Synopsis of Biological Data on the Chum Salmon, Oncorhynchus keta

Table 39.--Estimated mortality for chum salmon
from Hook Nose Creek, British Columbia, during
various life stages (Parker, 1962)
Life history
stage
Egg - fry
Coastal (juvenile)
Pelagic
Coastal ( adults)
Fishing
Total
Months
7
5
34
2
48
Survival
Percent
7 . 8
5.4
56.6
93 . 0
35.0
0 . 08
Instantaneous
mortality
(i) 1
2.55
2.91
0 .57
0 . 07
1.05
7 .15
1 Instantaneous mortality (i) loge (N2iNl)
where Nl and N2 are the numbers <strong>of</strong> fish present
at times 1 and 2.
4.42 Factors causing or affecting
mortality
Egg mortality.-- Most <strong>of</strong> the mortality from
egg fertilization to early fry stage occurs
while eggs are incubating in the gravel. Hunter
(1959), who examined redds in Hook Nose
Creek, British Columbia, found that loss <strong>of</strong>
eggs and a levins was 93.6 and 97.9 percent
in two y ears. Of there losses 95.9 percent
occurred in the pre-eyed stage. In some
southeastern Alaska streams, mortalitybefore
hatching exceeded 93 percent (McNeil, 1962).
Levanidov (1954) found mortality to the alevin
stage to be 70 to 75 percent in the Khor River,
U.S.S.R.
Environmental factors which may influence
egg survival <strong>of</strong> churn salmon are discussed in
alphab etical order.
Ammonia is a metabolic product <strong>of</strong> egg
respiration which has been suggested (McNeil,
1966) as pos sibly reaching toxic concentrations
when the density <strong>of</strong> eggs and larvae is high
and the circulation <strong>of</strong> intragravel water is
poor. Ammonia is the most toxic metabolite
<strong>of</strong> eggs.
Carbon dioxide is another metabolic product
<strong>of</strong> eggs. High levels <strong>of</strong> CO 2 (> 125 mg./ l.
milligrams per liter)) in laboratory experiments
produced mortality <strong>of</strong> developing eggs
by inhibiting the uptake <strong>of</strong> oxygen (Alderdice
and Wickett, 1958). Oxygen uptake was independent
<strong>of</strong> CO 2 below about 125 mg./ l.
The range <strong>of</strong> free CO 2 in spawning gravel
<strong>of</strong> some southeastern Alaska streams ,vas 2 to
24 mg. 1. (Mc eil, 1962). Intragravel CO 2 in
54
some Russian streams reached 25 to 30 mg./ l.
(Levanidov, 1954). CO 2 measured in natural
streams has not been shown to influence egg
survival.
Drought may cause egg mortality directly
by leaving redds dry (Smirnov, 1947; Levanidov,
1954; Neave, 1953) or indirectly by
allowing other mortality-causing factors to
operate. McNeil (1966) and Wickett (1958)
found low oxygen and exceptionally high egg
mortality when stream discharge was low
during and after spawning. Low stream flow
led to poor egg survival <strong>of</strong> the same brood
year (1958) in British Columbia, southeastern
Alaska, and the Amur River (Ricker and
Manzer , 1967; McNeil, 1966; Levanidov, 1964) .
In British Columbia, the poor survival was
attributed to low discharge and high water
temperatures in the fall and in southeastern
Alaska and the Amur River, to freezing at low
wa ter levels in the winter.
Erosion <strong>of</strong> eggs and young fish from the
streambed by floods has long been recognized
as a caus e <strong>of</strong> mortality during incubation
(Neave, 1947; Wickett, 1958; Smirnov, 1947).
In some southeastern Alaska streams (McNeil,
1966), erosion and shifting gravel destroyed
50 to 90 percent <strong>of</strong> eggs and larvae in some
years. Flooding during the last month <strong>of</strong> the
incubation season in Minter Creek, Wash.,
reduced fry survival to less than 50 percent
<strong>of</strong> the expected survival (Smoker, 1956). 11
Freezing during periods <strong>of</strong> low flow can
destroy large numbers <strong>of</strong> incubating eggs.
McNeil (1966) concluded that freezing de ­
stroyed up to 65 percent <strong>of</strong> the eggs in one
southeastern Alaskan stream in 1 year. In
tributary streams <strong>of</strong> the Arnur River in the
U.S.S.R., freezing in some years resulted in
95-percent mortality (Levanidov, 1954). Smirnov
(1947) reported that freezing <strong>of</strong> ,vater to a
depth <strong>of</strong> 1 m. caused complete egg mortality
in other U.S.S.R. streams.
Light is detrimental to churn salmon embryos
which normally develop in total darkness
within the streambed. Direct sunlight is
fatal, according to Disler (1953), and indirect
sunlight slows the rate <strong>of</strong> embryo development
(Soin, 1954). The harmful effects <strong>of</strong> light
decrease as the embryo grows. Soin (1954)
found greater mortality <strong>of</strong> eggs and lower
vitality <strong>of</strong> fry when eggs were incubated in
light than when they were incubated in darkness.
11Smoker, William A. 1956. Preliminary report on
Minter Creek biological studies. Part II. Effects <strong>of</strong>
Minter Creek stream flows on the juvenile production <strong>of</strong>
silver salmon, chum salmon, and steelhead trout. Wash.
Oep. Fish., 12 pp. text, [8 PP.] figs. (Processed.)