Food and foraging behavior in relation to microhabitat use and survival of age-0 Atlantic salmon

1998 ◽  
Vol 55 (1) ◽  
pp. 116-127 ◽  
Author(s):  
Keith H Nislow ◽  
Carol Folt ◽  
Marco Seandel
Keyword(s):  
Atlantic Salmon ◽  
Foraging Behavior ◽  
High Velocity ◽  
Field Experiments ◽  
Growth Period ◽  
Food Abundance ◽  
Invertebrate Drift ◽  
Microhabitat Use ◽  
Growth And Survival ◽  
Influence Of Food

We examined, using underwater snorkeling observations and field experiments, the influence of food availability on foraging behavior, habitat use, and survival of age-0 Atlantic salmon (Salmo salar) during the critical first-summer growth period. While most feeding attempts were directed at drifting invertebrate prey, we found a higher rate of benthic feeding forays than previously reported for salmon. Greater food abundance was associated with higher feeding foray rates, more time allocated to foraging, occupancy of higher microhabitat velocities, and greater first-year survival between two study streams. Experimental drift reduction reduced drift foray rates and triggered a change in behavior to increased benthic feeding. In contrast, within a single stream, greater predicted invertebrate drift in high-velocity microhabitats (1 m2) was unrelated to either microhabitat occupancy or drift foray rates of age-0 salmon. We suggest that, in some situations, salmonid foraging is related more directly to overall prey density than to the availability of high-velocity, high drift rate microhabitats. Differences in resource tracking (increased foraging, growth, or survival with increased food abundance) at different scales, along with the use of alternative predation modes, underscore the importance of considering behavior when linking food resources to growth and survival of stream salmonids.

Food Abundance, Intruder Pressure, and Body Size as Determinants of Territory Size in Juvenile Steelhead Trout (Oncorhynchus Mykiss)

Behaviour ◽  
1998 ◽  
Vol 135 (1) ◽  
pp. 65-82 ◽  
Author(s):  
◽  
Keyword(s):  
British Columbia ◽  
Body Size ◽  
Atlantic Salmon ◽  
Oncorhynchus Mykiss ◽  
Food Abundance ◽  
Territory Size ◽  
Invertebrate Drift ◽  
Steelhead Trout ◽  
Daily Ration ◽  
Fish Size

AbstractWe observed the behaviour of juvenile steelhead trout (Oncorhynchus mykiss) in two rivers in British Columbia, Canada, to determine the importance of invertebrate drift abundance, intruder pressure, and body size of territory holders as correlates of territory size. Territory size increased with increasing fish size, but fish smaller than 5 cm had relatively large territories for their body size, in comparison to fish that were larger than 5 cm in length. After statistically controlling for the effect of body size, territory size was inversely related to the abundance of drifting invertebrates. Territory size was not related to the number of intrusions observed on a territory per hour, but was inversely related to local fish density, a second measure of intruder pressure. Steelhead trout appear to defend territory areas that are most similar in size to juvenile Atlantic salmon. This study provides evidence that stream-dwelling salmonids scale territory size to body size in a manner that allows them to capture a maximum daily ration of food on their territories.

The effect of porcine somatotropin on growth, and survival in seawater of Atlantic salmon (Salmo salar) parr

1976 ◽  
Vol 54 (4) ◽  
pp. 531-535 ◽  
Author(s):  
M. P. Komourdjian ◽  
R. L. Saunders ◽  
J. C. Fenwick
Keyword(s):  
Growth Hormone ◽  
Atlantic Salmon ◽  
Salmo Salar ◽  
Growth Hormone Treatment ◽  
Hormone Treatment ◽  
Control Fish ◽  
Growth And Survival ◽  
Atlantic Salmon Salmo Salar ◽  
Porcine Somatotropin

The effects of porcine growth hormone on growth and salinity tolerance were studied in Atlantic salmon (Salmo salar) parr. Fish were held in freshwater at 11.5 °C during June and July under a photoperiod with light to dark periods opposite to the prevailing natural conditions. Fish treated with 1.0 μg/g body weight of growth hormone preparation on alternate days were significantly longer (P <.05), after 4 weeks, than placebo-injected controls. All hormone-injected fish survived transfer to seawater, 30‰ salinity. But under the same conditions, placebo-injected control fish showed a high mortality rate. Growth-hormone treatment caused a darkening of fin margins and a yellowing of the operculae and fin surfaces. The silvering which normally accompanies smoltification was not observed. The role of growth hormone in eliciting these actions and its possible role in the parr–smolt transformation are discussed.

Three-dimensional microhabitat use by young pool-dwelling Atlantic salmon and brown trout

1999 ◽  
Vol 58 (5) ◽  
pp. 1047-1059 ◽  
Author(s):  
GunnbjøRn Bremset ◽  
Ole Kristian Berg
Keyword(s):  
Atlantic Salmon ◽  
Brown Trout ◽  
Three Dimensional ◽  
Microhabitat Use

The effects of frequency and extent of defoliation, summer irrigation, and fertilizer on the production and survival of the grass Danthonia caespitosa Gaud

1976 ◽  
Vol 27 (6) ◽  
pp. 755 ◽  
Author(s):  
KC Hodgkinson
Keyword(s):  
Seed Production ◽  
Death Rate ◽  
Field Experiments ◽  
Seed Set ◽  
Floral Induction ◽  
Early Winter ◽  
Phosphorus Fertilizer ◽  
Nitrogen And Phosphorus ◽  
Plant Survival ◽  
Growth And Survival

The effects of extent and frequency of defoliation on the growth and survival of Danthonia caespitosa were measured in a series of field experiments. Additional treatments, of summer irrigation and application of nitrogen and phosphorus fertilizer, were included in some of the experiments to assess how they modified the effects of defoliation. During the summer, complete defoliation increased the shoot yield of plants which had not been irrigated, but yield was decreased in the irrigated treatments. Frequent, partial defoliation increased yields of irrigated plants but decreased yields of plants not irrigated. Depression of yields was caused by both tiller death and reduced regrowth of individual tillers. In an experiment lasting 2 years, plants were completely defoliated monthly, bimonthly or tri-monthly or left intact, and shoot yields, tillering characteristics and plant survival under the treatments were compared. Monthly defoliation depressed yields and rate of tillering and accelerated the death rate of plants, particularly during the summer and autumn periods. Plants also died when cut bimonthly but the rate was slower. Plants irrigated during the first summer generally died at a faster rate than plants not irrigated. Tillering was more rapid during the autumn and early winter months. Midwinter application of fertilizer to plants cut bimonthly greatly stimulated shoot yields and seed production in the spring but not in the following year. Examination of tiller apices showed that floral induction took place prior to the beginning of July. Many apices were elevated above the 'grazing level' by early September, and flowering and seed set occurred in October.

SENSITIVITY OF CROP PLANTS TO WATER STRESS AT SPECIFIC DEVELOPMENTAL STAGES: REEVALUATION OF EXPERIMENTAL FINDINGS

1995 ◽  
Vol 43 (2) ◽  
pp. 99-111 ◽  
Author(s):  
Zvi Plaut
Keyword(s):  
Water Stress ◽  
Irrigation Water ◽  
Field Experiments ◽  
Developmental Stages ◽  
Growth Period ◽  
Soluble Solids ◽  
Growth Stages ◽  
Mild Stress ◽  
Uniform Reduction ◽  
Different Growth Stages

It has been suggested that in many crops differences in sensitivity to water stress occur at different growth stages. Since identical amounts of water may be applied, irrespective of whether a crop is exposed to relatively severe and short periods of stress or to extended periods of mild stress, the responses to such differing conditions should be compared. Unfortunately, such a comparison has not been conducted in most studies on sensitivity to water stress at different growth stages. In the present study, based on three field experiments conducted for different purposes, such a comparison was made for three crops: corn, sunflower, and tomato. In corn, distinct responses of ear and kernel yields to the timing of water stress were found. Withdrawal of irrigation water during flowering and cob formation resulted in greater yield losses than during other stages, indicating that this is a critical growth stage. However, slight and uniform reduction of water during the entire growth period resulted in significantly less damage to kernel or ear production, although the total amount of water applied was similar to that under staged withdrawal. In sunflowers, the withdrawal of irrigation water even at noncritical growth stages caused a more marked reduction in grain yield than did a uniform reduction throughout the entire season. In tomatoes, on the other hand, the withdrawal of irrigation water during specific growth stages caused minimal damage to fruit and total soluble solids yield as compared with fully irrigated control; reduction of irrigation water throughout the season brought about a significant decrease in yield. The difference between these crops is interpreted on the basis of the determinance of their floral meristems.

Age at Sexual Maturity in Icelandic Stocks of Atlantic Salmon (Salmo salar)

1983 ◽  
Vol 40 (9) ◽  
pp. 1456-1468 ◽  
Author(s):  
Dennis L. Scarnecchia
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Sexual Maturity ◽  
Physical Factors ◽  
Thermal Gradients ◽  
Ocean Temperature ◽  
Growth And Survival ◽  
Atlantic Salmon Salmo Salar ◽  
Life History Pattern ◽  
Second Year

For Icelandic stocks of Atlantic salmon (Salmo salar) in 77 rivers, the combination of June ocean temperature, length of river ascended by the salmon, discharge of the river in July–September, and latitude explained much of the variation in percentages of grilse — 72% for females and 62% for males. For both sexes, percentage of grilse was directly related to ocean temperature but inversely related to length of river, discharge of river, and latitude. For stocks in 23 Southwest Coast rivers, length of river explained 72% of the variation in percentage of females that were grilse. Females in stocks south of the thermal gradients separating Atlantic from Arctic or Polar water tended to return as grilse; females north of the gradients tended to return after more than one winter at sea. The decline in percentages of grilse clockwise from southwestern to northeastern rivers corresponded closely with the decline in June ocean temperatures between these areas. I hypothesize that the salmon stocks have adapted their age at sexual maturity to the length and discharge of the rivers, natural mortality rates during their second year at sea, and average expected ocean temperatures, reflecting conditions for growth and survival, that the smolts encounter. Age at maturity appears not to be a direct causal response to any of these physical factors, and appears best understood only with reference to the entire life history pattern of each stock.

The marine phase of the Atlantic salmon (Salmo salar) life cycle, with comparisons to Pacific salmon

1998 ◽  
Vol 55 (S1) ◽  
pp. 104-118 ◽  
Author(s):  
L P Hansen ◽  
T P Quinn
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Life Histories ◽  
North Atlantic Ocean ◽  
Pacific Salmon ◽  
Mortality Factor ◽  
Growth And Survival ◽  
Atlantic Salmon Salmo Salar ◽  
The North ◽  
Wide Range

Atlantic salmon (Salmo salar) are distributed over large areas in the north Atlantic Ocean. They usually move very quickly from freshwater to oceanic areas, whereas there is considerable variation among Pacific salmon in early marine movements. In some areas, Atlantic salmon of exploitable size are sufficiently abundant that commercial high seas fisheries have developed. Such areas are off west Greenland, where North American and European fish are harvested, and in the Norwegian Sea, north of the Faroe Islands, where mainly European fish are exploited. Atlantic salmon feed on a wide range of large crustaceans, pelagic fish, and squid in the marine environment, supporting the hypothesis that Atlantic salmon are opportunistic feeders. In the ocean the salmon grow relatively quickly and the sea age when they become sexually mature depends on both genetics and on growing conditions. Natural marine mortality of salmon is highest during the first few months at sea and the major mortality factor is probably predation. However, marine mortality of Atlantic salmon has increased in recent years, apparently correlated with a decline in sea surface temperatures. Similar relationships between environmental conditions and the growth and survival of Pacific salmon have been reported. Atlantic salmon life histories most closely mimic stream-type chinook salmon or steelhead trout among the Pacific species. Finally, Atlantic and Pacific salmon return to their home rivers with high precision and possible mechanisms controlling the oceanic homing migration are presented and discussed.

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