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• 1. [Article] Juvenile coho salmon movement, growth and survival in a coastal basin of southern Oregon

  Juvenile salmonids display highly variable spatial and temporal movement patterns that are influenced by density dependent (e.g., competition, predation) and density independent (e.g., genetics, stream ...

  Citation × Citation Citation Abstract Copy Title: Juvenile coho salmon movement, growth and survival in a coastal basin of southern Oregon Author: Weybright, Adam D. Juvenile salmonids display highly variable spatial and temporal movement patterns that are influenced by density dependent (e.g., competition, predation) and density independent (e.g., genetics, stream discharge, physical habitat conditions) factors. The effects of these factors differ with fish life history stage, but will ultimately affect how salmonids utilize freshwater nursery habitats and influence their size at smolting. Although juvenile coho salmon (Oncorhynchus kisutch) (Walbaum 1792) movement patterns and their relationships with body mass have been previously examined, the temporal scale considered in most studies has been within individual seasonal periods. In this study, we monitored the movement of PIT tagged juvenile coho salmon throughout the period of freshwater residence in an entire southern Oregon coastal basin to identify the prevalent sedentary and mobile strategies these fish may adopt and to examine possible relationships between those strategies and fish body mass, growth and survival. Specific objectives include: 1) to describe juvenile coho salmon movement strategies and patterns during the freshwater residence period; 2) to determine the relative proportions of juvenile coho salmon that exhibit each movement strategy; 3) to establish whether juvenile coho salmon body mass and growth rates are related with a set of habitat variables recorded during this study; 4) to determine whether coho salmon body mass or growth rates are related to movement strategy; and 5) to evaluate whether winter survival of juvenile coho salmon is associated with movement strategy. Results revealed seasonally and spatially variable movement. More than half of coho salmon tracked throughout the period of freshwater residence exhibited movement behavior that differed between summer and winter seasons. Within seasonal periods, coho salmon in tidally affected reaches exhibited greater prevalence of mobile behavior relative to those in riverine reaches. Regression analysis indicated coho biomass density, habitat unit structural complexity and size at tagging were important in predicting summer growth of coho salmon. Juvenile coho salmon that were mobile during summer were either larger or no different in body mass in early summer relative to fish that exhibited sedentary behavior. Similarly, no consistent differences were observed between sedentary and mobile coho salmon in regards to summer growth. Coho salmon that were sedentary in summer and winter experienced higher apparent winter survival than mobile fish in each season, though the reach in which an individual resided at the start of winter appeared to also affect survival. Coho salmon residing in the tide gate reservoir reach and mainstem headwater reaches experienced greatest apparent winter survival. These results indicate that juvenile coho salmon movement within a stream basin is spatially and temporally variable and that mobility does not necessarily indicate inferior competitive ability. In a broader context, variable movement patterns reflect the capacity for plastic behavior in salmonids and this research demonstrates the importance of maintaining seasonally diverse freshwater and estuarine nursery habitats for juvenile fish. Title: Juvenile coho salmon movement, growth and survival in a coastal basin of southern Oregon Author: Weybright, Adam D. Juvenile salmonids display highly variable spatial and temporal movement patterns that are influenced by density dependent (e.g., competition, predation) and density independent (e.g., genetics, stream discharge, physical habitat conditions) factors. The effects of these factors differ with fish life history stage, but will ultimately affect how salmonids utilize freshwater nursery habitats and influence their size at smolting. Although juvenile coho salmon (Oncorhynchus kisutch) (Walbaum 1792) movement patterns and their relationships with body mass have been previously examined, the temporal scale considered in most studies has been within individual seasonal periods. In this study, we monitored the movement of PIT tagged juvenile coho salmon throughout the period of freshwater residence in an entire southern Oregon coastal basin to identify the prevalent sedentary and mobile strategies these fish may adopt and to examine possible relationships between those strategies and fish body mass, growth and survival. Specific objectives include: 1) to describe juvenile coho salmon movement strategies and patterns during the freshwater residence period; 2) to determine the relative proportions of juvenile coho salmon that exhibit each movement strategy; 3) to establish whether juvenile coho salmon body mass and growth rates are related with a set of habitat variables recorded during this study; 4) to determine whether coho salmon body mass or growth rates are related to movement strategy; and 5) to evaluate whether winter survival of juvenile coho salmon is associated with movement strategy. Results revealed seasonally and spatially variable movement. More than half of coho salmon tracked throughout the period of freshwater residence exhibited movement behavior that differed between summer and winter seasons. Within seasonal periods, coho salmon in tidally affected reaches exhibited greater prevalence of mobile behavior relative to those in riverine reaches. Regression analysis indicated coho biomass density, habitat unit structural complexity and size at tagging were important in predicting summer growth of coho salmon. Juvenile coho salmon that were mobile during summer were either larger or no different in body mass in early summer relative to fish that exhibited sedentary behavior. Similarly, no consistent differences were observed between sedentary and mobile coho salmon in regards to summer growth. Coho salmon that were sedentary in summer and winter experienced higher apparent winter survival than mobile fish in each season, though the reach in which an individual resided at the start of winter appeared to also affect survival. Coho salmon residing in the tide gate reservoir reach and mainstem headwater reaches experienced greatest apparent winter survival. These results indicate that juvenile coho salmon movement within a stream basin is spatially and temporally variable and that mobility does not necessarily indicate inferior competitive ability. In a broader context, variable movement patterns reflect the capacity for plastic behavior in salmonids and this research demonstrates the importance of maintaining seasonally diverse freshwater and estuarine nursery habitats for juvenile fish. Close

• 2. [Article] Variation in the timing of coho salmon (Oncorhynchus kisutch) migration and spawning relative to river discharge and temperature

  Coho salmon (Oncorhynchus kisutch) migration and spawning are unique components of the salmon life cycle because they require synchrony of behavior with other individuals as well as with acceptable fluvial ...

  Citation × Citation Citation Abstract Copy Title: Variation in the timing of coho salmon (Oncorhynchus kisutch) migration and spawning relative to river discharge and temperature Author: LovellFord, Rachel Coho salmon (Oncorhynchus kisutch) migration and spawning are unique components of the salmon life cycle because they require synchrony of behavior with other individuals as well as with acceptable fluvial conditions. As with other organisms that exhibit group mating behavior, it is likely that environmental cues trigger coho salmon movement to spawning grounds. These cues may also provide usable habitat for migration and spawning. River discharge, temperature, and length of day have long been assumed to be the environmental cues which trigger migration and spawning of coho salmon as coho return within the same season each year to spawn. Hatchery studies have also shown that the timing of reproductive behavior is heritable. If this heritability is determined by the fluvial conditions of the spawning grounds, then a predictable relationship should exist between reproductive behavior and the hydrologic and thermal regimes. Surprisingly, no defensible correlations between discharge thresholds and spawning or migrating activity have been identified for naturally reproducing coho salmon. Thermal, velocity, and depth limitations have been identified for coho salmon, but these values have not been examined in combination or within the context of a hydrologic and thermal regime. This study compares interannual patterns in the timing of coho mid-river migration in the North Umqua (180 km up river from the estuary) and the initiation of spawn timing in the Smith River basins (Oregon) with river discharge and water temperature data to ascertain whether these behaviors are driven by fluvial conditions. Additionally, we used this data to identify the window over which most migration and spawning takes place in our test systems. On the North Umpqua, coho salmon mid-river migration initiated (first 5% of migrants) after summer peak temperatures and following a threshold average daily temperature of 18 C°, but before fall storm events occurred. In most years, approximately 75% of the migrating coho salmon have moved past the Winchester Dam before fall storms initiated and when discharge remained less than the 11 year average for the month of November, more similar to summer than winter flow levels. Additionally, characteristic lengths and numbers of peaks within the distribution of annual migrations were attributable to the generational cohort that the migration belonged to despite the similarity in population size across all years. These patterns in the distribution of generational cohorts suggest an inherited timing response as well as highlight cohorts which may contain diminished sub-populations. The initiation of coho salmon spawning appears limited both by a thermal threshold of 12 C° in all basins, as well as by a minimal discharge threshold, which is unique to each stream. Continued spawning activity occurs as discharge remains elevated from fall levels. It is also notable that there was no statistical difference in the date of the initiation of spawning within each basin in a given year or across years at a given site. Together, these studies highlight the important role that the coho salmon genome plays in reproductive timing as well as the ways that fluvial thresholds limit reproductive behavior in time. Coho have survived because of their genome has been resilient when faced with environmental change. Future work should consider variability in fluvial conditions relative to coho salmon phenotypic plasticity over time. Coho salmon phenotypic plasticity will determine whether the rate of change of the hydrologic and thermal regimes important to coho salmon survival outpaces the coho’s ability to adapt. This study contributed to this future work by establishing baseline relationships between the behavior of a threatened species and measurable environmental thresholds. Title: Variation in the timing of coho salmon (Oncorhynchus kisutch) migration and spawning relative to river discharge and temperature Author: LovellFord, Rachel Coho salmon (Oncorhynchus kisutch) migration and spawning are unique components of the salmon life cycle because they require synchrony of behavior with other individuals as well as with acceptable fluvial conditions. As with other organisms that exhibit group mating behavior, it is likely that environmental cues trigger coho salmon movement to spawning grounds. These cues may also provide usable habitat for migration and spawning. River discharge, temperature, and length of day have long been assumed to be the environmental cues which trigger migration and spawning of coho salmon as coho return within the same season each year to spawn. Hatchery studies have also shown that the timing of reproductive behavior is heritable. If this heritability is determined by the fluvial conditions of the spawning grounds, then a predictable relationship should exist between reproductive behavior and the hydrologic and thermal regimes. Surprisingly, no defensible correlations between discharge thresholds and spawning or migrating activity have been identified for naturally reproducing coho salmon. Thermal, velocity, and depth limitations have been identified for coho salmon, but these values have not been examined in combination or within the context of a hydrologic and thermal regime. This study compares interannual patterns in the timing of coho mid-river migration in the North Umqua (180 km up river from the estuary) and the initiation of spawn timing in the Smith River basins (Oregon) with river discharge and water temperature data to ascertain whether these behaviors are driven by fluvial conditions. Additionally, we used this data to identify the window over which most migration and spawning takes place in our test systems. On the North Umpqua, coho salmon mid-river migration initiated (first 5% of migrants) after summer peak temperatures and following a threshold average daily temperature of 18 C°, but before fall storm events occurred. In most years, approximately 75% of the migrating coho salmon have moved past the Winchester Dam before fall storms initiated and when discharge remained less than the 11 year average for the month of November, more similar to summer than winter flow levels. Additionally, characteristic lengths and numbers of peaks within the distribution of annual migrations were attributable to the generational cohort that the migration belonged to despite the similarity in population size across all years. These patterns in the distribution of generational cohorts suggest an inherited timing response as well as highlight cohorts which may contain diminished sub-populations. The initiation of coho salmon spawning appears limited both by a thermal threshold of 12 C° in all basins, as well as by a minimal discharge threshold, which is unique to each stream. Continued spawning activity occurs as discharge remains elevated from fall levels. It is also notable that there was no statistical difference in the date of the initiation of spawning within each basin in a given year or across years at a given site. Together, these studies highlight the important role that the coho salmon genome plays in reproductive timing as well as the ways that fluvial thresholds limit reproductive behavior in time. Coho have survived because of their genome has been resilient when faced with environmental change. Future work should consider variability in fluvial conditions relative to coho salmon phenotypic plasticity over time. Coho salmon phenotypic plasticity will determine whether the rate of change of the hydrologic and thermal regimes important to coho salmon survival outpaces the coho’s ability to adapt. This study contributed to this future work by establishing baseline relationships between the behavior of a threatened species and measurable environmental thresholds. Close

• 3. [Article] Juvenile coho salmon movement and migration through tide gates

  Tidal marshlands in the upper estuary ecotone provide essential habitat for juvenile salmonids. In this environment, salmonids grow rapidly and acclimate to saltwater. Worldwide, tidal marshes have been ...

  Citation × Citation Citation Abstract Copy Title: Juvenile coho salmon movement and migration through tide gates Author: Bass, Arthur Langer Tidal marshlands in the upper estuary ecotone provide essential habitat for juvenile salmonids. In this environment, salmonids grow rapidly and acclimate to saltwater. Worldwide, tidal marshes have been diked and drained to provide agricultural and residential land. Tide gates are one-way doors integrated into dike systems that prevent saltwater flooding and allow upland drainage to the estuary during low tide. By preventing tidal exchange, tide gates have significant upstream effects on water temperature and chemistry, plant and animal community structure, and geomorphology. Since they are closed most of the day and may be difficult to pass when open, tide gates may act as fish passage barriers for juvenile salmonids. They may also affect juvenile salmon migration timing by altering environmental variables that influence emigration rate in upstream habitats. We conducted our research in Coos Bay, one of the many Oregon estuaries with extensive use of tide gates. We studied three streams, one with a top-hinged tide gate, one with a side-hinged gate, and one without any tide gates that acted as our reference site. Our study species was coho salmon, Oncorhynchus kisutch, which may encounter tide gates both in the subyearling and smolt life stages in our study streams. Our objectives were to: 1) quantify upstream and downstream fish passage occurrence at all three sites, 2) determine whether juvenile coho salmon passage is associated with a specific range of gate conditions, and 3) identify any associations between coho smolt emigration rate and environmental variables that are influenced by tide gates. We installed stationary passive integrated transponder (PIT) antennae around both tide gates and a tidal channel in the non-gated stream to record the movement of PIT tagged juvenile coho salmon. Coho salmon smolts passed upstream most frequently at the non-gated channel (48% of all smolts detected at the array), next the side-hinged gate (28%), and lastly, the top-hinged gate (3%). Juvenile coho salmon passed more frequently at a specific range of gate angles and tailwater depths at both top hinged and side-hinged tide gates. Smolts passed downstream more frequently at greater gate angles and tailwater depths than available on average at both tide gates. Subyearlings passed upstream more frequently during small gate angles and a narrow range of tailwater depths at the top-hinged gate but did not pass more frequently under a particular range of conditions at the side-hinged gate. At the top-hinged gate, conditions favorable for subyearling upstream passage occurred towards the end of the gate open period and therefore subyearlings were severely limited in their opportunities for passage. At multiple sites, emigration rate was associated with environmental variables that may be altered by tide gates. Increases in water temperature were associated with an increasing likelihood of smolt emigration at multiple sites. At a tide gate that allowed upstream estuarine influence, increasing salinity was associated with a decreasing likelihood of emigration. Our results suggest that tide gates may interfere with salmonid movement and migration by creating physical barriers to fish passage and potentially influencing migratory timing by altering environmental variables. When installing or retrofitting tide gates, these factors should be taken into consideration since a tide gate's design may determine the severity of its effects on salmonids. Our work should be considered a case study and the findings should not be assumed to be transferable due to the great diversity of tide gate installations in use. We recommend further research, including a more in depth analysis of the affects of tide gates on subyearling coho salmon and an investigation of piscivorous predator exploitation of tide gates. Title: Juvenile coho salmon movement and migration through tide gates Author: Bass, Arthur Langer Tidal marshlands in the upper estuary ecotone provide essential habitat for juvenile salmonids. In this environment, salmonids grow rapidly and acclimate to saltwater. Worldwide, tidal marshes have been diked and drained to provide agricultural and residential land. Tide gates are one-way doors integrated into dike systems that prevent saltwater flooding and allow upland drainage to the estuary during low tide. By preventing tidal exchange, tide gates have significant upstream effects on water temperature and chemistry, plant and animal community structure, and geomorphology. Since they are closed most of the day and may be difficult to pass when open, tide gates may act as fish passage barriers for juvenile salmonids. They may also affect juvenile salmon migration timing by altering environmental variables that influence emigration rate in upstream habitats. We conducted our research in Coos Bay, one of the many Oregon estuaries with extensive use of tide gates. We studied three streams, one with a top-hinged tide gate, one with a side-hinged gate, and one without any tide gates that acted as our reference site. Our study species was coho salmon, Oncorhynchus kisutch, which may encounter tide gates both in the subyearling and smolt life stages in our study streams. Our objectives were to: 1) quantify upstream and downstream fish passage occurrence at all three sites, 2) determine whether juvenile coho salmon passage is associated with a specific range of gate conditions, and 3) identify any associations between coho smolt emigration rate and environmental variables that are influenced by tide gates. We installed stationary passive integrated transponder (PIT) antennae around both tide gates and a tidal channel in the non-gated stream to record the movement of PIT tagged juvenile coho salmon. Coho salmon smolts passed upstream most frequently at the non-gated channel (48% of all smolts detected at the array), next the side-hinged gate (28%), and lastly, the top-hinged gate (3%). Juvenile coho salmon passed more frequently at a specific range of gate angles and tailwater depths at both top hinged and side-hinged tide gates. Smolts passed downstream more frequently at greater gate angles and tailwater depths than available on average at both tide gates. Subyearlings passed upstream more frequently during small gate angles and a narrow range of tailwater depths at the top-hinged gate but did not pass more frequently under a particular range of conditions at the side-hinged gate. At the top-hinged gate, conditions favorable for subyearling upstream passage occurred towards the end of the gate open period and therefore subyearlings were severely limited in their opportunities for passage. At multiple sites, emigration rate was associated with environmental variables that may be altered by tide gates. Increases in water temperature were associated with an increasing likelihood of smolt emigration at multiple sites. At a tide gate that allowed upstream estuarine influence, increasing salinity was associated with a decreasing likelihood of emigration. Our results suggest that tide gates may interfere with salmonid movement and migration by creating physical barriers to fish passage and potentially influencing migratory timing by altering environmental variables. When installing or retrofitting tide gates, these factors should be taken into consideration since a tide gate's design may determine the severity of its effects on salmonids. Our work should be considered a case study and the findings should not be assumed to be transferable due to the great diversity of tide gate installations in use. We recommend further research, including a more in depth analysis of the affects of tide gates on subyearling coho salmon and an investigation of piscivorous predator exploitation of tide gates. Close