FISH COMMISSION OF OREGON
Fin& Report
THE DEVELOPMENT AND TESTING OF TECHNIQUES
FOR STUDYING THE BEHAVIOR OF JUVENILE SALMONIDS
IN RESERVOIRS
Lawrence Korn
and
Robert T. G nsoius
This work was contracted with the United
States Fish and Wildlife Service, Bureau of
Commercial Fisheries, and financed by funds
provided under the Salton stall-Kennedy Act.
CLACK MAS, OREGON
JANUARY 1962
Fish Commission of Oregon
Final Report
THE DEVELOPMENT AND TESTING OF TECHNIQUES
FOR STUDYING THE BEHAVIOR OF JUVENILE SALMONIDS
IN RESERVOIRS
Lawrence Korn
and
Robert T. Gunsolus
This work was contracted with the United
States Fish and Wildlife Service, Bureau
of Commercial Fisheries, and financed by
funds provided under the SaltonstallKennedy Act.
Clackamas, Oregon
January 1962
TABLE OF CONTENTS
Page No.
INTRODUCTION
1
LITERATURE REVIEW
2
Equipment and Techniques
Equipment for Direct Observation
2
2
SCUBA
2
Television and Photography
3
Infrared Viewer
4
Equipment for Indirect Observation
Sonar
Equipment for Fish Capture
4
14
5
Gill Net
5
Electric Shock Devices
6
Tow Nets
7
Floating Trap
7
Fake Nets
8
Fishing With Lights
8
Environmental Factors Influencing the Behavior of
Juvenile Salmonids
8
Temperature
8
Light Intensity
9
Water Current
10
Turbidity
11
DESCRIPTION OF THE STUDY AREAS
11
SELECTION OF EQUIPMENT
15
General Operating Equipment
15
Equipment for Direct Observation
15
Equipment for Indirect Observation
16
TABLE OF CONTENTS (cont.)
Page No.
Equipment for Fish Capture
19
Hydrographic Equipment
20
20
RESULTS
20
Equipment for Direct Observation
SCUBA
20
Television Demonstration
40
Equipment for Indirect Observation
*******
40
Sonar
Equipment for Fish Capture
Gill Nets
.
Reservoir Limnology
.
43
71
RECOMMENDATIONS
72
SUMMARY AND CONCLUSIONS
75
ACKNOWLEDGMENTS
77
BIBLIOGRAPHY.
.
.
79
LIST OF TABLES
Page No.
Table No.
1
2
3
4
5
6
7
8
Numbers of Downstream-Migrant Juvenile Salmonids
Emigrating Past Pelton Dam, 1960-61
22
Numbers of Downstream - Migrant Juvenile Salmonids
Emigrating Past North Fork Dam, 1960-61
23
Night Counts of Fish in Selected Areas of Pelton
Reservoir by Snorkel-Equipped Divers, April 18, 1961.
25
Night Counts of Fish in Selected Areas of North Fork
Reservoir by Snorkel-Equipped Divers, April 26, 1961.
26
SCUBA Bottom-Transect Counts of Fish Observed, at
4-Hour Intervals Throughout a 24-Hour Period, Pelton
.
.
Reservoir, May 2-3, 1961.
28
Numbers of Fish Caught in Pelton Reservoir with Gill
Nets, by Species, Net Material, and Mesh Size,
1960-61
53
Numbers of Fish Caught in North Fork Reservoir with
Gill Nets by Species, Net Material, and Mesh Size,
1960-61
54
Gill-Net Catches at 3Hour Intervals Throughout a
24-Hour Period, North Fork Reservoir, March 21 and
22, 1961
71
LIST OF FIGURES
Figure No.
Page No.
1
Location of North Fork and Pelton Dams
13
2
Sonar Apparatus and Mounting AsseMbly
17
3
Mercury Vapor Light and Ballast Lamp Used in Attracting Fish at Night
31
SCUBA Hand Nets Showing Improvements from Left to
Right
35
4
5
6
SCUBA Diver with Hand Net Used to Capture Juvenile
Salmonids
37
Sonar Operation Using a Gill Net as the Target, North
Fork Reservoir
41
7
Schematic Diagram of Gill-Net Suspension Apparatus.
45
8
Portable Gill-Net Suspension Apparatus Used in Fluctuating Reservoirs as Seen from Beneath the Water Surface
49
Monthly Catch Per Net-Day of Chinook and Silver Salmon
and Rainbow-Steelhead Trout, North Fork Reservoir,
1960-61
57
Size Composition of Chinook Salmon Caught in 1 1/8inch Monofilament and Multifilament Nylon Gill Nets,
North Fork Reservoir
61
Size Composition of Silver Salmon Caught in 7/8- and
1 1/8-inch Monofilament and Multifilament Nylon Gill
Nets, North Fork Reservoir
63
Size Composition of Rainbow-Steelhead Trout Caught in
1 3/8-inch Monofilament and Multifilament Nylon Gill
Nets, North Fork Reservoir
65
Mean Length by Time Period of Silver Salmon Caught in
7/8- and 1 1/8-inch Monofilament and Multifilament Gill
Nets, North Fork Reservoir
69
Mean Length by Time Period of Chinook Salmon Caught in
1 1/8-inch Monofilament and Multifilament Gill Nets,
North Fork Reservoir
69
Photometer with Watertight Plastic Case
73
9
10
11
12
13
14
15
ABSTRACT
No pages are
missing. Blank
pages have been
removed.
The Oregon Fish Commission received a contract from the U. S. Fish and
Wildlife Service, Bureau of Commercial Fisheries, under the Saltonstall-Kennedy
Act for a study to develop methods for determining the behavior of juvenile
salmonids in reservoirs. The study, consisting of a literature survey and field
program, was conducted in Felton and North Fork Reservoirs on the Deschutes and
Clackamas Rivers, Oregon, between September 30, 1959 and January 31, 1962.
Pelton Reservoir contains chinook salmon (Oncorhynchus tshawytscha), blueback
salmon (0. nerka), and summer-run steelhead trout (Salmo airdneri); North Fork
Reservoir contains chinook salmon, silver salmon (0. kisutch 1 and winter-run
Equipment tested included SCUBA (self-contained underwater
steelhead trout.
breathing apparatus) for direct observation, gill nets for capture, and sonar
for indirect observation of fish.
SCUBA was tested through a temperature range of 140 to 71° F. and was
useful at Secchi disc readings of 5 feet or greater for both observing
salmonids at night and assisting in the operation of other underwater equipment. Divers observed chinook salmon at Pelton Reservoir and chinook and
silver salmon at North Fork Reservoir in the fry, intermediate, and smolt
stages. Blueback salmon were not observed even though substantial numbers
of hatchery fish were present in Pelton Reservoir. At night the fish were
generally located inshore and close to the bottom, and were easily approached
and captured by divers equipped with lights and specially constructed hand
nets. Fish were seldom seen in reservoirs during the day. The results of an
underwater television demonstration were unsatisfactory. Fish caught in gill
nets were not detected by sonar unless they were closely grouped or over one
foot in length, and moving objects of any size were difficult to track.
Malfunctioning equipment precluded a satisfactory test program.
The nylon gill nets were 75 feet long and composed of five equal
panels 30 feet long and 15 feet deep hung on a one-half basis. Each panel
was of a different mesh size: 5/8-, 7/8-, 1 1/8-, 1 3/8-, and 1 5/8-inch
stretch measure. A gill-netting technique utilizing a portable suspension
apparatus was developed for fluctuating reservoirs which allowed nets to fish
at a predetermined distance below the water surface.
The nets caught fish
in all water conditions encountered except during a Ulothrix bloom. Significant gill-net catches were made at North Fork Reservoir, but similarly designated
mesh sizes of monofilament and multifilament nylon caught fish of different
size compositions. Few salmonids were caught at Pelton, possibly due to crayfish predation. At North Fork, chinook salmon were caught most successfully
by 1 1/8-inch mesh, silver salmon by 7/8-inch mesh, and steelhead trout by
1 3/8-inch mesh. The size composition of silver salmon caught in the 7/8- and
1 1/8-inch mesh of both materials increased with time. Salmonids appeared to
be most vulnerable to gill nets at dusk and dawn.
Observations indicated physical and behavioral changes between seasons
for chinook and silver salmon in North Fork Reservoir. Similar changes were
not apparent for chinook salmon in Pelton Reservoir. Steelhead migrants were
observed at North Fork Reservoir only in the spring. It appeared that the
predator population was large at Pelton and small at North Fork.
THE DEVELOPMENT AND TESTING OF TECHNIQUES FOR STUDYING THE BEHAVIOR OF
JUVENILE SALMONIDS IN RESERVOIRS
INTRODUCTION
Flood control, hydroelectric power, and other wateruse benefits are
derived by impounding water.
Migratory fish inhabiting these waters must be
provided with adequate passage facilities to insure the completion of their
life cycle.
Many obstacles to successful passage are apparent, especially in
the downstream migration of juvenile salmonids.
Artificial outlets for
collecting these fish as they emigrate from reservoirs have met with varying
degrees of success.
One of the most important factors involved in successful
downstream passage from the standpoint of design, location, and operation of a
collection system is the behavior of juvenile salmonids in a reservoir.
The
first requisite of a behavior study is to obtain appropriate equipment and
develop techniques for its application.
The Oregon Fish Commission and the United States
Wildlife
Service, Bureau of Commercial Fisheries entered into a twoyear contract on
September 30, 1959, whereby the state agency would develop techniques for
studying the behavior of juvenile salmonids in reservoirs.
Funds in the
amount of $40,000 were made available to the Fish Commission under the
SaltonstallKennedy Act.
Subsequently, at no additional cost, the expiration
date was extended to January 311, 1962.
The program consisted of two phases:
a literature survey dealing with equipment for observing and capturing fish
and with salmonid behavior; and a field period for selecting, developing, and
testing equipment and techniques.
The reservoirs formed by Portland General Electric Company's Pelton Dam
on the Deschutes River and North Fork Dam on the Clackamas River in Oregon were
selected as the study areas.
Both projects possess upstream and downstream
migrant fish passage facilities.
The use of two work areas provided different
limnological conditions and a variety of wild and hatchery fish for experi
2.
mentation.
The species of anadromous fish included chinook (Oncorhynchus
tshawytscha), silver (0. kisutch), and blueback (0. nerka) salmon and steelhead trout (Salmo gairdneri).
LITERATURE REVIEW
The initial phase of the project was a survey of available literature
dealing with the behavior of juvenile salmonids in reservoirs.
This survey
provided important background information necessary to the procurement of
equipment and to the organization of the study.
general topics:
Emphasis was placed on two
(1) types of equipment for making direct or indirect observa
tions on fish; and (2) behavior of salmonids with respect to lake or reservoir
hydrography.
The more pertinent publications are included in the bibliography;
only those of immediate interest are cited.
Equipment and Techniques
This section of the literature review was directed towards equipment
and techniques used to observe or capture fish.
Many publications describing
studies on fish other than salmonids were included since equipment and methods
used in these studies might have application in salmonid behavior work.
publications examined were grouped into three categories:
The
(1) equipment for
direct observationsSCUBA, television, photography, and infrared viewer;
(2) equipment for indirect observation--sonar; and (3) equipment for fish
capture
gill nets, electric shock devices, trawls or tow nets, trap nets,
and fyke nets.
Equipment for Direct Observation
SCUBA.
Since World War II SCUBA (selfcontained underwater breathing
apparatus) has been widely used by sport and commercial divers and recently
has spread to fisheries research.
The Scripps Institution of Oceanography
made diversified use of the aqualung in studies on the ecology of kelp beds,
fish populations, observations on underwater gear, and geological mapping
3.
(Bascom, 1953).
Limbaugh (1957) studied the effect of waste disposal on
marine biota in California.
In Alaska2 divers observed the feeding and
reproduction activities of king crabs (Paralithodes camtschatica) held in
large undersea pens (Anon., 1960).
Spawning sockeye (blueback) salmon
were observed in Central Lake, Vancouver Island, at depths of 40 to 70
feet (Boyd, 1959).
Hassler and Villemonte (1953) found diurnal variation
in the schooling habits of yellow perch (Perca flavescens) in Lake Mendota,
Wisconsin.
Thomson (1957) observed and identified several species of fish
present in Michigan lakes which were undetected by gill nets, seines.
rotenone, and angling.
The use of SCUBA to gather quantitative data shows promise.
Brock
(1954) estimated the total weight of certain species of reef fish counted
An
along 500-yard bottom transect lines in the Pacific Ocean off Hawaii.
estimate of the fish population in a Maryland lake was based on dead fish
counted along survey lines after rotenoning (Walker, 1955).
Thomson (1957)
obtained some favorable results by comparing SCUBA counts with gill-net
catches of warm water fish.
Aleem (1956), Bardach (1959), and Boyd (1959)
also reported quantitative data on fish populations and other aquatic animals.
Thus far, diving has been limited generally to depths of 200 feet or
less due to the danger of nitrogen narcosis and the bends.
Special tech-
niques recently enabled divers to reach a depth of 700 feet (MacLeish, 1961).
Long (1960) reported a new invention called the diving saucer which was
designed by Cousteau and can reach a depth of 1,000 feet.
Television and Photography.
Louis Boutan invented the first successful
underwater photographic apparatus (Reighard, 1907).
The subsequent develop-
ment of remote-controlled underwater photography enabled scientists to take
photographs of the ocean bottom to depths of 18,000 feet (Cross, 1954).
The
advent of closed- circuit television after World War II increased the opportuni-
4.
ties for underwater observation.
Taylor (1953) in a comparison of three
methods of direct observation indicates that television has greater versatility than remote-control photography but, in some respects, less versatility than a diver, who can use photography for permanent records.
Cross (1954) describes four types of photosensitive tubes used
commonly in television cameras: image Orthicon, Iconoscope, image Iconoscope,
The image Orthicon camera showed better light-gathering
and Vidicon.
qualities than the Vidicon in a demonstration of the two at Woods Hole
Oceanographic Institute (Wilson, date unknown).
Currier, Schultz, and Salmon
(1953) used an image Orthicon camera to observe sticks, stumps, rocks, and
lake trout eggs to depths of 100 feet in a Canadian lake.
observations.
Turbid Water hindered
In a laboratory prototype study involving the use of television
in a large concrete tank, an 18-inch cod was identified at 16 feet in 73
per cent turbidity, and the twitching of crab antennules was visible at 6
feet in 63 per cent turbidity (Barnes, 1952).
Turbidity was measured "as
percentage transmission of the value in air."
Bureau of Commercial Fisheries
personnel working in the clear coastal waters of Florida observed the operation of fishing gear and the associated behavior of fish (Sand, 1956).
Infrared Viewer.
The principles involved in the use of infrared
light for night fighting during World War II have been adapted for the
study of fish behavior.
In a laboratory study Duncan (1956) found that
juvenile silver salmon were neither attracted nor repelled by infrared
radiation.
Northcote (1959) reports that infrared equipment was used to
observe the after-dark stream movements of rainbow trout fry, and a lake to
stream spawning run of kokanee (0. nerka).
Equipment for Indirect Observation
Sonar.
The United States Navy (1961) describes two types of sonar:
passive and active.
The passive type gathers sounds from the water.
The
active type initiates sounds which strike objects in their path and are
reflected or echoed back to the source.
The echoes are presented as either
light flashes on a screen (cathode ray tube) or a tracing on sensitized
paper (graphic recorders).
Echo sounding also employs the principle of
initiating sound; however, its sound beam is aimed vertically downward while
that of active sonar ranges over a quarter of a sphere.
A Norwegian ichthyologist, Oscar Sund, used an echo sounder in 1935
to locate fish (Bide, 1959).
More recently, other Norwegian investigators
used echo sounding and sonar to detect schools of herring (Clupea sp.) and cod
(Gadus sp.) and individual cod.
Tester (1943) used an echo sounder to locate
schools of herring in British Columbia waters; Smith and Ahlstrom (1948) did
the same with schools of sardines (Sardinops caerulea) off California.
In
freshwater, Hasler and Villemonte (1953) observed diurnal variations in the
schooling of yellow perch, and verified their results with SCUBA divers.
Trefethen (1955) identified schools of juvenile salmon at Baker Dam, Washington,
with sonar, and verified his results by capturing the fish in seines.
Adult
chinook salmon were observed with sonar in the navigation channel below Bonne
ville Dam on the Columbia River ( Trefethen, 1955).
Recent efforts indicate sonar may have a quantitative application.
Japanese experimenters located the deep scattering layer (plankton concentra
tions), set experimental gill nets in this layer, and obtained larger catches
of salmon than the average commercial set (Anon., 1959),
In an experiment in
the Barents Sea echoes from fish received on a cathode ray tube were counted
and a relationship was established between signal strength and the catch in
baskets of cod (Richardson, et al., 1959).
Equipment for Fish Capture
Gill Nets.
Natural fibers have been used for net making for thousands
of years (von Brandt, 1957).
The advent of synthetics during this century
6.
however, has revolutionized net construction.
Synthetic fibers generally have the
advantages of resistance to attack by microorganisms, resistance to internal
wetting, and, particularly in the case of nylon, greater strength than natural
fibers.
Some comparisons have been made between nets made of nylon and natural
fibers.
Lawler (1950) found that nylon gill nets were three times more effidient
than linen gill nets in the Lake Erb) whitefish fishery.
Hewson (1951) found
that nylon caught more fish than cotton when used in 3-inch gill nets in the
Lake Winnipeg winter commercial fishery.
Two types of nylon nets are in use: multifilament and monofilament.
In British Columbia, panels of monofilament nylon netting were inserted into
conventional multifilament nylon commercial gill nets (Carrothers, 1959). The
monofilament panels made larger catches during the day in "green" water, but
no difference in the catches were observed during the night or in the river.
Gill nets have proved useful in studies of fish behavior.
Cady, Dendy,
and Haslbauer (1943) and Dendy (1946) obtained information on the distribution
of warm -water fish in a reservoir in Tennessee.
In another reservoir study, Rees
(1955) determined the vertical and horizontal distribution of downstream migrating
juvenile salmOnids; each of the four mesh sizes used were selective to fish of
a particular size.
Size selectivity by mesh was also demonstrated in a brook
trout study (Anon., 1958).
Electric Shock Devices.
Alternating and direct current are commonly
used for fish shocking equipment.
Alternating current stuns or paralyzes fish
entering the electric field (Haskell, 1954), while direct current causes an
involuntary migration to the positive electrode (Haskell, McDougall and Geduldig,
1954).
A comparison of direct and alternating current fish shockers of equal
rating showed alternating current to be more efficient in the capture of trout in
a blocked off stream section (Webster, et al., 1955).
7.
In the past decade various investigators have adapted electro-fishing
methods for use in lakes and impoundments.
Haskell, Geduldig, and Snoek
(1955) describe an alternating current electric trawl used to collect fish
in a relatively shallow lake.
It was found that the electrode size needed
for direct current was too large to be practical.
Larimore, et al. (1950)
used an alternating current shocker on the bow of a rowboat to capture fish
in areas of lakes where seining and wading were not possible.
Loeb (1955 and
1957) describes an electric scow used to take game and scrap fish primarily
at night.
Field trials indicated a boat-mounted electric seine using
interrupted direct current may have a quantitative use (Smith, Franklin, and
Kramer, 1959).
All of the boat-mounted electric shock devices depended on
dip netting of shocked fish for capture.
Any reduction in visibility due to
turbid water or wave action made collection difficult.
Tow Nets.
During the past decade fisheries workers have developed tow
nets for the quantitative sampling of relatively large populations of juvenile
anadromous fish.
Calhoun (1953) describes a 15-foot-long tow net mounted on
skis used to sample striped bass (Roccus saxatilis) fry in the Sacramento-San Joaquin
delta.
A tow net 9 feet long and pulled by two boats was developed by Johnson
(1956 and 1958) for sampling juvenile sockeye salmon to determine their distribution and density in Canadian lakes.
the water surface.
Towing was effective only at dusk and near
The Fisheries Research Institute (University of Washington)
developed a tow net similar to Johnson's to sample juvenile sockeye salmon in
.Alaskan lakes (Anon., 1959 and 1961).
The California Department of Fish and Game
is currently testing a midwater trawl for use in a study to enumerate migrating
juvenile salmonids (Anon., 1961).
Floating Trap.
important.
The live capture of juvenile salmonids without injury is
Thompson (1955) found that floating traps fished along a lake shore
would capture all age groups of juvenile sockeye salmon.
8.
Fyke Nets.
Fyke nets generally require current to fish properly.
Craddock
(1959) describes a fyke net used to capture and hold juvenile salmonids migrating
downstream in velocities ranging from 3 to 5 c.f.s.
Koo (1959) sampled sockeye salmon
smolts in a fyke net located at the outlet of an Alaskan lake.
Burner (1949) obtained
data on the vertical distribution of juvenile salmonids in the Bonneville Dam forebay
by fishing Tyke nets at various depths a short distance upstream from the turbine
intakes.
Fishing With Lights.
In the early history of fishing, light in the form of
fire was used as a fish attractant (Anon., 1959).
During the present century,
electric lights have shown significant potential as a fishing aid.
Israeli fisher-
men, using techniques learned from the Italians and Yugoslays, mount powerful lamps
on small searcher boats (Cohen, 1957).
fish with nets.
Other boats capture the light-attracted
In Japan special mercury lamps using either alternating or direct
current were successfully used in the sardine, mackerel, salmon, and squid fisheries (Anon., 1959).
Environmental Factors Influencing the Behavior
of Juvenile Salmonids
Physical, chemical, and biological properties of reservoirs such as
temperature, light intensity, water current, turbidity, wind action, barometric
pressure, habitat geography, plankton concentration, oxygen and carbon dioxide
concentration, pH, and alkalinity may affect the habits of young salmonids.
Publications dealing with several of these subjects are included in the bibli.
ography.
Only temperature, light intensity, water current, and turbidity were
chosen for study.
Temperature
Researchers have shown that temperature affects the biology and movements
of young salmon, particularly in initiating the downstream migration.
A study
on downstream migrant salmonids in the Snake River determined that the chinook
fingerling migration was triggered in March by a rise in water temperature from
9.
45 to 500 F.; juvenile steelhead migrated when the water reached 50° F.
(Anon., 1954).
In a study on Atlantic salmon (4. salar), White and Huntsman
(1938) found that a rise in water te
erature during the first part of the
run, coincident with the advance of the season, was correlated with the down
stream migration.
In contrast, Hoar (1958) states that the mass exodus of
young salmon from streams may occur while the water temperatures are relatively
low and the day to day variations small; howesTer, a sharp rise in temperature
Clemen
may have an important effect on tho e fish remaining in the streams.
(1958) found that sockeye smolts left lake
4.5 (40° F.) to 100 co (50° F.).
when the temperature raised from
When the temperature exceeded 100 C. the
smolts remained in colder, deeper water and failed to
ome under the influence
of an outflowing current.
Temperature may also determine the habitability of a body of water for
salmon.
Brett (1952) determined the maxi um and minimum lethal limits of
temperature for fry of the five species of Pacific :salmon.
Light Intensity
The effect of light on saimonid behavior appears to vary by species and
stage of development.
In an early experiment wi
coho (silver) salmon, Hoar
(1951) found that fry have a higher threshold than smolts to ph tic
both day and night.
Hoar (1958) summarized juvenile
ti ulation
almonid reactions with
respect to light stating that they vary by pecies and stage of development.
The effect of light on the schooling or aggregation of salmonids is
pointed out in a laboratory
tudy by Field and Finger (1954) who state that
the necessity for a visual stimulus to hold fish together is indicated by
their immediate dispersion in the dark.
The importance of light with respect t. the migrational habits of
Pacific salmon has been ubjected to considerable study.
McDonald (1960)
found that sockeye, pink (0. gorbuscha), coho and chum (00 keta) fry
10.
migrating downstream traveled at night and ceased moving at the approach of day.
Hoar (1953) states that the phenomena of mass exodus of sockeye salmon from a
lake will occur when fish accumulate in large numberi prior to periods of
critically low light intensities.
Gauley, Anas, and Schlottex'beck (1958)
determined that the migration of fingerling salmonids at Bonneville Dam on
the Columbia River is predominantly nocturnal, although in occasional years
it maybe diurnal.
Water Current
The reaction of salmonids to water current may vary by species.
Hoar
(1951) determined that coho, pink, and chum fry display positive rheotaxis; but
coho are less tolerant of high velocities.
Kerr (1953) found that chinook finger-
lings have an unerring sense for finding low velocity areas of a channel.
McDonald (1960) captured the largest numbers of sockeye and pink fry in the
center area of a test flow where the velocity was greatest.
Certain aspects of salmonid downstream migration appear to be related to
current.
Brett (1953) determined that the sockeye response of rising to or near
the surface of a lake and into the more accelerated waters was invariably
associated with the downstream migration.
Hoar (1953) states that juvenile
salmon are transported seaward by the current and without relation to the bottom.
Hoar (1958) further states that when fish lose contact with their environment and
are suddenly displaced they may school with apparent disregard for the current, or
swim rapidly with it.
McKinnon and Brett (1955) found that the rate of migration
of chum and pink fry through a small impounded water basin was in excess of the
current velocity.
The downstream migration of salmonids with respect to the flow stage also
appears to differ by species.
In the Snake River chinook fingerlings reached their
peak of downstream migration one month prior to maximum water flow, while steel-
head migrants reached their peak at the maximum flow (Anon., 1950.
11.
Turbidity
Water turbidity appears to have an indirect effect on the movement of
juvenile salmonids.
Gauley, Anas, and Schlotterbeck (1958) state that due to
its influence on light penetration, turbidity is probably closely associated
mith9 or affects, day-night movement.
DESCRIPTION OF THE STUDY AREAS
Pelton Dam is located on the Deschutes River, about 95 miles above
its confluence with the Columbia River, in arid surroundings near Madras,
Oregon (Figure 1).
The dam has an hydraulic head of about 150 feet, and at
normal pool (19580 feet above mean sea level) the reservoir has a surface
area of 611 acres and a total storage capacity of 37,300 acre feet.
The
reservoir is 8 miles long and the Deschutes and Metolius Rivers enter at
the upstream end.
7 feet
Pool fluctuation averages 5 feet daily with a maximum of
The three 16-foot-diameter penstocks are submerged 142
feet and lead to Francis-type turbines.
The plant is operated on a peaking
schedule and the units are usually shut down at night between approximately
10:00 p.m. and 7:00 a.m.
of four exits:
Downstream migrants may leave the reservoir by one
(1) the artificial outlet or skimmer provided for the purpose
of passing migrants downstream, (2) the exit from the fish ladder which opens
into the reservoir near the skimmer, (3) the turbines, or (4) the spillway.
Spill is anticipated once in 20 years.
Spring chinook and blueback salmon
and summer-run steelhead trout are present.
Hatchery releases of approxi-
mately 45,000 chinook, 40,000 blueback, and 20,000 steelh ad were mad
in
the Metolius River 25 miles above the reservoir as part of the Pelton fish
facility evaluation project.
North Fork Dam is located on the Clackamas River in a wet, forested
region near Estacada, Oregon (Figure 1).
It is 29 miles upstream from the
Willamette River, a major tributary of the Columbia River.
The dam has an
LL
w
ASTORIA
Figure 1.
-..
has
0
10
20
Scale of Miles
0
C>
0
0
Metolius
River
DAM
PELTON
Location of North Fork and Pelton Dams.
PORTLAND
RIVER
WASHINGTON
Zef MADRAS
4Z,
0
z
15.
hydraulic head of about 150 feet, and at normal pool (665 feet above mean sea
level) the reservoir has a surface area of 350 acres and a total storage capacity of 7,500 acre feet.,.
The reservoir is 4 miles long and is entered at the
upstream end by the main stem of the Clackamas Rivers the North Fork tributary
enters at about mid-reservoir«
Pool fluctuation averages 4 feet daily with a
maximum of 19 feet anticipated.
The two 14-foot-diameter penstocks are sub=
merged 140 feet and lead to Francis-type turbines.
a peaking schedule similar to that at Pelton.
the reservoir by one of three exits
The plant is operated on
Downstream migrants may leave
(1) the artificial outlet which is
coincident with the ladder exit, (2) the penstocks, or (3) the spillway.
is estimated that spill will occur 7.4 per cent of the year.
It
Spring chinook
and silver salmon and winter-run steelhead trout are present.
SELECTION OF EQUIPMENT
Equipment was selected and procured after evaluation of the literature
survey results and consultation with personnel from various fishery agencies
in the Pacific Northwest.
It was decided to test at least one type of gear
from each of the three general categories reviewed
(1) equipment for direct
observations (2) equipment for indirect observation, and (3) equipment for
fish capture.
Each item was selected for its applicability, simplicity, avail-
ability, and cost.
General Operating Equipment
A 15-foot fiberglass boat, 18-horsepower outboard motor, and a boat
trailer were purchased3 and a station wagon was rented for the study period.
Equipment for Direct Observation
Direct visual observations on fish in reservoirs may be restricted by
factors such as water turbidity, available light, field of view, reactions of
fish to the observer or observing mechanism, and others.
own peculiarities.
Each method has its
SCUBA diving involves some personal risk, and has limita-
16.
tions on depth and time in the water.
Television and photography have a limited
field of view, a particular drawback for observing a moving subject, and also
have little depth perception, little contrast, and generally less light sensi
tivity than the human eye.
SCUBA diving was selected as the primary method for making direct
visual observations due to the maneuverability and visual versatility of an
individual.
The SCUBA equipment obtained was recommended by an experienced
commercial diver.
Each person was equipped with a standard wet suit with a
vest for added warmth, mask, fins, snorkle, 96 c.c. air tank with an sj valve
providing a reserve air supply, regulator, 15 pound weight belt, depth gauge,
SCUBA tote boots for holding the fins securely to the feet, and an underwater
flashlight.
Cameras for use underwater were borrowed or rented, and a glass viewer
was constructed for making shallow water observations under optimum conditions.
A commercial diving concern provided an underwater television demonstration.
Equipment for Indirect Observation
The Bureau of Commercial Fisheries loaned the project a Minneapolis
Honeywell "Sea Scanar", model 24 Dl, similar to equipment used at Baker Dam
for making observations on schools of juvenile salmon.
Although the Sea Scanar
was not compared with any of the numerous other types of sonic equipment avail
able, it was known to be highly sensitive.
The Sea Scanar is composed of three basic units;
(1) the indicator
panel unit containing the cathode ray tube with calibrated screen and all
the operating controls; (2) the transmitterreceiver power unit; and (3) the
hull unit containing the transducer which transmits and receives sound.
600watt generator served as the power source.
The sonar mount consisted of
a plank frame extending across the gunwales, immediately behind the deck
(Figure 2).
A
17.
Figure 2.
Sonar Apparatus and Mounting Assembly.
19.
Equipment for Fish Capture
The fish capture device was selected for its ability to fish equally
well at several depths and through various types of water conditions.
The
literature review indicated that small-mesh gill nets were used more extensively
and with greater success than any other type of fish-capture gear.
Other
fish-capture gear such as electric shock devices, tow nets, and traps are more
bulky, more expensive, and less consistent in their catches than gill nets.
It was decided to use both multifilament and monofilament nylon gill nets and
compare them as fish-capture devices.
The dimensions of the gill nets were arbitrarily set at 75 feet long
and 15 feet deep hung on a 1/2 basis, i.e., 150 feet of netting was used to
make a 75-foot-long net.
Six multifilament nylon nets (thread size 210 d/2
ply) and six monofilament nylon nets (thread size 0.234 mm.) were obtained.
In addition, two nets
alternate panels of multifilament and
monofilament nylon were procured to compare these materials side by side.
The single material nets were composed of five, 30-foot-long panels of the
following mesh sizes:
mea ure.
5/8-9 7/8-9 1 1/8-, 1 3/8= and 1 5/8-inch stretch
The nets alternating the two materials contained three mesh sizes:
7/8-, 1 1/8-, and 1 3/8-inch stretch measure.
The mesh sizes were chosen after
comparing catch data from a gill-net, experiment at Baker Dam, Washington,
(Rees, 1955) with the size composition of salmonids caught at the Pelton Dam
skimmer.
After many procurement difficulties, the entire order was placed with
a firm in Japan. A single multifilament nylon gill net of the desired dimensions was purchased from a local firm to facilitate the solution of some of
the anticipated problems associated with fishing these nets in reservoirs.
This net had only one mesh size (1 1/8-inch stretch measure, 110 d/2 ply)
since initial concern dealt more with the fishing technique than with the
20.
size of fish caught.
All of the nets used in the study were hung by experienced
commercial fishermen.
Hydro graphic Equipment
Since the development of equipment for studying the habits of juvenile
salmonids in reservoirs was the primary objective of the project, it was deemed
inadvisable to complicate the program with an involved hydrographic study.
It
was decided to study temperature, light, and turbidity so a bathythermograph2
photometer, and turbidimeter were obtained.
Appropriate instruments could not
be obtained for studying current patterns.
RESULTS
After completing the literature survey in May the project personnel
examined the two reservoirs selected for study and became familiar with the
operation of the sonar.
Possessing no previous diving experience, they
received instruction in the use of SCUBA from a commercial diver.
Field
operations were placed on a regular schedule in September with the acquisi
tion of gill net and SCUBA equipment.
Equipment for Direct Observation
SCUBA
The lack of published material on the use of SCUBA in juvenile salmonid
studies made it difficult to formulate a definite pattern of investigation.
Initial efforts were limited to simple observations.
Between August 1960 and
May 1961 both reservoirs were explored during numerous daylight dives.
The
few fish seen (less than one-dozen each dive) moved off rapidly on sight.
At
times fish were seen from the surface but could not be detected by SCUBA observers.
Observations ranged from the surface to a depth of 100 feet, but the fish were
usually found in the top 15 feet.
Schools of two or three dozen fingerling
silver and possibly chinook salmon, several rainbow trout, and a school of
almost two dozen juvenile steelhead were observed in a stream-type pool at the
21.
junction of the Clackamas River and North Fork Reservoir.
The steelhead were
seen in the spring and were identified by their uniform length (6-8 inches)
and bright silver coloration.
Rainbow trout and whitefish (Pro or:dim
eilliamsoni) were also observed in a small tributary to the Metolius River.
In general these fish were not frightened by divers.
Di ers made night observations at Pelton Reservoir from November 1960
through May 1961.
The divers usually observed several dozen salmonidSn
including chinook fingerlings and rainbow trout to 10 inches
and dozens of
scrap fish in any given night in an area located 1/4 mile upstream from the
dam.
Most fish appeared to be in a torpid condition and permitted the divers
to approach within one or two feet.
The strong flashlights used for night
diving appeared to blind and confuse fish and in some in tances seemed to
attract them.
Larger juvenile salmon9 possibly two-year-olds9 and trout over
10 inches long were wary and quickly moved out of sight.
Salmonids were
oriented closely to the bottom and were found from the shoreline to a depth of
10 feet.
Scrap fish were similarly distributed but some were fund try a depth
of 50 feet.
Fewer salmonids (less than one dozen per night) were seen in Feb-
ruary than in other months even though the counts at the Pelton downstream
collection system were rising at that time (Table 1).
e numbers of chinook
fingerlings observed on night dives in the lower reservoir area declined in
May after the peak outmigrant counts.
Over
ne- hundred chinook salmon fry were observed in the upper and mid-
dle areas of Pelton Reservoir in a mid,-April night di
Salmon fry were not
seen in the lower reservoir survey area at any time.
Juvenile steelhead migrants
were not positively identified at Pelton due to the presence of large numb rs of
resident rainbow trout of various sizes.
No obvious external physical differ=
ences could be recognized among the numerous rainbow and steelhead bserved.
Juvenile blueback salmon were not seen by the divers although approximately
402000 hatchery fish were released into the Metolius River in March 1961.
22.
Table 1.
Month
Numbers of Downstream-Migrant Juvenile Salmonids
Emigrating Past Felton Dam, 1960-61. 1/
Chinook Salmon
Hatchery
Wild
Blueback
Salmon
Hatchery
Rainbow-Steelhead Trout
Wild
Hatchery
1960
Sept.
oct.
Nov.
Dec.
7
0
0
0
0
749
1,494
646
2
1
3
0
3
2
17
7
0
2
0
0
212
1,525
1,189
9,864
5,394
933
0
0
0
1
0
3,292
4,140
1,788
1,100
0
151
279
378
194
19
98
840
1,990
2,054
0
0
373
470
697
22,013
10,332
1,005
5,024
1,540
1261
Jan.
Feb.
Mar.
Apr.
May
June
Total
1/ Data provided by Portland General Electric Company.
2/ Hatchery releases made in March and April 1961.
Floods and turbid water prevented night diving at North Fork Reservoir
until Januaiy 1961.
From one to several hundred fingerling silver salmon and
a few dozen fingerling rainbow trout and scrap fish were observed on each of
several dives through April 1961.
These fish also appeared to be in a torpid
condition and were easily approached by the divers.
The incidence of finger-
ling silvers observed in the reservoir fell sharply in May even though several
dozen were caught in gill nets and subsequent outmigrant counts numbered in
the thousands (Table 2).
night.
They no longer were found inshore on the bottom at
Fingerling silvers were observed milling off the bottom on one occasion
when attracted with an artificial light.
They were also observed in a pool
of the Clackamas River immediately above the reservoir both day and night
during the same period.
Both day and night observations in this river pool
showed that the fish were in midwater and moving about in loose aggregations.
23.
Table 2.
Month
Numbers of Downstream-Migrant Juvenile
Salmonids Emigrating Past North Fork
Dam, 1960-61. 1/
Chinook
Salmon
Silver
Salmon
RainbowSteelhead
Trout
1960
Sept.
Oct.
Nov.
Dec.
0
250
3,277
936
0
673
0
0
0
0
2,868
1,257
1961
Jan.
Feb.
Mar.
Apr.
May
June
July
Total
1/
654
47
131
525
57
0
0
0
3,427
13,177
1,090
2
49
118
18,716
19,649
74
18,768
43,986
17,694
876
10,809
1,786
0
Data provided by the Portland General Electric
Company.
Less than one dozen fingerling chinook salmon were seen on any of the
night dives in January and none were seen in subsequent months even though
their presence is indicated by counts at the North Fork Dam skimmer.
Those
observed were extremely wary and their parr marks were obscured by guanine as
early as January.
In contrast chinook at Pelton were easily approached and
retained their parr marks through the end of diving in May.
Several dozen silver and chinook salmon fry were observed in the upper
areas of North Fork Reservoir from April through June when field operationd
ended.
Approximately two dozen juvenile steelhead were observed in the
reservoir in May during night diving.
24.
In April surface night reconnaissance counts, using snorkels but not air
tanks, were made at various points throughout both reservoirs in order to com=
pare the concentrations of fish by location within a reservoir for a given
night (Tables 3 and 4).
Just prior to dark three divers traveled by boat to
the upper end of a reservoir*
Two men entered the water at different locations
and swam downstream along the shoreline for 15 minutes, counting fish seen by
species, if possible.
The third man remained in the boat and maintained sight
contact with the divers lights*
This procedure was repeated at several
predetermined locations down the reservoir*
The Pelton survey was completed
but the North Fork survey was abbreviated due to turbid water caused by boat
traffic in the lower half of the reservoir.
The upper reservoir was not
adversely affected due to the inflow of clear river water,
were chosen in part due to variations in topography.
Thy areas surveyed
Most fish were observed
over mud flats having slight gradient; some were seen along banks of loos
rock and moderate slope; but few were seen along steep, rock banks*
Those
found along steep banks were generally located in isolated, shallow pockets*
The counts may reflect the abundance of fish present in the area
surveyed,
but are not necessarily an indication of reservoir distribution.
The distribu,-
tion of juvenile salmon within a reservoir at night may be determined by the
location of slight gradient bottom type.
The ability of SCUBA divers to observe juvenile salmonids in a reservoir
at night but not during the day stimulated curiosity as to the whereabouts and
behavior of these fish during daylight hours.
In January divers entered North
Fork Reservoir in late afternoon, approximately one hour prior to dark*
At
first no fish were seen, but near dusk a small school of fish, believed to be
salmonids, was observed swimming along the shoreline,
They shied away from
the divers immediately and were not positively identifiedo
The divers observed
silver salmon moving about near the bottom at depths of 25 feet and shallower
Total
B
slight
slight
steep
m.
r. & m.
m.
m.
r.
sm. r.
r. & m.
r. & m.
m.
r. & m.
317
58
4
6
19
8
11
14
20
56
34
33
12
m. r
5/
r.
12
3
26
1
126
0
0
2
0
0
1
4
0
7
13
70
2
1
8
8
10
Chinook Chinook
Fry2/
Fingerlings 1/
r.
sm. r.
r.
r. 4/
Bottom
Composition
90
3
4
3
0
8
4
13
2
4
9
5
2
0
10
2
21
RainbowSteelhead
Fingerlings--fish more than one-year old from the time of egg deposition.
Fry fish less than one-year old from the time of egg deposition.
Includes brown trout (Salmo trutta) and Dolly Varden trout (Salvelinus malma).
rock
mud
12:55-1:10 a.m.
C
12:10-12:25 a.m.
0.6
C
12:00 M.-I2:10 a.m.
1.5
C
slight
steep
steep
A
11:25-11:40 p.m.
C
slight
slight
moderate
slight
slight
slight
steep
steep
slight to
steep
steep
Slope
A
2.7
u
10:5-11:00 p.m.
2.8
to
C
A
10:20-10:35 p.m.
3.7
9:30-9:45 p.m.
4.5
A
A
8:50-9:05 p.m.
6.8
A
B
Diver
tl
8:15-8:30 p.m.
(PST)
Time
92
4
0
7
1
3
6
20
3
1
5
2
8
5
12
0
15
Other
Trout
3/
67
0
0
0
0
0
0
0
0
0
0
56
0
5
1
0
5
Unidentified
Salmonids
515
66
56
12
59
25
55
98
21
59
46
0
9
2
11
1
2
Scrap
Fish
1,207
131
22
72
79
43
78
44
151
138
96
77
122
25
38
74
17
Species
All
Total
Night Counts of Fish in Selected Areas of Felton Reservoir by Snorkel-Equipped Divers, April 18, 1961.
7.5
(miles)
Distance
Above Dam
Table 3.
1/
u
1/
10:07-10:22 p.m.
u
9:00-9:15 p.m.
"
8:20-8:35 p.m.
(PST)
Time
40
o
0
0
0
0
93
rock
and mud
rock
mud
slight
steep
steep
23
186
90
392
26
0
26
0
-
12
0
12
53
103
153
Species
All
Total
45
14
9
5
Scrap
Fish
5
35
94
0
0
rock
0
moderate
to steep
0
Unidentified
Salmonids
mud
55
RainbowSteelhead
slight to
moderate
93
Silver
Fingerlings
moderate
Bottom
Composition
small rock
and mud
Slope
Night Counts of Fish in Selected Areas of North Fork Reservoir
by Snorkel-Equipped Divers, April 26, 1961.
Survey terminated due to poor visibility created by heavy boat traffic during the day.
Total
11
1.7
U
3.0
1,
3.4
(miles)
Distance
Above Dam
Table 4.
27.
in the half-light just prior to dark.
A flashlight beam directed at a fish
during this period tended to immobilize it.
the fish moved away from the divers.
When the light was turned off
After dark several hundred silver salmon
and a few dozen fingerling rainbow trout and scrap fish were seen and easily
approached in the shallows on the bottom.
A second daylight-to-dark survey was made at North Fork in May.
fish were observed during the daylight period.
No
As twilight approached, sucker
fry appeared near the bottom in water less than 10 feet deep.
After dark
several hundred sucker fry, a few dozen dace, cottids, and whitefish fry, and
less than one dozen fingerling rainbow trout were seen on the bottom at the
same depth.
Only salmonids were identified by species.
SCUBA observations were made at Pelton Reservoir at 4-hour intervals
throughout a 24-hour period in May to obtain the diurnal depth distribution
of fish.
Fish were counted along 50-yard transects parallel to the shoreline
at the surface and at depths of 15, 30, and 50 feet.
was located over open water at the same depths.
each counting the fish on his side.
are shown in Table 5.
A second set of transects
Two divers swam the transects
The results of the bottom-transect counts
Fingerling chinook salmon were seen mostly at night and
only along the shoreline transect.
shore during one daylight period.
Two chinook were observed swimming near
All but one scrap fish were observed at
night; however, they were distributed along the bottom to a depth of 50 feet.
The largest concentration of scrap fish was at 15 feet.
No fish were observed
during any time period along the open water transects.
In reservoirs salmonids were wary of divers during the day, but not at
night; in streams they were easily observed day and night.
Salmonids were
also studied under controlled conditions to obtain further information on
their reaction to divers by making underwater observations in hatchery
raceways, the Pelton fish ladder, and a 20-acre pond.
Divers entered
28.
Table 5.
SCUBA Bottom-Transect Counts of Fish Observed, at 4-Hour Intervals
Throughout a 24 Hour Period, Peiton Reservoir, May 2-3, 1961.
Time
Date
(PST)
2:00 p.m.
May 2
6s00 p.m.
10200 p.m.
2:00 a.m.
May 3
6:00 a.m.
10:00 a.m.
Total
1/
Depth
in Feet
Chinook
0
15
30
50
0
0
0
0
0
0
1
0
0
0
1
0
Other 1/
Fish
Total
0
0
0
0
15
30
50
0
0
0
0
0
0
0
0
15
30
9
6
9
3
0
15
3
5
1
8
16
5
1
0
0
50
0
0
0
0
15
30
50
5
0
0
0
16
9
3
0
0
0
0
0
15
30
50
0
0
0
0
0
0
0
0
0
0
15
30
50
2
0
0
0
1
0
0
0
3
0
16
45
61
0
0
Includes one brown trout seen at the surface at 10200 p.m.; remainder
are scrap fish.
hatchery raceways at the Metolius River hatchery and matched the reaction of
chinook and blueback salmon and steelhead trout.
These fish generally were not
startled by the observers; however, blueback exhibited the strongest avoidance
tendency.
The concentration of hatchery fish coupled with their feeding procedure
probably gave them a high threshold for external disturbance.
29.
Using snorkel gear, divers swam a two-mile section of the Pelton fish
ladder which transports migrant juvenile salmonids from the skimmer to the
river 2.8 miles downstream.
Each of the pools nearest the counting station,
at the upper end of the ladder, contained several hundred chinook salmon
fingerlings.
These fish were distributed throughout the pools and did not
appear to be disturbed by the divers.
Approximately three dozen fingerlings
per pool were found in lower sections of the ladder.
These fish appeared
wary and were not seen until the divers reached the weir at the end of each pool.
The final observation on salmonid reaction to divers occurred in
20-acre Wahkeena pond containing approximately 100,000 silver salmon.
During
the day the fish moved away if approached but appeared unconcerned after the
divers stopped.
Most of the silvers seen in daylight hours were in loose
aggregations and congregated in the cold water flowing through the old stream
bed; however, a diver sitting motionless on the bottom of the pond observed
about two hundred silver salmon mill in his exhaust bubbles for several minutes.
The fish disappeared when the diver moved.
After dark hundreds of fish were
observed distributed throughout the pond close to the bottom.
The greatest
density per unit area remained in the old stream channel.
The problem of finding fish in a reservoir during the day may involve
their dispersion, and the difficulty divers have in making extensive sub=
surface observations in open water without reference to the bottom or
shoreline.
A mercury vapor light (Figure 3) was used at North Fork Reservoir in
mid-June in an attempt to attract fish for observation.
The divers swam a
section of the bottom outside the area to be lighted at depths ranging from
the surface to 20 feet.
Numerous Chinook and silver salmon fry were seen
along the shoreline but only three fingerling silvers were seen in the
entire area.
The divers swam the area below the lamp before it was turned on
31.
Figure 3.
Mercury Vapor Light and Ballast Lamp Used
in Attracting Fish at Night.(The ballast
lamp is used to light the mercury lamp.)
33.
but no fish were seen.
The mercury lamp, located approximately 1 1/2 feet
above the water surface, was then lighted and the area below it was not disturbed
for 20 minutes.
At the end of this time the divers entered the water and
stationed themselves on the bottom just below the lamp at a depth of 7 feet.
A school of fingerling salmon (probably silvers) were observed milling in the
lighted area.
They moved constantly and shied away at the divers' slightest
A total of 51 fish were counted by one observer in a 10minute
action.
period; some fish were undoubtedly counted twice.
The vulnerability of juvenile salmonids at night to SCUBA divers
stimulated the development of a fish capture method.
Initially, fish were
captured by herding them into a short handled smelt net with a flashlight.
It appeared that the heavy cotton material frightened the fish; hence, subse
quent nets were made of 5/8inch stretch measure monofilament netting
(Figure 4).
The first successful net using monofilament material was a bag
net approximately 18 inches long fitted to a onehalf inch diameter tubular
plastic frame.
The monofilament netting did not collapse over the net opening
but was stiff and remained extended.
The method of capture was to place the
net over a fish, the rim in contact with the bottom.
When aware of the net,
a fish sought to escape along the bottom, and eventually moved up into the
bag and was captured by folding the net across the rim, sealing off the
opening.
attempted.
Fish were easily caught but escrped when multiple captures were
This net was improved by placing a short fyke at its mouth, and
making the bag rigid by using a framework of two cross wires.
This apparatus
retained fish better than the bag net, but fish were hesitant to enter the fyke.
To induce fish to enter more rapidly, a net was constructed of a
series of supported, concentric wire rings (Figure 5).
the mouth of the net and had the smallest diameter.
The bottom ring formed
The netting sloped out
from this ring to a second, larger ring forming the outside edge of the trap
35.
Figure 4.
SCUBA Hand Nets Showing Improvements from
Left to Right. (Diameter at mouth of nets,
9 inches.)
37.
Figure 5.
SCUBA Diver with Hand Net Used to Capture Juvenile
Salmonids. (Note salmonids inside the net oriented
in same direction as diver.)
39.
floor.
The floor was attached to the second ring at 4inch intervals allowing
small slits through which fish could. enter the trap.
The third and largest
ring was located below and outside of the second ring creating an overhang of
the trap floor which prevented fish from escaping.
with a handle grip formed the top of the trap.
for both capturing and retaining fish.
A trout landing net frame
This device proved successful
Once in the traps, fish did not appear
frightened.
The gill nets were observed in fishing positions by divers on several
occasions, and new ideas were formed for making modifications to this gear.
At times the divers made adjustments to the gear while it was fishing.
Cray
fish predation on fish caught in the nets was observed at Pelton Reservoir.
Observations made on the gill nets at night showed hundreds of crayfish
feeding on dead and dying fish.
In one instance divers observed a fingerling
chinook salmon enmeshed in a net at dusk.
Later that evening the fish was
half eaten5, and by morning no trace of the fish remained.
Visibility-was an important consideration for making SCUBA observations.
A minimum Secchi disc reading of 8 feet was desirable, but at a reading of 5
feet, fish were observed with much tedious searching.
In late summer Secchi
disc readings of 8 to 10 feet proved moderately good for SCUBA observations
in both Pelton and North Fork Reservoirs, but in late September an algae bloom
at Pelton prevented observations except at the confluence of the Metolius and
Deschutes Rivers.
Visibility improved by November and remained excellent
through the winter and spring except for a brief period in March after a rain
fall.
The high Secchi disc reading was 33 feet in January.
Visibility remained
moderately good at North Fork until late November when a flood caused turbid
water lasting until early January.
There were alternate periods of clear and
muddy water from then until April depending on the incidence and quantity of
rain.
From April through the end of field work in June visibility was good at
4o.
North Forkvhowever the shoreline waters became turbid during periods of heavy
boat traffic.
The high Secchi disc reading was 17 feet in May.
Television Demonstration
A closed circuit television demonstration was given at North Fork Reservoir
in May 1961 by Commercial Divers, Inc., of Portland with a Vidicon camera having
an f:105 Elgeet wide angle lens.
receiver.
Reception wag on an ordinary television
A school of juvenile salmonids and several adult steelhead, apparently
spawnedr,out-were present in the reservoir in the vicinity of the downstream
migrant collection system at the dam.
The camera was lowered into the water
at the entrance to the collector and fish were Chummed with salmon eggs to
At this distance-they-sere seen is dark
within 2 or 3 feet of the lens.
shadows on the television screen, but species identification was impossible.
Visibility-was fair at the time.
Equipment for Indirect Observation
Sonar
After a-period of indoctrination the gear was first used for sounding
the bottom of the reservoirs
Next, the sonar beam was aimed at known objects
and the resulting signal was studied.
The Sea Scanar gave a recognizable
presentation of a log boom at North Fork Dam.
From a stationary platform the
sonar beam was trained on a swaying, 20-pound concrete anchor suspended from
a log boom at a depth of 25 feet, but it was difficult to obtain more than an
intermittent signal.
Mien a SCUBA diver was used as the target, a signal was
obtained if the sonar operator knew his exact location; however, it was difficult to establish contact when the diver was out of sight, even though his
general location was known.
Gill nets and fish caught in the nets were good targets for study
(Figure 6).
Echo signals were recognized from the large anchor floats and
from the float and lead lines of the nets, but the mesh did not return an
Figure 6.
Sonar Operation Using a Gill Net as the Target,
North Fork Reservoir
43.
echo.
Of the fish caught in the gill nets, those 5 to 10 inches long in
close proximity to one another and individual fish 1 foot or longer gave
a recognizable signal, but echoes were not received from individual small
fish.
A dead, adult steeihead approximately 2 feet long was suspended at
a depth of 5 feet below an anchored styrofoam float, and was easily detected
at a range of 5 to 50 feet.
Beyond 50 feet the target became increasingly
difficult to find even though the sonar operator could see the styrofoam
float from which it was suspended.
Movement of the fish by wave action
coupled with the movement of the boat undoubtedly contributed to the problem.
Similar results were obtained using a one-gallon jug suspended from the float.
The final phase of the sonar work involved searching the reservoirs
for fish.
Mechanical malfunctions of the sonar set and generator and lengthy
delays for repairs limited development of a search technique.
Activities
consisted of anchoring or cruising in the reservoir while the sonar was in
operation, in an effort to pick up signals.
Some unidentified echo signals
were received on the sonar from mid-water depths while cruising the reservoirs.
On one occasion a group of 4 to 5-inch fish created considerable surface
activity near the boat at North Fork Reservoir, but they could not be detected
on the sonar screen.
Equipment for Fish Capture
Gill Nets
Accessory gill-net equipment was developed which allowed the nets to be
fished at various depths, was not affected by reservoir fluctuation, and was
portable.
The suspension apparatus (Figure 7) required two anchor lines loc-
ated 75 feet apart (the length of the nets).
Each anchor (a) weighed approx-
imately 60 pounds and was attached to a line (b) leading to a large styrofoam
float (c) at the water surface.
The anchor line traveled over two pulleys
(d) attached to an inverted T-shaped galvanized pipe assembly (e) with the
4C.
Warning Sign
c.
ci. 6
WATER SURFACE
Q.
4-)
a)
g.
i.
75 feet
Figure 7.
Schematic Diagram of GillNet Suspension Apparatus.
47.
vertical bar of the T through the center of the styrofoam float.
A 20-pound
counterweight (f) was tied to the loose end of the anchor line.
The gill net
(g) had a 5-pound sash weight (h) at each end of the lead line (i) to sink it
to the desired depth.
Large snaps (j), tied to each corner of the net,
fastened onto the anchor lines enabling the net to travel freely down the
lines.
A line (k) connected the net to the float to control the depth at
which the net fished.
The result was that the styrofoam floats rose or fell
with any fluctuation in the reservoir and the anchor and counterweight lines
remained taut (Figure 8).
This allowed the net to remain at the same depth
with relation to the water surface except when the net was set on the bottom.
The gill nets were fished in a variety of locations and positions and
under differing conditions to obtain knowledge of the mechanical problems
involved with their use.
As a result, fishing procedures were not standard-
ized and the quantitative comparison of catches may not be reliable for
determining distribution or abundance.
The fishing technique was successful on both a level bottom and a
steep, mud bank.
It was difficult, however, to prevent the anchors from
sliding on a steep, rocky slope.
The nets were fished in clear and turbid
water, and through most algae growths; however, a green filamentous algaeUlothrix,
prevented them from fishing by clogging the meshes and weighting the nets
into an unnatural position.
Nets were fished at any depth in slack water;
but current caused them to bag, drawing the styrofoam floats toward one another.
The resulting bow in the anchor lines prevented the nets from slipping down
the lines below a depth of 30 feet.
their fishing ability.
Bagging did not appear to interfere with
The nets fished satisfactorily in all velocities
encountered in the reservoirs studied.
The nets were fished in three positions: (1) perpendicular to the shoreline, (2) parallel to the shoreline, and (3) vertically on end.
Positions (1)
119.
Figure 8.
Portable Gill-Net
Suspension
in Fluctuating
Apparatus Used
Reservoirs as Seen from
Beneath the Water Surface.
510
and (2) were in common use and both caught fish.
determine which was most successful.
No comparison was made to
In the fall and spring when fish appeared
to be moving both into and out of the reservoirs the perpendicular (1) position
was used with the most success.
The SCUBA observation that fish moved inshore
at night led to the successful use of the parallel position during the winter
and spring.
On two occasions, once at Pelton and once at North Fork, a 1 1/8-
inch multifilament net was fished with its length stretching from the water
surface to the bottoms i.e. in a vertical positions to obtain qualitative
information o
the depth occurrence of fish.
Few fish were caught.
Tables 6 and 7 summarize the gill-net catches made at Pelton and North
Fork Reservoirs by species, net materials and mesh size.
Small numbers of
salmonids and large numbers of scrap fish were caught in the nets at Felton;
64 per cent of the total catch consisted of the common chiselmouth (Acrocheilus
alutaceus).
The apparent lack of success at capturing salmon fingerlings may
be attributed, at least in part;
to crayfish predation.
SCUBA divers ,observed
crayfish devouring fish of all species and sizes caught in the nets.
Fish
skeletons up to one foot in length and partially eaten fish (including several
salmon) were removed from the nets.
Salmon fingerlings, generally 4 to 6
inches long, could have been easily devoured before the nets were checked
after an overnight set.
Up to 60 crayfish were caught in a single net.
Large Dolly Varden and brown trout and squawfish (Ptychocheilus oregonensis)
were caught, possibly while preying on gill-netted fish.
In contrast salmonids dominated the gill net catch at North Fork Reser=
voir.
Crayfish were caught rarely and predation was evident on only one occasion.
No Dolly Varden or brown trout or squawfish were captured or observed at North
Fork; only one rainbow trout over 10 inches was caught
Chinook salmon finger-
lings were caught most effectively by the 1 1/8-inch mesh, silver salmon fingerlings by the 7/8-inch mesh, and rainbow-steelhead trout by the 1 3/8-inch mesh.
5
0
0
3
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Blueback (fingerlings)
Rainbow- Steelhead
Rainbow trout (over 8 inches)
Brown trout
Dolly Varden
Whitefish
Chiselmouth
Squawfish
Sucker
Sculpin
Dace
Carp (a-prin.-us carcio)
Total
46
0
1
0
2
1
24
2
0
1
0
1
2
12
127
0
0
1
6
10
88
5
3
3
0
8
2
1
146
0
0
0
19
8
94
3
3
6
1
330
0
1
1
27
20
209
10
6
10
1
20
10
1
11
15
0
SubTotal
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5/8
Net Material
1/ Net composed entirely of 1 1/8-inch multifilament nylon.
11
0
0
0
2
7/8
0
5/8
Monofilament
Mesh Size
1 1/8 13/8 1 5/8
6
0
0
0
0
0
2
1
0
0
0
2
0
1
7/8
24
1
0
0
1
2
11
3
0
0
0
1
2
3
85
0
0
0
9
6
63
1
2
0
0
2
1
1
136
0
0
0
31
7
84
0
1
4
1
7
1
0
Multifilament
Mesh Size
1 1/8 1 3/8 15/8
251
1
0
0
141
15
160
5
3
4
1
12
/4
5
SubTotal
Numbers of Fish 'Caught in Pelton Reservoir with Gill Nets, by Species,
Net Material, and Mesh Size, 1960-61.
Chinook (fingerlings)
Species
Table 6.
186
1
0
0
9
142
120
2
1
4
0
4
0
3
11/81/
767
2
1
1
77
77
489
17
10
18
2
36
14
23
Total
1,092
191
478
164
156
423
1
35
2/ Jacksmature males less than 22 inches in length.
1/ Net composed entirely of 1 1/8-inch multifilament nylon.
94
175
94
52
5
128
42
2
30
5
0
10
0
11
2
Total
Sculpin
9
2
6
2
0
116
17
48
1
0
1
67
17
25
5
38
12
0
0
Sucker
23
0
9
5
0
3
1
0
14
3
3
8
0
0
Whitefish
0
0
0
0
0
0
0
1
0
0
1
0
0
Steelhead (adults)
4
90
23
44
18
5
0
74
15
41
14
3
1
Rainbow- Steelhead
0
2
1
0
1
0
0
0
0
0
0
0
0
Silver (jacks)1/
13
222
0
2
76
144
0
190
0
2
67
120
Silver (fingerlings)
1
0
1
1
0
0
0
0
0
0
0
0
0
0
Chinook (jacks)2/
1
168
2
425
1
314
171
76
0
12
63
Total
1
1
1/82
0
1
67
0
8
3
0
Chinook (fingerlings)
SubTotal
7/8
1 5/8
Multifilament
Mesh Size
1 1/8 1 3/8 1 5/8
5/8
SubTotal
Net Material
56
7/8
11/8 1 3/8
Monofilament
Mesh Size
Numbers of Fish-Caught in North-Fork Reservoir with Gill Nets by Species,
Net Material, and Mesh Size, 1960-61.
5/8
Species
Table 7.
f".
v.L
55.
The term rainbow-steelhead was used due to the problem of distinguishing between small rainbows and juvenile steelhead, it includes fish 8 inches
or under in size.
Only three fish were caught in the 5/8-inch mesh size
although several hundred fish small enough for this mesh size were observed
by SCUBA divers.
The monthly catch per net-day (21L hour period) was determined for
chinook and silver salmon and rainbow-steelhead trout to compare the relative
abundance through time for each species of gill-net caught fish at North Fork
Reservoir (Figure 9).
mesh nets.
The data include only catches made by the variable
The chinook salmon catch per net-day was maximal in November and
December; it declined thereafter through April.
No chinook were caught in
May and June even though outmigrant counts indicate the largest numbers were
then leaving the reservoir (Table 2).
Silver salmon catches were minimal in
December and January, and maximal in June, the month having the largest outmigrant counts.
The catch of rainbow-steelhead was insignificant until April
when it rose sharply, and peaked in June even though most of the fish leaving
the reservoir were counted out by the end of May.
The June catch per net-day
for silvers and rainbow-steelhead is probably not representative since it is
essentially the result of one day's catch in a single net.
The catch of
rainbow-steelhead otherwise corresponded closely to the North Fork outmigrant
counts in that both occurred mainly in the spring, and suggest that most of
the gill-net-caught fish in this category were steelhead migrants rather than
resident rainbow trout.
In addition certain physical attributes, noted in
the SCUBA section, indicate they were steelhead.
The catch per net-day may
not be an exact reflection of the occurrence of each species through time due
to the lack of standardization in the fishing method.
At North Fork Reservoir monofilament and multifilament nets were fished
in pairs to compare their effectiveness.
Mhen it was observed that better
4-)
OT,
+;
A
Z
o
rx.
0
5
10
15
20
1%...
1960
'
....
Jan.
I
..0 pa VW
e
e
.-.
e
Feb.
ar...
em'
.
.
/
I
1961
Apr.
May
t."-------....1
i -°-- Rainbow-Steelhead
. e.-e.,
,
Mar.
I
.... .....
I
I
June
1
.
_
Monthly Catch Per Net-Day of Chinook and Silver Salmon
and Rainbow-Steelhead Trout, North Fork Reservoir, 1960-61.
Dec.
Figure 9.
Nov.
1 Gm . 4.
.. .
4_--Chinook
e.
e
Silvers
I
I
I
I
I
I
I
I
catches occurred in one position of a pair regardless of net material, the
net positions were alternated over two nights.
It then became apparent that
a fishing area was "fished out" temporarily since few fish were caught in
either position on the second night.
As the fieldwork progressed, other
complications arose.
In comparing the fishing efficiency of the two types of material the
length frequencies (fork length measurement) for each species of fish caught
in each mesh size were compared to determine if the two materialt fished on
the same segments of the populations.
Figures 109 112 and 12 show the size
composition of chinook and silver salmon and rainbow-steelhead trout for those
mesh sizes capturing enough fish for comparative purposes.
In the case of
silver and chinook salmon a difference is evident between the two materials
for a given mesh size.
Chi-square tests showed that monofilament nets caught
significantly larger fish.
The size compositions of rainbow-steelhead caught
in 1 3/8-inch monofilament and multifilament nets did not differ statistically.
The mesh sizes were measured for each of the test nets and it was
determined that the monofilament averaged 1/25-inch larger than multifilament
in the 7/8-inch mesh size and 1/17-inch larger in the 1 1/8-inch mesh size
than specified.
The two net materials also differed in texture.
Multifila-
ment netting was soft and fish caught were entangled and usually dead, while
monofilament netting was stiff and fish caught were gilled in a simple manner
and generally alive.
Fish often fell out of the monofilament nets as they
were pulled into the boat.
It was not determined whether the length-frequency
differences were attributable to the fractional differences in the mesh sizes,
differences in net material quality, or a combination of the two.
The fishing
efficiency of monofilament and multifilament nets were not compared because of
sampling problems and since similar mesh sizes caught statistically different
61.
Multifilament: N = 61
40
30
!.
4-,
r--- Monofilament:
0
U
20
N = 57
.
NM.
10
r;?r---1
0
11.0
Figure 10.
11.5
12.0
12.5
13.0
Length in Centimeters
13.5
14.0
Size Composition of Chinook Salmon Caught in 1 1/8-inch
Monofilament and Multifilament Nylon Gill Nets, North
Fork Reservoir.
63.
40
1 1/8-inch mesh
30
Multifilament: N =
Monofilament: N = 64
20
10
0
9.0
14
134
40
10.0
11.0
12.0
13.0
14.0
7/8 -inch mesh
Multifilament: N = 140
30
+ Monofilament: N = 118
20
10
0
9.0
Figure 11.
10.0
11.0
12.0
Length in Centimeters
13.0
14.0
Size Composition of Silver Salmon Caught in 7/8- and 1 1/8-inch
Monofilament and Multifilament Nylon Gill Nets, North Fork
Reservoir.
10
30
Figure 12.
11.0
13.0
14.0
16.0
15.0
Length in Centimeters
17.0
18.0
19.0
Size Composition of Rainbow-Steelhead Trout Caught in 1 3/8-inch Monofilament
and Multifilament Nylon Gill Nets, North Fork Reservoir.
12.0
Multifilament:N = 48
Monofilament: N = 39
67.
size segments of the chinook and silver salmon populations.
Insufficient
numbers of rainbow-steelhead were caught for comparative purposes.
An analysis of variance showed statistical differences in the mean
size of silver salmon caught in different time periods for 7/8- and 1 1/8.-inch
mesh for both types of nylon.
When these means were ranked by time period
according to Li (1957), it was found that they increased (Figure 13).
Not all
the means from a given mesh size and material were statistically different.
With some overlap the differences were essentially between the periods
November-December, January-April, and May-June.
Similar treatment of chinook
salmon catches in 1 1/8-inch mesh size of both materials showed no significant
difference in mean lengths of fish caught in the monofilament material and a
barely significant value for fish caught in multifilament nets; the means
could not be ranked in either case (Figure 14).
The progression of the mean size of juvenile silver salmon caught in
the gill nets may be an indication of: (1) growth; (2) changes in the body
conformation or condition factor; or (3) recruitment to the reservoir of fish
of increasing size due to widespread distribution of the spawning areas, and
extended spawning season.
Adult silver salmon pass North Fork Dam from late
October through February, and probably spawn during all those months; the
hatching period may be of corresponding length.
Adult chinook salmon appear
to spawn during a one-month period from mid-September to mid-October, which
may account for the small size variation with time for these juveniles.
Diurnal availability of juvenile salmonids to the gill nets was tested
on one occasion at North Fork Reservoir,
A group of eight gill nets was
fished in pairs over a 24-hour period (March 21-22, 1961), and were tended
and reset every three hours.
Each pair fished an average of 2 1/2 hours per
set; 1/2 hour was needed to pick up a pair of nets, remove the fish, and reset.
Two peak catch periods occurred, one at dusk and the other at dawn (Table 8).
69.
13
...we
1 1/8-inch monofilament
12
".
d
/
.
/16.
..0
....
...
--4"
°- . ...
....
... ....,
-"' - ...
.............
do
ti
.......m".0.
'II"
1 1/8-inch multifilament
40
3
dr
.049
7/8-inch monofilament
Of
1
A
10
aro
gag
Ol
w ig
40*
al+
moo
....
i
Figure 13.
dr
°"*".
01, am,
7/8-inch multifilament
i
Nov.-Dec.
1960
dr
Jan.-Feb.
i
'
Mar.
Apr.
i
May-June
1961
Mean Length by Time Period of Silver Salmon Caught
in 7/8- and 1 1/8-inch Monofilament and Multifilament
Nylon Gill Nets, North Fork Reservoir.
Nov.-Dec.
1960
Figure 14.
Jan.-Feb.
Mar.-Apr.
1961
Mean Length by Time Period of Chinook Salmon
Caught in 1 1/8-inch Monofilament and
Multifilament Nylon Gil]. Nets, North Fork
Reservoir.
71.
It was not possible to determine which period was best since the removal of
fish from an area at dusk may have reduced the numbers available at dawn.
Table 8.
Gill-Net Catches at 3-Hour Intervals Throughout a 24,-Hour
Period, North Fork Reservoir, March 21 and 22, 1961.
Time Nets
were Pulled
12:00 N-2:00 p.m.
3200-5:00 p.m.
6:30-8:10 p.m.
9:30-11:30 p.m.
12:00 M-2:00 a.m.
3:00-5:00 a.m.
6:10-8:00 a.m.
9:15-11:00 a.m.
Total
1/
Ch.
Sil.
0
0
4
0
0
26
14
0
1
0
Catch
Rb-Sh
0
0
2
6
0
0
4
1
1
1
1
13
46
10
2
1
5
Other!
Total
0
0
11
1i3
0
0
3
22
1
5
5
0
2
25
9
17
1
94
Includes whitefish, suckers, sculpins.
Reservoir Limnology
Temperature, turbidity, and visibility data were collected from both
reservoirs.
Variable fishing locations and gear, and lack of continuity in
the field program due to the necessity of one crew working both reservoirs,
precluded correlating the gill-net catch with hydrographic data from either
reservoir.
Between July 1960 and May 1961 the surface water temperature at North
Fork Reservoir ranged from 41 to 71° F.; the high temperature was in July and
the low occurred from November through January.
A weak thermocline occurred
between the surface and a depth of 10 feet in August 1960.
Visibility as
expressed by Secchi disc readings ranged from 2.5 feet in December to 17 feet
in May.
At Felton Reservoir the surface water temperature ranged from 450 to
63° F. between September 1960 and May 1961; the high temperature occurred in
72.
September and the low in January.
No thermocline was observed at any time.
Secchi disc readings ranged from 5 feet in September to 33 feet in January.
Problems in the construction of a watertight case prevented use of the
photometer for obtaining light intensity readings*
After several failures
and the repair of a water-damaged photocell, a successful case (Figure 15) was
obtained at the end of the field program.
RECOMMENDATIONS
Equipment and techniques for studying the behavior of juvenile salmonids
in reservoirs should be developed further.
These include: (1) a method of live
trapping (floating traps, Oneida Lake traps, night seining, barge-mounted electric shock device, and enclosure traps); (2) a tag for fingerling salmonids;
(3) a method for making extensive open-water SCUBA explorations (towing appar
atus, etc.); (IL) a comparison of monofilament and multifilament gill nets;
(5) an improved SCUBA hand net; and (6) a device for measuring water currents
in reservoirs.
Since inter-reservoir differences are indicated the behavior patterns
of juvenile salmonids should be determined through continuous observations in
both Pelton and North Fork Reservoirs to establish the feasibility of reservoir
collection and facilitate the adaptation of existing or proposed fish collection facilities at dams to specific habits or vulnerable behavior patterns.
The following objectives should be considered for each species and distinguishable race of migratory salmonid:
(1) vertical and horizontal distribution,
diurnally and seasonally; (2) local migrations or movements within a reservoir;
(3) time of appearance and duration of stay; (Ii) effect of biology on behavior
(size and age at entrance and exit, effect of size on migration); and (5)-effect
of physical and chemical properties of environment on behavior.
73.
Figure 15.
Photometer with Watertight Plastic Case.
75,
SUMMARY AND CONCLUSIONS
A study to develop methods and techniques for determining the behavior
of juvenile salmonids in reservoirs was conducted by the Oregon Fish Commission
during the period September 30, 1959-January 31, 1962 with Saltonstall-Kennedy
funds provided by the United States Fish and Wildlife Service, Bureau of
Commercial Fisheries.
Available literature was reviewed to obtain information on juvenile
salmonid behavior and applicable study equipment.
Field studies were conducted on the reservoirs formed by Pelton Dam
on the Deschutes River and North Fork Dam on the Clackamas River.
Equipment chosen for development included SCUBA for direct observation,
sonar for indirect observation, and gill nets for capture of fish.
Day and night SCUBA observations were made to a depth of 100 feet
through the fall, winter, and spring in water temperatures ranging from 140 to
71
F.
Fish were observed with difficulty in water having a Secchi disc read-
ing of 5 feet, and a reading of at least 8 feet was desirable.
Improved fish-
ing methods resulted from SCUBA observations of gill nets in operation.
Several indications of nocturnal salmonid behavior were obtained with SCUBA
at both reservoirs that were not determined by the use of sonar or gill nets;
SCUBA was the only tool yielding significant information on salmonid behavior
at Pelton.
Divers observed that salmon entered both North Fork and Pelton
Reservoirs as fry and in later stages of development.
All species of fish observed moved inshore and oriented themselves
near or on the bottom at night; they were easily approached and captured by
divers equipped with specially constructed hand nets.
During the day fish
apparently moved offshore and were not readily found in reservoirs; but they
were found in streams and, if diver movement was restricted, in a rearing
pond containing large numbers of silver salmon.
In May, coincident with the
76.
downstream migration, silver salmon in North Fork Reservoir were no longer
oriented near the bottom at night as they were from January through April, but
were found swimming off the bottom.
An underwater television camera was tested on one occasion, but gave
unsatisfactory results.
Large stationary objects were easily detected with sonar, but moving
objects were difficult to detect and follow.
In the gill nets, closely grouped
fish 5-10 inches long and individual larger fish yielded an echo signal; however, the smaller individual fish were not detected by the sonar.
Mechanical
malfunctions prevented thorough field testing of the sonar.
Monofilament and multifilament nylon gill nets 75 feet long and hung
on a one-half basis were tested.
Each net was composed of five equalpanels
30 feet long and 15 feet deep and each panel was of a different mesh size.
The mesh sizes were 5/8-, 7/8-, 1 1/8-, 1 3/8 -, and 1 5/8-inch stretch measure.
A portable gill-netting operation was developed for fluctuating reservoirs
which allowed nets to fish at a predetermined distance below the water surface.
The nets caught fish in clear and turbid water and in slight current, but were
rendered useless by a Ulothrix bloom.
The gill nets caught significant numbers of juvenile salmonids at North
Fork Reservoir; but few salmonids were found in the nets at Felton, possibly
due to crayfish predation. At North Fork Reservoir chinook salmon fingerlings
were caught best with 1 1/8-inch mesh, silver salmon with 7/8-inch mesh, and
rainbow-steelhead trout with 1 3/8-inch mesh.
The gill-net catch per net-day may not be an indication of the relative
abundance of a particular species of salmonid since the fishing method was not
standardized.
Monofilament and multifilament nets were not compared due to sampling
problems; similarly designated mesh sizes captured fish of different size compo-
77,
sitions.
This size difference may be due to a slight mesh size difference
observed, to differences in the characteristics of the two materials, or both.
The size composition of silver salmon caught in the 7/8- and 1 1/8-inch mesh
sizes of either material increased with time.
This may have been due to
growth, or variations in the life history of the fish.
Salmonids appeared
to be most vulnerable to gill nets at dusk and dawn.
Physical and behavioral characteristics of chinook salmon varied
between the two reservoirs.
At Pelton, chinook exhibited no apparent behav-
ioral changes between seasons, and their parr marks were visible until May;
but at North Fork few chinook were seen at night or caught in gill nets after
January, and those seen had their parr marks obscured by guanine.
It appeared
that more predaceous fish were present in Pelton than in North Fork.
Most steelhead appeared to enter and pass through North Fork Reservoir
during a short period in the spring.
This may not have been evident at Pelton
because resident rainbow trout were abundant and easily confused with the
juvenile steelhead.
The limited limnological data collected could not be correlated with
either SCUBA observations or gill-net catches because continuous data at each
reservoir could not be obtained by a single crew.
It was recommended that equipment and techniques for studying behavior
of juvenile salmonids in reservoirs should be further developed, and that the
behavior pattern of juvenile salmonids in both Felton and North Fork Reservoirs
should be determined through continuous observations.
ACKNOWLEDGMENTS
Mark G. DeCew assisted with the literature survey, field work, and
compilation of data but was transferred from the project prior to the writing
of the final report.
Other members of the Oregon Fish Commission aided in
various phases of the project:
Delbert R. Hanks, compilation of data; Earl F.
78.
Fulford, statisticP1 advice; Mrs. Winona Richey, Librarian, aid in literature
survey.
Members of the Bureau of Commercial Fisheries provided advice and
loaned the project a sonar set and bathythermograph.
Portland General Electric
Company allowed the use of certain facilities at North Fork and Felton Reser
voirs and provided information on the numbers of juvenile salmonids leaving
the two reservoirs.
MinneapolisHoneywell Company gave the project personnel
instruction in the use of sonar.
Members of Commercial Divers, Inc., Harold
Maiken, Thomas E. Amerman, and Fred D. Kribs and Amerman's Divers Supplies
gave advice on diving and loaned various items of equipment.
loaned the project a camera and watertight case.
John I. Cranor
79.
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