Synopsis of Biological Data on the Chum Salmon, Oncorhynchus keta

Survival rates from the egg to fry stage fo r
various types <strong>of</strong> environment are pres ented
in table 37. Survival has usually averaged l e ss
than 10 percent in natural streams; although
it averaged as much as 2 8 percent in the Memu
River, Japan, over 3 years (Nagasawa and
Sano, 1961) • Survival has been increas ed in
natural streams by control <strong>of</strong> stream flo w
(table 37). In Nile Creek, British Columbia,
survival was increas ed from 1.5 to 7.5 percent
after regulation <strong>of</strong> the flow. In the Big
Qualicum River, British Columbia, survival
was increased from 11 to 25 p e rcent.
In Asian hatcheries, egg-to-fry survival has
been about 70 to 90 percent. The rate <strong>of</strong> r e turn
<strong>of</strong> adults from hatchery - releas ed fry doe s not
increase in proportion to the increase in eggto-fry
survival, howeve r. The Japan Fishe ries .
Resource Cons ervation As sociation (1 966) e stimated
that mortality <strong>of</strong> hatche ry fry , f rom the
time <strong>of</strong> their releas e as fry until th eir r eturn
as adults, was about t wice that <strong>of</strong> naturally
produced fry.
Estimates <strong>of</strong> return p e r spawner are gi ven
in table 38 . For central and southeaste r n
Alaska, the estim ate s indicate that r e production
rates hav e declined from about 3 to 4
returns per spawner for 19 20- 29 to about 1.5
to 2 returns per spawne r for 1950-59 . The
return per spawner in the Johnstone Strait
a rea <strong>of</strong> British Columbia was similar to that
i n central and southeaste rn Alaska. Estim ates
for Hokkaido ch u m salm on (Japan Fishe ries
R esource C ons e rvation A ssociation, 1966 ),
including r eturns from artifi cial and natur a l
spawning, a veraged about four r eturns p e r
s pawner for 193 1-49 and inc reased to six
r eturns per spawner in the 1950 1 s. The inc
reas e was attributed to improved hatchery
t echniques.
4.32 Factors t hat affect reprodu c ti o n
Neave (1953) s e parated factors that i nfluence
population levels into three categor i es:
1) compensatory mortality whic h b e comes
elatively heavier as the d ensity <strong>of</strong>the popula ­
tion increases, (2) depensatory m ortality which
b ecomes relatively greater a s th e population
decreases, and (3) extra-pensatory m o r tality
w hich is independent <strong>of</strong> population density.
C ompensatory m ortality occurs prim a rily
during the period <strong>of</strong> reproduction. When a dults
a re crowded in spawning areas, interference
b etween fish may r e sult in egg r etention,
removal <strong>of</strong> eggs fro m the g ravel b y later
spawners, displacement <strong>of</strong> a dults i nto unfavorable
spawning areas, and m ortality <strong>of</strong>
eggs during incubation b ecause o f the inab ility
<strong>of</strong> the streambed environment to meet biological
needs.
51
Depensat o r y mortality, whi ch is inversely
r e l a t ed to population dens i ty , occu rs primarily
during fry migration. Predato rs take a rela ­
tivel y fixed number rathe r than a percentage
<strong>of</strong> do wns tream migrants. Thus , the percentage
morta lity decreases with increasing numbers
<strong>of</strong> f r y migr ants.
Extra-pensatory m ortality may be caused
by fishing and b y e nvironmental conditions such
as extremes <strong>of</strong> stream flow a nd temperature.
The specific effec t s <strong>of</strong> various factors on reproduction
are discu ss e d in section 4.42.
4 . 33 R ecruitment
Historically the s a l m o n fishery has operated
nea r the coast and in r ivers where the fish
are concentrated during their spawning migration.
In addition t o being more easily caught,
the fish have reached their maximum size.
Since 19 52, the J apanese have developed a
h igh-seas fishery which takes maturing fish
several week s b e fore they normally reach
coastal waters ; it a l s o takes some immature
fish. See section 5 . 3 for fishing seasons.
Estimates by Neave (1961) fo r 1936-39 in-
. dicated that the a nnual recruitment <strong>of</strong> chum
salmon to the fis hable s tock was 510, 000
metric tons. T h e annual catch for this period
was e stimated to be 275,000 metric tons.
Recent catch figu res indicate that present
recruitment levels are much lower. From 1961
to 1964, wo rld cat ches <strong>of</strong> chum salmon have
varied fro m a b out 134, 000 to 149,000 metric
tons (Fo o d and Agricultural Organization
[FAO], 1965a).
4.4 Mortality and morbidity
4.41 Mortality
Parke r (1962) esti mated total and instantaneous
mor tality fo r one population <strong>of</strong> chum
salmon throughout its life history (table 39).
Parker states tha t his estimates were based
on assumptions for which little information
was available. Mo r tality was highest (at least
on a per-month basis) during the juvenile
coastal p e r i od, a nd next highest during the egg
to fry stages in f r esh water. Mortality was
much lower in the other life stages.
Mortality for the total marine period <strong>of</strong> life,
including fishing m ortality, was estimated to
range from 97.4 to 99.2 percent for chum
salmon from Hook Nos e C r eek (Hunter, 1959) .
Levanidov (196 4) estim ated total marine and
fresh- water mortality fo r summer r un chum