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• 41. [Article] Juvenile Coho Salmon (Oncorhynchus kisutch) Diet in Brackish and Freshwater Habitats in the Stream-estuary Ecotones of Coos Bay, Oregon

  Loss of lowland estuarine and freshwater off-channel habitats along the Pacific Northwest coast has contributed to the decline of salmonid populations. These habitats serve as nursery grounds for juvenile ...

  Citation × Citation Citation Abstract Copy Title: Juvenile Coho Salmon (Oncorhynchus kisutch) Diet in Brackish and Freshwater Habitats in the Stream-estuary Ecotones of Coos Bay, Oregon Author: Mackereth, Kailan F. Loss of lowland estuarine and freshwater off-channel habitats along the Pacific Northwest coast has contributed to the decline of salmonid populations. These habitats serve as nursery grounds for juvenile salmonids providing them with food, winter shelter, and a transition zone between freshwater and saltwater. Lowland areas have undergone anthropogenic alterations (e.g., installation of tide gates, construction of dikes, channelization) to increase the net area of land suitable for agriculture and development resulting in watershed fragmentation and reduction in the amount of habitats with high intrinsic potential to support populations of juvenile salmonids. Until recent years, sub-yearling coho salmon found in lowland riverine habitats and estuarine marshes were assumed to have been displaced from optimal upland reaches by competition and high water discharge. Recent studies have concluded that early estuarine migrant behavior is volitional and these fish return as 20-40% of the spawning population, but there are few studies that delve into the capacity of estuarine habitat to support early estuarine life history strategies in systems heavily altered by human practices. This study documented differences in diet and condition factor (K) between sub-yearling and yearling coho salmon foraging concurrently in brackish or freshwater lowland habitat of the upper estuarine intertidal zone. Fish stomach contents were sampled by means of gastric lavage in three coastal lowland creeks in Coos Bay on the southern Oregon coast. Prey found in the samples were sorted, counted, identified, and dried to obtain dry weight biomass. Condition factor (K) and total dry weight prey biomass of fishes were not different between brackish and freshwater habitat; however, non-metric multidimensional scaling indicated that prey composition was substantially different between habitat and age class. These findings suggest that early migrating sub-yearlings and yearling smolts diverge in their diets whether they occupy the same or different habitats in the stream to estuary transition zone. Insects were important prey within the diets of yearling and sub-yearling freshwater foragers and sub-yearling brackish water foragers while crustaceans were important in the diets of yearling brackish water foragers. Future research exploring prey abundance and availability in relation to prey selected by juvenile coho salmon would denote habitat foraging quality and habitat exploitation by early estuarine migrants. Expanding this research to contrast natural intertidal habitats with those regulated by tide gates would be beneficial towards understanding the impact different styles of tide gates have on biotic communities and hydrological attributes (e.g., flow, chemistry, temperature, tidal exchange). Identification of factors that influence habitat selection in the stream-estuary ecotone by alternative early life history strategies of juvenile coho salmon is essential towards enhancing genetic diversity thereby strengthening the resiliency of the population. Title: Juvenile Coho Salmon (Oncorhynchus kisutch) Diet in Brackish and Freshwater Habitats in the Stream-estuary Ecotones of Coos Bay, Oregon Author: Mackereth, Kailan F. Loss of lowland estuarine and freshwater off-channel habitats along the Pacific Northwest coast has contributed to the decline of salmonid populations. These habitats serve as nursery grounds for juvenile salmonids providing them with food, winter shelter, and a transition zone between freshwater and saltwater. Lowland areas have undergone anthropogenic alterations (e.g., installation of tide gates, construction of dikes, channelization) to increase the net area of land suitable for agriculture and development resulting in watershed fragmentation and reduction in the amount of habitats with high intrinsic potential to support populations of juvenile salmonids. Until recent years, sub-yearling coho salmon found in lowland riverine habitats and estuarine marshes were assumed to have been displaced from optimal upland reaches by competition and high water discharge. Recent studies have concluded that early estuarine migrant behavior is volitional and these fish return as 20-40% of the spawning population, but there are few studies that delve into the capacity of estuarine habitat to support early estuarine life history strategies in systems heavily altered by human practices. This study documented differences in diet and condition factor (K) between sub-yearling and yearling coho salmon foraging concurrently in brackish or freshwater lowland habitat of the upper estuarine intertidal zone. Fish stomach contents were sampled by means of gastric lavage in three coastal lowland creeks in Coos Bay on the southern Oregon coast. Prey found in the samples were sorted, counted, identified, and dried to obtain dry weight biomass. Condition factor (K) and total dry weight prey biomass of fishes were not different between brackish and freshwater habitat; however, non-metric multidimensional scaling indicated that prey composition was substantially different between habitat and age class. These findings suggest that early migrating sub-yearlings and yearling smolts diverge in their diets whether they occupy the same or different habitats in the stream to estuary transition zone. Insects were important prey within the diets of yearling and sub-yearling freshwater foragers and sub-yearling brackish water foragers while crustaceans were important in the diets of yearling brackish water foragers. Future research exploring prey abundance and availability in relation to prey selected by juvenile coho salmon would denote habitat foraging quality and habitat exploitation by early estuarine migrants. Expanding this research to contrast natural intertidal habitats with those regulated by tide gates would be beneficial towards understanding the impact different styles of tide gates have on biotic communities and hydrological attributes (e.g., flow, chemistry, temperature, tidal exchange). Identification of factors that influence habitat selection in the stream-estuary ecotone by alternative early life history strategies of juvenile coho salmon is essential towards enhancing genetic diversity thereby strengthening the resiliency of the population. Close

• 42. [Article] Factors associated with dusky Canada goose nesting and nest success on artificial nest islands of the western Copper River Delta

  The population of dusky Canada geese (Branta canadensis occidentalis; hereafter, dusky geese) nesting on the western Copper River Delta (CRD) in south- central Alaska has been in decline since the late ...

  Citation × Citation Citation Abstract Copy Title: Factors associated with dusky Canada goose nesting and nest success on artificial nest islands of the western Copper River Delta Author: Maggiulli, Nicole Marie The population of dusky Canada geese (Branta canadensis occidentalis; hereafter, dusky geese) nesting on the western Copper River Delta (CRD) in south- central Alaska has been in decline since the late 1970s. In an effort to alleviate mammalian predation, increase nest success, and avoid a listing under the U.S. Endangered Species Act, an artificial nest island (island) program was implemented on the western CRD in 1983. The installation of new islands on the CRD is the sole management action of the Pacific Flyway Council on the breeding grounds, but no comprehensive evaluation of the program has been published. I examined general trends in island use and nest success over time for three island types (donut islands, fiberglass floater islands, and sandbag islands) from 1984-2005. I used data from the island program to identify factors associated with dusky Canada goose nesting (hereafter, use) and nest success on islands from 1996-2005. I generated a series of candidate models and used logistic regression with model selection techniques to determine how variables representing pond characteristics, vegetative characteristics, interactions with conspecifics and larid species, the previous year’s island status, and the distance to predator corridors were associated with island use and nest success for each year. Use of islands by dusky geese nesting on the western CRD increased between 1987 and 2005 from a low of 10% in 1987 to 44% in 2005. There was annual variability in factors associated with island use; however, use of islands was most consistently and strongly associated with the previous year’s island status. The odds of a nest being placed on an island that contained a successful nest the previous year were 2.91 to 6.62 times greater than for islands not used the previous year. There was also evidence for an increased likelihood of island use further from shore and for islands with up to 55% aerial shrub cover and shrubs up to 1 m tall. Nest success was consistently high, indicating islands have long term potential for increasing dusky goose nest success on the Copper River Delta. Compared to island use, my analysis of nest success and habitat features resulted in many more competitive models (average 10 v. 2 per year) with fewer strong (95% confidence intervals for parameter estimates excluded zero) associations between explanatory variables and nest success. Explanatory variables representing vegetative characteristics, interactions with conspecifics and larid species, and the distance to predator corridors had a relatively low capacity to explain nest success on artificial islands. However, there was some evidence for an increased likelihood of nest success on islands further from shore with shorter shrubs. Lower variability in factors associated with island use is likely because factors associated with nest site selection are controlled by decisions of the nesting goose. The importance of previous year’s island status on island use likely reflects high site fidelity by breeding adult geese, with fidelity being higher for birds that have successful nests. Alternately, dusky geese use cues from the previous year’s nesting activity when prospecting for island nest sites. In contrast, nest success is dependent on a more complex combination of factors that vary within and among years outside the control of a nesting goose. Inter-annual variation in the timing and magnitude of eulachon (Thaleichthys pacificus) spawning runs on large sloughs of the CRD and prey-switching by important dusky goose nest predators may have considerable influence on dusky goose nest success on islands, similar to mainland- nesting dusky geese. The inability to control for eulachon presence and abundance may have confounded my analysis of habitat features important to nest success. Therefore, factors such as presence of alternate prey (and predator abundance) may be more important to dusky goose nest success on islands than habitat features. Current use of available nest islands is at a program high of 44% and nest success also remains high (63%); suggesting the artificial nest island program is valuable for dusky geese. However, the contribution of island-nesting dusky geese to the dusky goose population on the Copper River Delta is unclear. There is a need for a population model that incorporates all recent information on dusky goose reproductive ecology to determine if artificial nest islands can increase dusky goose population size, and if so, how many islands are needed. Title: Factors associated with dusky Canada goose nesting and nest success on artificial nest islands of the western Copper River Delta Author: Maggiulli, Nicole Marie The population of dusky Canada geese (Branta canadensis occidentalis; hereafter, dusky geese) nesting on the western Copper River Delta (CRD) in south- central Alaska has been in decline since the late 1970s. In an effort to alleviate mammalian predation, increase nest success, and avoid a listing under the U.S. Endangered Species Act, an artificial nest island (island) program was implemented on the western CRD in 1983. The installation of new islands on the CRD is the sole management action of the Pacific Flyway Council on the breeding grounds, but no comprehensive evaluation of the program has been published. I examined general trends in island use and nest success over time for three island types (donut islands, fiberglass floater islands, and sandbag islands) from 1984-2005. I used data from the island program to identify factors associated with dusky Canada goose nesting (hereafter, use) and nest success on islands from 1996-2005. I generated a series of candidate models and used logistic regression with model selection techniques to determine how variables representing pond characteristics, vegetative characteristics, interactions with conspecifics and larid species, the previous year’s island status, and the distance to predator corridors were associated with island use and nest success for each year. Use of islands by dusky geese nesting on the western CRD increased between 1987 and 2005 from a low of 10% in 1987 to 44% in 2005. There was annual variability in factors associated with island use; however, use of islands was most consistently and strongly associated with the previous year’s island status. The odds of a nest being placed on an island that contained a successful nest the previous year were 2.91 to 6.62 times greater than for islands not used the previous year. There was also evidence for an increased likelihood of island use further from shore and for islands with up to 55% aerial shrub cover and shrubs up to 1 m tall. Nest success was consistently high, indicating islands have long term potential for increasing dusky goose nest success on the Copper River Delta. Compared to island use, my analysis of nest success and habitat features resulted in many more competitive models (average 10 v. 2 per year) with fewer strong (95% confidence intervals for parameter estimates excluded zero) associations between explanatory variables and nest success. Explanatory variables representing vegetative characteristics, interactions with conspecifics and larid species, and the distance to predator corridors had a relatively low capacity to explain nest success on artificial islands. However, there was some evidence for an increased likelihood of nest success on islands further from shore with shorter shrubs. Lower variability in factors associated with island use is likely because factors associated with nest site selection are controlled by decisions of the nesting goose. The importance of previous year’s island status on island use likely reflects high site fidelity by breeding adult geese, with fidelity being higher for birds that have successful nests. Alternately, dusky geese use cues from the previous year’s nesting activity when prospecting for island nest sites. In contrast, nest success is dependent on a more complex combination of factors that vary within and among years outside the control of a nesting goose. Inter-annual variation in the timing and magnitude of eulachon (Thaleichthys pacificus) spawning runs on large sloughs of the CRD and prey-switching by important dusky goose nest predators may have considerable influence on dusky goose nest success on islands, similar to mainland- nesting dusky geese. The inability to control for eulachon presence and abundance may have confounded my analysis of habitat features important to nest success. Therefore, factors such as presence of alternate prey (and predator abundance) may be more important to dusky goose nest success on islands than habitat features. Current use of available nest islands is at a program high of 44% and nest success also remains high (63%); suggesting the artificial nest island program is valuable for dusky geese. However, the contribution of island-nesting dusky geese to the dusky goose population on the Copper River Delta is unclear. There is a need for a population model that incorporates all recent information on dusky goose reproductive ecology to determine if artificial nest islands can increase dusky goose population size, and if so, how many islands are needed. Close