recently hatched “alevin” develop beneath the gravel their parents spawned in.
Each species has evolved to occupy specific habitat niches at different times and sizes to minimize competition for limited resources and maximize survival. Chum are the historical “bread and butter” of oceanside rivers such as the Englishman, Little Qualicum and Big Qualicum. The thousands of kilograms of marine-derived nutrients they sequester from the Pacific and return to our watersheds are the “Miracle Grow” that make our streams so productive.
When chum fry emerge from the river gravels in March and April, they quickly turn tail and head for the ocean in large schools that regularly favour the top of the water column. This often makes these ~50mm fish the easiest to observe along stream edges, in estuarine channels, beside docks and marinas, and along beaches when the winds allow. But with low returns of chum salmon in the last couple years, the juveniles of this species may not be the most abundant salmonid entering the Salish Sea this spring.
Pink and chinook salmon eggs are also incubating and will hatch throughout spring. Pink salmon are the first to spawn each fall and produce fry that head to the ocean immediately. Meanwhile, Chinnok fry are “90-day wonders”, growing to a more optimal size of ~75mm (3”) before entering the Salish Sea in June.
Coho salmon can be the last to spawn, with fry emerging in late spring. Each coho fry spends a whole year in its natal stream, weathering the drought flows of summer and the flood flows of fall through early spring. With this lifecycle, both fry and smolts (~120mm; 5”) are present in rivers each spring, but only the smolt are in the estuaries in May, acclimating to the marine environment. Also in the salmonid family, both steelhead and cutthroat trout enter the Salish Sea each spring as two or three year-old smolts.
Steelhead and cutthroat are large from spending so much time in freshwater, reaching sizes of ~175mm (7”) on average. While the steelhead prefer larger rivers with higher flows, the cutthroat have evolved to occupy smaller tributaries and headwater creeks further upstream. Because cutthroat and steelhead are the last to spawn (February to May), their progeny are the last to emerge from the gravel – up to mid-July for some steelhead stocks. With so many species and lifecycles, there’s a constant supply of small and large juvenile salmonids entering the estuaries and the Salish Sea each year from March through July.
Many marine bird species rely on these juvenile salmonids as a food source, as do larger marine fish and marine mammals. Juvenile salmonids are frequently found amongst eelgrass, the brant’s primary food source, where they feed on various zooplankton and small invertebrates.