(DRAFT) - Taxonomy
Species salmon, coho
Species Id M010027
Date 26 AUG 96

TAXONOMY

NAME - salmon, coho

OTHER COMMON NAMES - coho salmon, silver salmon, silver trout (in freshwater), coho, sea trout, blueback and hooknose

ELEMENT CODE -

CATEGORY - Fish

PHYLUM AND SUBPHYLUM - Vertebrata,

CLASS AND SUBCLASS - Osteichthyes,

ORDER AND SUBORDER - Salmoniformes,

FAMILY AND SUBFAMILY - Salmonidae,

GENUS AND SUBGENUS - Oncorhynchus,

SPECIES AND SSP - kisutch,

SCIENTIFIC NAME - Oncorhynchus kisutch

AUTHORITY - Walbaum

TAXONOMY REFERENCES - 88 and 232

COMMENTS ON TAXONOMY -
Common names include coho salmon, silver salmon, silver trout (in
freshwater), coho, sea trout, blueback, and hooknose *88*.

Caution must be used when extending information from one stock of coho
salmon to another stock. Environmental conditions of one area must not be
treated as absolute; the stocks (races) have acclimated or evolved over time
and space to habitat conditions that can vary greatly *232*.

Taxonomy - 1 (DRAFT) - Status
Species salmon, coho
Species Id M010027
Date 26 AUG 96

STATUS

Coded Status
Sport Fish
Commercial
Commercial/consumption
Migrant
Existing, FMP exists
See Comments

REFERENCES FOR STATUS - 88 and 232

COMMENTS ON STATUS -
Coho salmon constitute a valuable part of the commercial and sport fisheries
of the west coast freshwater and marine environments. They are the object
of extensive hatchery rearing and release programs *88*.

The Alaska Board of Fisheries develops regulations governing the commercial,
sport, and subsistence harvest of salmon in Alaska. The Alaska Department
of Fish and Game manages salmon populations in the fresh waters of the state
and in the marine waters to the 3-mi limit *232*.

The North Pacific Fishery Mangaement Council is composed of 15 members, 11
voting and 4 nonvoting members. The 11 are divided as follows: 5 from
Alaska, 3 from Washington, and 3 from state fishery agencies (Alaska,
Washington, Oregon). The four nonvoting members include the director of the
Pacific Marine Fisheries Commission, the director of the U.S. Fish and
Wildlife Service, the commander of the 17th Coast Guard District, and a
representative from the U.S. Department of State. The council prepares
fishery management plans, which become law and apply to marine areas between
the 3-mi limit and the 200-mi limit. With regard to salmon, the only plan
prepared to date is the Salmon Power Troll Rishery Management Plan *232*.

The International North Pacific Fisheries Commission (INPFC), a convention
comprised of Canada, Japan, and the United States, has been established to
provide for scientific studies and for coordinating the collection,
exchange, and analysis of scientific data regarding anadromous species.
With regard to salmon, the INPFC has also prepared conservation measures
that limit the location, time, and number of fishing days that designated
high seas (beyond the 200-mi limit) areas may be fished by Japanese
nationals and fishing vessels *232*.

Coho salmon are anadromous and migrate into freshwater to spawn *232*.

Status - 1 (DRAFT) - Distribution
Species salmon, coho
Species Id M010027
Date 26 AUG 96

DISTRIBUTION

Distribution - 1 HABITAT ASSOCIATIONS

NATIONAL WETLAND INVENTORY CODES

NWI NWICLS NWIMOD NWISPEC

Marine OW0 V 1
Marine OW0 V 1
Riverine SB1 H 0
Riverine SB1 H 0
Riverine SB1 H 0

REFERENCES FOR NWI - 88

COMMENTS ON HABITAT ASSOCIATIONS -
Coho salmon are anadromous, entering freshwater to spawn. Early studies
indicated that coho salmon did not migrate far offshore, but more recent
high-seas research has shown differently. They have been captured as far
as 1,930 km away from their point of origin on the North American west
coast. As a rule, adult coho salmon spend two growing seasons at sea, and
then return to their natal streams to spawn. The fish usually spawn in
small streams, but also use large main streams, though seldom more than 240
km above the mouth. They spawn in relatively fast water (0.3 to 0.5 m/sec
vs. 0.1 m/sec for sockeye), normally in riffles or where ground seepage
occurs. Redds (nests) are dug out in gravel. Fry live in shallow gravel
areas. Optimum rearing habitat for coho consists of a mixture of pools and
riffles, abundant instream and bank cover, water temperatures that average
between 10 and 15 deg C in the summer, dissolved oxygen near saturation,
and low amounts of fine sediment *88*.

Habitat Associations - 1 (DRAFT) - Food Habits
Species salmon, coho
Species Id M010027
Date 26 AUG 96

FOOD HABITS

TROPHIC LEVEL -
CARNIVORE

REFERENCES FOR TROPHIC LEVEL - 88 and 232

LIFESTAGE FOOD FOOD PART
General Crustaceans Larva stage
General Osteichthyes Not Specified
Adult Osteichthyes Not Specified
Adult Clupeiformes Not Specified
Adult Salmoniformes Not Specified
Adult Perciformes Juvenile stage
Juvenile Crustaceans Larva stage
Juvenile Crustaceans Not Specified
Juvenile Insects Not Specified
Juvenile Plecoptra Not Specified
Juvenile Ephemeroptera Not Specified
Juvenile Diptera Not Specified
Juvenile Osteichthyes Not Specified
Juvenile Salmoniformes Juvenile stage
Juvenile Clupeiformes Not Specified
Juvenile Polychaetes Not Specified
Juvenile Brachiopods Larva stage
Juvenile Perciformes Juvenile stage
Important Osteichthyes Not Specified
Important Crustaceans Larva stage
Juvenile Insects:terrestrial Not Specified
Juvenile Diptera Not Specified
Juvenile Diptera Larva stage
Juvenile Diptera Pupa stage
Juvenile Diptera Adult stage
Juvenile Hymenoptera Not Specified
Juvenile Homoptera Not Specified
Juvenile Thysanoptera Not Specified
Juvenile Invertebrate Cordates Not Specified
Juvenile Arachnids Not Specified
Juvenile Coleoptera Not Specified
Juvenile Collembola Not Specified
Juvenile Zooplankton Not Specified
Juvenile Zooplankton Not Specified
Juvenile Salmoniformes Juvenile stage
Juvenile Crustaceans Not Specified
Juvenile Clupeiformes Not Specified
Juvenile Perciformes Not Specified
Juvenile Osteichthyes Not Specified
Juvenile Molluscs Not Specified
Juvenile Squid, Octopus Not Specified
Adult Osteichthyes Not Specified
Adult Invertebrate Cordates Not Specified
Adult Clupeiformes Not Specified
Adult Salmoniformes Not Specified
Food Habits - 1 (DRAFT) - Food Habits
Species salmon, coho
Species Id M010027
Date 26 AUG 96

LIFESTAGE FOOD FOOD PART
Adult Myctophiformes Not Specified
Adult Atheriniformes Not Specified
Adult Gadiformes Not Specified
Adult Perciformes Not Specified
Adult Molluscs Not Specified
Adult Squid, Octopus Not Specified
Adult Cirripeds Not Specified
Adult Malacostraca Not Specified
Adult Cnidaria Not Specified
Adult Crustaceans Not Specified
General Myctophiformes Not Specified
Juvenile See Comments; Food See Comments
Adult See Comments; Food See Comments
General See Comments; Food See Comments

REFERENCES FOR GENERAL FOOD - 88 and 232

REFERENCES FOR IMPORTANT FOOD - 88

REFERENCES FOR ADULT FOOD - 88 and 232

REFERENCES FOR JUVENILE FOOD - 88 and 232

REFERENCES FOR LARVAE FOOD - 88

COMMENTS ON FOOD -
Coho salmon fill different niches in freshwater and in saltwater. The
alevins living in gravel do not feed, but depend on the yolk sac for
nourishment. Even though part of the yolk sac may remain after emergence,
the fry begin to feed immediately after emergence. Juvenile salmon in
Washington, depending on the season and stream, ate various lifestages of
aquatic insects (mostly at the surface), such as dipterans, ephemeropterans,
plecopterans, and other insects, as well as crustaceans and fishes. If
their normal food is scarce, juvenile coho will eat insect exuviae, even
though this provides no nutrition. Alaskan coho fingerlings prey on
sockeye salmon fry (Onchorhynchus nerka); 30% of coho captured between May
and July had sockeye remains in their stomachs. They ate the sockeye even
though sticklebacks were more abundant.
The food of coho salmon was categorized by zones in the Puget Sound and
other Washington marine waters. Juvenile fish from sublittoral habitats had
stomach contents consisting mainly of decapod crustacean larvae, plus fishes
(mostly herring), amphipods, and polychaetes. In the nearshore pelagic
zone, some juveniles examined had brachyuran crab larvae as their primary
food item. Young coho from the offshore pelagic zone ate euphausids, fishes
(mainly herring), gammarids, and decapod larvae. Fishes formed the highest
biomass, but occurred in only 30% of the coho salmon stomachs. Offshore in
the Pacific, near the Columbia River, young adult coho examined were larger
than those in Puget Sound and ate mostly fishes, including anchovy, surf
smelt, whitebait smelt, herring, juvenile chinook, and juvenile rockfish.
They also fed on euphausids and crab larvae off Oregon and Washington. In
the Great Lakes, coho and other salmon have confirmed hopes that they would
Food Habits - 2 (DRAFT) - Food Habits
Species salmon, coho
Species Id M010027
Date 26 AUG 96

consume the smelt and alewives present there in abundance *88*.

Types of Feeding Areas Used: Young juveniles feed in low-velocity areas
along streambanks and in backwater pools and current eddies. Feeding is
generally near the surface, with drifting invertebrates the prey; young coho
salmon feed infrequently on bottom-dwelling organisms. As they grow in
size, the juveniles may become serious predators of other small fish,
including other salmon species. When the young coho salmon migrate to the
sea, they tend to stay fairly close to shore at first. The oceanic
movements of coho salmon in the southern part of the range (i.e.,
Washington, Oregon, British columbia) seem to be chiefly along the coast,
with some fish apparently never venturing far from the coast. By contrast,
northern fish, particularly those from Alaska streams, spread out all across
the North Pacific and into the Bering Sea. Available evidence from
commercial fishries and research vessels indicates that while at sea coho
salmon occur most frequently near the surface. Individuals have been taken
at greater depths, but most coho salmon have been caught in the upper 10 m
*232*.

Factors Limiting Availability of Food: Sedimentation is one of the major
factors affecting freshwater food availability. Excessive sedimentation may
inhibit production of aquatic plants and invertebrate fauna. Primary food
production is lowered above levels of 25 JTU (Jackson Turbidity Unit) and
visual references lost above levels of 30 JTU *232*.

Feeding Behavior: Food varies from place to place and with time. While on
the high seas, schools may become involved in a feeding frenzy and have been
found to be eating blue lanternfish and sauries. Upon entering fresh water,
adult salmon no longer feed but live off the fat they stored up while in the
ocean *232*.

COMMENTS ON ADULT FOOD -
Offshore in the Pacific, near the Columbia River, young adult coho examined
were larger than those in Puget Sound and ate mostly fishes, including
anchovy, surf smelt, whitebait smelt, herring, juvenile chinook, and
juvenile rockfish. They also fed on euphausids and crab larvae off Oregon
and Washington. In the Great Lakes, coho and other salmon have confirmed
hopes that they would consume the smelt and alewives present there in
abundance *88*.

The food of marine adults is more pelagic and more varied than that of many
Pacific salmon. Fishes make up 70 to 80% of the coho salmon's food,
invertebrates 20 to 30%, and include the following: pilchard, herring,
anchovy, coho salmon, capelin, lanternfish, Pacific saury, hake, whiting,
rockfishes, black cod, sculpins, sand lance, squid, barnacles, isopods,
amphipods, euphausiids, crab larvae, and jelly fish. Herring and sand lance
make up 75% of the volume. Some populations, however, remain on the
crustacean diet, such coho generally not growing as big as those that eat
fish *232*.

COMMENTS ON JUVENILE FOOD -
Juvenile salmon in Washington, depending on the season and stream, ate
various life stages of aquatic insects (mostly at the surface), such as
Food Habits - 3 (DRAFT) - Food Habits
Species salmon, coho
Species Id M010027
Date 26 AUG 96

dipterans, ephemeropterans, plecopterans, and other insects, as well as
crustaceans and fishes. If their normal food is scarce, juvenile coho will
eat insect exuviae, though this provides no nutrition. Alaskan coho
fingerlings prey on sockeye salmon fry; 30% of coho captured between May
and July had sockeye remains in their stomachs. They ate the sockeye even
though sticklebacks were more abundant.
The food of coho salmon was categorized by zones in the Puget Sound and
other Washington marine waters. Juvenile fish from sublittoral habitats had
stomach contents consisting mainly of decapod crustacean larvae, plus fishes
(mostly herring), amphipods, and polychaetes. In the nearshore pelagic
zone, some juveniles examined had brachyuran crab larvae as their primary
food item. Young coho from the offshore pelagic zone ate euphausids, fishes
(mainly herring), gammarids, and decapod larvae. Fishes formed the highest
biomass, but occurred in only 30% of the coho salmon stomachs. Offshore in
the Pacific, near the Columbia River, young adult coho examined were larger
than those in Puget Sound and ate mostly fishes, including anchovy, surf
smelt, whitebait smelt, herring, juvenile chinook, and juvenile rockfish.
They also fed on euphausids and crab larvae off Oregon and Washington. In
the Great Lakes, coho and other salmon have confirmed hopes that they would
consume the smelt and alewives present there in abundance *88*.

Upon hatching, young alevin remain in the gravel for two or three weeks
until the yolk sack has been absorbed. Following emergence from the gravel,
the juveniles begin feeding at or near the surface. Major food items at
this time are terrestrial insects, especially species of flies (Diptera) and
wasps and bees (Hymenoptera), and perhaps also aphids and thrips. Midges
(chironomids) were dominant in stomach samples of juvenile coho salmon in
the Kenai River, Alaska. Juvenile coho salmon food habit studies during
August and September in sloughs and clearwater tributaries of the middle
reach of the Susitna River suggest that the range and diversity of
invertebrates in their diet indicate an ability to adapt to variable
conditions. Specimens collected during the study had consumed both
terrestrial and aquatic invertebrates. Based on numbers consumed, they
relied mainly on midge (Diptera: Chironomidae) larvae, pupae and adults.
Although not contributing much in terms of dry wieght, the major components
of their terrestrial diet were usually small aphids (Homoptera: Aphidae),
small Depterans (Phoridae, Simuliidae, and Scaridae), and small (less than 5
mm) Hymenopterans. The diet can also include mites, beetles, springtails
(Collembola), spiders, and small zooplankton. As the young fish grow they
consume larger food items and often consume young sockeye salmon. In
Chignik Lake, Alaska, young coho salmon have been found to eat seven times
as many juvenile sockeye salmon as do Dolly Varden, and in other localities
coho salmon may be equally serious predators. Large numbers of chum and
pink salmon are also taken by coho salmon. Upon entering the sea, young
coho feed on various planktonic crustaceans, pink and chum salmon fry,
herring, sand lance, other fishes, and squid *232*.

COMMENTS ON LARVAE FOOD -
Coho alevins living in gravel do not feed, but depend on the yolk sac for
nourishment *88*.

Food Habits - 4 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

ENVIRONMENTAL ASSOCIATIONS

G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Water Temperature: Below 15 degrees C
G Water Depth Preference: Specified in Comments
G Water Velocity [Instream Flow Group Increments]: Specified in Comments
G Turbidity: Specified in Comments
G Terrestrial Features: Specified in Comments
G Aquatic Features: Riffles
G Aquatic Features: Pool areas
A Water Temperature: Below 15 degrees C
A Water Depth Preference: Specified in Comments
A Water Velocity [Instream Flow Group Increments]: Specified in Comments
A Bottom Type [Aquatic]: Gravel
A Terrestrial Features: Specified in Comments
A Estuarine habitat zone: offshore
J Water Depth Preference: Less than 1 ft.
J Water Depth Preference: 1-5 ft.
J Water Velocity [Instream Flow Group Increments]: Specified in Comments
J Dissolved Oxygen: High [greater than 7 mg/l] oxygen concentrations
J Water Velocity [Instream Flow Group Increments]: 0.5-1.0 fps
J Turbidity: Specified in Comments
J Aquatic Features: Riffles
J Aquatic Features: Pool areas
L Bottom Type [Aquatic]: Gravel
L Water Temperature: Below 15 degrees C
L Terrestrial Features: Specified in Comments
L Dissolved Oxygen: High [greater than 7 mg/l] oxygen concentrations
E Water Temperature: Below 15 degrees C
E Dissolved Oxygen: High [greater than 7 mg/l] oxygen concentrations
E Turbidity: Specified in Comments
LIM Dissolved Oxygen: Low [less than 5 mg/l] oxygen concentrations
LIM Water Temperature: Between 21-27 degrees C
E Water Temperature: Below 15 degrees C
E Water Temperature: Specified in Comments
LIM Water Temperature: Between 21-27 degrees C
LIM Water Temperature: Specified in Comments
J Water Temperature: Between 21-27 degrees C
J Water Temperature: Specified in Comments
J Water Temperature: Below 15 degrees C
J Bottom Type [Aquatic]: Rooted aquatic vegetation
J Bottom Type [Aquatic]: Specified in Comments
G Bottom Type [Aquatic]: Rooted aquatic vegetation
Environment Associations - 1 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Bottom Type [Aquatic]: Specified in Comments
J Aquatic Vegetation [specified type]: Specified in comments
G Aquatic Vegetation [specified type]: Specified in comments
FJ Water Temperature: Between 15-21 degrees C
FJ Water Temperature: Below 15 degrees C
FJ Water Temperature: Specified in Comments
BA Water Temperature: Below 15 degrees C
BA Water Temperature: Specified in Comments
G Water pH: Between 6.5-8.5
G Water pH: Between 8.5-10.0
G Water pH: Specified in Comments
BA Dissolved Oxygen: Specified in Comments
A Dissolved Oxygen: Specified in Comments
BA Dissolved Oxygen: Specified in Comments
E Substrate: Rocks
E Substrate: Specified in Comments
E Bottom Type [Aquatic]: Gravel
E Bottom Type [Aquatic]: Specified in Comments
J Substrate: Rocks
J Substrate: Specified in Comments
J Bottom Type [Aquatic]: Gravel
J Bottom Type [Aquatic]: Rubble
J Bottom Type [Aquatic]: Specified in Comments
G Dissolved Oxygen: High [greater than 7 mg/l] oxygen concentrations
G Dissolved Oxygen: Specified in Comments
E Turbidity: Specified in Comments
J Turbidity: Specified in Comments
G Turbidity: Specified in Comments
E Water Depth Preference: Specified in Comments
E Water Velocity [Instream Flow Group Increments]: Specified in Comments
J Aquatic Features: Pool areas
J Aquatic Vegetation [specified type]: Specified in comments
J Aquatic Habitat Zonation: Shallows with emergent vegetation [littoral zone]
J Aquatic Habitat Zonation: Specified in Comments
J Aquatic Features: Backwaters
J Aquatic Features: Specified in Comments
A Water Depth Preference: Specified in Comments
J Water Velocity [Instream Flow Group Increments]: Specified in Comments
J Aquatic Features: Riffles
J Aquatic Features: Specified in Comments
FJ Aquatic Habitat Zonation: Specified in Comments
FJ Water Depth Preference: Specified in Comments
FJ Water Velocity [Instream Flow Group Increments]: Specified in Comments
FJ Coastal Features: Specified in Comments
E Dissolved Oxygen: Specified in Comments
E Water Temperature: Specified in Comments
E Water Velocity [Instream Flow Group Increments]: Specified in Comments
E Substrate: Specified in Comments
E Gradient: Specified in Comments
BA Aquatic Features: Specified in Comments
BA Aquatic Features: Riffles
E Water Temperature: Below 15 degrees C
Environment Associations - 2 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
E Water Temperature: Specified in Comments
BA Water Depth Preference: Less than 1 ft.
BA Water Depth Preference: 1-5 ft.
BA Water Depth Preference: Specified in Comments
G Water Depth Preference: Less than 1 ft.
G Water Depth Preference: Specified in Comments
FA Water Depth Preference: 25-50 ft.
FA Water Depth Preference: Specified in Comments

REFERENCES FOR ENVIRONMENTAL ASSOC_ - 88 and 232

REFERENCES FOR LIMITING ENVIRONMENTAL ASSOC_ - 88 and 232

REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 88 and 232

REFERENCES FOR RESTING ADULT ENVIRONMENTAL ASSOC_ - 88

REFERENCES FOR BREEDING ADULT ENVIRONMENTAL ASSOC_ - 88 and 232

REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 232

REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 88 and 232

REFERENCES FOR RESTING JUVENILE ENVIRONMENTAL ASSOC_ - 88

REFERENCES FOR FEEDING LARVAE ENVIRONMENTAL ASSOC_ - 88

REFERENCES FOR RESTING LARVAE ENVIRONMENTAL ASSOC_ - 88

REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 88 and 232

COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
HABITAT ZONE: Coho salmon are anadromous, inhabiting the open ocean and
returning to coastal areas near the outlets of their natal streams,
entering freshwater to spawn.
TEMPERATURE: Preferred temperatures for coho salmon in streams range
between 11.8 and 14.6 deg C.
DEPTH: Most coho salmon are found within 10 m of the sea surface except
when covered by a shallow layer of "tuna" water.
WATER VELOCITY: Adults can swim in water velocities as high as 2.44 m/sec,
with even faster bursts of speed.
DISSOLVED OXYGEN: Coho salmon prefer highly oxygenated water.
SUBSTRATE: Coho salmon in streams are found over a gravel substrate.
SEDIMENT: Coho prefer areas of low siltation. In a study of the
reactions of coho and chinook salmon to Mt. St. Helens volcanic ash and
mudflow sediment in two rivers, 96-hr LC50's at 1,217 and 509 mg/l of
suspended mud and ash were obtained for coho presmolts and smolts,
respectively. A comparative static bioassay with ash produced 96-h LC50's
at 18,672 and 28,184 mg/l for presmolts and smolts, respectively. A static
Environment Associations - 3 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

96-h bioassay using mudflow sediments produced mortality in smolts at
29,580 mg/l.
COVER: Salmon abundance has been linked to available cover in a stream.
Overhead cover provides shade and protection from terrestrial predators,
while submerged cover provides shelter from current and predators *88*.

There is no optimum pH value for fish in general; however, in waters where
good fish fauna occur, the pH usually ranges between 6.7 and 8.3. State of
Alaska water quality criteria for freshwater growth and propagation of fish
specify pH values of not less than 6.5 or greater than 9.0, with variances
of no more than 0.5 pH unit from natural conditions *232*.

State of Alaska water quality criteria for growth and propagation of fish
state that "D.O. shall be greater than 7 mg/l in waters used by anadromous
and resident fish. Further, in no case shall D.O. be less than 5 mg/l to a
depth of 20 cm in the interstitial waters of gravel utilized by anadromous
or resident fish for spawning ... In no case shall D.O. above 17 mg/l be
permitted. The concentration of total dissolved gas shall not exceed 110
percent of saturation at any point of sample collection." *232*.

Excess velocities and shallow water may impede migrating fish. Pacific
Northwest coho salmon require a minimum depth of 0.18 m, with velocities
less than 2.44 m/sec for migration *232*.

COMMENTS ON LIMITING ENVIRONMENTAL ASSOC_ -
Under laboratory conditions, upper lethal temperature limit of juvenile
coho salmon was found to be 25.0 oC *232*.

COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Adult entry into fresh water may be triggered in part by a rise in water
temperature *232*.

Adult swimming performance is adversely affected by reduction of D.O.
concentrations below air saturation level. It is desirable that D.O.
concentrations be at or near saturation and that it is especially important
in spawning areas, where D.O. levels must not be below 7 ppm at any time
*232*.

Turbid wter will absorb more solar radiation than clear water and thus
indirectly raise thermal barriers to adult upstream spawning migration
*232*.

Undercut banks and deep water pools provide protection for adults *232*.

The oceanic movements of coho salmon in the southern part of the range
(i.e., Washington, Oregon, British columbia) seem to be chiefly along the
coast, with some fish apparently never venturing far from the coast. By
contrast, northern fish, particularly those from Alaska streams, spread out
all across the North Pacific and into the Bering Sea. Available evidence
from commercial fishries and research vessels indicates that while at sea
coho salmon occur most frequently near the surface. Individuals have been
taken at greater depths, but most coho salmon have been caught in the upper
10 m *232*.
Environment Associations - 4 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
HABITAT ZONE: Coho salmon are anadromous, inhabiting the open ocean and
returning to coastal areas near the outlets of their natal streams,
entering freshwater to spawn.
TEMPERATURE: Preferred temperatures for coho salmon in streams range
between 11.8 and 14.6 deg C.
DEPTH: Most coho salmon are found within 10 m of the sea surface except
when covered by a shallow layer of "tuna" water.
WATER VELOCITY: Adults can swim in water velocities as high as 2.44 m/sec,
with even faster bursts of speed.
DISSOLVED OXYGEN: Coho salmon prefer highly oxygenated water.
SUBSTRATE: Coho salmon in streams are found over a gravel substrate.
SEDIMENT: Coho prefer areas of low siltation. In a study of the
reactions of coho and chinook salmon to Mt. St. Helens volcanic ash and
mudflow sediment in two rivers, 96-hr LC50's at 1,217 and 509 mg/l of
suspended mud and ash were obtained for coho presmolts and smolts,
respectively. A comparative static bioassay with ash produced 96-h LC50's
at 18,672 and 28,184 mg/l for presmolts and smolts, respectively. A static
96-h bioassay using mudflow sediments produced mortality in smolts at
29,580 mg/l.
COVER: Salmon abundance has been linked to available cover in a stream.
Overhead cover provides shade and protection from terrestrial predators,
while submerged cover provides shelter from current and predators *88*.

COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
WATER VELOCITY: Water velocities preferred by invertebrate food items are
in the range of 0.15 to 1.22 m/sec.
TURBIDITY: High levels of suspended sediments can curtail feeding.
Sediment also may destroy food supplies *88*.

COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
WATER VELOCITY: Coho spawn in relatively fast water (0.3 to 0.5 m/sec vs.
0.1 m/sec for sockeye).
HABITAT ZONE: Coho usually spawn in small streams, but also use large main
streams, though seldom more than 240 km above the mouth.
HABITAT FEATURES: Spawning normally occurs in riffles or where ground
seepage occurs.
TEMPERATURE: Spawning takes place at temperatures of 0.8 to 7.7 deg C in
Kamchatka, U.S.S.R. and at 4.4 to 9.4 deg C on the west coast of the United
States.
DEPTH: Adult coho salmon can spawn in shallow water (0.18 m).
SUBSTRATE: A gravel size range of 1.3 to 10.2 cm is necessary for spawning
*88*.
Environment Associations - 5 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

Adult entry into fresh water may be triggered in part by a rise in water
temperature. Spawning occurs over a wide range of water temperatures.
Water temperatures during spawning in Kamchatka, USSR, rivers were as low
as 0.8 oC and as high as 7.7 oC. A study suggests that 4.4 to 9.4 oC is a
more preferred temperature range for spawning *232*.

The groundwater that is typical of coho salmon spawning beds is usually
highly oxygenated *232*.

It is desirable that D.O. concentrations be at or near saturation and that
it is especially important in spawning areas, where D.O. levels must not be
below 7 ppm at any time *232*.

Turbid wter will absorb more solar radiation than clear water and thus
indirectly raise thermal barriers to adult upstream spawning migration
*232*.

Velocity is also important in redd construction because the water carries
dislodged substrate materials from the nesting site. Measured flow rates at
0.12 m above the streambed include 19.2 to 69.2 cm/sec in Oregon and 7.6 to
61.0 cm/sec in the Columbia River and tributaries. Minimum water depths at
these spawning sites ranged from 0.122 to 0.153 m in Oregon and from 0.305
to 0.458 m in the Columbia River and tributaries. Spawning velocity (as
measured 0.12 m above streambed) and minimum depth ciriteria for Oregon
coho salmon is recommended to be 21.0 to 70.0 cm/sec and 0.15 m,
respectively. A study lists measured velocities for the Kenai River and one
tributary stream as 21.4 to 30.5 cm/sec pit velocity and 51.8 to 82.8
cm/sec tailspill velocity. The pit depths at these redds were 54.5 to 76.3
cm, and the tailspill depths were 25.0 to 45.0 cm *232*.

COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Under laboratory conditions, the upper lethal temperature limit of juvenile
coho salmon was found to be 25.0 oC. Preferred temperatures for rearing
juveniles is listed as 11.8 to 14.6 oC. During winter studies on a small
stream in Vancouver, British Columbia, it was found that at 7 oC or less
the young coho were associated with water velocitites of less than 15
cm/sec. It also noted that as water temperature decreased from 9 to 2 oC
the coho salmon moved closer to cover (e.g., logs, uprooted tree roots,
debris accumulations, overhanging banks, and overhanging brush) *232*.

During laboratory tests of sustained swimming speeds of juvenile coho
salmon, the reduction of oxygen concentration of air saturation levels to
7,6,5,4, and 3 mg/l usually resulted in reduction of the maximum sustained
swimming speed by about 5, 8, 13, 20, and 30%, respectively *232*.

Prolonged exposure to turbid water causes gill irritation in juveniles,
which can result in fungal and pathogenic bacterial infection. Excess
turbidity from organic materials in the process of oxidation may reduce
oxygen below safe levels, and sedimentation may smother food organisms and
reduce primary productivity. From investigation of the Susitna River in
Southcentral Alaska, turbid wtaer was found to be a strong factor that
influenced juvenile fish ditributions. This study indicates that rearing
Environment Associations - 6 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

Environment Associations - 7 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

coho salmon apparently avoid turbid water *232*.

Juveniles after emerging from the gravel stay almost entirely in pools,
avoiding riffle areas. During studies on the Kenai River, Alaska, and its
tributaries, it was found that recently emerged juveniles (less than 50 mm
long) in the main stem of the river were close to banks and often in
reaches where the river had flooded terrestrial areas. Most of these
juveniles were found in zones of zero water velocity, and almost 80% were
captured in areas of less than 6.1 cm/sec mean water column velocity.
Larger juvenile coho salmon (51 to 71 mm) were typically captured in creek
mouth basins, backwater pools, and man-made canals. Ninety percent of
these fish were in habitat having no measurable water velocity. In
contrast to these findings, the juveniles in Kenai River tributary streams
were found in pool-riffle habitat. Sooner-emerging chinook salmon
juveniles may be displacing main stem spawned coho salmon into tributaries,
canals, and basins. Since the main stem age 0 coho salmon do not appear to
be attaining the same growth as similar age fish in the Deshka or Susitna
rivers, the areas to which they have been forced is probably not their
preferred habitat and may not supply the drift food items that are a major
contributor to salmonid diets. Competition with stickleback may also play
a role in the lower coho salmon growht rates. An optimum wter velocity for
coho salmon fry is from 15.2 to 18.3 cm/sec. Stream velocity is important
to juveniles because it is the most important parameter in determining the
distribution of aquatic invertebrates (food sources) in streams *232*.

Substrate composition regulates production of invertebrates, which are food
sources for juveniles. Highest invertebrate production is from gravel and
rubble-size materials associated with riffle areas *232*.

Emergent terrestrial vegetation was the dominant cover type used by
juvenile coho salmon in their backwater pool-rearing areas in the main stem
Kenai River *232*.

Juvenile coho salmon were associated with water velocities of less than 15
cm/sec when the water temperature was 7 oC or less. As the temperature
dropped from 9 to 2 oC young coho salmon moved closer to cover provided by
such things as logs, uprooted trees, debris accumulations, overhanging
banks, and overhanging brush *232*.

Young juveniles feed in low-velocity areas along streambanks and in
backwater pools and current eddies. Feeding is generally near the surface,
with drifting invertebrates the prey; young coho salmon feed infrequently
on bottom-dwelling organisms. As they grow in size, the juveniles may
become serious predators of other small fish, including other salmon
species. When the young coho salmon migrate to the sea, they tend to stay
fairly close to shore at first. The oceanic movements of coho salmon in the
southern part of the range (i.e., Washington, Oregon, British columbia)
seem to be chiefly along the coast, with some fish apparently never
venturing far from the coast. By contrast, northern fish, particularly
those from Alaska streams, spread out all across the North Pacific and into
the Bering Sea. Available evidence from commercial fishries and research
vessels indicates that while at sea coho salmon occur most frequently near
the surface. Individuals have been taken at greater depths, but most coho
Environment Associations - 8 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

salmon have been caught in the upper 10 m *232*.

COMMENTS ON RESTING JUVENILE ENVIRONMENTAL ASSOC_ -
DEPTH: Juvenile coho salmon prefer water depths of 0.3 to 1.2 m. Most
juvenile coho are found within 10 m of the sea surface.
TEMPERATURE: Optimum rearing temperatures range from 10 to 15 deg C in the
summer.
WATER VELOCITY: Juvenile rearing must take place in water velocities of
well under 1 m/sec.
DISSOLVED OXYGEN: Juvenile coho prefer highly oxygenated water. Growth
and food conversion decline at levels below about 4 mg/l. Swimming ability
of juveniles can also drop in unsaturated water.
TURBIDITY: Low siltation is important for survival of juveniles. Silt
loads of less than 25 mg/l have been listed as best *88*.

COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
DEPTH: Juvenile coho eat various life stages of aquatic insects, mostly at
the surface of streams *88*.

While feeding in the ocean, maturing coho salmon have been found in areas
where surface temperatures have ranged from 4.0 to 15.2 oC, with most being
found in the 8 to 12 oC range. Various evidence, however, indicates that
coho may occur in even colder waters *232*.

Environment Associations - 9 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Alevin development has occurred over a wide range of temperatures *232*.

Sedimentation causes high mortality alevin by reducing water interchange in
the redd *232*.

Sufficient water velocity and depth are needed to allow proper intragravel
water movement (apparent velocity) so that dissolved oxygen is transported
to alevins and in turn metabolic wastes are removed *232*.

Alevin development occurs in substrates ranging widely in size and
composition. The ADF&G states that optimum substrate composition is
small-to-medium gravel. Generally, sediments less than .64 cm diameter
should comprise less than 20 to 25% of the incubation substrate *232*.

COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
SUBSTRATE: Larvae live over a gravel substrate.
HABITAT FEATURES: Optimum rearing habitat for coho consists of a mixture
of pools and riffles and abundant instream and bank cover.
TEMPERATURE: Optimum rearing occurs in water temperatures between 10 and
15 deg C.
DISSOLVED OXYGEN: Coho larvae prefer highly oxygenated water, near
saturation.
TURBIDITY: Larvae prefer low amounts of fine siltation. Large amounts of
deposited silt restrict oxygen flow to fry, and trap fry attempting to
leave the gravel. It was reported that chronic turbidity affected the
emergence and rearing of young coho salmon *88*.

COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
SUBSTRATE: The alevins living in substrate do not feed, but depend on the
yolk sac for nourishment *88*.

COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
DISSOLVED OXYGEN: Coho salmon embryos prefer highly oxygenated water.
Reduced oxygen levels inhibited growth and lengthened incubation time for
coho embryos. Low oxygen concentrations reduced survival of coho embryos.
TURBIDITY: Low siltation is important for the survival of coho eggs.
Silt loads of less than 25 mg/l have been listed as best *88*.

Egg incubation has occurred over a wide range of temperatures. Recommended
incubation temperatures for coho salmon is suggested to be 4.4 to 13.3 oC
*232*.

Sedimentation causes high mortality to eggs by reducing water interchange
in the redd. If 15 to 20 % of the intragravel spaces become filled with
sediment, salmonid eggs have suffered significant (upwards of 85%)
mortality *232*.

Sufficient water velocity and depth are needed to allow proper intragravel
water movement (apparent velocity) so that dissolved oxygen is transported
to eggs and in turn metabolic wastes are removed *232*.

Egg incubation occurs in substrates ranging widely in size and composition.
Environment Associations - 10 (DRAFT) - Environment Associations
Species salmon, coho
Species Id M010027
Date 26 AUG 96

The ADF&G states that optimum substrate composition is small-to-medium
gravel. Generally, sediments less than .64 cm diameter should comprise less
than 20 to 25% of the incubation substrate *232*.

Environment Associations - 11 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

LIFE HISTORY

MORPHOLOGY/IDENTIFICATION AIDS: Dorsal fin 9-12 rays; adipose present;
anal fin 12-17 rays; pectoral fin 13-16 rays; ventral fin 9-11 rays with
axillary process; lateral line scales 121-148; pyloric caeca 45-83;
vertebrae 61-69; gill rakers 18-26 on first gill arch; branchiostegal rays
11-15. Measurements as percent: body depth 24 (in standard length); head
length 22 (in total length); head longer in spawning males.
Body fusiform, somewhat compressed laterally; fork length usually 46 to 61
cm, maximum 98 cm; and 3.6 to 4.5 kg, with a maximum 14 kg in marine
population.
Pigmentation: Juveniles colored blue-green dorsally, with silvery sides,
and 8 to 12 widely spaced, narrow parr marks; dark adipose fin; orange
caudal fin; and large orange anal fin with three long anterior rays and
black posteriorly. Ocean-dwelling adults steel-blue to greenish dorsally;
silvery sides, and white ventral surface; small black spots on back, upper
sides, dorsal fin base, and upper lobe of caudal fin. Before spawning,
males acquire darker, dusky blue-green back, with bright red stripe on dull
sides, grey to black ventral surface.
Pale gums in marine adult coho distinguish it from chinook salmon
(Oncorhynchus tshawytscha), which have black gums. Spotting confined to
upper lobes of caudal fin (spotting on both lobes in chinook), and number of
pyloric caeca less than 83 in coho and greater than 140 in chinook.
Juvenile coho have pigmentation over entire adipose fin, while juvenile
chinook have an unpigmented adipose.

SPAWNING AND EGGS: Coho are anadromous, entering freshwater to spawn.
Beginning in July, but later than August in some areas such as Gray's
Harbor, they return from the open ocean to coastal areas near the outlets of
their natal streams. They enter rivers on all but peak floods, moving
upstream primarily in daylight. Runs take place from August to February. A
November peak was reported in a Washington stream.
Coho salmon spend 30 to 60 days in freshwater, and in North America, peak
spawning occurs from late September to January, and continues as late as
March. The fish usually spawn in small streams, but also use large main
streams, though seldom more than 240 km above the mouth. They spawn in
relatively fast water (0.3 to 0.5 m/sec vs. 0.1 m/sec for sockeye), normally
in riffles or where ground seepage occurs. Although numbers of males and
females in a spawning run are similar males may predominate early in the run
and females later. More males are present overall due to jacks (sexually
precocious males that return early), while females predominate slightly in
the older adults. More than one male often competes for a spawning female.
Spawning takes place at temperatures of 0.8 to 7.7 deg C in Kamchatka,
U.S.S.R. and at 4.4 to 9.4 deg C on the west coast of the United States.
Fecundity of coho salmon is variable depending on the size of the female,
geographic area, and year. A range of about 1,440 to 5,700 eggs for females
44 to 72 cm long in Washington and an average of 2,100 to 2,789 eggs per
female (no lengths given) in British Columbia has been cited. Estimates in
Kamchatka put coho salmon second to chinook salmon in fecundity, but no
lengths were given. The following fecundity formula was developed in 1954:
Number of eggs = 0.01153 x fork length^2.9403.
The female may deposit eggs in 3 or 4 redds (nests), which she digs by lying
on her side and beating out the gravel with her tail. A dominant male moves
Life History - 1 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

in and joins the female; the spawning act consists of vibration by both
fish, with gaping mouths, and the release of eggs and milt. The eggs are
covered with gravel displaced from the upstream side of the nest. Eggs are
demersal, large (about 4.5 to 6.0 mm), and red. The female guards the nest
for a short time, but both parents die soon after spawning. Incubation time
apparently varies inversely with temperature, as shown by the following
observations:
38 days at 11 deg C average
48 days at 9 deg C average
86-101 days at 4.5 deg C.

LARVAE, FRY, AND SMOLTS: Newly hatched larvae possess a large yolk sac,
which they absorb while remaining in the gravel for 2 to 3 weeks following
hatching. They are at first photonegative, but become photopositive, and
face upcurrent as well. Newly emerged fry have been observed from March to
July. The fry live in shallow gravel areas, at first schooling; after a
short time they disperse up- and downstream. Optimum rearing habitat for
coho consists of a mixture of pools and riffles, abundant instream and bank
cover, water temperatures that average between 10 and 15 deg C in the
summer, dissolved oxygen near saturation, and low amounts of fine sediments.
Small numbers of coho salmon may migrate to sea, but at least a year's
residence in freshwater is normal. However, there is a gradation from 1
year in freshwater in Washington up to 2 years in freshwater in central
British Columbia, with more northerly fish usually spending 2 years in
freshwater. For example, fish in the Yukon River drainage spend 2 years in
freshwater. As they grow, the fry move to deeper water, feeding on
progressively larger foods. In winter they feed and grow little. The
juveniles usually migrate downstream from April to August of the year
following their hatching, with peak migrations in May in nearly all areas.
Nighttime migration appears to be the rule.
Size and age of the fish, as well as stream conditions, trigger
outmigration. The radical physiological and behavioral changes that occur
during smoltification make salmon in this stage particularly sensitive to
environmental stress factors. For example, elevated water temperatures can
accelerate the onset of smoltification and shorten the smolting period,
sometimes resulting in seaward migration of smolts at a time when conditions
are unfavorable. Larger juveniles are believed to be the first to go
downstream, but aggression by larger fry may induce early downstream
movement by smaller ones soon after emergence.

OCEAN LIFE: Early studies indicated that coho salmon did not migrate far
offshore, but more recent high-seas research has shown differently. They
have been captured as far as 1,930 km away from their point of origin on the
North American west coast. Movement of these fish is not random, since
marked adult fish from the Columbia River are rare in Alaska salmon catches.
Offshore migrations by juveniles commence in July and August, as evidenced
by sharp declines in inshore catches of juveniles at that time. There are
two migration types of coho salmon in Washington and British Columbia:
"ocean," or high-seas dwellers, migrate great distances, while "inshore"
fish such as those living as residents in the Strait of Georgia or Puget
Sound migrate very little and stay near their river of origin. Four types
of life histories occur in the Puget Sound-Georgia Strait area: (1) ocean
migrants that go to sea in the spring of the second year; (2) resident fish
Life History - 2 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

that go to the ocean in the fall of the second year after spending the
summer in inside marine waters; (3) resident fish that go to the ocean in
the spring of their third year after 1 year in inside marine waters; and
(4) true residents that spend their entire lives in the inside marine
waters. Each of these groups is progressively smaller in average size, due
to less time in the open ocean. High-seas fish of North American origin
probably winter south of 45 deg N. lat., and move north in mid- to late
summer, later than do other salmon.
Coho salmon apparently concentrate in the Gulf of Alaska in the summer,
dispersing coastward from there. Migrations are mostly direct rather than
along shore. Fish reportedly move slowly, wandering as they migrate,
although they have averaged up to 30 mi per day over long distances. The
delays are attributed to intensive feeding until late in their journey.
Most coho salmon, including juveniles and adults, are found within 10 m of
the sea surface except when covered by a layer of warmer "tuna" water.
This zone is where the sport fishery concentrates its efforts.
As a rule, adult coho salmon spend two growing seasons at sea, appearing
offshore near their rivers of origin in the second summer after they enter
saltwater. In southeast Alaska and northern Britsh Columbia, they arrive in
large numbers in July, and in southern British Columbia, Washington, and
Oregon their arrival is later, with a general timing gradation that is
progressively later the more southerly the run. They home almost entirely
to the streams of their origins, and the small percentages that do stray
migrate primarily to nearby streams.

SURVIVAL: Various studies were used by the Washington Department of
Fisheries to derive a composite life sequence to predict average smolt
production per female coho salmon. From this, an average production of 75
smolts/female was estimated. This is applicable only to the 3-year-old fish
that spend 2 years at sea in the southern part of their range, south of
central British Columbia.

GROWTH CHARACTERISTICS: Most coho salmon reside in the the ocean for two
growing seasons, returning at the end of the second summer. These are
designated age 3(2) or 4(3) upon return for spawning (integer is total age
and subscript [in parentheses] is year of life at outmigration). Those that
spend 1 year in freshwater would be 3(2), while those that spend 2 years in
freshwater before outmigrating would be age 4(3). The precocious males
("jacks") or females ("jills" or "jennies") that return to spawn after only
1 summer are designated as 2(2).
California coho salmon averaged 16 cm at outmigration, and grew an average
of about 52 cm while at sea. Kamchatkan coho salmon were similar, with
ocean growth much faster than freshwater growth for both 3(2) and 4(3) fish.
The Kamchatkan returnees averaged 60 cm FL (range 40-87 cm) and 3.5 kg
(range 1.5-6.5 kg). Males were larger than females. The California
returnees' sex, age, and average fork length were as follows: 2(2) males,
46 cm FL; 3(2) males, 64.7 cm; 3(2) females, 63.9 cm. Males were
typically larger than females.

ECOLOGICAL ROLE: Coho salmon fill different niches in freshwater and in
saltwater. The alevins living in gravel do not feed, but depend on the yolk
sac for nourishment. Even though part of the yolk sac may remain after
emergence, the fry begin to feed immediately after emergence. Juvenile
Life History - 3 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

salmon in Washington, depending on the season and stream, ate various life
stages of aquatic insects (mostly on the surface), such as dipterans,
ephemeropterans, plecopterans, and other insects, as well as crustaceans and
fishes. If their normal food is scarce, juvenile coho will eat insect
exuviae, though this provides no nutrition. Alaskan coho fingerlings prey
on sockeye salmon fry (Oncorhynchus nerka); 30% of coho captured between
May and July had sockeye remains in their stomachs. They ate the sockeye
even though sticklebacks were more abundant.
The food of coho salmon was categorized by zones in the Puget Sound and
other Washington marine waters. Juvenile fish from sublittoral habitats had
stomach contents consisting mainly of decapod crustacean larvae, plus fishes
(mostly herring), amphipods, and polychaetes. In the nearshore pelagic
zone, some juveniles examined had brachyuran crab larvae as their primary
food item. Young coho from the offshore pelagic zone ate euphausids, fishes
(mainly herring), gammarids, and decapod larvae. Fishes formed the highest
biomass, but occurred in only 30% of the coho salmon stomachs. Offshore in
the Pacific, near the Columbia River, young adult coho examined were larger
than those in Puget Sound and ate mostly fishes, including anchovy, surf
smelt, whitebait smelt, herring, juvenile chinook, and juvenile rockfish.
They also fed on euphausids and crab larvae off Oregon and Washington. In
the Great Lakes, coho and other salmon have confirmed hopes that they would
consume the smelt and alewives present there in abundance.
Coho salmon themselves are the prey of a variety of animals. Coho juveniles
are taken by other fishes, including other coho salmon, trout, squawfish,
and sculpins. Birds that prey upon coho include mergansers, kingfishers,
and loons. Spawning adults are eaten by animals such as bears and eagles.
Seals and killer whales prey on ocean-dwelling salmon, while man and
parasitic lampreys prey on coho in marine and freshwater environments.
The predation by adult coho salmon on juvenile sockeye salmon, chinook
salmon, and coho salmon is indicative of their aggressiveness. Coho salmon
also eat chum and pink salmon fry. Coho fry are aggressive and territorial
soon after emergence, and establish intraspecific dominance hierarchies.
Where coho and chinook fry occur together in streams, the coho were socially
dominant, defending territory accessible to incoming food. Coho were the
faster growing of the two, and were heavier than chinook fry of the same
length.
Production of juvenile coho salmon in three Oregon streams averaged 9
g/m^2/yr over 4 years. Measurements were made over 14 months of stream
residence time. Monthly averages were 1.9 to 2.8 g/m^2 following emergence,
dropping to 0.2 to 0.3 g/m^2 by winter. Coho production per unit area was
found to be higher in pools with large riffles upstream than in pools
downstream of small riffles, because of a greater available food supply.
Fry expand their territories at 1.5 to 2 months. The reduction in density
may be a result of predation, which may be a major factor in an observed
decline in numbers following the peak of emergence *88*.

Reproductive Habitat: Short coastal streams are usually preferred, but coho
salmon are known to spawn in spring-fed tributaries of the Yukon River
drainage from the Bonasila River at least as far upstream as the Fishing
Branch River in the headwaters of the Porcupine River system. Although
spawning may occur in main channels of large rivers, locations at the head
of riffles in shallow tributaries or narrow side channels are preferred.
Because of the effects of dewatering and freezing, the amount of available
Life History - 4 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

habitat at the time when adult salmon are spawning is a poor indicator of of
the amount of actual habitat that is available as potential incubation
habitat. Estimates of available incubation habitat must take into account
the differential effects of dewatering and freezing in various habitat
types *232*.

Reproductive Seasonality: In Alaska, coho salmon enter freshwater streams
from mid July through November. Actual spawning generally occurs between
September and January. In the Norton Sound area, coho salmon spawn during
late August. As a rule, fish in the northern part of the range enter fresh
water earlier in the season, with runs occurring progressively later to the
south *232*.

Reproductive Behavior: As with other salmon, adult coho salmon return from
the sea and move into their natal freshwater streams to spawn. The female
selects the spawning site and digs the redd (nest) by turning on her side
and thrashing her tail up and down. The current washes loosened substrate
material downstream, and a depression 8 to 51 cm (average about 20 to 25 cm)
deep is formed in the river bottom. Eggs and sperm (milt) are released
simultaneously and deposited in the redd. After egg deposition, the female
moves to the upstream margin of the redd and repeats the digging process.
Dislodged substrate is washed over the eggs. In this manner, the eggs are
covered and prevented from washing away. The process is repeated many
times, and the redd appears to move upstream. As a result of the continued
digging, the redd may grow to become 1.2 m2 to 6.6 m2, with a general
average of about 2.8 m2 for columbia River basin redds. A female may dig
several redds and spawn with more than one male *232*.

Age at Sexual Maturity: The age at which coho salmon reach sexual maturity
ranges from two to six years, although most usually return from marine
waters to spawn at ages 3 or 4. The number of four- and five-year-old fish
usually increases northward *232*.

Fecundity: The number of eggs varies with the size of the fish, the stock,
and sometimes the year. Numbers have been reported from 1,440 to 5,770; the
average probably lies between 2,500 and 3,000. Studies of Kamchatkan salmon
sites average number of eggs as 4,883 *232*.

Frequency of Breeding: As with all Pacific salmon, the spawning cycle is
terminal. Both male and female die after spawning *232*.

Incubation Period/Emergence: The amount of time required for eggs to hatch
is dependent upon many interrelated factors, including 1) dissolved oxygen,
2) water temperature, 3) apparent velocity in gravel, 4)biological oxygen
demand, 5) substrate size (limited by percentage of small fine material), 6)
channel gradient, 7) configuration, 8) water depth, 9) surface water
discharge and velocity, 10) permeability, 11) porosity, and 12) light.
Generally speaking, factors 4 through 12 influence or regulate the key
factors 1,2, and 3. In Alaska, hatching usually takes place from mid winter
to early spring, the amount of time varying with the water temperature.
Hatching times have ranged from 38 days at 10.7 oC to 48 days at 8.9 oC in
California, and they postulate that it might take 42 to 56 days farther
north. Incubation takes six to nine weeks and may require as long as five
Life History - 5 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

months. After hatching, the alevin remain in the gravel for 2 to 3 weeks
(some may take up to 10 weeks) and emerge from the gravel sometime from
April to June *232*.

Size of Use Areas: Juvenile coho salmon after emerging from the gravel take
up residence not far from redds, especially near the banks, where they tend
to congregate in schools. As they grow they disperse and become aggressive
and territorial. Laboratory experiments show that juveniles are aggressive
and territorial or hierarchical in behavior. Heirarchies and territories
were organized on the basis of fish size, and smaller fish tended to move
downstream because of the continuous harassment by the larger fish. Stocks
found that rearing coho salmon were more aggressive than chinook salmon,
tolerated fewer individuals of their own species than did chinook salmon,
and defended positions at the upstream end of a riffle where drifting food
organisms were first available to fish. Studies suggest that a conservative
figure for the number of pairs of salmon that can satisfactorily utilize a
given area of spawning gravel may be obtained by dividing the area by four
times the average size of the redds. Redd area can be computed by measuring
the total length of the redd (upper edge of pit to lower edge of tailspill)
and the average of several equidistant widths. Columbia River basin coho
salmon redds averaged 2.8 m2. Redds in the Kenai River were 1.5 and 0.9 m
long x 1.2 and 0.6 m wide *232*.

Timing of Movements and Use of Areas: The young coho salmon normally spend
a year in fresh water before going to sea, although some may go to sea at
the end of their first summer. Others, as in the Karluk River on Kodiak
Island, Alaska, may stay two, three, or even four years in fresh water. In
Bristol Bay streams coho juveniles stay in fresh water mainly two or more
years. In the Taku River of Southeast Alaska, downstream movement of
juveniles bound for the sea is usually at night, and the trip is completed
during the period mid April through mid June. Studies of smolt
out-migration in the Bear Lake system, near Seward, indicate that very few
smolts migrate prior to stream temperatures attaining 3.9 oC, and for this
system the seaward movement of natural stocks commences during mid May and
continues through late September, with 50% of the migration passing the
sampling weir by mid June. Kenai River seaward migration occurs probably
from July to November. Having spent two or three years in the ocean, mature
coho salmon first arrive in appreciable numbers in coastal waters of
central and southeastern Alaska early in July, and the runs extend into
August or September. Alaska Peninsula coho salmon spend only one year in
salt water. Returns of western Alaska stocks begin in late July in the
Kuskokwim and Yukon rivers and extend through August. Returning adult coho
salmon are found in the bays and estuaries of Norton Sound from early to mid
August. Adult upstream migration and intensive entry into a river is
associated with the beginning of a rising tide, whereas schooling off the
mouth of a river, in brackish waters, occurs during the period of the
falling tide. They ascend the rivers during both rising and falling water
levels but cease movement during peak floods. When in the river, they move
upstream mainly during daylight hours *232*.

Migration Routes: Rivers and streams serve as corridors for smolt
out-migration. Barriers to adult upstream movement include excess
turbidity, high temperatures (20.0 oC or more), sustained high-water
Life History - 6 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

velocities (greater than 2.44 m/sec), and blockage of streams (log jams,
waterfalls). Results of seining and tagging operations have demonstrated
that juvenile North American coho salmon make extensive migrations. Alaskan
coho salmon enter the Alaskan gyre (a generally counterclockwise flow of
water moving westerly near the south side of the Alaska Peninsula and
Aleutian Islands) and travel "downstream," making one complete circuit per
year. They disperse widely in both coastal waters and in the Gulf of Alaska
and eastern North Pacific Ocean (including the Bering Sea) to as far south
as 40 deg N at least. Tag recoveries have shown that juvenile coho salmon
that originate in streams tributary to the Bering Sea penetrate into waters
south of Adak Island in the North Pacific Ocean at least as far west as 176
deg 51' W and at least as far south as 45 deg 24'N. Coho salmon of Western
Alaska origin (e.g., Yukon River and Kuskokwim River drainages) are also
known to enter the central Gulf of Alaska to at least as far east as 145 deg
W and well to the south of 50 deg N. During early spring and summer, as
surface water temperatures warm, North American coho salmon begin a
generally northly movement. There is not yet sufficient information that
would indicate clearly from what locations or at what times the continued
migrations of particular stocks become more positiviely directed toward home
streams. Tagging data do suggest, however, that this does happen - that is,
that a general northward movement over a broad east-west front of many mixed
stocks changes to migrations by individual stocks or particular groups of
stocks that vary in relation to the locations (and probably distances also)
of their ultimate destinations *232*.

Natural Factors Influencing Populations: Coho juveniles especially when
aggregated and abundant, are preyed on by a variety of fishes (e.g., coho
salmon smolts, cutthroat and rainbow trout, Dolly Varden, and sculpins),
mergansers, loons, kingfishers, other birds, and some small mammals. The
adults during their spawning run are taken by bears, other mammals, and
large birds. In the ocean, lampreys, and aquatic mammals (e.g., seals and
killer whales) are the chief predators. The greatest natural mortality
occurs in fresh water during the early life stages and greatly influenced by
environment; therefore, deleterious changes in the freshwater quality,
quantity, or substrate are most detrimental *232*.

Human-related Factors Influencing Populations: A summary of possible
impacts from human-related activities includes: alteration of preferred
water temperature, pH, dissolved oxygen, and chemical composition;
alteration of preferred water velocity and depth; alteration of preferred
stream morphology; increase in suspended organic or mineral material;
increase in sedimentation and reduction in permeability of substrate;
reduction in food supply; reduction in protective cover (e.g., overhanging
stream banks or vegetation); shock waves in aquatic environment; and human
harvest *232*.

LIFE HISTORY CODES -
Foraging Sites: Standing water - Littoral zone
Foraging Sites: Flowing water - riffles
Breeding/Spawning Season: January
Breeding/Spawning Season: February
Breeding/Spawning Season: March
Breeding/Spawning Season: September
Life History - 7 (DRAFT) - Life History
Species salmon, coho
Species Id M010027
Date 26 AUG 96

LIFE HISTORY CODES -
Breeding/Spawning Season: October
Breeding/Spawning Season: November
Breeding/Spawning Season: December
Nest/Den Site: Depression
Spawning Site: Flowing Water
Spawning Site: Gravel
Gestation/Incubation Period: 1-2 months
Gestation/Incubation Period: 3-4 months
Average Number of Offspring/Reproductive Effort: 1,00
Parental Care of Young: No care given young
Dispersion: Clumped
Breeding/Spawning Season: August
Nest Materials: Gravel
Mating System (Single breeding season): Polyandry (fe
Gestation/Incubation Period: 5-6 months
Territoriality: Defends feeding territory only
Periodicity: Active in day

REFERENCES FOR LIFE HISTORY- 88 and 232

Life History - 8 (DRAFT) - Management Practices
Species salmon, coho
Species Id M010027
Date 26 AUG 96

MANAGEMENT PRACTICES

RESULT MANAGEMENT PRACTICE

Existing Regulating harvest of species being described
Beneficial Maintaining/protecting riparian habitats
Beneficial Stocking captive-reared wild-strain animals
Beneficial Developing/maintaining suitable pH
Beneficial Controlling water levels
Beneficial Controlling sedimentation
Beneficial Establishing/maintaining nesting and escape cover
Beneficial Developing/maintaining stream bank vegetation
Beneficial Developing/maintaining stream structures
Beneficial Regulating harvest of species being described
Beneficial Other management practices [specified in comments]

REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 88 and 232

REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 88

COMMENTS ON MANAGEMENT PRACTICES -
Current management objectives of the Washington Department of Fisheries are
toward maximum sustained harvest, with the treaty Indian Tribes under the
Boldt Decision (United States vs. State of Washington) having a legal right
to 50% of the catchable allocation. Preseason run sizes for each individual
river are estimated and escapement goals for each river are predicted; an
escapemant goal is the number of spawners necessary to maintain the run of a
given size, and a goal may vary from year to year. In-season run
reassessments are also made. From these predictions and projections each
year, the catchable allocation of coho salmon in each individual river is
made with non-Indians receiving 50% and treaty Indians receiving 50%. The
non-Indian share is then divided between commercial fishermen and sport
anglers.
Management methods for coho and other salmon must include freshwater habitat
assessment, stock assessment including run size, habitat protection and
improvement, and artificial propogation. The Washington Department of
Fisheries has been using Smoker's preseason method in Puget Sound to predict
coho salmon catches from stream discharge data, as well as the previous
year's jack run size. Such factors, however, as environmental extremes,
saltwater environmental variations, and fishing intensity also play a role.
Other methods are being developed and used in other areas by cooperative
efforts between State biologists and tribal biologists.
Good run forecasts with accurate and timely reassessments are important in
salmon management. Also, runs dependent on hatcheries could be harvested at
a higher rate than wild runs because of high survival of juveniles in
hatcheries. Where two stocks coexist geographically, maximum sustained
yield should be defined for the weaker stock, with the surplus fish taken
where the stronger stock is easier to target. There are arguments against
depending on user groups, i.e., fishermen, for sound management; the
vitality of the resource should be the primary criterion used in designing
management procedures *88*.

Management Practices - 1 (DRAFT) - Management Practices
Species salmon, coho
Species Id M010027
Date 26 AUG 96

A summary of possible impacts from human-related activities includes:
alteration of preferred water temperature, pH, dissolved oxygen, and
chemical composition; alteration of preferred water velocity and depth;
alteration of preferred stream morphology; increase in suspended organic or
mineral material; increase in sedimentation and reduction in permeability of
substrate; reduction in food supply; reduction in protective cover (e.g.,
overhanging stream banks or vegetation); shock waves in aquatic environment;
and human harvest *232*.

Management Practices - 2 (DRAFT) - References
Species salmon, coho
Species Id M010027
Date 26 AUG 96

References

88* Laufle, J.C., G.B. Pauley, and M.F. Shepard. 1986. Species profiles:
life histories and environmental requirements of coastal fishes and
invertebrates (Pacific Northwest)--coho salmon. U.S. Fish Wildl. Serv.
Biol. Rep. 82(11.48). U.S. Army Corps of Engineers, TR EL-82-4. 18 pp.

References - 1