Habitat Requirements for Southern Chum Salmon Populations
General Life History
Chum salmon have the most extensive distribution of all the salmon species. Southern
chum populations in British Columbia spawn in coastal systems ranging from streams near the
U.S. border in the south to the northern end of Vancouver Island. More than 400 populations
originate from this area but 45 of them account for 85 % of the total production with the Fraser
River stocks being the largest producers. Southern chum stocks are divided into two groups
based on the timing of spawning migration. The summer run chum stocks migrate between June
and August and spawn in September and early October. These are generally smaller populations
the largest of which return to Knight and Bute inlets on the mainland coast. The fall run chum
stocks migrate in September, October and November and spawn between October and January.
The vast majority of southern chum salmon production comes from the fall run complex.
Spawning migration timing for all southern chum stocks is later than for northern populations
and age at maturity is younger with either three or four year old fish dominating the return.
Early timing stocks tend to have a higher proportion of older fish than those that enter spawning
streams later in the year.
Chum salmon spawn most commonly in the lower reaches of rivers from areas of tidal
influence to about 200 km from the sea. Areas selected for redd construction are either in the
mainstem of the river or in side channels and are generally immediately upstream of turbulent
flows or where there is a source of upwelling water. When fish reach the spawning grounds, the
female selects a nest site with the appropriate features including adequate depth, flow and nearby
cover, and begins digging a pit referred to as a redd, where eggs will be deposited. The digging
process removes sand, silt and fine gravel from the nest site creating a favourable environment
for incubation of the eggs. Once the nest is complete, the female deposits the eggs which are
fertilized by one or more males and then moves to the area immediately upstream of the nest and
begins digging another pit. The material removed by this digging action covers the fertilized
eggs to protect them from predation and from being washed away by the scouring action of the
river or stream. This process may be repeated several times resulting in multiple nests
containing eggs from one female.
The length of time required for the eggs to incubate is partially dependent on water
temperature. In general, the lower the water temperature, the longer the incubation period
required. Upon hatching, the juvenile chum salmon (called alevins) move within the spaces
between the gravel particles varying distances depending on gravel size. The newly hatched fish
have an attached yolk sac that provides the required nutrition. Towards the end of incubation
(late winter to early spring), alevins move up through the gravel to emerge as fry. This process
occurs at night which helps to minimize predation and generally coincides with the complete
absorption of the yolk sac. The survival of chum salmon eggs from spawning to emergence
varies widely between systems and years and is influenced by stream flow, water temperature,
dissolved oxygen, gravel composition, spawning timing and spawner density. Typically, around
10% of the eggs deposited by females will survive to the fry stage.
After emergence, chum salmon fry migrate quickly downstream to the estuary where they
spend time rearing before making the transition to saltwater. The timing of this migration ranges
from February to May. Chum fry do not school as strongly as either pink or sockeye salmon and
predation rates can be significant during fry migration. One study found that predation mortality
ranged from 20 to 85 % over a 2.6 km migration path.
Chum salmon are highly dependent on estuaries for rearing and preparing for life at sea.
Entry into the estuary is timed to take advantage of plankton production in this nutrient rich
habitat. Juvenile chum stay in the estuary longer than most other salmon species spending up to
several months in tidal creeks, sloughs and side channels where their movements are often
coordinated with the pulse of the tides. The period of residence in estuarine and near shore
waters around river mouths appears to be the most critical phase in the life history of chum
salmon and plays a major role in determining the size of the subsequent adult return. As chum
salmon fry leave the estuary they generally remain close to the shoreline feeding in the
productive, shallow, near shore marine habitat until large enough to move offshore. Food items
consumed include various zooplankton species as well as adult and larval insects. As they grow,
the juveniles begin to migrate northward along the coast where they are often found together
with pink salmon juveniles relatively close to shore. During the fall or early winter, a general
dispersion from the coastal belt occurs and southern chum mingle in off shore waters with other
stocks from around the north Pacific basin. During the spring and early summer of their final
year at sea, maturing chum salmon depart the open ocean areas of the Gulf of Alaska and begin
the long migration back to their home streams to spawn.
Habitat Requirements by Life History Stage
The health of all Pacific salmon is closely linked to the availability of productive
freshwater, coastal and marine environments. Southern chum salmon populations require quality
freshwater spawning and incubation habitats to thrive and remain productive. Since chum
salmon are not significantly dependent on fresh water as a rearing habitat, it is the quantity of
prime spawning and incubation areas that determine freshwater production potential. Estuary
and near shore environments are also vital and the rate of survival through the rearing period
spent in these habitats greatly influences the return run size. Healthy habitat is challenged by
human competition for accessible land and fresh water, for ocean spaces and for the
interconnecting estuarine and coastal areas. The loss or degradation of quality habitat in any of
these important zones will have a negative impact on chum salmon populations.
Spawning
Adult chum salmon require access to their home spawning grounds in order to
successfully reproduce. Features such as dams, debris jams, waterfalls, or rock/mud slides that
block upstream migration can limit access to spawning areas and impact production. Also, if
conditions such as high water temperature or extreme high or low flows are encountered when
spawners arrive at their river or stream of origin, fish often mill about in the vicinity of the river
mouth for long periods, waiting for conditions to improve. This delay in river entry can have a
detrimental affect on survival and on spawning success as fish are exposed to predation from
marine mammals and, since feeding has stopped in preparation for spawning, vital energy
reserves are used up. As a result, it is important to critically assess any activities that impact
river flows or water temperatures when chum salmon are returning to spawn and to ensure
that fish have unimpeded access to spawning grounds.
Chum salmon require spawning sites within the stream or river where water velocity,
depth and gravel size are optimal for the incubation of developing eggs. The substrate must be
small enough to be moved by the fish and large enough to allow good intragravel water flow to
the incubating eggs and developing alevins. Chum salmon prefer moderately sized gravel with
minimal fine sediments and some upwelling. Water depth must be sufficient to cover the redd at
all times. A lack of prime spawning habitat can limit chum salmon production as later
spawners may be forced to build redds in secondary locations or on top of previously
constructed redds resulting in reduced overall production. When spawner densities are high,
the digging up of redds by later spawners has resulted in up to 50% of the total eggs lost as they
are exposed and washed downstream. This situation may be magnified during years when
spawner of both pink and chum salmon are abundant as they often compete for the same
spawning areas.
Incubation
The survival of chum salmon eggs from spawning to emergence varies widely between
systems and years and is influenced by stream flow, dissolved oxygen, gravel composition,
water temperature, spawning timing and spawner density. Studies indicate that survival of
chum salmon embryos and alevins is higher in more stable flow regimes. In one southern
system, survival to emergence averaged 11.2 % before flow control structures were installed and
averaged 24.9 % after the installation. Successful incubation requires flow rates that are
adequate to supply the required level of oxygen but not high enough to cause gravel movement
and streambed scour which could expose eggs to predators or wash them downstream. Data
shows that the average flow rate preferred by chum salmon is approximately 50 cm/s.
The percentage of chum salmon eggs and alevins that survive depends to a large extent
on stream and stream bed conditions. Studies have found that higher survivals were correlated
with high gravel permeability which ensured that the developing eggs and alevins were supplied
with a constant current of water that delivered oxygen and removed waste. Spawning areas with
slightly larger gravel size and low rates of sedimentation consistently generate higher survival
rates. In cases where large amounts of silt build up in spawning beds survival rates are greatly
reduced. This situation can occur in areas where streamside activities such as logging, road
building, or agricultural practices result in high sediment runoff into the river or where high
flows move sediments from upstream areas into spawning beds.
Incubation temperatures outside the ideal range can cause hatching and emergent
times that reduce survival. In extreme cases, freezing of redds can result in the loss of all eggs
in the affected areas. Studies indicate that while chum salmon eggs and alevins can withstand a
wide fluctuation in temperature, decreased survival and impaired development occurs at
incubation temperatures below 4.5 0C and above 14 0C. The removal of streamside (riparian)
vegetation can result in lower winter temperatures and higher summer temperatures and it is
important that healthy, natural growth remains undisturbed along the banks of salmon bearing
streams.
The water surrounding pink salmon redds must be non-toxic and of sufficient quality to
provide the basic requirements of incubation. There are many types of pollution that can affect
water quality including waste water, pesticides, toxic chemicals, petroleum products and organic
compounds. All efforts must be made to minimize the introduction of such pollutants into
salmon incubation area.
Juvenile Migration and Rearing
After emergence from the gravel, chum salmon juveniles typically begin an immediate
migration towards the ocean. The period of emergence usually coincides with the high river
runoff and most migrations are short with juveniles reaching the estuary on the first night of
travel. Those fry not completing the journey on the first night typically seek out refuge areas as
predation during seaward migration can be a major sources of mortality on chum fry. In one
study, researchers found that almost 85 % of the emergent chum fry were lost to predators during
migration. Although cover requirements are not well understood, the fry are known to hide in
the spaces between bottom substrates during the day as they migrate downstream. As a result,
an unimpeded migration path with cover from predators is important to the survival of chum
fry traveling to the estuary.
Water temperature is an important environmental variable for seaward migrating
chum salmon fry. Temperature can affect the timing of downstream migration, as well as the
growth, survival and smolting of chum fry. The recommended temperature range for successful
downstream migration is from 6.7 to 13.3 0C. Temperatures above 15 0C have a detrimental
effect on fry behaviour and performance and may cause premature migration. As mentioned
earlier, alterations to streamside vegetation can impact stream temperatures and it is important to
maintain healthy riparian growth in all salmon bearing streams.
The period of residence in estuarine and near shore waters around river mouths is a
critical phase in the life history of chum salmon and appears to play a major role in determining
the size of the subsequent adult run back to freshwater. Coastal estuaries are important as they
provide an environmental transition zone, early opportunities for feeding and growth, and
refuge from predators. As environmental transition zones, brackish estuaries allow out-migrant
chum salmon the opportunity to acclimate from freshwater to saltwater and between waters of
differing temperatures. They provide the first substantial opportunities for feeding and growth
for species like chum salmon that migrate to sea soon after hatching, and typically have higher
food productivities than adjacent ocean or freshwater areas. Estuaries may thus offer the
opportunity for enhanced growth and therefore, larger size at ocean entry which is known to
correlate with higher marine survival. One final role of estuaries is to provide refuge from
predators. The higher turbidity often associated with estuarine areas limits the ability of visual
predators to key on salmon juveniles thus reducing their exposure to the fish and birds that feed
on salmon fry. All of these factors point to the importance of estuaries in the life of chum
salmon and emphasize the need to protect these fragile areas from any activities that may be
detrimental.
Ocean Phase
Chum salmon are dependent on nearshore marine habitats and survival during this period
of early ocean residence can greatly influence total production. Studies have indicated that chum
salmon remain in the near shore environment for varying periods depending on factors such as
food availability, competition, predation and environmental conditions. Coastal areas provide a
rich habitat with opportunities for feeding and growth, which are important since survival in the
ocean is size dependent with larger fish surviving at much higher rates. Throughout this period,
kelp and other shoreline vegetation provide an important refuge from predators as well as a
productive environment for plankton, a major dietary component for juvenile chum. Therefore,
the health of coastal ocean ecosystems plays a key role in the production of chum salmon
stocks.
While nearshore conditions are important, factors operating in the offshore or open
ocean regions also have an impact on chum salmon productivity. Studies indicate that length
at maturity is related to environmental conditions experienced while at sea including sea surface
temperature and the amount of cloud cover. Other factors such as competition with other species
such as pink salmon for food resources also influence growth and survival. While migration
patterns and other aspects of their marine ecology remain poorly understood, ocean residence is
recognized as a very important component of the life cycle of all Pacific salmon. During their
time at sea, chum salmon migrate varying distances while increasing in size and acquiring the
energy reserves required for reproduction. While distribution patterns vary between years and
stocks, all chum salmon utilize coastal and off shore habitats during a period of rapid growth that
is critical to reproductive success.
References
Anon. 1995. Fraser River sockeye salmon. Report prepared by the Fraser River Action Plan,
Fishery Management Group, Fisheries and Oceans, Canada.
Bax, N. J. 1983. Early marine mortality of marked juvenile chum salmon (Oncorhunchus keta)
released into Hood Canal, Puget Sound, Washington, in 1980. Can. J. Fish. Aquat. Sci.
40: 426-435.
Beacham, T. D. 1984. Age and morphology of chum salmon in Southern British Columbia.
Trans. Am. Fish. Soc. 113(6): 727-736.
Beacham, T. D., and C. B. Murray. 1986. Comparative development biology of chum salmon
(Oncorhynchus keta) from the Fraser River, British Cloumbia. Can. J. Fish. Aquat. Sci.
43: 252-262.
Brown, T.G. 2002. Floodplains, flooding and salmon rearing habitats in British Columbia: A
review. Canadian Science Advisory Secretariat Research Document. – 2002/07.
Cordone, A.J. and D.W. Kelly. 1961. The influence of inorganic sediment on the aquatic life of
streams. Calif. Fish and Game. 47(2): 189-228.
DFO. 1999. Inner South Coast Chum Salmon. DFO Science Stock Status Report D6-09
(1999).
Hale, S. S., T. E. McMahon, and P. C. Nelson. 1985. Habitat suitability index models and
instream flow suitability curves: Chum salmon. U.S. Fish Wildl. Serv. Biol. Rep. 82
(10.108). 48 pp.
Hargreaves, n. B., and R. J. LeBrasseur. 1986. Size selectivity of coho (Oncorhynchus kisutch)
preying on juvenile chum salmon (O. keta). Can. J. Fish. Aquat. Sci. 43: 581-586.
Johnson, O. W., W. S. Grant, R. G. Kope, K. Neely, F. W. Waknitz, and R. S. Waples. 1997.
Status review of chum salmon from Washington, Oregon and California. U.S. Dept.
Commer., NOAA Tech. Memo. NMFS-NWFSC-32, 280 p.
Lloyd, D.S. 1987. Turbidity as a water quality standard for salmonid habitats in Alaska. N.
Amer. J. Fish. Manag. 7: 34-35.
Mason, J. C. 1974. Behavioral ecology of chum salmon fry (Oncorhynchus keta) in a small
estuary. J. Fish. Res. Board Can. 31: 83-92.
Pauley, G. B., K. L. Bowers and G. L. Thomas. 1988. Species profiles: life histories and
environmental requirements of coastal fishes and invertebrates (Pacific Northwest) –
chum salmon. U. S. Fish Wildl. Serv. Biol. Rep. 82(11.81) U. S. Army Corps of
Engineers, TR EL-82-4. 17pp.
Quinn, T. P. 2005. The behaviour and ecology of Pacific salmon and trout. Univ. Wash. Press.
278p.
Salo, E. O. 1991. Life history of chum salmon (Oncorhynchus keta). In: Pacific Salmon Life
Histories. Edited by C. Groot and L. Margolis. UBC Press. P 232 – 309.
Simenstad, C. A., and E. O. Salo. 1982. Foraging success as a determinant of estuarine and
near-shore carrying capacity of juvenile chum salmon (Oncorhynchus keta) in Hood
Canal, Washington, p. 21-37. In: B. R. Melteff and R. A. Neve (eds.). Proceedings of the
North Pacific Aquaculture Symposium. Alaska Sea Grant Rep. 82-2.
Williams, G. L. 1989. Coastal/Estuarine fish habitat description and assessment manual. Part I.
Species/Habitat outlines. Prepared for DFO by G.L. Williams and Associates.