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The dates given for each life stage represent the
approximate norm for fall chum salmon. Each individual stock of salmon
has adapted to the unique set of environmental and biological conditions
that influence all stages of its life in freshwater and the ocean. These
adaptations can cause the timing of the various life stages of each stock
to vary substantially.
The sizes presented below for individual life stages are
from two sources. The sizes for juvenile stages are from Salo (1991) and
represent approximate rates of growth for Minter Creek fall chum salmon
in the 1940s. Adult sizes are from Pratt (1974) and are based on samples
from the 1970 Puget Sound chum salmon return. Sizes of chum salmon are
highly variable for different stocks and in different years, and the values
below are presented only for illustrative purposes. These sizes should not be used to represent the actual or approximate growth rates
for any current chum salmon populations.
As with the growth rates, the survival rates for various
chum salmon life stages are presented only to provide an indication of
the nature of the mortalities that can occur throughout the life of these
fish. The survival rates below are based on values reported by Parker
(1962), and represent a chum stock from a small coastal British Columbia
stream. Survival rates vary tremendously by stock and by year, and the
following values should not be used to represent actual or approximate
rates for any Washington chum stocks.
The numbers given for surviving progeny at various life stages begins
from a theoretical single year's spawning population of 100 pairs of spawners
(or 200 total fish). It is assumed that this is a healthy population of
chum salmon, surviving at average rates and able to support fishery removals
of 65% of the returning adults. The numbers are based on the population
replacing itself, and the resulting total of the three-, four-, and five-year
old chum salmon surviving to spawn equal the original population of 200
parent spawners.
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November-March
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Incubation
- Eggs are deposited in the stream gravels during the November
through December spawning season. The chum embryos develop within
the eggs and hatch after approximately four months. At this time the
young fish are called alevins, and they continue to reside in the
gravel as they absorb their yolk sacks. After about a month and a
half, the alevins emerge from the stream bottom as 1 to 1½ inch long
fry. The potential total number of eggs for the 100
female spawners is 300,000 eggs.
This number is reduced by factors like: eggs lost during spawning,
predation, erosion of redds during floods, siltation, etc. The remaining
progeny of 200 spawners when the fry emerge from the gravel total 23,400 fry. |
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February-July
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Migration
to Sea - The newly emerged fry immediately begin downstream migration
to marine waters. A very small number of chum fry may reside in freshwater
until the end of summer. When the fry first enter saltwater they assemble
in small schools and reside close to shore to avoid predators. As
the young fish grow, they gradually move to deeper waters and generally
migrate towards open ocean waters. Mortalities during this early marine
life period are primarily the result of predation by birds and other
fish species. By mid- to-late summer the juvenile chum have reached
ocean waters. At this time they are approximately 4 to 6 inches long.
Some chum salmon juveniles will remain in nearshore marine waters
until late in their second year before migrating to the open ocean. |
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May-December
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Ocean
Growth - When the juvenile chum salmon leave nearshore waters
they migrate generally northward along the Washington and British
Columbia coastlines. Their ultimate destination is the Gulf of Alaska,
where they will feed and grow for the next 2 to 3 years. The rate
of mortality drops as the fish increase in size, with predation continuing
to be the primary impact on survival. The remaining progeny of 200
spawners at the end of the first year total 1,265
juvenile chum salmon. These juvenile chum salmon average approximately
11 inches in length and weigh about 0.5 pounds. |
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January-December
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Ocean
Growth - The second year of life is spent in the northeast Pacific
Ocean, as the immature chum continue to feed and grow. Those chum
salmon that remained in nearshore coastal waters migrate to open ocean
waters in the second half of year two. The exact distribution of Washington
chum salmon in the northeast Pacific and the Gulf of Alaska is unknown,
however, it likely varies from year to year depending on environmental
conditions. Mortality rates continue to drop as the fish increase
in size, with losses primarily caused by predation by various fish
species and marine mammals. |
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January-December
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Ocean
Growth - The immature chum salmon continue to migrate, feed, and
grow in the waters of the northeast Pacific. During the year, those
the fish that will mature and spawn at age three begin their migration
back to Washington waters. The chum that will mature in coming years
(as 4- and 5-year old fish) continue their pattern of ocean feeding
and growth. The portion of the progeny of 200 spawners that leave
the ocean during year three total 215 three- year old maturing adults. |
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September-November
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Adult
Return - As the maturing three-year old chum salmon return to
coastal waters they are subjected to low levels of predation mortality,
primarily from marine mammals and large fish species like sharks.
The remaining progeny of 200 spawners entering nearshore marine
waters total 200 three- year old adults.
These chum salmon average about 26 inches in length and average
about 8.2 pounds in weight.
The
chum salmon returning to Washington waters are managed for harvest
by recreational, commercial, and tribal fishers. Only those fish
in excess of the numbers needed for spawning are subjected to harvest.
This example assumes a healthy chum population that can accept a
65% harvest rate. The remaining progeny of 200 spawners after fisheries
total 70 three- year old mature adults.
A small percentage of the remaining fish will suffer pre-spawning
mortalities from causes such as predation or environmental conditions. |
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November-December
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Spawning
- Most fall chum spawning occurs during November and December.
Females select preferred sites for spawning and begin the construction
of the nest or redd by displacing gravel with her body and tail. Males
compete with one another for access to the female. Fertilized eggs
are deposited in multiple pockets within the redd over a span of several
days. When the redd is complete the female will guard the site until
she weakens and dies. Males continue to compete for mates until they
die. The spawning process averages about 10 days from start to finish.
The progeny of 200 parent spawners that successfully complete spawning
in the third year total 60 three- year old spawners. |
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January-December
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Ocean
Growth - The remaining immature chum salmon continue to migrate,
feed, and grow in the waters of the northeast Pacific. During the
year, the fish maturing at age four will begin their migration back
to Washington waters. Those chum that will mature as age-five fish
continue to feed and grow in the northeast Pacific. The portion of
the progeny of 200 spawners that leave the ocean during year four
total 465 four- year old maturing adults. |
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September-November
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Adult Return
- As the four-year old fish enter coastal waters they are subjected
to predation mortality by marine mammals and some large fish species.
The remaining progeny of 200 spawners entering nearshore marine
waters total 430 four- year old adults.
These chum salmon average about 28 inches in length and average
about 10.4 pounds in weight.
Those fish in
excess of the numbers needed for spawning are harvested by recreational,
commercial, and tribal fishers at a 65% harvest rate, suitable for
a healthy chum population. The remaining progeny of 200 spawners
after fisheries total 150 four- year old mature
adults. A small percentage of the remaining fish will suffer
pre- spawning mortalities from causes such as predation or environmental
conditions.
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November-December
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Spawning - The four-year old chum spawners enter their natal
stream and complete the spawning act as described above for the age-three
fish. Typically, the four-year old fish make up the majority of the
spawning population. The progeny of 200 parent spawners that successfully
complete spawning in the fourth year are 130
four- year old spawners. |
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January-October
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Ocean
Growth - The remaining immature chum salmon continue to migrate,
feed, and grow in ocean waters. During the year, the final group of
fish to mature begin their migration back to Washington waters. The
portion of the progeny of 200 spawners that leave the ocean during
year five total 35 five- year old maturing adults. |
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September-November
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Adult
Return - The remaining fifth year fish return to coastal waters
and are subjected to limited levels of predation by marine mammals
and large fish species. The remaining progeny of 200 spawners entering
nearshore marine waters total 30 five- year
old adults. These chum salmon average about 29.5 inches in
length and average about 11.8 pounds in weight.
Managed
fisheries for recreational, commercial, and tribal fishers will
harvest those fish in excess of the numbers needed for spawning
at a 65% harvest rate. The remaining progeny of 200 spawners after
fisheries total 12 five- year old mature adults.
A small percentage of the remaining fish will suffer pre-spawning
mortalities from causes such as predation or environmental conditions. |
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November-December
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Spawning
- The
five-year old chum spawners enter their natal stream and spawn as
described above for the age-three fish. The five-year old chum spawners
typically make up less than 10% of the spawning population, and
very rarely a sixth year fish returns. The progeny of 200 parent
spawners that successfully complete spawning in the fifth year total 10 five- year old spawners.
At
the conclusion of spawning by the five-year old spawners, the cycle
has been completed. The progeny of the original 200 parent spawners
returned as three-, four-, and five-years old fish and spawned,
starting new generations of chum salmon. In total, 200 fish successfully
returned to their streams and spawned, replacing their parents and
renewing the life cycle. |
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This
timeline followed the life history of the progeny of 200
chum salmon spawners. The 100 female
spawners in the original population had a potential of 300,000
total eggs for deposition in the stream gravels. After mortalities
during egg deposition and the period of incubation, a total of 23,400
fry emerged from the gravel and migrated to saltwater. At
the end of the first year of feeding and growth in estuaries and
marine waters a total of 1,265 juvenile chum
salmon remained. The second year of life was spent feeding
and growing in the northeast Pacific Ocean. During the third, fourth,
and fifth years of life, individual chum salmon began to mature
and return to Washington waters. Over the three years a combined
total of 715 maturing adults returned
from the ocean. Of this total, 660 adults survived to enter nearshore marine waters, 232
mature adults remained after fisheries, and a total of 200
chum salmon survived to successfully spawn. Over the three
years of return, 60 three- year old, 130 four-
year old, and 10 five- year old chum salmon returned to their
natal streams, successfully spawned, and then died. These spawners
replaced the original 200 parent spawners,
and renewed the chum salmon cycle of life.
Parker,
R.R. 1962. A concept of the dynamics of pink salmon populations,
p. 203-211.. In Wilimovsky, N.J. (ed.), Symposium on pink salmon.
H.R. MacMillan Lectures in Fisheries. U. Brit. Columbia, Vancouver.
Pratt, D.C. 1974. Age, sex, length, weight, and scarring of adult
chum salmon (Oncorhynchus keta) harvested by Puget Sound commercial
net fisheries from 1964 through 1970. Wash. Dept. Fish. Suppl. Prog.
Rept. 78 p.
Salo,
E.O. 1991. Life history of chum salmon (Oncorhynchus keta), p. 231-309.
In Groot, C. and L. Margolis (eds.), Pacific Salmon Life Histories.
Univ. B.C. Press, Vancouver, B.C., Canada.
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