PROGRESS MEMORANDUM, FISHERIES
NUMBER 2
RESEARCH DIVISION
Oregon State Game Commission
'I
.
j
THE NATURAl REARING OF JUVENilE
SAlMONIDS IN IMPOUNDMENTS, 1961-66
...
r
THE NATURAL REARJNG OF JUVENILE
SALMONIDS IN IMPOUNDMENTS
by
Robert L. Garrison
Oregon State Game Commission
Research Division
Oregon state University
Corvallis, Oregon
August 21, 1967
T.I\BLE OF CCNTENTS
Page
I . St1nu:na. ey • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • . • • • . . • • •
1
II. Introduction. . • • • . • . • • . . . • . . . . • • • . . • • • • • • • • . • . • . . . . . . . . . • • . . .. • . . .
2
III. Methods and
r ..
DJa. terials.
••••. ••••. •••••••. •• . . . •••••••••••••••••••.
2
Rearing ponds ••••••••.•••••••••••••••••.••••••••••••••.••• , • • • •
2
Medco pond ................................................... .
2
Hemlock Meadow-s Pond. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
4
'Ml.istler 1 s Bend Pond.. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
4
Li.nt Slough • • • • • • • • • • • • • • • • • .• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
4
Limnology of the rearing ponds •••••••••••••••••••••••••••••••••
5
Chemical characteristics of the water and soil ••••••••••••••
5
&linity •••• ·• •••••••••••••••••••••••••••••••••••••••••••••••
8
Pllotosynthesis mtes •••.•••.••..••••••••••••••••••••••.•••••
8
Experimental populations and results, descriptions of experimenta 1 populations • • • • • • • • • • • • • . • • • • • • . • • • • • • • . • • • • . • • • • • • • • • • • 10
............................................ 10
Pond A• ..................................................... 14
Medco Pond ••••••
Ponds C, D, and E ••••••••.•••••••••••••••••••••••••••••••••• 15
Hentl.ock Meadows • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 16
\VIlistler ' s Bend. • • . • • • • • • • • . • • • • • • • • • • • • • • • • • • . • • • . • . • • . • . . . 16
Lint Slough. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • . • • . • • • • • 18
Population estimates •••.••••••••..•••••••••••••••••••••.••••••• 19
IV. Discussion ••••
................................................... 24
Growth. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 24
Quality of the environment •••••••••••••
.....................
25
Ti.m.e · o-f stocking. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 29
Page
Density. • • • • • • .. • • • • • • • • . • • . • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • •
29
Fertilization. • . . . . • . • . • • • . • . . . . • . • • . • • . . . • • . . . . . . • . . . . • . • .
34
.................................
35
Size of fish stocked...... • • . • • • . • • • • • • • • • • • • • . • • • • • • . • • • • • •
35
...............................
39
Survival ra. tes ••••••••••••.•.
Predation and competition •••
.................................
Chemical pollution •••••••••.•••• .................... .. .....
Stratification ••••••••.•••
40
41
Sa.ltVJater sllr'V"ival ra. tes. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
41
Yield ••••••••••• , • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
41
Freshwater production ••
....................................
Medco production. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
42
Whistler's Bend production .•..•••••••••••••••••.•••••••••••
42
Ss.ltwater production.... . • . . • • • • . • • • • • • • • • • • • • • • • . • • • . • . • • •
4.4
Adult returns ••••.•..•••.••.•••.•.•.••••.•••••.••.•.••••••••••
SUinm.er steelhead returns.. . • • . • • • • • • • • • • • . • • • • • . • • • • • • • • • • •
46
Spring chinook. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • . • •
49
............................................
49
Coho returns. ·••
Criteria for the construction of a natural rearing pond....
52
Considerations for the operation of a natural rearing pond....
53
LIST OF TABLES
Table
1.
2.
Page
Seasonal range of selected chemical characteristics of
Medco and Whistler's Bend ponds...............................
5
Trace element analysis of Medco Pond and fuiley Creek,
Augu.st 21, 1964. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
J.
Soil analysis of Medco and
Bend ponds ••••••.•••••••
·7
4.
Experimental populations of salmonids reared in impoundments..
11
5.
Resul.ts of na.tural rearing....................................
12
v~istler's
6. Fish harvested from natural rearing ponds ••.•.••.•••••.••••••• 13
7.
The daily mortality rates for Populations 2, 27, and 28.......
21
8.
Estimated marked summer steelhead returns for the Rogue
Rl..ver in 1965.................................................
47
The percentage of marked summer steelhead returning to the
Rog11e Ri.ver in 1965 . . • . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . .
47
9.
10.
The percentage of marked summer steelhead returning to the .
North Umwua Ri.ver. . . . . . . . . . • . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . . • . 48
11.
The average length of coho returning to Lint Slougn in 1965...
51
LIST OF FIGURES
-.
..
Page
Figure
1.
Med. co Pond. . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.
Lint Slough. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
3.
Photosynthesis rate measurements at Medco Pond ••••••••••••..••.
9
4.
The average lengths and weights of steelhead from Medco Ponds
C, D, and E.................................................... 17
5.
Population estimates for Population 2 •••••••••••••••••••••••••• 22
6.
Population estimates for Population 27 •••••••••••••••••.••••••• 22
7.
Population estimates for Population 28 ••••••••••••••.•••••••••• 23
8.
The growth rate of summer steelhead reared in !1edco Pond I. •••• 26
9.
The growth rate of summer steelhead reared in Medco Pond II. •.• 26
10.
The growth rate of summer steelhead reared in Hemlock Meadows •• 27
11.
The growth rate of spring chinook reared in Whistler's Bend... • 27
12.
The growth rate of salmonids reared in Lint Slough ...•••••••••• 28
13.
The average weight of summer steelhead released from Medco
Pond plotted against the surviving density ••••••••••••.••••••.• 31
14.
A comparison of coho growth rates from Lint Slough, Lint Creek
and Drift Creek . .....................•.......... .• . . . . . . . . . . • . . . 33
15.
16.
A comparison of salmonid growth rates from three methods of
rear1ng. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . 36
The size of steelhead fry in relation to survival rates in
Medco Pond. • • • • . • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 36
:.
...
~
--
17.
The survival rates of 2-year-old steelhead reared in Medco
Ponds C, D, and E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
18.
The returns of marked summer steelhead in the Rogue and Umpqua
rivers in relation to size at release ••••••••••••••••••.••••••• 50
19.
The percentage of male and female coho salmon in 1-pound size
groups returning to Lint Creek in 1965 ••••••••••••••••••••••••• 50
IMPOUNDHENT STUDIES
Robert L. Garrison
SUMMARY
The influence of density, time of stocking, fertilization and the
environment on the growth, survival and yield of salmonid fry reared in
freshwater impoundments and a brackish water slough are discussed.
Suggestions are offered for consideration in the construction and operation
of a rearing pond for salmonids.
A limited freshwater supply permitted partial control of dissolved
oxygen, temperature and salinity in the rearing ponds.
Dra ining the im-
poundments permitted evaluation of survival and yield.
Fry grew best vvhen stocked in the early spring.
Growth rate was
influenced by rearing density, pond fertility, and survival rat e .
Extreme
t emperatures, low dissolved oxygen and high salinities inhibited growth
and reduced survival.
Growth and yield were increased by fertilization.
Two races of summer steelhead (Salmo gairdnerii) had different growth
rates at a similar stocking density.
Coho produced a yield of 134 pounds
per acre in two months of rearing in brackish water.
Coho smelts released
after three months of rearing in brackish water returned as adults of
normal weight at two years _of age.
The release of larger steelhead smelts
from freshwater ponds produced a higher percentage of adult return.
Accidental flooding of the brackish-water pond permitted establishment of competitors and predators that reduced growth and survival of
salmonids.
_.
2.
INTRODUCTION
The purpose of the impoundment rearing project is to determine the
feasibility of raising juvenile salmonids from fry to smolt in a controlled
aquatic environment utilizing the available natural food supply.
The natural rearing of surruner and winter steelhead, spring and fall
chinook and coho salmon has been tested.
This report discusses the factors
that influence growth, survival and yield in one experimental saltwater and
three freshwater natural rearing impoundments operated by the Oregon Game_
Commission.
Criteria f0r construction and c-o nsiderations for tlae operation
of a success£Ul
natural · r~a~ing
pond are
disc~ssed.
HETHODS AND NA TERIALS
Rearing ponds
The bodies of water studied include the Medco, 1rJhistler 1 s Bend and
Hemlock
~~eadows
freshwater impoundments and the Lint Slough saltwater
lagoon.
Nedco Pond
Nedco Pond (Figure 1) is a 70.5-acre former log pond leased from the
~1edford
Corporation.
It is located on fuiley Creek, midway between Butte
Falls and Prospect, Oregon in the South Fork Rogue River drainage at an
elevation of 3,051 feet.
The bottom consists of a clay soil with 14 inches
of black silt covering a layer of woody debris.
Potamogeton pusillus,_f.
natans, Elodea canadensis, and Chara sp. are present in the shallow areas.
A 24-inch drain pipe with gate valve was installed at the 22-foot
depth in the dam to permit complete draining.
A concrete trap and holding
pen were constructed below the drain tube to collect all migrants.
).
MEDCO
Figure l .
Hedco Pond .
POND
4.
In June, 1963, an upper dike was completed to divide the pond in two sections;
Pond I has an area of 23.6 acres with a maximum depth of 8 feet and Pond II
has an area of 46.6 acres with a maximum depth of 22 feet.
A series of
water supply ditches was constructed to permit the introduction of water
from the . Btick Creek-Jeppert Creek spring area and Daile,y Creek into the
ponds at several locations.
The ditch system permits partial control of
dissolved oxygen and water temperature during the summer.
In June, 1963, six small ponds were constructed on the east shore of
Pond II.
The small ponds that are used for pilot experiments are identified
as A, B, C, D, E, and F, and range from 0.12 to 0.14 acres each.
Hemlock Meadows Pond
Hemlock Meadows is a high, cold, alpine type · of pond.
surface area of 26 acres when full.
It has a
It has a maximum depth of 50 feet.
A leak in the bottom lowers the level of the pond during the summer to
approximately 11 surface acres.
Fall runoff refills the pond.
It is
located at 4,700 feet elevation and is covered with ice most of the winter.
The pond is poor in fish food production.
vJhistler 's Bend Pond
The impoundment site, originally a sheep pasture, is located on a
bluff above the North Umpqua River, 14 miles east of Roseburg.
It has a
surface area of 35 acres with a maximum depth of 18 feet, and is filled
with runoff water from a small drainage basin of about one square mile.
No summer water supply is available (Cache, 1964) •
.__,
Lint Slough
The Lint Slough brackish water impoundment is located near lrJaldport
5.
on Alsea Bay (Figure 2).
The 35-acre pond has a maximum depth of 6.5 feet
and an average depth of 3 feet.
It utilizes freshwater from Lint Creek
and saltwater from Alsea Bay that can be mixed gradually to change the
salinity concentration during the rearing period.
A vertical and hori-
zontal gradation of salinities occurs with freshwater on the surface near
the creek inlet and the higher salinities on the bottom near the bay.
Spirogyra sp., Melosira sp., and Enteromorpha tubulosa exhibit peaks of
abundance during the rearing
~cle.
The most abundant fish food organisms
were Corophium spinicorne, Neomvsis spp., Exosphaeroma spp., Polvdora spp.,
and chironomids.
Acartia clausi was present but never in large quantities
{Lyford, 1966).
Limnology of the rearing ponds
Chemical characteristics of the water and soil
Chemical characteristics are presented in Table l.
Table l
Seasonal range of selected chemical characteristics
of Nedco and Uhistler's Bend ponds
Tempera- Dissolved
oxygen
ture
OF
(ppm)
Pond
Total
dissolved
Alkasolids
linity
mg/1
pH
(ppm)
Medea U1ax.)
Medco (Min.)
82
32
14
10.0
0
7.3
v!nistler Is (Max.)
whistler's (Min.)
82
32
14
0
9.8
7.4
Total
hardness
mg/1
co 2
60
30
80
22
80
36
1. 50
46
25
94
32
52
46
1. 25
0.30
The seasonal range of water temperatures was from 32° to 82°F.
0.26
In
Lint Slough a saltwater lens on the bottom was 4° to 5°F warmer than the
fresher surface layer.
6.
Figure 2.
Lint Slough
7.
Dissolved oxygen values up to 14 ppm were recorded.
Anaerobic
activity lowered oxygen values on the bottom to zero on some occasions.
Phosphate measurements from 0.024 to 0.006 milligrams per liter and
nitrate from 0.15 to 0.04 milligrams per liter were recorded at
~~istler's
Bend.
1rtlater samples from Nedco Pond and Il:!.iley Creek were analyzed for
trace elements (Table 2).
The pond water contained 40 percent less phosThis-s~ggested
phate than the stream.
that phosphate was being depleted
and could be limiting photosynthesis.
Table 2
Trace element analysis of Hedco Pond and D3.iley Creek,
August 21, 1964
..
Magnesium Manganese
(ppm)
(ppm)
Boron
(ppm)
Copper Zinc Molyb- Phos- Ni(ppm) (ppm) denum phate trate
Medco Pond
3.3
0.01
0.05
0.041 0.08
0.05
0.06 0.1
Iailey Creek
4.6
0.01
0.02
0.006 0.03
0.05
0.10 0.1
A soil sample from Medco and
~ vhistler
's Bend showed sufficient phos-
phorous present in the soil but it was not directly available to the plants
(Table 3).
Crude pulverized phosphate rock vJas dissolved in sulfuric acid
and introduced into Medco Pond in 1964 and 1965, providing phosphate that
plants could assimilate.
Table 3
Soil analysis of Medco and Whistler's Bend ponds
QH
Phosphorous
lbsLacre
Potassium
lbs Lacre
Calcium Nagnesium Boron
lbsLacre lbsLacre ( m2ml
Medco
6.2
32
546
2,360
696
o. 5
1rf uistler' s
6.1
16
211
10,840
4,512
0.5
8.
Ss.linity
Salinity levels up to 32 p3.rts per thousand were recorded in Lint
Slough.
The normal procedure was to fill the pond with freshwater, then
gradually increase the salinity throughout the rearing period.
and horizontal gradation of salinities occurred.
A vertical
Freshwater existed on the
surface at the upper end and seawater (32 ppt) occurred on the bottom near
the bay.
A large area of the pond was maintained below the· tqlerance level
·of the salmonids. ·Fish could ·seek the sal:\nity _they preferred.
a cdimation increasea their salinit.Y tolerance..
p3. tt ern of salinities eXist ed ln "Lint Slough.
~ ~ording
to the tolerance of the fi sh.
Gradual
No regular s easonal.
The salinities weve r egula t-ea
Fish food organisms wer e most
abundant at concentrations between 4 arili l6 _parts _p:e.r thousand.•
Photosynthesis rates
Figure 3 presents the photosynthesis estimates of primary production
from Nedco for 1961, 1962, and 1963 (open symbols) when no fertilization
took place.
Phosphate and sodium molybdate were added every other day for
a six v1eek period, the last two weeks in June and four weeks in July, 1964.
Photosynthesis estimates were significantly higher for the fertilization
period than for similar estimates in 1961, 1962, and 1963.
Photosynthesis
dropped to the level of the three previous years after fertilization.
;;
The
use of fertilizer in October caused another increase in photosynthesis not
as high as that occurring in June and July but significantly higher than
rates in previous years.
the summer of 1965.
The pond was fertilized with
on~
phosphate in
Photosynthesis rate measurements in June were higher
than 1961, 1962, and 1963 but not as high as 1964.
dropped to the level of the non-fertilization years.
In July, production rates
This suggested that
9.
3.0
R EARI N G CYCLE
1 961-62
0
~
1962-63
0
1 9 6 3 -6 4
1 9 6 4- 65
19 65 - 66
A
•
2.5
•
>-
<l: 2.0
0
A
~
~
0
1.5
A
o
'{)A
V1
2
<l:
0:::
e
A Jt..
0
e
A
o A
!:-.
A
!:-.
A
~
e
A
1.0 -
<.9
~ ~oA
0
6
0
0 .5
~~
(5
I\
6
!:-.
0
0
0.0
6
0
t,
0
e o.}'o
A
0
~~
[] .J
n
6
-----L....__t _....J.__
JULY
Figure 3.
AO
0
0
SEPT
NOV
J AN
MAR
Photosynthe sis rate measurements at 1-'Iedco Pond .
6
10.
phosphate alone was not the only nutrient limiting photosynthesis, but
sodium molybdate was essential for the increased production.
Experimental populations and results
Descriptions
of · exp~rimental
pppulations
The 35 experimental populations of salmonids reared in the impoundments
between 1961 and 1965 are described in Table 4.
The primary variables tested were: density, size at stocking, fertilization, freshwater versus saltwater rearing, species, and pond type.
The
influence of each variable on the growth and survival rate of fish and the
yield from their environment was tested.
Nedco Pond
Population 1 consisted of 113,600 unfed Rogue summer steelhead fry
stocked at a density of 1,600 fish per acre.
An attempt to destroy a
population of bullhead with rotenone, before the steelhead were stocked,
failed.
A large number of catfish survived and spawned which produced young
that ccmpeted with small salmonids.
The 8 tons of catfish harvested were
responsible for the low steelhead survival of 1.2 percent.
Three treatments of rotenone, wade before Population 2 was stocked,
controlled the catfish.
drained in Hay, 1963.
Only 65 catfish were recovered when the pond was
Over 79.2 percent of Population 2 survived after
the catfish were reduced (Table 5).
The total harvest for Medco decreased from 109 pounds for Population
1 to 97 pounds per acre for Population 2 (Table 6).
increased from 1 to 77 pounds per acre.
The yield of migrants
11.
Table 4
Experimental populations of salmonids reared in impoundments
Population
group
number
-
~
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
-:<origin:
-.-
Race
and
specj es
~~(R)S. st.
(R)S.st.
(R)S.St.
(R)S.St.
(R)S.St.
(U)S.St.
(R)S. St.
(R)S.St.
(R)S.St.
(U)S.St.
(U)S.St.
(R)S. St.
(U)S.St.
(U)S.St.
(R)S.St.
5 spp.
Kokanee
Coho
F. Chinook
Sp. Chinook
S. steelhead
(R)S.St.
(R)S. St.
(R)S.St.
(U)S.St.
(U)S. St.
(U)S.St.
(U)S.St.
(U)Sp.Ch~
(R)Sp.Ch.
(A) Coho
(A) Coho
(C)F.Ch.
(A) vJ.St,
(A)Coho
R
U
A
C
= Rogue
= Umpqua
=Alsea
= Columbia
Fish
per
Brood
year
61
62
63
63
63
63
63
64
64
64
64
65
65
65
65
65
65
65
65
64
64
64
64
64
65
61
62
63
64
63
64
64
65
65
Pond
Hedco
Ned co
Medco
Nedco
Hedco
I•:edco
hedco
Hedco
Jviedco
Med co
r,iedco
Hedco
Eedco
Medco
Medco
J!Iedco
:tv:edco
Medco
I
II
II
II
F
I
I
II
II
I
I
II
II
A
A
A
1~1edco A
Hedco A
Nedco A
Nedco C
Hedco D
l [edco E
Hemlock
Hemlock
VJhistler IS
~vhistler 1 s
tJhistler 1 s
VV
histler IS
Lint
Lint
Lint
Lint
Lint
Weeks
pmmd
fed
3,649
504
1,011
1,011
146
150
1,011
2,275
263
1,057
324
2,600
1,594
1,5 94
2,600
0
6
3
3
2,600
428
370
606
21
23.7
22.0
24.5
619
293
3,338
1,530
660
888
890
305
1,325
101
1,120
Density
per
a ere
1,500
2,310
2,722
3,896
"Runts"
3,896
"Runts"
3,896
2, 93 9
3
2
5,000
8
5,000
2
3,000
8
3,000
2
2,000
2,000
2
2,000
2
2
2,000
2,247
6
158
670
670
670
79
1 year old 1,000
1 year old 1,500
l year old 2,000
8
800
10
2, 743
0
2,000
2
3,000
1,235
2-4
1,800
2-4
2
2,600
8
6,139
2
7,000
16
8,300
2
20,000
12.
Th.ble 5
,.
Results of natural rearing
Population
group
number
1
2
3
4
5
6
7
8
0
/
10
11
.-
~
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Fish
Fish liean
per
length
pound (em)
harvested
liean
weight Percent
(grams) survival
324
300
315
315
265
260
315
304
287
287
280
365
365
342
323
17.3 13.5
23.5 12.9
22.2 12.8
29.6 ' 11.6
32.9 11.2
36.0 10.8
17.4 13.6
21.6 12.7
15.7 14.6
15.6 13.8
12.0 15.8
16.8 14.2
15.3 14.6
15.0 14.8
16.3 13.7
25.1
19.2
20.4
15.3
13.8
12.9
26.0
21.0
28.8
29.9
37.7
26.9
29.5
39.0
27.8
345
374
374
374
300
383
383
383
315
310
329
331
285
295
90
60
82
23.8
10.3
19.3
23.1
6.8
9.2
8.4
9.5
13.7
90.0
10. 8
46.7
12.3
8. 5
23.0
30.0
36.0
12.6
16.0
13.0
12.3
18.7
16.7
17.2
16.9
14.7
8.4
15.8
10.1
14.7
16.2
12.3
10.9
9.8
19.0
44.0
23.4
19.6
66.7
49.3
53.8
47.7
33.0
5.0
42.0
9.7
36.8
53.5
19.6
14.9
12.4
Iays
reared
1.2
79.2
50.8
64.0
44.4
55-5
42.0
29.6
34.0
29.3
27.9
39.9
41.8
62.0
55.6
65.2
80.0
56.4
71.8
62.4
80.0
57.0
23.0
9.0
47.4
37.5
11.3
37.4
30.3
13.0
34.8
65.6
7.0
Surviving
density
fish per
acre
20
1,813
1,382
2,293
2,293
2,293
1,230
1,025
1,025
903
903
693
693
1,175
1,175
1,467
1,467
1,467
1,467
1,467
1,467
616
349
189
366
969
185
1,129
290
237
1,003
4,027
467
13.
Table 6
Fish harvested from natural rearing ponds
Rearing
cycle
Pond
--
Medea
1961-62
Ned co
1962-63
Medea I
1963-64
Medea II
1963-64
Medea F
1963-64
Medea I
1964-65
Medco II
1964-65
Medco I
1965-66
Medea II
1965-66
Medco A
1965-66
Medco C
1965-66
Medco D
1965-66
Medco E
1965-66
Hemlock
1964-65
Hemlock
1965-66
Whistler's 1961-62
Whietler 's 1962-63
'rJhistler 's 1964
Whistler's 1965
Lint
1964
Lint
1965
Lint
1965
Fish harvested
Eer acre~
Total Competitors Migrants
~Eounds
Species
S. steelhead
S. steelhead
S. steelhead
S. steelhead
s. steelhead
S. steelhead
S. steelhead
S. steelhead
S. steelhead
5 species
S. steelhead
S. steelhead
S.steelhead
S. steelhead
S. steelhead
S. steelhead
S. steelhead
Sp. chinook
Sp. chinook
Coho
F. chinook
Coho
109
97
93
96
91
74
88
79
121
114
86
61
40
47
58
64
88
75
40
164
108
.20
32
22
20
32
32
36
43
20
20
20
20
1
77
61
74
71
42
56
43
78
94
66
41
30
34
35
60
30
27
11
17
24
29
28
45
12
134
28
30
20
Remarks
Catfish
Pond divider
washed out
Flooded
Flooded
2-year-olds
2-year-olds
2-year-olds
Stratification
Stratification
Stratification
Polliwogs
Flooded
Flooded
Population 3 consisted of 64,200 Rogue surrmer steelhead stocked at
2,722 per acre in Pond I.
Population 4 consisted of 5,000 Rogue summer
steelhead stocked at 3,896 per acre in Pond II.
Populations 5 and 6 con-
sisted of 13,000 and 50,400 "runts 11 , graded out as small fish from the
Rogue and Umpqua races of summer steelhead.
per pound when steel ed in Pond II.
They averaged 146 and 150 fish
The dividing structure between
Ponds I and II washed out during the 1964 draining operation.
Populat ions
3, 4, 5, and 6 beca;rte mixed but were separated by analysis of the marks
-.
recovered.
The total harvest for the 1963 rearing period was 93 and
96 pounds per acre for Ponds I and II.
14.
Population 7 consisted of a pilot fertilization experiment in
Pond F, utilizing 3-week-fed Rogue summer steelhead fry.
Populations 8, 9, 10, and 11 represent fish stocked in Nedco in
1964.
Population 8 contained 106,900 Rogue summer steelhead fry fed
2-weeks before being stocked in Pond I at a density of 5,000 per acre.
Population 9 consisted of 5,000, 8-week-fed Rogue summer steelhead stocked
in Pond I.
Population 10 contained 133,900 2-week-fed Umpqua summer
steelhead stocked in Pond II at a density of 3,000 per acre.
Population
11 consisted of 5,000 8-week-fed Umpqua summer steelhead fry, that weighed
324 fish per pound when stocked in Pond II.
Ponds I and II were fertiliz ed
with phosphate and sodium molybdate during 1964.
A large loss of experi-
mental fish occurred during the December 24, 1964 flood at Medea Pond.
The total weight of fish harvested for 1964 was 74 and• 88 pounds per acre
in Pond I and II respectively.
The yield of migrants was 42 and 56 pounds
per acre.
Populations 12, 13, 14, and 15 consisted of 2-week-fed summer steelhead
fry stocked at a density of 2,000 per acre for the 1965 rearing period.
Population 12 contained 45,700 Rogue fry stocked in Pond I.
13 contained 5;000 Umpqua steelhead stocked in Pond I.
tained 95 ,4oo- -u~Equa fry- stocked in .Pond II.
Population
Population 14 con-
Both ponds were fertilized
with phosphate.
The total harvest was 79 and 121 pounds per acre in
Ponds I and II.
The yield of Digrants was 43 and 78 pounds per acre.
Pond A
Population 16, a composite of Populations 17 through 21, contained
20 kokanee, 85 coho, 85 spring and 85 fall chinook fry and 10 sunrner
steelhead yearling stocked at a densit y of 2,247 fish per acre.
The five
15.
groups of salmonids (Populations 17 through 21) were stocked in Pond A
in 1965.
One of the objectives of the experiment was to test the effect
of different food habits on total yield.
of 2,247 fish per acre.
Pond A was
stocl~ ed
at a density
The 1,466 fish per acre harvested represented
a survival of 65 percent and produced 94.3 pounds per acre.
Kokanee, principally a plankton feeder,
158 fish per acre.
was stocked at a density of
They had a survival of 80 percent and grew from 0.17
to 19 grams in 345 days but contributed only 5.3 pounds per acre to the
total harvest.
Coho, stocked at a density of 670 fish per acre, grew from 1.06 to
44 grams in 374 days and had a 56 percent survival rate.
Coho produced
36.7 pounds of migrants per acre.
Seventy-two percent of the fall chinook stocked at a density of 670
fish per acre survived ·and grew from 1.22 to 23.4 grams.
They produced
24.9 pounds of smolts per acre.
The spring chinook had a survival rate of 62 percent and grew from
0.75 to 19.6 grams, producing 18 pounds per acre.
Steelhead yearlings reared a second year at a density of 79 fish per
acre grew from 21.5 to 66.7
gra~ s.
They had a survival of 80 percent
and produced a weight of 9.3 pounds per acre.
The total yield of 94 pounds per acre from Pond A suggests that a
larger harvest of salrnonid.s is possible if several species with different
food habits are stocked together.
Ponds C, D, and E
Populations 22, 23, and 24 consisted of yearling steelhead stocked
in Ponds C, D, and Eat densities of 1,000, 1,500, and 2,000 fish per
acre.
They produced 66, 41, and 20 pounds of migrants per acre but
16.
showed a net yield of only 21, minus 26, and minus 62 pounds per acre.
The yearlings were divided into one centimeter size groups, marked and
reared during 1965.
No significant difference occurred in the overall
growth rate of Populations 22, 23, and 24 but a significant difference did
occur in the growth rate of the different size groups.
Figure 4 presents
the average length and weight of fish stocked and harvested for the three
populations.
They grew from an average weight of 8.4 to 42.8 for an
increase of 34.4 grams and from 9.7 to 16.0 for an average increase in
length of 6.4 centimeters.
Fish stocked in the 18 to 19 centimeter size
group lost weight from an average of 58.5 to 55.8, for a loss of 3.6 grams.
There was no change in average length for the 18 to 19 centimeter fish.
Hemlock Meadows
Population 25 contained 20,000 Umpqua summer steelhead stocked at a
density of 800 fish per acre.
They produced 27 pounds of migrants per
acre.
Population 26 consisted of 71,394 Umpqua summer steelhead fed 10 weeks
at a density of 2,743 per acre.
They numbered 293 per pound when stocked
and grew to 90 per pound during the 329 days of rearing.
Whistler's Bend
Population 27 contained 72,6oO unfed Umpqua summer steelhead stocked
at a density of 2,000 fish per acre.
They produced 17 pounds of migrants
per acre and had a survival of 11.3 percent.
The smelts averaged 10.8 fish
per pound.
Population 28 consisted of 110,000 2-week-fed Umpqua summer steelhead
fry stocked at a density of 3,000 per acre.
Twenty-four pounds of migrants
and 34 pounds of polliwogs per acre were harvested in
~~y,
1963.
17.-
----- -
"AdRP AN
1/)18
0::
w 16
1w
2: 14
z 12
W1Q
60
50
1/)40
2:
<!
0:: 30
(9
.,
F,'!
.
...,
.·
~:,:.,
1
,.,
:-:
>
_r ·},
9
"?)
,,
LP
AdRV
'!
11
1-YEA '"<
r
OLD n
2-YEAk O L C'
1!1
.,
~~
"
'-
~
~
~:
'
h
"A
l!'i·
~
t."
'
I
~
""
J J
'
''
,.
·.
..~.
·'
,~
~
.,
.,
''
H.
r
ri .
10
·.
I
11
(
r
12
.
13
I
_l
I
14
15
16
CEN TI METER
Figure 4.
RP
J
~
!1
,.
20
10
LV
RV
RVLV Ad
I
1-
u
D
I
-----
SIZE
The average lengths and weights of
C, D, and E.
I
17
GROUPS
18 -19
~te· ~~e~d· from
Medco Ponds
18.
Population 29 contained 45,000 Umpqua spring chinook stocked at a
density of 1,235 fish per acre.
They produced 29 pounds of migrants per
acre.
Population 30 contained 63,500 Rogue spring chinook stocked at a
density of 1,800 fish per acre.
Over 60 pounds of bullfrog polliwogs
and 28 pounds of migrants per acre were harvested in,November, 1965.
Lint Slough
Population 31 contained 86,500 coho stocked in Lint Slough at a
density of 2,6oo fish per acre.
After 90 days of rearing 26,000 coho
smelts (45 pounds per acre) were marked and released.
The non-smelts were
left in Lint Slough and reared through the summer and fall.
December 24, 1963 permitted many of the fish to escape.
A flood on
Only 3,479 coho
remained when the pond was drained in January.
Population 32 contained 184,200 8-week-fed coho stocked at a density
of 6,139 fish per acre.
Population 32 averaged 30 fish per pound after
60 days of rearing and had a survival rate of 65.6 percent.
produced 134 pounds of migrants per acre in two months.
Population 32
Ma.ny small · _ · · .
stickleback and predators were also harvested.
Population 33 contained 209,500 Columbia River fall chinook stocked
at a density of 7,000 fish per acre.
A flood in January permitted the
entrance of many predatory cutthroat trout and coho yearlings.
The 12
pounds of migrants per acre that survived the 82 days of rearing accounted
for only 7.0 percent of the fry stocked.
19.
Population 34 contained 250,100 Alsea winter steelhead stocked at a
density of 8,300 fish per acre.
of them to escape.
No
est~ate
A flood in December, 1965
all~1ed
most
of survival and growth rate was made.
Population 35 contained 600,300 coho stocked at a density of 20,000
fish per acre.
A flood occurred on Varch 12, 1966 that eliminated the
experiment
Population estimates
:.
The size of a fish population and the rate and cause of mortality
are important in pond management.
The size and approximate number of
fish to be produced can be controlled if the primar,y production and
mortality rate is known.
The first step necessar,y to increase fish production at Medea was
to reduce nortality.
The inlets and outlets were screened and the pre-
dators reduced in 1962.
A higher survival resulted for 1962-63 than for
the 1961-62 rearing period.
The next step was to deterrnine the shape of the mortality curve in
order to obtain clues that would lead to the prevention of additional
population losses.
Since the number of fish stocked and harvested was
known, a mark and recover,y prograrr was conducted to obtain estimates of
the population size at intervals throughout the rearing period.
of fish were captured with an Oneida trap net.
Samples
The fish were anesthetized
vdth NS-222 and marked by removal of one or a combination of fine.
The
fish were allowed to recover in a live box for 48 hours before release in
the center of the pond.
and marking was noted.
Any immediate delayed mortality from handling
20.
Bailey's mark and recover.y formula was used:
N=
N(C=l)
R+l
where,
N = the population estimate for the marks released
M = the number of
~~rks
released
C = sample size or catch
R = the number of liJarks recaptured
.:
Use of the formula is justified only when the following assumptions
are met:
1. Tha. t marked fish suffer from the saa e natural mortality as
unmarked fish.
2. That marked fish are as vulnerable to sampling as unmarked fish.
3. That marked fish become randomly mixed with unmarked fish.
4.
That all marks are recognized and recovered.
5. That only a negligible amount of recruitment occurs.
Assumptions 2, 3, 4, and 5 were met for Populations 2, 27, and 28.
The trap net captures a random sample of fish from the same year class.
Previously-trapped fish might have tended to avoid the trap at later
sampling periods.
The final sample for each population consisted of
all the fish captured as the pond vtas drained.
moved with rotenone.
Residual fish were re-
All of the fish were examined for marks.
screened inlets and outlet prevented
recr~itment.
The
Regeneration of a few
excised fins occurred but identification was possible by their small size
and imperfect shape.
The assumption that the marked fish suffered the same mortality as
the unmarked fish r:tight be questioned.
Any immediate mortality caused by
21.
handling and fin clipping could be disregarded since the fish were held
48 hours after marking.
The difference in the daily mortality rates
might be the result of increased predation on the marked fish.
Marking
might have reduced ability of the fish to escape from predators.
Fish
marked by removal of pectoral or pelvic fins showed a higher mortality
rate than fish with only the adipose removed (T-able 7).
Table 7
=
The daily mortality rates for Populations 2, 27, and 28
Po:Eulation
27
28
Mark
2
Ad
RV
LV
RP
RVAd
LVAd
RVLV
RPLV
0.17
0.07
0.30
0.22
0.39
0.16
0.28
0.27
0.43
0.47JJ
0.891
0.36
0.39
0.22
0.37
1/Runts introduced into the pond from a hatchery were subjected to greater
intraspecific predation
Population estimates are presented in Figures 5, 6, and 7.
Final
estimates (solid circles) were made using the marks recaptured during
draining.
The sample size for the final estimate consisted of the entire
remaining population of fi sh.
The solid squares represent the known
population sizes at stocking and draining.
Population estimates
(~olid
~ade
using the marks recovered on draining
circles) should produce the best mortality curve.
Errors from
non-random mixing of the marked fish 't.vith the unmarked population, and
non-random sampling, were eliminated.
The principle source of bias
appeared to be between the rates of mortality experienced by each group
22.
I
'
r
I
I
I
I
0
350
if)
0
z300
<C.
iJ)
:::>
0
I 250
......
•
0
:~:'
•
iJ)
200
lL
•
150
0
0
MAY
. -
--
JULY
SEPT
•
0
I
'--s
•
n
I
NOV
JAN
"
MAY
MAR
- -
Figure 5.
Population estimates for Population 2.
70 114 •
iJ)
I
I
I
I
I
I
60
0
~50
0
iJ)
:::>
040
I
......
i
I~30
0
iJ)
-
I.L
0
20
••
10
••
0
0
MAY
0
JULY
SEPT
NO/
JAN
- -- -- · -
Figure 6.
-
Population estimates for Population 27
•
MAR
MAY
23.
160
I
I
I
I
I
I
_,
0
0
z~ 120
(j)
gO
0
0
0100
I
8
r~
I
80
(j)
-I.L
0
8
~
0
0
60
0
••
•
:J
0
8
8
•
8
0
0
0
40
0
•
0
0
-
•
20
I
MAY
SEPT
JULY
·· -
Figure
I
•
140
(j)
I
--
NOV
JAN
·-
7. Population estimates for Populati on 28 .
\
MAR
----
MAY
-
-- .
-
24.
of fish.
curve.
Estimates from Population 27 produced a reasonable mortality
Populations 2 and 27 indicate that the mortality was higher on
the marked fieh.
Table 7 shows that the particular fin mark used could
effect the mortality rate.
The increased mortality rate caused a high population estimate.
Bias
in population estimates made from trap sampling {open circles) could be
caused by the marked fish staying in the vicinity of release and not
mixing thoroughly with the unmarked population.
Such action would cause
non-random sampling.
Limits exist on the reliability of the intermediate population
estimates.
DISCUSSION
Growth
The growth of juvenile salmonids in a natural aquatic environment
1r1as dependent on the stocking density, amount of available food, presence
of predators, race and species of fish reared, time of stocking, size of
fry stocked, quality of the environment and length of the rearing pond.
Growth, the result of a balance between the energy expended by the fish
and the energy obtained in its food, was influenced by the temperature of
the environment.
At low temperatures, when the metabolism of an organism
is reduced, less food is consumed, and less energy is available for growth.
Fish under stress at a high temperature experience difficulty regulating
body functions and have less energy available for growth.
salmonids grew best at temperatures between 50° to 70°F.
The juvenile
Density, the
presence of predators, and the time of stocking indirectly influenced the
amount of food available to the fish.
25.
Quality of the environment
Temperature, dissolved oxygen, and salinity might have an influence
on gro"rth rate of young salmonids.
Low temperatures, associated vfith
90 days o.f ice cover, reduced the growth of fish reared in Hedco Pond
in 1965-66.
Figures 8 and
Hedco Ponds I and II.
9 illustrate the growth of steelhead in
Slow growth occurred for Population 14 during
the period of ice cover from December 15 to
}~rch
13.
Ice cover also occurred at Hemloclc Leadows during the winter of
1965-66.
Figure 10 illustrates the growth of summer steelhead in
Population 26.
They averaged 6.75 grams on November 16.
The average
weight decreased during the winter to 5. 03 grams on Nay 13 as a result
of the stocking density (2, 743 fish •per acre) and a low food potential
during the long period of ice cover.
A problem of
~tratification
occurred at k.ihistler's Bend with a warm.
layer of water on the s urface and a cold layer, low in oxygen, on the
bottom.
The living space vJas reduced as the two layers gradually approached
each other.
The fish were under stress and showed little growth when the
layers overlap.
Considerable mortality occurred at this time.
Figure
11 illustrates the growth of spring chinook in vJhistler 1 s Bend during
1964 and 1 965 .
The slow growth in June, July, and August was caused by
poor wat er quality during stratification.
Winter steelhead that averaged 4.35 graEs were stocked in Lint
Slough on August 30, 1965 at a density of 8,900 fish per acre (Figure 12).
An attempt was made to lower water temp eratures in Lint Slough during September
through the introduction of a large volume of salt I·Jater.
were under stress in the higher salinities.
The steelhead
They became black , emaciated,
26.
28
24
Vl
~
20
<!
cr
<.9 16
~---~
:r:
12
<.9
w 8
~
4
JULY
Figure 8.
SEPT
NOV
MAR
JAN
MAY
The growth rate of summer steelhead reared in Medea Pond I
32
28
1./)
~ 24
<{
cr
(.') 20
\
........ 16
•'
I
(.')
-
w 12
~
s
4
o~~~~~---L--~~--~--~~---L--~~~~
MAY
SEPT
MAR
NOV
JAN
MAY
JULY
Figure 9.
The growth rate of summer steelhead reared in Medea Pond II.
27.
28
24
Vl
L
20
<{
cr
(.!)
16
~---~
12
I
(.!)
w 8
~
4
0
-MAY
Fi gure 10 .
JULY
SEPT
I\OV
JAN
MAR
MAY
The growth rate of summer steelhead reared in Hemlock Meadows .
50
Vl
~40
<{
0:::
<.9
~---~ 30
I
<.9
w 20
~-
10
O~d=~~I-~--L--L~L--L~--~~--~~
JAN
Figure 11 .
MAR
MAY
JULY
SEPT
NOV
JAN
The growth rate of spring chinook reared in Whi stler's Bend .
28.
20
~
.. . .
F. CHIN-.r0K
COHU
w.
STEFLHEAD
__ .___
t
'
.
~
{9
/
33,f 31 ...
I
.
I
34 ....
8
I
II'
/
/I
w
/~
~
'
4
~
/
J
"·'
...
··········•·
OL_~~~~--~~-L~--~~-L~~
JAN
Figure 12.
MAR
MAY
JULY
SEPT
NOV
JAN
The growth rates of salmonids reared at Lint Slough.
29.
and grew slowly during the late summer and fall.
7.5 grams after 50 days of rearing.
They averaged only
Low flow in Lint Creek and a leak
at one of the outlets prevented addition of freshv-rater until the fall
=
rains.
Growth was slow throughout the winter.
The fish averaged only
11.2 gran,s on January 20 after 143 days in the pond.
Time of stocking
Time of stocking as it affects the growth of juvenile salmonids is
closely tied to the amount of food available.
Food production began
increasing in March, April, and May, reached
peak in June a-nd July, t hen
tapered off in August and September.
fall and winter was lm.r .
&
Food production during the late
Photosynthesis was reduced by cloudy weather,
short days, turbid water and cold temperatures.
in M'a rch and April.
Growth increased again
Figures 11 and 12 illustrate the growth of chinook,
coho and steelhead stocked at different times throughout the yea r .
Spring
chinook stocked in t'Jhistler 1 s Bend in January and February had a slow
initial growth rate (Figure 11) which increased around the middle of
lif.arch.
Fall chinook stocked in Lint Slough on January 27 also showed
slow growth until }'Jarch (Figure 12).
Coho stocked in Lint Slough on
Larch 20 began to grow rapidly as soon as they were stocked.
Sununer
steelhead stocked in Medco in June and July also showed rapid growth
(Figures 8 and 9).
Density
An increase in density caused a decrease in the growth of salmonids
and conversely, a decrease in density subsequently caused an increase
in growth.
A comparison of the surviving densities in Table 5 demon-
strates the influence of population size on growth.
For example,
30.
steelhead from Populations 12 and 13 that averaged 26.9 and 29.5 grams,
had a surviving density of 693 fish per acre while fish from Population
3 that averaged 20.4 grams, had a surviving density of 1,282 fish per
acre.
The increased density produced slower growth but a larger yield.
Populations 12 and 13 produced only 43 pounds of migrants per acre
while Population 3 yielded 61 pounds.
The larger number of fish
utilized the available food more efficiently.
Such might not always
be true since survival rates can be influenced by factors that are not
apparent.
The average weight of summer steelhead released from :Medco
were plotted against their surviving density in Figure 13.
As expected,
the average size of fish recovered was swaller when the surviving densities
were high.
Populations 12, 13, 14, and 15 were reared during 1965-66.
group of fry was fed two weeks prior to stocking.
a density of 2,000 fish per acre.
summer of 1965.
The ponds were fertilized during the
lations 14 and 15 were reared in Pond II.
steelhead.
All were stocked at
Populations 12 and 13 were reared in Pond I.
Umpqua surrmer steelhead.
Each
Popu-
Populations 13 and 14 were
Populations 12 and 15 were Rogue summer
The principal variables between Populations 12, 13, 14, and
15 were the river of origin. .and the pond in which they were reared.
An
analysis of covariance was made on the vreights of surviving steelhead
from the four populations.
between the two races.
A significant difference in growth occurred
No difference
in growth occurred in the two
ponds.
Populations 8, 9, 10, and 11 were 1964 brood swmner steelhead.
Populations 8 and 9 were Rogue fish stocked at 5,000 fry per acre in Pond
I.
Populations 10 and 11 were Umpqua fry reared in Pond II at a density
3L
:
..
-· --I
(/) 38 f2:
<(
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-
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30 1- 013
10
~
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-
•7
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03
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14
I
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14
18
SURV IVING DENSITY,
Figure 13 .
4
.5
f-
6
-
/
.>
-· F I S H /
-
,6.0
26
22
ACR E
X
10 0
The average wei ght of summer steeThead released from Medco
Pond pl otted against the surviving density .
----------
32.
of 3,000
of 1964.
to the acre. The ponds were fertilized during the summer
fi~h
A flood permitted the escape of many fish and reduced the
survival rate.
Most of the growth occurred prior to the flood.
The
difference in the size of smolts released demonstrated the influence of
density and size of fry stocked on growth rate.
Populations 8 and 10
consisted of fry fed two weeks prior to stocking.
confisted of fish fed eight weeks.
Populations 9 and 11
The difference in the size of fry
stocked was the primary variable between the four populations.
There was
a significant difference between the growth rates of the Rogue fry in
Pond I and the Umpqua fry in Pond II.
of density.
The difference bejng the result
The larger fry, fed eight weeks produced a significantly
larger migrant.
~Populations
3~896
· 4, 5, and 6 from the 1963 brood were stocked at
fish per acre in Pond II.
Pond II was not fertilized during 1963.
Population 4 consisted of ungraded Rogue fry fed three weeks.
The primary
variables were the presence of two races, Rogue and Umpqua, and the snall
graded fry of Populations 5 and 6.
Samples from Populations 5 and 6
indicated a difference in growth rate between the Rogue and Umpqua races
stocked as fmall graded fry.
The 15.3 and 13.8 gram fish from Populations
4 and 5 showed that growth of the non-gra ded Rogue fry was faster than
for the small graded Rogue fry reared in Pond II.
A comparison of growth rates for coho reared in three different
environrnents is illustrated in Figure 14.
The average weight of coho
from Populations 31 and 32 reared in Lint Slough at densities of 2,600
and 6,139 fish per acre are compared in Figure 14 to the growth rates
of wild coho reared in Lint Creek and Drift Creek.
Drift ' Creek is a
tributary to Alsea Bay entering the estuary approximately 4 miles
33.
::.
COMPARISON
OF
COHO
GROWTH
20
(1)16
LINT CREEK C G H :J
~
<!
0::
(9
12
~--~
I
(9
8
w
WILD
~
D f'< IFT CREEK
4
90
180
270
AGE,
DAYS
360
450
\
Figure 14.
A comparison of coho growth rates from Lint Slough, Lint Creek
and Drift Creek.
34.
above Lint Creek.
~fild
coho from Drift Creek reached a size of 6. 6
grams in 450 days while wild fish in Lint Creek were 20 grams after
330 days of rearing.
Coho stocked in Lint Slough, Population 31, at
2,600 fish per acre averaged 19.7 grams after 90 days.
reared 52 days averaged 14.9 grams.
Population 32
The abundant supply of food in
Lint Slough and the 60° to 70°F temperature were the primary causes for
the accelerated growth rates.
The food potential in Lint Slough is several
the three freshwater ponds.
t~nes
greater than in
Fall chinook stocked in Lint Slough on
February 27, 1965 at a density of 7,000 fish to the acre averaged 36 to
the pound in 82 days.
Coho 1rrere stocked in Lint Slough on February 14, 1966 at a density
of 20,000 fish per acre.
Flooding prevented an accurate estimate of
total yield and survival to be made, but prior to the loss, the growth
rate appeared to be norw.al.
The maximum stocking dens ity that will
produce coho smelts in Lint Slough has not been reached.
The length of
the rearing period and the size of smolt desired govern the density
which is dependent upon available food and concequent growth rate.
For
example, fall chinook, reared for approximately 90 days, could be stocked
at a higher density than 1rrinter steelhead that normally require a full
year of rearing.
Fertilization
Fertilization of Medea produced a significant increase in the fish
food available, permitting a higher stocking density and causing a
faster growth rate.
Hedco Pond was divided into two sections in 1964.
Pond I had a
35.
stocking density of 5,000 Rogue and Pond II 3,000 Umpqua summer steelhead per acre.
The growth for the first 180 days of rearing in 1964 in
Pond I was similar to the growth rate for the same period in 1963 at
approximately one-hal.f the stocking density. · The growth in Pond II at
3,000 fish to the acre, a density ccmparable to former years, was approximately 100 percent greater.
Figure 15 depicts growth and compares the Lint Slough coho reared
in salt water at 2,600 fish to the acre, to steelhead stocked in Hemlock
Neadows at 800 fish per acre, and the steelhead stocked in Ned co at a
density of 3,000 fish per acre for the 1964 fertilization period.
growth rates from the three rearing methods were similar.
The
Therefore it
appears that the size of migrants desired can be regulated by manipulating
such environmental factors as density and pond fertility.
Survival rates
The survival of salmonids in natural rearing ponds was influenced by
the size and condition of fish stod:ed, the presence of predators and
competitors, floods, stratification and chemical contamination. The
survivals in the freshwater impoundments ranged from 0.2 to 80 percent.
Size of fish stocked
Larger fry generally produced a higher survival rate.
In Figure 16
the survival rate of steelhead in Populations 2, 3, 4, 12, and 14 from
Medea are plotted against the size of fry stocked.
Populations 1, 5, 6,
7, 8, 9, 10, 11, 13, and 15 were affected by a variable other than
stocking size and were not considered.
when unmarked Populations 2, 3,
4, 12, and 14 were considered, a higher survival occurred among the
larger fry.
36.
28
24 -
20
V)
~
<t
a:::
(916
1-:-~
12
I
<9
w 8
~
4
0~--~--~----~--~----~--~----~--~
0
50
100
150
200
DAYS IN POND
Figure 15.
_J
A comparison of salmonid growth rates from three methods
of rea ring .,
80
~
>
a::: 70
::>
V)
.2
.3
SIZE
.4
OF
.6
.5
FRY, GRAMS
--
Figure 16.
----
~-
The size of steelhead fry in relation to survival rates in
Medco Pond.
. )
--
. .
··---- ...
37.
A comparison was made between Rogue steelhead Populations 8 and 9,
reared at a density of 5,000 fish per acre in 1964-65.
variable was the size of fry stocked.
Populations 8 and 9 were stocked
at 2,275 and 263 fish per pound respectively.
December, 1964.
The primar,y
The pond was flooded in
It can be assumed that the same proportion of the two
}t>pulations left the pond during the flood.
They produced smelts that
averaged 21 and 28.8 grams with survival rates of 29.6 and 34 percent, the
larger fry producing bigger migrants with a higher survival rate.
A similar comparison was made between Populations 10 and 11, the 1964
Umpqua steelhead stocked in Pond II at 3,000 fish per acre and at sizes
of 1,057 and 324 fish per pound.
Populations 10 and 11 produced survival
rates of 29.3 and 27.9 percent, respectively, with smelts that averaged
29.9 and 37.7 grams.
The larger Umpqua steelhead fry also produced bigger
smelts but the smaller fry produced a slightly higher survival rate.
Regeneration of the marked fins for fish in Population 11 might have caused
a low estimate of survival.
Populations 4, 5, and 6 demonstrate the difference between survival
rates of non-graded and small, graded fish.
Non-graded Population 4 had
a 64 percent survival rate while small, graded Populations 5 and 6 had
survival rates of 44 and 55 percent.
The survival of 2-year-old steelhead, from Populations 22, 23, and
24 are presented in Figure 16.
Stocking densities of 1,000, 1,500 and
2,000 fish per acre produced survival rates of 57, 23, and 9 percent,
respectively, showing an inverse relationship between stocl ·ing density
and survival rates. Figure 17 presents the range and mean survival for
1-cm size groups.
The larger size groups had higher survivals at a density
of 1,000 fish per acre.
The survival rates of the size groups at densities
of 1,500 and 2,000 fish per acre were similar.
38.
AdRP
AN
D
100
RVLV
Ad
GROUP
A
22
0
23
24
0
MEAN •
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u
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9
10
12
13
CENTIMETER
11
14
15
16
17
18
19
SIZE GROUPS
Figu re 17 . . The survival rates of 2- year- old steelhead reared in
Medea Ponds C, D, and E.
39.
Spring chinook, Populations 29 and 30, stocked in vfuistler's Bend
at 660 and 888 fish per pound survived at rates of 30.3 and 13 percent.
The larger chinook fry produced the best survival.
survival influenced the size of smolts produced.
The difference in
Populations 29 and 30
produced migrants that averaged 12.3 and 8.5 per pound respectively.
The
summer stagnation problem previously mentioned also contributed to the
high mortality rates.
Predation and competition
Aquatic and avian predators were responsible for a large part of the
fry mortality.
Competition reduces the available food while limited
growth caused the fingerlings to be vulnerable to predation for a longer
period of time.
Population 1 produced approximately 8 tons of bullhead
catfish that ranged from 2 ounces to 4 pounds.
Competition with the
small catfish and predation by the adults resulted in a 98.8
mortality in Population 1.
perc~nt
An intensive rotenone treatment in 1962
reduced the catfish and a survival of 79 percent occurred for Population 2.
Bullfrogs preyed on the salmonids in the freshwater ponds.
Approxi-
mately 80 percent of the bullfrogs collected contained one or two steelhead.
One 4-inch bullfrog had the tail of a 6-inch steelhead protnuding
from its mouth.
Food utilized by competitors removed part of the energy
that would otherwise have been available to the salmonids.
Table 6
presents the weight of competitors and migrants compared to the total
harvest from the rearing ponds.
Residual salmonids that stayed in the impoundment a second year were
a serious predator.
The 1966 draining of Medea Pond I resulted in the
capture of 54 yearling steelhead up to 40 centimeters in length.
Population
40.
estiwates indicate that a drop occurred in the size of Populations 12 and
13
ear~
in the season.
A similar drop was not apparent in Populations
14 and 15 in Pond II where only seven large 2-year-old steelhead were
captured.
Survivals in Pond I were 39.9 and 41.8 percent while in
Pond II they were 62 and 55.6 percent.
The stickleback was the primary competitor in Lint Slough.
Young
of the year enter the impoundment through the screens with the salt water.
Three to four months after the slough has been treated with rotenone, the
sticklebacks become serious competitors.
Herring, sea perch, and flounder
are also competitors and predators on the fry.
Floods that occurred
during the rearing of Populations 31, 33, 34, and 35 pern1itted the entrance
of many aquatic predators and caused a large loss of fry.
The slough
flooded two days after 210,000 fall chinook of Population 33 were stocked.
Only 7 percent of the chinook were harvested 82 days later.
A total of
776 yearling coho and 70 large cutthroat was captured when the slough
was drained.
Predators and the escapement of chinook during the flood
were responsible for the low survival rate.
Stratification
Low dissolved oxygen and high temperature stratification caused the
low salmonid survival in Whistler's Bend.
Survivals of 11.3 and 37.4
percent for the Umpqua steelhead reared at Whistler's Bend were
significantly lower than the 55.5, 41.8, and 63 percent survivals for
steelhead reared at
~edco.
Populations 10 and 11 survived at rates of
29.3 and 27.9 percent in Medco for the flooded 1S64-65 rearing period.
Population estimates for groups 27 and 28 indicated the number of fish
rapidly decreased at Whistler's Bend when stratification occurred during
41.
the summer.
The mortality rate diminished in the autumn and winter after
the fall turnover.
Spring chinook Populations 29 and 30 were large in the
spring but declined rapidly during the summer.
The poor year-around water
supply that permitted summer stagnation was the basic reason for the slow
growth and low survivals at Whistler's Bend.
The pond was mixed with
an air lift in 1962 (Oregon Game Commission Research Division, 1963 Report).
Water was pumped from the North Umpqua River to cool and aerate the pond
in 1963 and 1964 and the layers were mixed by pumping in 1965.
All three
methods failed to maintain an environment of high quality through the
summer.
Chemical pollution
Whistler's Bend was contaminated in 1963 with a chlorinated hydro- · .· ·
carbon that caused a mortality of 99.8 percent of the 70,000 summer steelhead stocked.
The spraying of dieldrin for insect control was the sus-
pected cause of pollution.
Saltwater survival rates
The annual winter floods reduced survival rates of salmonids reared
in brackish water at Lint Slough.
Flooding occurred when a strong on-
shore wind pushed a high tide into the bay and prevented adequate runoff
after a heavy rain.
The result was a loss ef experimental fish and the
introduction of predators.
survivals.
As a result, Populations 31 and 33 had low
No survival estimates were made for Populations 34 and 35
which were also flooded.
Population 32, the only group of salmonids
reared in Lint Slough which was not flooded, had a survival of 65.6 percent.
Yield
Yield is referred to here as a measurement of the productive capacity
42.
of a natural rearing impoundment in terms of the harvest of migrants and
competitors.
produced.
The yield of migrants is a measure of the weight of fish
The net yield is the difference between the weight of fish
stocked and the standing crop harvested.
When fry are stocked, yield
measurements for the rearing ponds are essentially the same as standing
crop since all of the fish are removed when the ponds are drained, but
when fingerlings are stocked there is a considerable difference.
The
yield of migrants is dependent upon the number of competitors, amount
of fish food, rate of photosynthesis, amount of nutrients available in
the water, rate of nutrient turnover in the plants, animals and algae,
and the water quality.
Freshwater production
Yield measurements were taken for Medco, Whistler's Bend and Hemlock
Meadows ponds.
Total production estimates were made for all groups of
salmonids reared at Nedco and for the 1961 and 1962 cycle of steelhead
reared at Whistler's Bend.
Yield estimates are presented in Table 6.
Medco production
The 1961-62 rearing period at Medco produced 109 pounds per acre,
made up of 108 pounds of bullhead catfish and one pound of steelhead.
The 1962-63 rearing period produced a total of 97 pounds per acre that
included 70 pounds of steelhead and 20 pounds of bullfrogs and tadpoles.
The pond was divided into two sections for the 1963-64 rearing period.
Ponds I and II produced 93 and 96 pounds per acre.
A pilot experiment conducted in Medco Pond F during the 1963-64
season produced a total of 91 pounds per acre that included 20 pounds of
competitors and 71 pounds of steelhead.
~uggest
The large smolts raised in Pond F
that enrichment might improve the growth rate of steelhead.
43.
The total harvest for the years 1961, 1962, and 1963 before Medea
Pond was fertilized remained relatively constant at 109, 97, and 93 pounds
per acre.
Medea was fertilized with phosphate and sodium molybdate for
a 6 week period in June and Jul;y- and 3 weeks in October, 1964.
A
substantial increase in steelhead growth folloHed the fertilization.
Unfortunately a flood occurred in December, 1964 and permitted a loss of
many of the experimental fish.
reduced by the flood.
The 1964 standing crop was obviously
Yields of 74 and 88 pounds per acre from Ponds I
and II included only 42 and 56 pounds of steelhead.
Crude phosphate was introduced three times per week throughout the
summer of 1965.
A heavy mortality occurred shortly after the fry were
stocked in Pond I which was attributed to the presence of a large number
of yearling steelhead that remained in the impoundment.
A harvest of 79
and 121 pounds per acre was produced in Ponds I and II in May, 1966.
The
early mortality of fry was responsible for much of the difference between the 43 and 78 pounds of migrants per acre from Ponds I and II.
The different growth rates in Pond A for kokanee, coho, spring and
fall chinook and steelhead were caused by their food preference and
abundance, their specific optimum temperature for growth, and their
aggressive behavior.
The experiments conducted in Ponds C, D, and E during 1965 tested
the yield of 2-year-old steelhead reared at densities of 1,000, 1,500,
and 2,000 fish per acre.
Pond C, D, and E produced a total of 86, 61,
and 40 pounds per acre and were made up of only 66, 41, and 20 pounds
of migrants.
The net yield for Pond C was 21 pounds per acre while in
C and D a loss of 26 and 62 pounds per acre, respectively, occurred.
The
44.
survival rates were 57, 23, and 9 percent.
The 21 pounds per acre net
yield of 2-year-old steelhead from Pond C was significantly less than
the 42 and 77 pounds from Ponds I and II.
Therefore it would appear
that maximum yield cannot be obtained by utilizing two-year rearing.
The next question then is whether maximum yields of small migrants
produced each year would give a higher return of adults than a lower
yield of larger smolts produced in two years in the large ponds.
This
question is being investigated.
Whistler's Bend production
The 1961 rearing period at Whistler's Bend produced a total of
47 pounds per acre including 30 pounds of competitors and 17 pounds of
migrants.
The low yield of migrants was the result of an 11.3 percent
survival rate.
A higher density and survival rate during the 1962-63
rearing period produced 24 pounds of steelhead per acre.
Stratification
reduced living space throughout much of the summer and was p3.rtially
responsible for the low yields.
Spring chinook rearing experiments at
Whistler's Bend produced totals of 64 and 88 pounds per acre in 1964 and
1965 that included only 29 and 28 pounds of migrants.
polliwogs was also harvested in 1965.
A large crop of
A comparison of the migrants produced
at Whistler's Bend and Medco demonstrates that summer stagnation has a
detrimental effect on yield.
Saltwater production
Good standing crop estimates for saltwater rearing have been difficult to obtain.
Only one is available from the five populations of
salmonids reared at Lint Slough.
An
competitors was difficult to obtain.
accurate estimate of the weight of
Large numbers of sticklebacks
45.
passed over the rotary screens during draining.
The flooding of
Populations 31, 33, 34, and 35 caused a large loss of fish and prevented any estimate of standing crop to be made for Populations 34 and
45.
Population 31 produced 45 pounds of smolts per acre that were re-
leased after 90 days of rearing, and a total harvest of 75 pounds of
migrants per acre.
The flood that occurred shortly after Population 33
was stocked allowed predators to come into the pond causing a mortality
cf 93 percent and a harvest of only 12 pounds of fall chinook per acre.
There were 28 pounds of coho and cutthroat intruders harvested per acre.
Population 32, the 1965 cycle of coho stocked at a density of 6,139 fish
per acre, produced 134 pounds of smolts and only 30 pounds of competitors
per acre in two months.
This amounted to a yield of 67 pounds of
~oho
migrants per acre per month which is outstanding and might only be produced
during the spring and summer when the food potential in Lint Slough is
at its peak.
Only a high density population of either coho or fall
chinook that completely utilized the food potential in Lint Slough could
possibly produce a higher yield.
The salinity and temperature levels
maintained in Lint Slough affected the food potential, and indirectly
the yield, of salmonids.
The most productive period was during the
spring when the impoundment was maintained at salinity concentrations
between 4 and 16 parts per thousand.
A mass mortality of chironomids
occurred when a high concentration of salt water was introduced in
July, 1964.
The large schools of Neomysis sp. that occurred at inter-
mediate salinities were not present at higher concentrations.
Bottom
sample counts of 950 Corophium per square foot have occurred at salinity
levels between 4 and 16 parts per thousand.
Corophium numbers were lower
when the impoundment was maintained at higher salinities.
46.
Adult returns
The success of the rearing program will be measured by the number
of adults that return from the ocean.
The size and quality of smelts
released and the time of liberation are important factors that influence
the adult return.
Summer steelhead returns
A summary of the marked summer steelhea.d returns in the Rogue River
for 1965 are presented in Table 8 as enumerated at the Gold Ray Dam
counting station.
One hundred ninety-four of the 1,447 summer steelhead
that passed Gold Ray Dam in 1965 were examined.
The percentage of marks
that occurred in the sample is presented in Table 8.
Creel checks in the
middle and lower Rogue fishery districts resulted in the examination of
93, and 2,008 summer steelhead, respectively.
It was estimated that 40
percent of the 10,324 summer steelhead caught in the Rogue River in
1965 were taken in the middle and 60 percent in the lower Rogue districts.
The total estimated return of marked summer steelhead in the Rogue
includes an expansion of the marked fish ratio obtained at the Gold Ray
Counting Station and in the catch from the middle and lower river fishery
districts.
The estimated percentages of marked summer steelhead that returned
to the Rogue River in 1965 are presented in Table 9.
The small sizes of
23.5 and 29.6 fish per pound for the 1962 and 1963 brood steelhead released
from Medea produced returns of only 0.018 and 0.07 percent.
Of special
interest is the return of marked adults from Population 6 reared at Medea
in the Rogue River drainage and released in the North Umpqua River.
produced a 0.28 percent return to the Rogue River and a 0.01 percent
They
47.
return to the Umpqua River.
Hatche~
Rogue summer steelhead reared at the Bandon
and released at sizes of 14.8 and 9.9 fish per pound returned at
rates of 0.14 and 0.96 percent.
Table 8
Estimated marked summer steelhead returns for the Rogue River in 1965
Yark or
population
number
2
AdLM
4
. ~
AdRM
Brood
year
Reared
1962
1962
1963
1963
1963
Medea
Bandon
Medea
&ddon
Bandon
Sample size
Hiddle
Gold Ray Rogue
percent
percent
observed in catch
Mean length
Lower
Estimated
in fish
Rogue
percent
total 1/ sampled in
inches
in catch return
5.67
0.50
1.03
5.20
0.50
3.2
1.0
0.0
0.0
4.2
0.2
0.05
0.95
194
93
2,008
226
52
74
75
311
o.o
2.1
18.75
20.00
18.00
21.75
18.00
1/Estimated total return includes the percentage of adults passing Gold Ray
and the percentage of the estimated catch from the Middle and Lower Rogue.
An estimated total catch of 10,324 summer steelhead occurred in 1965, of
which 4,130 or 40 percent were in the Middle and 6,194 percent were
in the Lower Rogue districts.
Yumpqua summer steelhead "runts" reared at Medea (Rogue drainage) were
released in the North Umpqua and returned to the Rogue River.
Table 9
The percentage of marked summer steelhead returning to the
Rogue River in 1965
Mark or
population
number
Brood
year
Rearing
site
Number
released
2
4
6
AdLM
AdRM
1962
1963
1963
1962
1963
Medea
Medea
Medea
Bandon
Bandon
126,949(R)
l00,964(R)
26,850(U)
37,03l(R)
32,290(R)
Size of
migrants
released
12er 12ound
Estimated
return
23.5
29.6
36.0
14. 8
9.9
226
74
75
52
311
Percent
return
0.18
0.07
0.28
0.14
0.96
The return of marked stimmer steelhead to the North Umpqua River is
48.
pres ented in Table 10.
Steelhead reared at 111Jh istler 's Bend from
Population 27 released at 10.8 fish per pound returned at a rate of
6.0 percent.
Steelhead released at 46.7 per pound from the 1962 brood
had only a 0.23 percent return.
The 200 summer steelhead from the 1963
rearing period at Whistler's Bend that survived chemical contamination
-vrere released at 6 fish per pound and produced a 9. 5 percent ret urn.
Summer steelhead reared at the Bandon Hatchery and released at 8.1 and
9.7 fish per pound produced a return of 1.98 percent.
Table 10
The percentage of marked summer steelhead returning to the
North Umpqua River
Hark or
population
number
Brood
year
Rearing
site
27
28
AdRVLVIM
6
AdiM
196is
1962s
1963s
1963s
1963s
1rJhistler 's
l:vnistler 's
VJhistler 's
Hedco
Bandon
Number
released
5,900
39,0001}
1
200
26,850?:./
8,505
73,907
Size at
release
per pound
Estimated
return
10.8
46.7
6.0
36.0
8.1
354
89
19
4
6.00
0.23
9.50
0:01
9.7
1,836
1.98
Percent
return
1/survivors of the 1963 brood summer steelhead reared at Whistler's Bend
when chemical contamination caused a 99.8 percent mortality. The
migrants were released September 11, 1963.
£/survivors of Population 6, Umpqua "runts 11 reared at Medea Pond.
The marked summer steelhead returns in the Rogue and North Umpqua
River are plotted against the size of migrants released in Figure 18.
Summer steelhead smelts, 10 to the pound or greater, produced a higher
return of adults than smaller migrants.
The influence of the size of
migrants released on the percentage of adult return is similar to the
49.
information presented for winter steelhead on the Alsea, Wilson and
Sandy rivers.*
Spring chinook
Spring chinook released from Whistler's Bend will be returning as
adults during 1966, 1967, and 1968 in the North Umpqua River.
A return
of 8 spring chinook jacks was observed at the Winchester counting station
from 13,300 smelts released in November, 1964.
Coho returns
Coho from Population 31, that were reared 90 days in Lint Slough
returned to Lint Creek after 18 months in the ocean.
life
histo~J
pattern was reduced to 2 years.
The normal 3-year
Length, weight, and scale
samples were taken from 85 wild and 147 Lint Slough-reared adult coho at
the Lint Creek trap.
Thirty wild precocious 1963 brood males returned
from 7,777 adipose-marked coho smelts for a jack return of 0.10 percent.
The 55 adults examined from the 465 wild non-marked 1962 brood coho that
returned to Lint Creek had spent 16 months in freshwater and 18 months
at sea.
Three adipose-left pectoral marked precocious males returned
from the 3,479 smelts of Population 31 released in January, 1965, for a
0.08 percent return.
There were 110 males and 34 females from Population
31 that had spent 18 months in the ocean.
The combined total of 552 adipose-right pectoral-left ventral marked
coho taken in the ocean, sport and commercial fishery and those that
returned to Lint Creek produced a 2.12 percent return from 26,000 Bmolts
released.
The bar graph in Figure 19 represents the percentages of male
and female coho in one-pound-size groups for the fish examined in the weir.
~~Fishery
Report No. 5., 1967.
Wagner, H. H., O.S.G.C.
50.
6
1QO
6.0
e 27
3.0
z
cr
:J
1--
w
cr
1.0
1--
A
z
w
u .6
cr
w
Q.
.3
• 6
REARED
WHISTLER S BEN D
e
ME DCO POND
II
BA NDON H ATCHERY t:.
28 0
• 2
t:.
":_,
.1.
0
10
20
30
40
WEI GHT,
Figure 18 .
60
50
70
80
GR AM S
The r et urns of m.ark ed summe r s t eelhead in the Rogue and
Umpqua rivers i n r elation to size at re l ease .
8
(/)
!JJ
~ ---. ~· . 1 [[1JL~1JJJLJ
:
I
24
(/)
w
_j
6 2 63
<l: 18 -
1-
z
BROO D~
D ~ W ILD CO HO
2:
0
12
LINT SLOUGH
COHO
!J.J
u
cr:
w
6
o._
0
..
1
Figure 19 .
2
3
4
W EIGHT ,
PO UN D S
'I"ne pe rc entage of ma J e and f ema l e c oh o sa l mon in 1-pound
s j ze groups rehJr i' i r1g t.o Li nt Creek i n 1965 .
51.
The weight distribution of the wild 3-year-olds and the 2-year-old
Lint Slough coho are similar.
The wild population contained 35 percent
2-year-old precocious males and 65 percent 3-year-old adults.
The weights
of 2-year-old females were comparable to the weights of the 3-year-old
wild females.
The average weight of the 2-year-old Lint Slough males
was less than the wild 3-year-old males but heavier than the normal 2-yearold precocious males (Table 11).
l 3:1 male to female sex ratio occurred
for the fast growing Lint Slough coho and a 2:1 ratio for the
~nld
fish.
Only the faster-growing fish reared in Lint Slough were released after
90 days.
¥~ny
of the slower-growing fish that were not released were
lost in the flood of December, 1964.
It is possible that the process of
marking only the faster-grm1ing fish selected more males and produced the
higher sex ratio.
Table 11
The average length and weight of coho returning to Lint Slough in 1965
Average
Average
weight
length
(pounds) (centimeters)
Group
I. Wild coho
A. Males
3-year-old adults
2-year-old jacks
Total wild males
B. Females 3-year-old adults
58.1
5.67
2.01
44.1
3.84
51.1
8.15
68.1
4.61
58.3
8.55
68.0
II. Lint Slough reared coho (Ad-RV-LM mark)
A. Yales
B. Females
2-year-old
2-year-old
The size of mature female coho was more dependent on the time spent
in the ocean than on chronological age.
The female growth rate in the
52.
ocean was similar regardless of the age the smolts entered the sea.
The
growth rate of the males in salt vater was slower than for the females
of either wild or Lint Slough populations.
Criteria for the construction of . a natural rea·ring pond
Natural rearing of juvenile salmonids can be practical if proper
consideration is given to planning, design and construction of the
impoundment.
A successful rearing pond should be located in a moderate
climate where the heat of summer and cold in winter are not major problems.
The most important requirement is -v.ater of good quality, available
the year around to control the environment within specific physical
limits.
In a rare instance, summer auxiliary flow might not be necessary
but the determination of the need is tailored to physical conditions.
The pond should be situated where a large volume of water can be made
available for rapid filling, but where flood waters which cause high
turbidity and reduce photosynthesis can be by-passed.
A year-around
source of high quality water is necessary to provide good circulation
during the summer stagnation period except in rare instances.
Circulation is the key to good ox,ygen and temperature control.
Small ponds fed by runoff from agricultural land might receive seasonal
water high in nutrients, but contaminated with agricultural chemicals.
A rearing pond should be completely drainable in order to permit
the harvest of fish and aid in the elimination of aquatic predators.
Enumeration of the number and size of smelts produced is necessary to
evaluate production.
Incomplete harvest of migrants might leave residual
predators in the next rearing period.
53.
Aquatic and avian predator control is necessary for highest
efficiency.
Draining the impoundment, poisoning the potholes and screeni ng
all the inlets and outlets will reduce or eliminate the aquatic predators.
Partial control of predatory birds can be accomplished by the use of
scaring devices.
Currently, there are no effective methods for predatory
bird control that do not require a large amount of time and manpower.
A natural rearing pond for purposes of production should be large
enough to produce a significant number of smelts.
Steep banks with at
least 2 feet of water at the shoreline are necessary to prevent the
encroachment of aquatic vegetation and to limit the area available to
wading predatory birds.
Considerations for the:operation of a natural rea~ihg pond
The success of a natural rearing pond is measured by its contribution
of adult fish to the stream.
The adult return is largely dependent on the
size and quality of smelts released.
Since the yield of a pond is usually
relatively constant, the size of migrants is dependent on the density
and survival rate during the rearing period.
Environmental factors
such as temperature, salinity, dissolved ox,ygen, competition, and
predation, affect the growth and survival of the young salmonids.
Time
and size of stocking are also important factors to be considered.
In some instances, higher yields of migrants are possible if artificial enrichment is combined with environmental control and population
manipulation.
No fertilization is necessary for brackish water impoundments that
have a potential for high production.
Post Office Box 3503
Portland, Oregon 97208