……objective science for conservation…….

The Pacific WildLife Foundation is a non-profit coastal and marine research and education society  that inspires an appreciation for objective scientific research and conservation of the ocean. We conduct original research, develop novel education programs, and inspire an appreciation for conservation of the ocean. 

Chum Salmon Oncorhynchus keta

Chum salmon is an important component of river, estuary and open ocean ecosystems. Early in life it is eats a variety of river and estuary insects and becomes prey for predatory fish, birds and mammals. Later in life, it adds nutrients to the river ecosystem derived mostly from the Pacific Ocean when its spawned carcasses decompose and as food for large carnivores such as eagles, bears, gulls, and seals (see Quinn 2005 for the role of salmon in river biodiversity).  Chums spawn in small and large streams and take to the sea soon after hatching. The young salmon disperse widely and return to the homes stream to spawn 2 to 7 years later.

For over 40 years, the Mossom Creek hatchery has relied on volunteers from Centennial School and Port Moody to assist in caring for eggs and young salmon. A quarter of a million salmon fry are reared each year at the hatchery. The PWLF works closely with the Mossom Creek hatchery to assist in rebuilding coastal ecosystems that enhance the survival of chum salmon.

Distribution and Migration

The chum salmon has the widest distribution of the salmon ranging around the north Pacific Ocean (Salo 1991). In British Columbia, the inner South Coast chums arrive in streams in summer and fall runs. Summer chums migrate between June and August, and spawn in September and early October. Fall run chums migrate from September to November to spawn between October and January. The migration to the spawning streams by chum salmon slows as it approaches the destination. Salmon tagged in Johnstone Strait were recovered in the Strait of Georgia, the mouth of the Fraser River and in Puget Sound (Quinn 2005). They travel on average about 25 km/day between Johnstone Strait and the Fraser River but the journey slows as they approach the river. In northern Strait of Georgia the trip slows to about 16 km/day and 10 km/ day in the southern Strait. The total journey to the Fraser River estuary requires about three weeks. Another three weeks passes before the salmon swim upstream, spawn and die. 

Population Trend

Salo (1991) reviewed the literature on the life cycle of this species. In brief, spawning chum salmon are more abundant in even years and pink salmon are more abundant in odd years in the Fraser River tributaries (Gallagher 1979). Spawning in southern British Columbia occurs between early October and late December (Salo 1991). The young salmon leave the rivers soon after hatching to grow in estuaries. The food web of the estuary provides a vital source of food in this process. In spring, the juvenile chums leave for the ocean in time to consume plankton blooming in offshore waters. They then move north to mature in the Gulf of Alaska before returning 3-5 years later to natal streams to spawn and die.

Chum Spawning Behaviour

As the autumn rains fill the creeks and rivers, chums enter the spawning channels to lay eggs. They swim far upstream because they prefer the flat early stretches of rivers for spawning. Males generally precede females to the spawning beds. Each female seeks out a stretch of unoccupied gravel to defend against newcomers. There she digs out a redd with movements of her tail, testing the depth of the depression with her anal fin. At the same time, males begin to court her.  A male ready to mate will position himself beside and slightly behind the female and can be observed crossing back and forth over her back and sometimes shivering violently. Large males dominate smaller competitors and get the most matings but a few small males ( called ‘jacks’) lie in wait downstream to sneak into position and fertilize eggs at the same time as the large males are preoccupied in fertilizing the eggs. Schroder (1982) estimated that these ‘satellite’ males were able to fertilize up to about one quarter of the eggs. Cutthroat trout ram head on into the side of a ripe female in order to force eggs out of the vent for consumption.  The female covers her eggs with gravel and begins to build a second nest. She repeats the same nest building and egg laying behaviour until three or more nests are finished.  She will remain at the site of these redds protecting them from overspawning until her energy is depleted and she drifts downstream to die. Much is known about the role of stream and water conditions on hatching of chum eggs (reviewed by Salo 1991) but in general chum eggs hatch between early March and early May. There is some experimental evidence that stonefly nymphs scavenge dead chum eggs thus reducing fungus growth on the living eggs (Nicola 1968). 

Upon hatching, alevins wriggle deeper into the gravel and emerge at night 1-3 weeks later to swim to the estuary. Fraser River chum migrate between February and June with most departing between mid-March and the end of April (Beacham and Starr 1982). The mass migration likely satiates the small number of predators in small streams allowing most chums a free passage to the river mouth. Young chum stay up to 3 weeks in the Fraser and Nanaimo river estuaries, sloughs and nearby creeks (Healey 1982) and move offshore as the coastal food supplies dwindle. The prime habitat for chum combines high carbon input from the river and expansive wetland and intertidal areas where the carbon is converted into prey eaten by the salmon. The detritus based food web is the factory that converts carbon into edible prey for the young chums (Simenstad et al. 1982). Favoured foods include chironomids (midges), copepods, adult insects and amphipods (crustaceans) in our estuaries (Levy and Northcote 1981) that are eaten in large numbers when high tides provide deepwater access to the marshes.

The shallow waters of the Strait of Georgia remain their home until about June.  Then the young chums move into deeper waters and eventually exit the Strait in July probably in pursuit of offshore plankton blooms (Salo 1991). There they join immense schools of sockeye and pink salmon in a broad front along the coast of British Columbia and Alaska (Hartt 1980). Some late migrants might not make such a long journey but instead remain along the outer coast of British Columbia. The schools that move north into the Gulf of Alaska mature there over the winter. The time spent at sea allows the salmon to grow rapidly into a mature fish on a diet of marine invertebrates and other fish. Most of the growth occurs in June and July and in the final year before spawning (Ricker 1964). Most chum salmon mature at 3-5 years of age. 

Chum Feeding Behaviour

Juvenile chum salmon enter the Strait of Georgia in southern Canada in spring when plankton blooms at the mouth of the Fraser River (Walters et al. 1978). Their entry timing is likely a balance between food requirements for further growth and attaining a size where they are willing to risk being caught by predators. They begin to sample a seafood smorgasbord of tiny animals known as copepods, euphasiids, larvaceans, chaetognaths, decapod larvae and fish larvae and amphipods (Salo 1991). Adult chum eat small fish such as herring and sandlance.

Population Trend

Based on Canadian catch statistics, the number of chums declined in the early 1940s and spawning returns were likely low in the early 1920s and 1930s. Catches increased between 1939 and the early 1950s but fell again through the 1960s from overharvesting (Fisheries and Oceans Canada 2006). By 1985 to 1994, total returns had increased but they dropped again in the late 1990s. Overfishing and low ocean productivity are problems for the conservation of chum stocks in recent years (Beamish et al. 2000). Fall chum salmon migrating through Johnstone Strait and the Strait of Georgia in the 1990s encountered seine, gill net and troll fisheries that removed an average of 68% of the entire Inner South Coast commercial catch of 800,000 chums annually  (Department of Fisheries and Oceans Canada 2006). The Fraser River fishery harvests predominately hatchery and rearing channel raised chum salmon from the Harrison, Chehalis, Inch, Stave and Chilliwack/ Vedder rivers (Fisheries and Oceans Canada 2006).  

Ecology of Salmon

One of the most remarkable ecological stories to emerge in the past few decades is the vital role of salmon in north Pacific ecosystems. An excellent review of the story can be found in Thomas Quinn’s book, The behavior and ecology of Pacific Salmon and Trout (University of Washington Press, 2005). Years ago fisheries biologists in Alaska knew that the carcasses of sockeye salmon enriched otherwise nutrient-poor lakes where the young sockeye grew before leaving to sea. Experiments showed that artificial fertilization of lakes sometimes enhances the growth of young sockeye. It appeared that the addition of nitrogen and phosphorous increased algal growth in lakes. The alga became food of zooplankton eaten by young sockeye. The next research breakthrough revealed the role of salmon carcasses in rivers and lakes. With the development of technology to measure isotopes, scientists were able to measure the relative contribution of marine and terrestrial sources of nitrogen and carbon in plants and animals along riverbanks. Kline et al (1990) showed that substantial amounts nitrogen and carbon in plants, insects and fishes was derived from marine sources. Biologists had long known that bears discard salmon carcasses along the edges of salmon spawning rivers but it was only recently that the fuller significance of bears to the forest ecosystem became clear. The size of bears and the number of cubs they raise is directly related to the amount of meat they consume (Hildebrand et al. 1999) and so large numbers of bears assemble along salmon spawning streams in autumn. They catch large numbers of large fish but eat mostly the brains and eggs, discarding about 70% of the carcass. This remaining protein is left to rot in the forest where it eventually is taken up by the forest plants, insects, birds, mammals and fish (Bilby et al. 1996, Helfield 2001, Reimchen et al. 2003, Wilkinson et al 2005).  

 Chum Salmon Photos

References

Bilby, R.E., B.R. Fransen and P.A. Bisson. 1996. Incorporation of nitrogen and carbon from spawning coho salmon into the trophic

system of small streams: evidence from stable isotopes. Canadian Journal of Fisheries and Aquatic Sciences 53:164-173.

Bilby, R.E., B.R. Fransen, P.A. Bisson and J.K. Walter. 1998. Responses of juvenile coho salmon (Oncorhynchus kistusch) and

steelhead (Oncorhynchus mykiss) to the addition of salmon carcasses to two streams in southwestern Washington, U.S.A. Canadian

Journal of Fisheries and Aquatic Sciences 55:1901-1918.

Healey, M.C. 1991. The life history of chinook salmon. Pp 311-393 in: Pacific Salmon Life Histories. C. Groot and L. Margolis (eds).

University of British Columbia Press.

Helfield, JM,  2001. Interactions between salmon, bear, and riparian vegetation in Alaska. PhD thesis, U of Washington, Seattle. 

Hilderbrand, G.V., Schwartz, C.C., Robbins, C.T., Jacoby, M.E., Hanley, T.A., Arthur, M.S., and Servheen, C. 1999. The importance

of meat, particularly salmon, to body size, population productivity, and conservation of North American brown bears.

Canadian Journal of Zoology  77: 132–138.

Kline, TC et al. 1993. Recycling of elements transported upstream by runs of Pacific salmon: 1. Canadian Journal of Fisheries and

Aquatic Sciences 50-2350-2365.

Quinn, T.P. 2005. The behavior and ecology of Pacific salmon and trout. UBC Press, Vancouver.

Reimchen, T. 2003. Some ecological and evolutionary aspects of bear-salmon interactions in coastal British Columbia. Canadian Jounral of Zoology 78: 448-458.

Wilkinson, C.E., M.D. Hocking and T.E Reimchen. 2005. Uptake of salmon-derived nitrogen by mosses and liverworts in coastal British

Columbia. Oikos 108: 85-98.