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• 51. [Article] Effects of elevated temperature on juvenile Coho salmon and benthic invertebrates in model stream communities

  Juvenile coho salmon (Oncorhynchus kisutch (Walbaum)) and aquatic invertebrates were subjected to experimentally increased, but naturally fluctuating, temperatures in a model stream channel. Coho of the ...

  Citation × Citation Citation Abstract Copy Title: Effects of elevated temperature on juvenile Coho salmon and benthic invertebrates in model stream communities Author: Iverson, Ronald Albert Juvenile coho salmon (Oncorhynchus kisutch (Walbaum)) and aquatic invertebrates were subjected to experimentally increased, but naturally fluctuating, temperatures in a model stream channel. Coho of the 1969, 1970, and 1971 year classes were reared in the heated model stream and in an unheated control stream, both located at the Oak Creek laboratory west of Corvallis, Oregon. The average increment of experimental over control temperature was 4.3 C over the entire experimental period of 22 months. Temperatures in the control stream were generally favorable for growth of coho if food organisms were scarce, while temperatures in the heated stream were favorable for growth if food organisms were abundant. Coho of the 1969 year class were reared for one winter as yearlings, and total production of this group was approximately the same in the two streams. Coho of the 1970 year class were reared from small fry to smolts over a one-year period. In this group, total production in the control stream was approximately twice as great as in the heated stream. While population size was nearly the same in the two streams, coho in the control stream grew much more rapidly than in the heated stream. Total production of coho of the 1971 year class, which were reared from the egg stage, was approximately five times as great in the control as in the heated stream when the experiment was terminated in August 1971. The difference in production resulted from larger population size and higher growth rate in the control stream. Production of aquatic stages of insects was approximately twice as great in the control as in the heated stream over the period May 1970-May 1971. This difference between streams was especially marked in mayfly and stonefly nymphs, which were the most abundant insects in both streams, and which appeared to be the major sources of food for coho. The reduced growth rates of coho in the heated as compared to the control stream probably resulted from effects of temperature on the invertebrate food supply as well as from direct effects of temperature on the coho in raising their standard metabolic rates so that energy available for growth was reduced. Winter growth rates of coho in the heated stream were generally higher than in the control, probably as a result of an increase in appetite with increased temperature. Winter growth rates of the 1969 year class were high, probably because young coho fry were available as food. Winter growth rates of coho of the 1970 year class, which had a more natural food supply, were low in both streams. The insect fauna of the Oak Creek area is probably adapted to cool water temperatures, and this adaptation presumably contributed to the reduced insect production in the heated model stream. If heat tolerant species of insects were present in or able to migrate into a stream receiving a heated effluent, the simplication of the invertebrate fauna caused by the thermal pollution might increase the amount of food available to the top carnivore. Such heat-tolerant forms apparently were not present in the model streams or, if present, were not able to contribute significantly to total production. Title: Effects of elevated temperature on juvenile Coho salmon and benthic invertebrates in model stream communities Author: Iverson, Ronald Albert Juvenile coho salmon (Oncorhynchus kisutch (Walbaum)) and aquatic invertebrates were subjected to experimentally increased, but naturally fluctuating, temperatures in a model stream channel. Coho of the 1969, 1970, and 1971 year classes were reared in the heated model stream and in an unheated control stream, both located at the Oak Creek laboratory west of Corvallis, Oregon. The average increment of experimental over control temperature was 4.3 C over the entire experimental period of 22 months. Temperatures in the control stream were generally favorable for growth of coho if food organisms were scarce, while temperatures in the heated stream were favorable for growth if food organisms were abundant. Coho of the 1969 year class were reared for one winter as yearlings, and total production of this group was approximately the same in the two streams. Coho of the 1970 year class were reared from small fry to smolts over a one-year period. In this group, total production in the control stream was approximately twice as great as in the heated stream. While population size was nearly the same in the two streams, coho in the control stream grew much more rapidly than in the heated stream. Total production of coho of the 1971 year class, which were reared from the egg stage, was approximately five times as great in the control as in the heated stream when the experiment was terminated in August 1971. The difference in production resulted from larger population size and higher growth rate in the control stream. Production of aquatic stages of insects was approximately twice as great in the control as in the heated stream over the period May 1970-May 1971. This difference between streams was especially marked in mayfly and stonefly nymphs, which were the most abundant insects in both streams, and which appeared to be the major sources of food for coho. The reduced growth rates of coho in the heated as compared to the control stream probably resulted from effects of temperature on the invertebrate food supply as well as from direct effects of temperature on the coho in raising their standard metabolic rates so that energy available for growth was reduced. Winter growth rates of coho in the heated stream were generally higher than in the control, probably as a result of an increase in appetite with increased temperature. Winter growth rates of the 1969 year class were high, probably because young coho fry were available as food. Winter growth rates of coho of the 1970 year class, which had a more natural food supply, were low in both streams. The insect fauna of the Oak Creek area is probably adapted to cool water temperatures, and this adaptation presumably contributed to the reduced insect production in the heated model stream. If heat tolerant species of insects were present in or able to migrate into a stream receiving a heated effluent, the simplication of the invertebrate fauna caused by the thermal pollution might increase the amount of food available to the top carnivore. Such heat-tolerant forms apparently were not present in the model streams or, if present, were not able to contribute significantly to total production. Close

• 52. [Article] Population dynamics of the coho salmon and its response to logging in three coastal streams

  This study examines the ecology and dynamics of coho salmon (Oncorhynchus kisutch) in environments experimentally altered by logging. The objective was to evaluate processes that stabilize or regulate ...

  Citation × Citation Citation Abstract Copy Title: Population dynamics of the coho salmon and its response to logging in three coastal streams Author: Au, David Wah Kwai This study examines the ecology and dynamics of coho salmon (Oncorhynchus kisutch) in environments experimentally altered by logging. The objective was to evaluate processes that stabilize or regulate the populations. Two small watersheds in Oregon's Coast Range were logged in 1966, one clear-cut, the other patch-cut. A third adjacent watershed was left uncut as a control. The influence of these treatments on the biology of the coho was assessed. Attention was concentrated on populations of the six year classes 1963 to 1968. The natural variability of streamflow-related conditions influencing both the magnitude and pattern of coho recruitment each year was increased in the logged watersheds. Peak flow during storms increased; intragravel dissolved oxygen levels decreased in the stream draining the clear-cut watershed. These changes, however, were apparently within the range of variation that the coho naturally experience. Increased stream temperatures and mortalities, due to the logging effects, altered the post-recruitment life conditions of the coho in that stream but did not significantly affect the final smolt yield. The nocturnal behavior of recently emerged fry leads to recruitment along the stream length. Fry tend to emerge en masse from the redds at night, and large numbers proceed immediately to disperse downstream. This migration continues for several successive nights, beginning each night soon after dark. Evidence is presented indicating that fry emigration is primarily a dispersal mechanism that distributes fry from redd sites to nursery areas. It is hypothesized that the series of events leading from fry dispersal to be quiescent behavior at night, characteristic of resident fry, is a developmental sequence involving the physiology and maturity of the fry, modified by agonistic activity. Adjustments in coho population size were largely accomplished by fall, resulting in stable and characteristic population levels in each stream. A stable smolt yield was a further result. These adjustments are accomplished through high mortality during the months of the first spring and summer. This mortality is likely density dependent and related to the territorial and agonistic behavior of the fish. Growth, biomass, and net production varied greatly during each year. Seasonal changes in growth rate resulted in seasonal variations in biomass that were in contrast to the stabilized trends of population number. The pattern of net production rate was also largely determined by the seasonal growth pattern, and like biomass, did not show: a tendency to stabilize with time. It averaged 5 g/m² among the three streams for the period June 1 to April 15. The coho populations seem naturally regulated most importantly with respect to number. The patterns of biomass and rate of net production may be understood as an interaction of seasonally variable growth rate with stabilizing population numbers. This study has shown that coho streams normally produce characteristic levels of smolt yield in spite of large natural variations in fry input and conditions for growth. The range of environmental variation for which this result holds may include short-term changes due to logging. However a normal population response to such a severe alteration as occurred on Needle Branch is very likely conditional upon a program that at least includes vigorous stream clearance, the restriction of additional mortality to early summer, when population adjustments are far from complete, and the encouragement of streamside revegetation. A streamside buffer strip of trees is an effective way of protecting aquatic resources. Title: Population dynamics of the coho salmon and its response to logging in three coastal streams Author: Au, David Wah Kwai This study examines the ecology and dynamics of coho salmon (Oncorhynchus kisutch) in environments experimentally altered by logging. The objective was to evaluate processes that stabilize or regulate the populations. Two small watersheds in Oregon's Coast Range were logged in 1966, one clear-cut, the other patch-cut. A third adjacent watershed was left uncut as a control. The influence of these treatments on the biology of the coho was assessed. Attention was concentrated on populations of the six year classes 1963 to 1968. The natural variability of streamflow-related conditions influencing both the magnitude and pattern of coho recruitment each year was increased in the logged watersheds. Peak flow during storms increased; intragravel dissolved oxygen levels decreased in the stream draining the clear-cut watershed. These changes, however, were apparently within the range of variation that the coho naturally experience. Increased stream temperatures and mortalities, due to the logging effects, altered the post-recruitment life conditions of the coho in that stream but did not significantly affect the final smolt yield. The nocturnal behavior of recently emerged fry leads to recruitment along the stream length. Fry tend to emerge en masse from the redds at night, and large numbers proceed immediately to disperse downstream. This migration continues for several successive nights, beginning each night soon after dark. Evidence is presented indicating that fry emigration is primarily a dispersal mechanism that distributes fry from redd sites to nursery areas. It is hypothesized that the series of events leading from fry dispersal to be quiescent behavior at night, characteristic of resident fry, is a developmental sequence involving the physiology and maturity of the fry, modified by agonistic activity. Adjustments in coho population size were largely accomplished by fall, resulting in stable and characteristic population levels in each stream. A stable smolt yield was a further result. These adjustments are accomplished through high mortality during the months of the first spring and summer. This mortality is likely density dependent and related to the territorial and agonistic behavior of the fish. Growth, biomass, and net production varied greatly during each year. Seasonal changes in growth rate resulted in seasonal variations in biomass that were in contrast to the stabilized trends of population number. The pattern of net production rate was also largely determined by the seasonal growth pattern, and like biomass, did not show: a tendency to stabilize with time. It averaged 5 g/m² among the three streams for the period June 1 to April 15. The coho populations seem naturally regulated most importantly with respect to number. The patterns of biomass and rate of net production may be understood as an interaction of seasonally variable growth rate with stabilizing population numbers. This study has shown that coho streams normally produce characteristic levels of smolt yield in spite of large natural variations in fry input and conditions for growth. The range of environmental variation for which this result holds may include short-term changes due to logging. However a normal population response to such a severe alteration as occurred on Needle Branch is very likely conditional upon a program that at least includes vigorous stream clearance, the restriction of additional mortality to early summer, when population adjustments are far from complete, and the encouragement of streamside revegetation. A streamside buffer strip of trees is an effective way of protecting aquatic resources. Close