Aggressive Behavior in Juvenile Coho Salmon as a Cause of Emigration

1962 ◽  
Vol 19 (6) ◽  
pp. 1047-1080 ◽  
Author(s):  
D. W. Chapman
Keyword(s):  
Aggressive Behavior ◽  
Coho Salmon ◽  
Growth Opportunities ◽  
Fish Size ◽  
Natural Stream ◽  
Large Numbers ◽  
Dominant Fish ◽  
Early Fall ◽  
Resident Populations ◽  
Downstream Movement

Large numbers of coho fry (called nomads) move downstream from shortly after emergence through early fall. These fry are smaller than residual coho. Study of behavior showed coho to be aggressive and territorial or hierarchical. Nomadic coho placed in stream aquaria barren of resident fish tended to remain in the aquaria rather than continuing downstream movement, while nomads added to resident groups of coho were dominated by the resident dominant fish and tended to leave the channels. Hierarchies were organized on the basis of fish size, with larger fry having better growth opportunities. Feeding of coho in excess of requirements did not alter holding capacity of stream aquaria. Aggression observed in natural stream areas was frequent, probably virtually continuous. Nomads transferred to natural stream areas barren of other coho remained there, while nomads added to resident populations tended to move downstream. It was concluded that aggressive behavior is one important factor causing downstream movement of coho fry.

Density, growth, and change in density of coho salmon and rainbow trout in three Lake Michigan tributaries

1983 ◽  
Vol 61 (5) ◽  
pp. 1120-1127 ◽  
Author(s):  
L. M. Carl
Keyword(s):  
Rainbow Trout ◽  
Growth Rates ◽  
Lake Michigan ◽  
Coho Salmon ◽  
Daily Growth ◽  
Salmon Fry ◽  
Daily Change ◽  
Early Fall ◽  
Growth And Change ◽  
Downstream Movement

Coho salmon spawning peaked in the late fall. Spawning densities ranged from fewer than 5 coho salmon per hectare up to 90 fish per hectare. Subyearling coho salmon densities ranged from 10 to 60 fish per 100 m2 in June and dropped to 5–20 fish by early fall. Coho salmon fry increased in length from 40 mm in early May, to over 120 mm by smolt out-migration in the following April. Coho salmon instantaneous daily change in density coefficients ranged from 0.004 to 0.019 and were dependent on initial coho density. Daily coho salmon growth rates ranged from 0.38 to 0.60 mm per day and were not dependent on initial coho salmon density. Downstream movement of rainbow trout fry began in May, and continued into July. In the spring 10–20 yearlings and one to five 2-year-olds per 100 m2 were present. Most fry emerged in June at a size of 25 mm and grew to 85 mm by fall. Daily growth rates varied from 0.23 to 0.45 mm per day for yearling rainbow trout and were not correlated with rainbow trout density.

Osmoregulatory Ability of Wild Coho Salmon (Oncorhynchus kisutch) and Dolly Varden Char (Salvelinus malma) Smolts

1988 ◽  
Vol 45 (8) ◽  
pp. 1487-1490 ◽  
Author(s):  
Scott W. Johnson ◽  
Jonathan Heifetz
Keyword(s):  
Water Temperature ◽  
Coho Salmon ◽  
Oncorhynchus Kisutch ◽  
Dolly Varden ◽  
Salvelinus Malma ◽  
Small Stream ◽  
Fish Size ◽  
Dolly Varden Char ◽  
Seawater Challenge ◽  
Osmoregulatory Ability

Osmoregulatory ability of wild coho salmon (Oncorhynchus kisutch) and Dolly Varden char (Salvelinus malma) smolts migrating from a small stream in southeastern Alaska was assessed by plasma Na+ levels after a 24-h seawater challenge. Osmoregulatory ability of coho salmon was unaffected by time of out-migration, water temperature, and fish size. Osmoregulatory ability of Dolly Varden char was apparently affected by time of out-migration or water temperature but not by fish size. Char migrating in the first half of the migration period, when water temperature was usually < 8.0 °C, had lower plasma Na+ levels than did char migrating in the second half when temperatures were [Formula: see text]. A plasma Na+ threshold of 170 mmol∙L−1, used by others to separate smolts from silvery parr, indicated that 70% of the coho salmon and 80% of the Dolly Varden char we sampled were physiologically prepared to enter seawater. The remaining fish may have suffered some level of osmoregulatory stress.

Stomach Contents of Salmon and Steelhead Trout in the Northeastern Pacific Ocean

1966 ◽  
Vol 23 (1) ◽  
pp. 85-100 ◽  
Author(s):  
R. J. LeBrasseur
Keyword(s):  
Pacific Ocean ◽  
Chum Salmon ◽  
Coho Salmon ◽  
Pink Salmon ◽  
Stomach Contents ◽  
Northwestern Pacific ◽  
Steelhead Trout ◽  
Fish Size ◽  
Northeastern Pacific

Stomachs of pink, chum, sockeye, and coho salmon and steelhead trout caught during the summer of 1958 in gillnets fished overnight in the northeastern Pacific Ocean contained mainly zooplankton (Limacina, amphipods, copepods, and euphausiids), squid, and fish. Except for sockeye, there were no differences in contents related to fish size or state of maturity. Differences were found between species in the kinds of stomach contents present. The predominant organisms were amphipods and fish in pink salmon, crustaceans in immature sockeye, euphausiids and squid in maturing sockeye, euphausiids, fish, and squid in coho, and fish and squid in steelhead stomachs. The stomach contents of chum salmon were notable in that most of their contents were too well digested to identify. Comparison with the findings of workers in the northwestern Pacific showed no significant differences in the kinds of stomach contents, however, a greater amount of material was present in the stomachs they examined. The contents of stomachs from fish taken in various ocean domains were compared. Greater differences were noted in the stomach contents of fish from different domains than from different species. It is suggested that feeding is associated more with availability rather than with preferences for specific organisms.

Emigration and Production of Hatchery Coho Salmon (Oncorhynchus kisutch) Stocked in Streams Draining an Old-growth and a Clear-cut Watershed

1987 ◽  
Vol 44 (8) ◽  
pp. 1397-1407 ◽  
Author(s):  
Robert E. Bilby ◽  
Peter A. Bisson
Keyword(s):  
Coho Salmon ◽  
Oncorhynchus Kisutch ◽  
Old Growth ◽  
Trophic Conditions ◽  
Temperature Changes ◽  
Gross Photosynthesis ◽  
Clear Cut ◽  
Salmon Fry ◽  
Streamflow Change ◽  
Downstream Movement

Downstream movement of coho salmon fry (Oncorhynchus kisutch) stocked in old-growth and clear-cut watersheds occurred in three phases: (1) a brief period of heavy emigration immediately after stocking, (2) relatively little movement throughout most of the summer, and (3) intermittent heavy emigration during early autumn freshets. Coho emigrated whenever a streamflow change ≥ 3%∙d−1 occurred, but movement nearly ceased at flows above a certain level. Temperature changes were less important than discharge in triggering movement. When high densities were stocked, emigrant fry were smaller than residents. When low densities were stocked, emigration after the initial pulse of downstream movement was generally lower and there were no size differences between emigrants and residents. Production in the clear-cut was greater than in the old-growth watershed. Proportionately fewer fish emigrated from the old-growth stream, but when population densities were high, mortality in the old-growth exceeded the clear-cut. Greater emigration from the clear-cut site was possibly related to a scarcity of pools. Although the old-growth stream possessed better rearing habitat, less food may have been available, as suggested by gross photosynthesis rates 50% lower than in the clear-cut stream. Coho production therefore appeared to be most strongly influenced by trophic conditions, while volitional residency was most strongly influenced by habitat quality.

The Behaviour of Chum, Pink and Coho Salmon in Relation to their Seaward Migration

1951 ◽  
Vol 8b (4) ◽  
pp. 241-263 ◽  
Author(s):  
William S. Hoar
Keyword(s):  
Fresh Water ◽  
Coho Salmon ◽  
Pink Salmon ◽  
Water Levels ◽  
Salmon Fry ◽  
Seaward Migration ◽  
Active Swimming ◽  
Increased Activity ◽  
Downstream Movement ◽  
Marked Tendency

In fresh water, chum and pink salmon fry form schools or mills, are constantly active both day and night, show positive rheotaxis and move into fast water. This activity takes them into the swiftest currents. At night loss of visual and contact stimuli reduces the intensity of the rheotactic response and results in downstream movement. An active swimming downstream occurs only with unusually high temperatures. Coho salmon fry occupy and defend territory, maintain definite positions in relation to particular objects in their environment, show a less marked tendency to move into fast water and are quiet at night. They are thus displaced downstream to a much lesser degree. Coho smolts, in contrast to the fry, demonstrate a lowered threshold for stimulation both day and night, a tendency to aggregate and a lessening in territory behaviour. During the day smolts group in deeper water or under cover. At night they rise to the surface and manifest increased activity which, in swift water, will result in displacement seaward. Pronounced changes in temperature modify these reactions. Sudden elevation of water levels hastens the downstream displacement.

Variations in the pituitary–interrenal axis and the abundance of circulating blood-cell types in juvenile coho salmon, Oncorhynchus kisutch, during stream residence

1975 ◽  
Vol 53 (12) ◽  
pp. 1882-1891 ◽  
Author(s):  
D. J. McLeay
Keyword(s):  
Blood Cell ◽  
Cell Size ◽  
Seasonal Variations ◽  
Coho Salmon ◽  
Oncorhynchus Kisutch ◽  
Secretory Activity ◽  
Cell Types ◽  
Temperature Acclimation ◽  
Small Lymphocyte ◽  
Natural Stream

According to histological and histometric indices, the pituitary–interrenal axis of juvenile coho salmon residing in a natural stream was inactive in postalevin fry sampled in the spring, and in summer and fall samples of fingerlings, compared with a December sample or with smolts captured the next spring. Interrenal nuclear diameters, interrenal cell size, and epsilon (adrenocorticotropin) cell nuclear diameters were highly positively correlated.The numbers of circulating small lymphocytes and thrombocytes were highest in summer samples. Numbers of circulating large lymphocytes and neutrophils (per thousand cells of all types) were small and did not differ from sample to sample.Histometric indices of pituitary–interrenal axis activity were negatively correlated with numbers of circulating small lymphocytes but were unrelated to thrombocyte counts. Water temperature during sampling was highly negatively correlated with interrenal number and cell size and epsilon-cell nuclear diameters, and positively correlated with small lymphocyte and thrombocyte counts.It was concluded that the pituitary–interrenal axis in juvenile coho salmon was activated by both cold-temperature acclimation and smoltification. Unlike thrombocytes, the seasonal variations in numbers of circulating small lymphocytes were attributed to adrenocortical secretory activity.

Food-searching behaviour of the common merganser (Mergus merganser) II: Choice of foraging location

1985 ◽  
Vol 63 (6) ◽  
pp. 1271-1279 ◽  
Author(s):  
C. C. Wood
Keyword(s):  
Coho Salmon ◽  
Search Pattern ◽  
Flock Size ◽  
Searching Behaviour ◽  
Natural Stream ◽  
Mergus Merganser ◽  
Visit Duration ◽  
The Common ◽  
Common Merganser ◽  
Time Required

Factors influencing the choice of foraging location by the common merganser (Mergus merganser) were investigated by baiting three adjacent, enclosed sections of a natural stream with various densities of juvenile coho salmon (Oncorhynchus kisutch). Merganser abundance within 1 km of the enclosure site increased from < 3 to > 10 birds within 1 week of stocking the enclosures with 43-g coho smolt. Although abundance declined gradually thereafter (as expected from seasonal trends on other nearby streams), the frequency of visits to the enclosure site continued to increase for 22 d until the enclosures were stocked predominately with smaller (2-g) coho fry. Visits were more frequent when other mergansers were already present at the site. Also, the proportion of mergansers flying overhead that landed near a decoy "flock" increased with decoy flock size. In general, the duration of visits to the site was not affected by the number of birds present. Visit duration increased exponentially with increasing fish density and decreased with searching time required until first capture. Mergansers spent more time searching in the most profitable enclosure. Allocation of searching time among the enclosures was not consistent with a "giving up time" decision rule; however, mergansers appeared to follow an area-restricted search pattern both within and among the enclosures.

Effect of Changes in Streamflow on the Microhabitat Use and Movements of Sympatric Juvenile Coho Salmon (Oncorhynchus kisutch) and Chinook Salmon (O. tshawytscha) in a Natural Stream

1994 ◽  
Vol 51 (7) ◽  
pp. 1644-1652 ◽  
Author(s):  
C. S. Shirvell
Keyword(s):  
Chinook Salmon ◽  
Coho Salmon ◽  
Oncorhynchus Kisutch ◽  
Microhabitat Use ◽  
Net Energy ◽  
Optimal Position ◽  
Juvenile Chinook Salmon ◽  
Natural Stream ◽  
Juvenile Chinook ◽  
Seasonal Streamflow

The microhabitats at positions selected by juvenile coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) following a change in streamflow differed from microhabitats occupied at normal streamflows. At drought streamflow (37% mean seasonal streamflow (MSF)), juvenile coho salmon selected slower, darker, and higher sites above the streambed (P < 0.05) than sites selected at normal (75% MSF) or flood (159% MSF) flows. Juvenile chinook salmon microhabitat use changed similarly with changes in streamflow, but the differences were not significant. Up to one fifth of the fish chose positions with faster water velocities than those available either 30 cm above or 30 cm lateral to them. These fish chose positions inconsistent with the hypothesis of optimal position selection based on maximizing net energy gain. On average, fish moved 6.8 m following a change in streamflow. Juvenile coho salmon generally moved upstream in response to decreasing streamflows and downstream in response to increasing streamflows. Juvenile chinook salmon tended to move offshore and downstream in response to all streamflow changes. These results show that juvenile coho and chinook salmon will move to find suitable microhabitat following a change in streamflow and that the microhabitats are not the same at all streamflows.

COMPETITIVE DISPLACEMENT OF PARATRECHINA LONGICORNIS (LATREILLE) (HYMENOPTERA: FORMICIDAE) FROM BAITS BY FIRE ANTS IN MATO GROSSO, BRAZIL

1989 ◽  
Vol 24 (3) ◽  
pp. 381-391 ◽  
Author(s):  
W. A. Banks ◽  
D. F. Williams
Keyword(s):  
Aggressive Behavior ◽  
Solenopsis Invicta ◽  
Fire Ants ◽  
Competitive Displacement ◽  
Mato Grosso ◽  
Large Numbers ◽  
Paratrechina Longicornis ◽  
Solenopsis Invicta Buren

Studies of competitive foraging for three baits by Paratrechina longicornis Latreille, and Solenopsis invicta Buren were conducted in Brazil. Paratrechina longicornis discovered the foods, honey, meat, and cookie, first and recruited large numbers of foragers, dominating the baits for the first 20–30 min of the tests. Solenopsis invicta was slower to discover the baits but their ability to recruit additional foragers and their aggressive behavior resulted in displacement within 45–60 min of most P. longicornis and other ants from the baits and foraging arena. Four other species of ants observed in the study site: a Mycocepurus sp., an Acromyrmex sp., and two Conomyrma spp. occasionally fed on the baits but were not effective competitors for the former two species.

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