Juvenile Coho Salmon (Oncorhynchus Kisutch) Diet in Brackish and Freshwater Habitats in the Stream-estuary Ecotones of Coos Bay, Oregon
Juvenile Coho Salmon (Oncorhynchus Kisutch) Diet in Brackish and Freshwater Habitats in the Stream-estuary Ecotones of Coos Bay, Oregon

Author: Kailan F. Mackereth

Publisher:

Published: 2016

Total Pages: 44

ISBN-13:

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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.

Over-wintering Diet, Growth, and Prey Available to Juvenile Coho Salmon (Oncorhynchus Kisutch) in the West Fork Smith River, Oregon
Over-wintering Diet, Growth, and Prey Available to Juvenile Coho Salmon (Oncorhynchus Kisutch) in the West Fork Smith River, Oregon

Author: Anthony O. Olegario

Publisher:

Published: 2007

Total Pages: 114

ISBN-13:

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Over-winter growth of juvenile salmonids may be linked to ocean survival and thus species persistence. Diet, growth, and prey available to juvenile coho, Oncorhynchus kisutch, were examined from December 2004 to April 2005 in four tributaries of the West Fork Smith River (WFSR), Oregon. Juvenile coho growth rate and condition were greatest in spring. Growth rate varied through winter and was highest in Crane Creek, a small intermittent stream (4.3km2 basin area) and lowest in Beaver Creek (7.5 km2), a perennial stream. Prey availability and growth rate decreased in January and February as temperatures dropped, however stomach fullness was highly variable and not correlated to growth rate. The stomach contents of 477 juvenile coho (age-0), were quantitatively examined using an index of relative importance. Juvenile coho fed primarily on benthic invertebrates; rarely consumed non-insectan food included coho fry, salmon eggs, aquatic snails (Juga silicula), salamanders (Dicamptodon tenebrosus), and terrestrial invertebrates. The major portions of their diets, in order of relative importance, were aquatic chironomid larvae (Diptera), baetid mayfly larvae (Ephemeroptera), limnephilid caddisfly larvae (Trichoptera), and winter stonefly larvae (primarily Capniid Stonefly). Similarities in Relatively Important prey distinguished the two intermittent streams from the two perennial streams. In the WFSR tributaries, juvenile coho appear to rely on a variety of food sources to sustain growth and condition during winter. Small intermittent headwater streams may be disproportionately more important to stream fish with greater availability of prey than larger perennial streams highlighting the need to conserve and restore these habitats.

Juvenile Coho Salmon Movement, Growth and Survival in a Coastal Basin of Southern Oregon
Juvenile Coho Salmon Movement, Growth and Survival in a Coastal Basin of Southern Oregon

Author: Adam D. Weybright

Publisher:

Published: 2011

Total Pages: 110

ISBN-13:

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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.

Contribution of Subyearling Estuarine Migrant Coho Salmon (Oncorhynchus Kisutch) to Spawning Populations on the Southern Oregon Coast
Contribution of Subyearling Estuarine Migrant Coho Salmon (Oncorhynchus Kisutch) to Spawning Populations on the Southern Oregon Coast

Author: Katherine E. Nordholm

Publisher:

Published: 2014

Total Pages: 66

ISBN-13:

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The typical coho salmon life history has been characterized by juvenile fish that spend their entire first year in freshwater habitats before migrating into estuaries as smolts. However, reports of early migrating coho fry (age 0), including migration downstream to estuarine habitats, date back to the 1960s. Until a few years ago, these individuals were considered to be displaced surplus fish with low chances of survival. Recent studies have suggested that subyearling estuarine migrating coho salmon could be an alternative life history in coastal populations, but their return as jacks or mature adults needed to be documented for this life history to be considered a viable strategy. The goal of our study was to track the return of spawning coho salmon that had been individually tagged in either estuarine or riverine nursery habitats, and determine return percentages for each life history strategy as well as independently verify the presence of subyearling estuarine migrating coho salmon through otolith analysis on spawning populations. We used Passive Integrated Transponder (PIT) tags to identify individual fish as they passed through a series of antennas deployed in two coastal lowland streams on the southern Oregon coast. Percentage return of estuary tagged parr (fish e"60 mm tagged in spring and summer of their first year) was variable between years and streams. For the 2010 return year, subyearling estuarine migrants was 2.5 times higher than stream residents in Palouse Creek. Fork length at estuary entrance was reconstructed for one return year of spawning fish based on otolith Sr:Ca and Br:Ca. Four main life history strategies were identified based on their fork length at time of estuary/ocean entrance: early migrating fry (60 mm fork length), early migrating parr (60 - 70 mm fork length), early migrating parr that returned to freshwater before migrating as yearlings ("nomads"), and yearling migrating smolts ( 70 mm fork length). Overall, 30% (Larson Creek) to 42% (Palouse Creek) of the 2009 spawning run was made up of fish that displayed evidence of estuarine residence during their first year. This study confirms that subyearling estuarine migrating coho salmon survive to reproductive age and contribute to subsequent generations. The survival of this life history type likely varies between years with changing ocean and stream conditions. It is hypothesized that their life history serves as a "bet hedging" strategy that supports coastal populations in years of poor stream conditions. In the face of rising sea levels, this life history may represent a key to the future viability of coho salmon stocks in coastal watersheds.

Winter Ecology of Juvenile Coho Salmon (Oncorhynchus Kisutch) in Modified and Unmodified Sections of a Coastal Stream
Winter Ecology of Juvenile Coho Salmon (Oncorhynchus Kisutch) in Modified and Unmodified Sections of a Coastal Stream

Author: Stephen Homes Phillips

Publisher:

Published: 1986

Total Pages: 124

ISBN-13:

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Natural and gabion modified habitats containing coho salmon (Oncorhynchus kisutch) were observed and measured seasonally in East Fork Lobster Creek, a fifth order stream in western Oregon. Coho salmon usually inhabited backwater and secondary channel pools in winter. Large wood debris complexes and undercut banks were the primary sources of cover in winter. Beaver activity played a vital role in creating summer and winter habitat. Discharge rates seemed to have more influence than temperature in regulating coho winter hiding behavior. Lower than usual stream discharges of the 1984-85 winter allowed many fish to move out from cover, and a large portion of the coho were found more than 2 meters from cover. Coho were also not as dependent on cover during the low flows of spring and summer, and these low discharges allowed fish to inhabit less complex sites. Study sites with gabions maintained large numbers of fry throughout the spring and summer. Fish were attracted to the gabion-created plunge pools in low stream discharge months but not in high discharge months. During winter high discharges, gabion sites with backwater pool habitat held relatively larger numbers of fish than gabion sites without such habitat.