Joseph L. Ebersole

Research in Thermal Biology: Burning Questions for Coldwater Stream Fishes

With the increasing appreciation of global warming impacts on ecological systems, in addition to the myriad of land management effects on water quality, the number of literature citations dealing with the effects of water temperature on freshwater fish has escalated in the past decade. Given the many biological scales at which water temperature effects have been studied, and the growing need to integrate knowledge from multiple disciplines of thermal biology to fully protect beneficial uses, we held that a survey of the most promising recent developments and an expression of some of the remaining unanswered questions with significant management implications would best be approached collectively by a diverse research community. We have identified five specific topic areas of renewed research where new techniques and critical thought could benefit coldwater stream fishes (particularly salmonids): molecular, organism, population/species, community and ecosystem, and policy issues in water quality. Our hope is that information gained through examination of recent research fronts linking knowledge at various scales will prove useful in managing water quality at a basin level to protect fish populations and whole ecosystems. Standards of the past were based largely on incipient lethal and optimum growth rate temperatures for fish species, while future standards should consider all integrated thermal impacts to the organism and ecosystem.

Juvenile Coho Salmon Growth and Survival across Stream Network Seasonal Habitats

Abstract Understanding watershed-scale variation in juvenile salmonid survival and growth can provide insights into factors influencing demographics and can help target restoration and mitigation efforts for imperiled fish populations. We assessed growth, movement, and apparent overwinter survival of individually tagged juvenile coho salmon Oncorhynchus kisutch in a coastal Oregon watershed from June 2002 to June 2003 and related growth and survival parameters to stream characteristics. Fall body size of juvenile coho salmon was a good predictor of smolt size and survival, but smolt size was also influenced by overwintering location. This was due to strong spatial patterns in winter growth rates associated with residency and movement into a small intermittent tributary. Though nearly dry in midsummer, this stream supported high densities of spawning coho salmon in the fall, and juveniles rearing there exhibited relatively high growth rates and emigrated as larger smolts. Improved winter growth and surviva...

Managing climate change refugia for climate adaptation

Refugia have long been studied from paleontological and biogeographical perspectives to understand how populations persisted during past periods of unfavorable climate. Recently, researchers have applied the idea to contemporary landscapes to identify climate change refugia, here defined as areas relatively buffered from contemporary climate change over time that enable persistence of valued physical, ecological, and socio-cultural resources. We differentiate historical and contemporary views, and characterize physical and ecological processes that create and maintain climate change refugia. We then delineate how refugia can fit into existing decision support frameworks for climate adaptation and describe seven steps for managing them. Finally, we identify challenges and opportunities for operationalizing the concept of climate change refugia. Managing climate change refugia can be an important option for conservation in the face of ongoing climate change.

Coho salmon dependence on intermittent streams

In February 2006, the US Supreme Court heard cases that may affect whether intermittent streams are jurisdictional waters under the Clean Water Act. In June 2006, however, the cases were remanded to the circuit court, leaving the status of intermittent streams uncertain once again. The presence of commercial species, such as coho salmon (Oncorhynchus kisutch), can be an important consideration when determining jurisdiction. These salmon spawn in the upper portions of Oregon coastal stream networks, where intermittent streams are common. In our study of a coastal Oregon watershed, we found that intermittent streams were an important source of coho salmon smolts. Residual pools in intermittent streams provided a means by which juvenile coho could survive during dry periods; smolts that overwintered in intermittent streams were larger than those from perennial streams. Movement of juvenile coho into intermittent tributaries from the mainstem was another way in which the fish exploited the habitat and illustrates the importance of maintaining accessibility for entire stream networks. Loss of intermittent stream habitat would have a negative effect on coho salmon populations in coastal drainages, including downstream navigable waters.

Influence of Summer Stream Temperatures on Black Spot Infestation of Juvenile Coho Salmon in the Oregon Coast Range

Abstract High summer water temperatures can adversely affect stream salmonids in numerous ways. The direct effects of temperature associated with increased metabolic demand can be exacerbated by other factors, including decreased resistance to disease and increased susceptibility to parasites. We quantified the occurrence of black spot infestation caused by a neascus-type trematode (family Diplostomidae) of juvenile salmonids in Oregons West Fork Smith River stream network during summer 2002 through fall 2003. The highest 7-d average of the daily maximum (ADM) temperatures was positively correlated with infestation rates in both years. We summarized the frequency and infestation severity of juvenile coho salmon Oncorhynchus kisutch by location within the network and summarized temperatures for 19 study reaches. Summer ADMs ranged from approximately 24°C near the watershed mouth to approximately 17°C in the upper reaches, while tributary ADMs ranged from approximately 16–18°C in the lower reaches to 12–17...

A Resource in Crisis: Changing the Measure of Salmon Management

An overriding focus on extraction of biomass and numerical goals in fishery management has promoted the depletion and biotic impoverishment of the Pacific salmon (Oncorhynchus spp.) resource. The prevalence of mechanistic thinking has marginalized or excluded critical ecological and cultural functions that sustain the resource and embody much of what humans value about it. This approach to salmon management has led to its own demise. We now face the task of forging a new approach to resource management, necessarily founded on restoration and longterm conservation of salmon, their ecosystems, and their non-commodity cultural contexts. We advocate a more contextual perspective of management and science, emphasizing that numerical performances are outcomes of underlying causal processes and relationships that determine the realized capacities of resources and ecosystems. Rather than striving to directly control resources to produce desired states or yields, management should foster and maintain the processes and relationships that determine the consumptive and nonconsumptive values of salmon and their ecosystems. We define restoration as the identification and alteration of activities and processes that presently constrain a biological resource and its environment, allowing the resource to re-express its intrinsic capacity. Management success is gauged by different empirical measures, including trends in spatial and developmental diversity, temporal continuity and spatial connectivity, life-history patterns and strategies, integrity of colonization pools, the reversibility of biological and physical processes, and the quality and sustainability of human experiences and communities.

Hierarchical Modeling of Late-Summer Weight and Summer Abundance of Juvenile Coho Salmon across a Stream Network

Abstract Spatial variation in stream habitat quality can lead to network-level patterns in the survival and growth of juvenile coho salmon Oncorhynchus kisutch that provide important insights into the factors influencing the freshwater population dynamics of this species. Our objectives were to quantify the relationships among summer habitat conditions, coho salmon density, and coho salmon parr abundance and weight across an extensive stream network over 3 years. We used hierarchical linear models to assess the factors influencing coho salmon weight and abundance at the levels of individual fish (fork length and parasite burden), habitat unit (surface area, cover, and density), reach (temperature and density) and stream (total nitrogen, soluble reactive phosphorus, and discharge). Habitat-unit-level surface area and stream-level minimum discharge were important predictors of both the abundance and weight of coho salmon parr. An area × discharge interaction term was also important in models of weight and r...

Habitat Selection Influences Sex Distribution, Morphology, Tissue Biochemistry, and Parasite Load of Juvenile Coho Salmon in the West Fork Smith River, Oregon

Abstract Given the strong influence of water temperature on salmonid physiology and behavior, in the summers of 2004 and 2005 we studied juvenile male and female coho salmon Oncorhynchus kisutch in two reaches of Oregons West Fork Smith River with different thermal profiles. Our goals were to compare the body morphology, tissue biochemistry, genetics, and parasite load and determine whether sex, tissue biochemistry, and infection with multiple parasite species influence swimming performance. Sex differences in habitat selection distribution were apparent; proportionately more females occupied the cooler, upper reach, and males predominated in the warmer, lower reach. Despite having similar genotypes, fish in the upper reach had deeper bodies and higher condition factors, regardless of sex. These fish also had higher blood lipids and elevated citrate synthase activity in epaxial white muscle, suggesting a greater potential for aerobic metabolism. Critical swimming speeds measured streamside at 18°C and en...

Predicting the occurrence of cold-water patches at intermittent and ephemeral tributary confluences with warm rivers

Cold water provided by small tributary streams can contribute to thermal heterogeneity in downstream receiving waters, thereby providing important thermal refuge habitat for cold-water aquatic taxa residing in warmer mainstem rivers. We investigated the potential function of small perennial and nonperennial tributary streams, including intermittent and ephemeral channels (some of which were dry) as sources of cold water to warmer receiving rivers. We used random forest analysis to model occurrence of cold-water patches at tributary confluences as a function of watershed and climatic characteristics and tested predictive performance with a 2-y data set of 68 tributary–mainstem confluence zones in northeastern Oregon, USA. Cold-water patches were present in 53% (36 of 68) of the tributary confluences. Of these, 14 occurred at tributaries that had no surface-water flow at the time of sampling. The likelihood of a tributary contributing a detectable source of cold water to a confluence zone during late July to early August was positively associated with an estimate of the water surplus available in the tributary basin at the end of the preceding wet season. Basin area and the presence of tributary surface flow at the time of sampling were relatively uninformative predictors of cold-water patch presence. Because surface flow was not evident in 39% of the tributaries where cold-water patches were observed, we conclude that the availability of thermal refugia for cold-water taxa, such as Pacific Salmon (Oncorhynchus spp.), in summer-warm streams is, in part, dependent upon the continued release of ground water from tributary basins during mid-summer, even after surface stream flow ceases. These findings highlight a potentially important ecological function of intermittent and ephemeral stream channels as sources of cold subsurface discharge to downstream waters during the dry season.

Modeling Stream Network-Scale Variation in Coho Salmon Overwinter Survival and Smolt Size

Abstract We used multiple regression and hierarchical mixed-effects models to examine spatial patterns of overwinter survival and size at smolting in juvenile coho salmon Oncorhynchus kisutch in relation to habitat attributes across an extensive stream network in southwestern Oregon over 3 years. Contributing basin area explained the majority of spatial variation (R 2 = 0.57-0.63) in coho salmon overwinter survival (range = 0.02-0.63), with highest survival rates observed in smaller headwater and intermittent streams. Other habitat attributes, including proportional pool area, percent exposed bedrock substrate, percent broadleaf canopy cover, and adult salmon carcass density, were relatively poor predictors of survival. Indices of individual fish condition, including fall parr fork length, condition factor, and parasite infestation rates, were also relatively uninformative in coho salmon overwinter survival models. Coho salmon smolt length was primarily a function of length at the time of fall tagging, bu...