Hiram W. Li

Landscapes to riverscapes: bridging the gap between research and conservation of stream fishes

R and streams, by their very nature long ribbons of aquatic habitat, are inherently difficult to study. Approaching the banks of a flowing-water (lotic) system, one can see only a short fragment of the entire stream, from one bend to another, and can gain little appreciation for important features that lie beyond view. Moreover, materials transported downstream by the flow, and organisms traveling up or down the hydraulic highway, are soon gone from the reach and the opportunity to study them is often lost. Lakes present their own challenges for study, but by contrast to streams, one can usually see large expanses from shore that encompass all major habitats needed for aquatic organisms to complete their life history, such as gravel shoals, beds of aquatic vegetation, and open water habitats. Much of our knowledge of the ecology of rivers and streams is based on observations and experiments on organisms and habitat in the short fragments we can view or quickly traverse on foot, and this limited understanding underpins our efforts at conservation of stream fishes. Here, we argue that this understanding is incomplete, like viewing only disjunct parts of a landscape painting through small holes in a curtain draping it. We propose that a continuous view of rivers is essential for effective research and conservation of their fishes and other aquatic biota—a view not just of disjunct reaches but of the entire spatially heterogeneous scene of the river environment, the riverscape, unfolding through time. One symptom of our incomplete understanding is the alarming rate of decline over the last 50 years of fishes that inhabit rivers and streams of North America. The public is aware that salmon are disappearing from the Pacific Northwest, with about a quarter of the 214 stocks of anadromous salmon and trout imperiled a decade ago (Nehlsen et al. 1991). Even little-known small fishes native to Great Plains and southwestern desert streams have suffered drastic declines (Minckley and Douglas 1991, Fausch and Bestgen 1997), and many are now either protected by federal or state listing as endangered or threatened species or are being considered for such protection. North America harbored the greatest diversity worldwide of temperate freshwater fishes (Warren and Burr 1994), crayfishes (Taylor et al. 1996), and mussels (Williams et al. 1993), but about 30% to 75% of the taxa in each group are at increased risk of extinction (i.e., categorized as rare, threatened, or endangered species). Fishes are also the most imperiled vertebrates worldwide (Allan and Flecker 1993, Leidy and Moyle 1998) and a large proportion spend at least part of their lives in streams.

MULTISCALE THERMAL REFUGIA AND STREAM HABITAT ASSOCIATIONS OF CHINOOK SALMON IN NORTHEASTERN OREGON

We quantified distribution and behavior of adult spring chinook salmon (Oncorhynchus tshawytscha ) related to patterns of stream temperature and physical habitat at channel-unit, reach-, and section-level spatial scales in a wilderness stream and a disturbed stream in the John Day River basin in northeastern Oregon. We investigated the effectiveness of thermal remote sensing for analyzing spatial patterns of stream temperature and assessed habitat selection by spring chinook salmon, evaluating whether thermal refugia might be responsible for the persistence of these stocks in rivers where water temperatures frequently exceed their upper tolerance levels (258C) during spawning migration. By presenting stream temperature and the ecology of chinook salmon in a historical context, we could evaluate how changes in riverine habitat and thermal spatial structure, which can be caused by land- use practices, may influence distributional patterns of chinook salmon. Thermal remote sensing provided spatially continuous maps of stream temperature for reaches used by chinook salmon in the upper subbasins of the Middle Fork and North Fork John Day River. Electivity analysis and logistic regression were used to test for associations between the longitudinal distribution of salmon and cool-water areas and stream habitat characteristics. Chinook salmon were distributed nonuniformly in reaches throughout each stream. Salmon distribution and cool water temperature patterns were most strongly related at reach-level spatial scales in the warm stream, the Middle Fork (maximum likelihood ratio: P , 0.01), and most weakly related in the cold stream, the North Fork (P. 0.30). Pools were preferred by adult chinook salmon in both subbasins (Bonferroni confidence interval: P # 0.05); however, riffles were used proportionately more frequently in the North Fork than in the Middle Fork. Our observations of thermal refugia and their use by chinook salmon at multiple spatial scales reveal that, although heterogeneity in the longitudinal stream tem- perature profile may be viewed as an ecological warning sign, thermal patchiness in streams also should be recognized for its biological potential to provide habitat for species existing at the margin of their environmental tolerances.

Influence of Habitat Complexity on Resistance to Flooding and Resilience of Stream Fish Assemblages

Abstract The structure of fish assemblages in five reaches of a high desert stream in north-central Oregon was determined by snorkeling before and after a summer flash flood and two spring floods. One reach in each of two other streams that were unaffected by the first flood was used as a reference system. Stream reaches varied in habitat complexity as measured by hydraulic retention. Following the floods, hydraulically complex stream reaches lost proportionately fewer fish, had generally higher fish diversities, and had higher fish assemblage similarity than hydraulically simple stream reaches. Fish assemblages were resilient, and certain species such as speckled dace Rhinichthys osculus were exceptionally good at recolonizing disturbed habitats. Successful recruitment of different fish species depended, in part, on flood timing. Young of the year of species that spawn in early spring (e.g., rainbow trout Oncorhynchus mykiss) were more negatively affected by early spring floods than summer floods. Specie...

The Ecological and Cultural Importance of a Species at Risk of Extinction, Pacific Lamprey

Abstract The cultural and ecological values of Pacific lamprey (Lampetra tridentata) have not been understood by Euro-Americans and thus their great decline has almost gone unnoticed except by Native Americans, who elevated the issue and initiated research to restore its populations, at least in the Columbia Basin. They regard Pacific lamprey as a highly valued resource and as a result ksuyas (lamprey) has become one of their cultural icons. Ksuyas are harvested to this day as a subsistence food by various tribes along the Pacific coast and are highly regarded for their cultural value. Interestingly, our review suggests that the Pacific lamprey plays an important role in the food web, may have acted as a buffer for salmon from predators, and may have been an important source of marine nutrients to oligotrophic watersheds. This is very different from the Euro-American perception that lampreys are pests. We suggest that cultural biases affected management policies.

Cumulative Effects of Riparian Disturbances along High Desert Trout Streams of the John Day Basin, Oregon

Abstract In a study of cumulative effects of riparian disturbance by grazing on the trophic structure of high desert trout streams, watersheds with greater riparian canopy had higher standing crops of rainbow trout Oncorhynchus mykiss, lower daily maximum temperatures (range, 16–23°C compared with 26–31°C), and perennial flow. Watershed aspect influenced the response of trophic structure to grazing influences. Standing crops of rainbow trout were negatively correlated with solar radiation and maximum temperature in watersheds flowing northward. A different relationship was observed for a set of watersheds with a southern aspect, perhaps due to the presence of spring seeps and stream desiccation in the heavily grazed stream. Trout biomass was negatively correlated with solar radiation, whereas positive relationships were found for discharge and depth. Algal biomass was positively correlated with solar insolation (r = 0.9 1), total invertebrate biomass (r = 0.77), and herbivorous invertebrate biomass (r = 0...

Qualitative predictions in model ecosystems

We compare qualitative predictions of press perturbation response from community matrix models with those of a range of numerical simulations on the same models. A technique of weighting the proportion of countervailing feedback cycles in qualitative response predictions (weighted predictions) was tested against quantitative predictions from the inverse community matrix. Specifically, in nine each of 5- and 10- variable models (of varying complexity) we randomly assigned quantitative values of interaction strength and measured correspondence with qualitative predictions in terms of response strength and sign. Based on the techniques and analyses presented herein, we report an expanded scope of inference for qualitative models of any size and complexity and conclude that system structure is of overriding importance.

Qualitative stability and ambiguity in model ecosystems.

Qualitative analysis of stability in model ecosystems has previously been limited to determining whether a community matrix is sign stable or not with little analytical means to assess the impact of complexity on system stability. Systems are seen as either unconditionally or conditionally stable with little distinction and therefore much ambiguity in the likelihood of stability. First, we reexamine Hurwitz’s principal theorem for stability and propose two “Hurwitz criteria” that address different aspects of instability: positive feedback and insufficient lower‐level feedback. Second, we derive two qualitative metrics based on these criteria: weighted feedback (wFn) and weighted determinants (wΔn). Third, we test the utility of these qualitative metrics through quantitative simulations in a random and evenly distributed parameter space in models of various sizes and complexities. Taken together they provide a practical means to assess the relative degree to which ambiguity has entered into calculations of stability as a result of system structure and complexity. From these metrics we identify two classes of models that may have significant relevance to system research and management. This work helps to resolve some of the impasse between theoretical and empirical discussions on the complexity and stability of natural communities.

Ecological Analysis of Species Introductions into Aquatic Systems

Abstract The introduction of new species into aquatic communities to increase fish production is a management technique that often has created more problems than it has solved. In large measure, this is due to the inability to correctly predict impact. Loop analysis is a tool of systems analysis and may be useful in predicting systems behavior of an aquatic community once an introduction is made, using the limited information usually available. Case histories of two lake systems examined by loop analysis suggest that nutrient-poor systems are most sensitive and become unstable after exotics become established. Rules developed by entomologists to guide selection of predators for biological control systems can be adapted for fisheries management. The “ideal” candidate for aquatic introduction is coadapted with some members of the new system, has a narrow niche breadth, is easily controlled if it escapes from the system, and is free of exotic diseases and parasites.

Allozyme and morphological divergence of rainbow trout (Oncorhunchus mykiss) above and below waterfalls in the Deschutes River, Oregon

We examined allozyme and morphological variation among populations of rainbow trout (Oncorhynchus mykiss) in the Deschutes River Basin. Populations isolated above a major waterfall in the White River (a tributary of the Deschutes River) represented a group of rainbow trout with plesiomorphic characteristics previously known only from isolated drainages of the northern Great Basin. White River populations were characterized by little or no variation at sSod-1 and Ldh-B2, fine scales, and few pyloric ceca. Other populations in the Deschutes River were more similar to anadromous populations east of the Cascade Mountains in the Columbia River. Our results suggest that the two forms in the Deschutes River and a persistent population in a desiccating drainage of the Great Basin in Oregon diverged from a common, ancestral population during the Pleistocene. We found no evidence that all isolated groups of rainbow trout with plesiomorphic characteristics in the White River, Oregon desert basins, and northern California represented a monophyletic group.

Energetic factors influencing foraging tactics of juvenile steelhead trout, Salmo gairdneri

Increases in water temperature and fish size should increase standard metabolism and food demand. Stream-dwelling trout may then, despite the increased cost of swimming, seek faster water where food is more abundant. We tested these predictions with juvenile steelhead trout, Salmo gairdneri, in a California stream and found that increased fish size and water temperatures did result in the increased selection of microhabitats with high water velocities. Faster water provided proportionally larger amounts of drifting invertebrate food. Higher velocity, shallower, and coarser substrate microhabitats also enabled fish to capture prey from portions of the water column substantially faster and more productive than at their resting positions. Velocities selected in this stream were similar to those which would result in a doubling of metabolic rate. Models evaluating trout habitat and effects of modifications should take energetic factors into account.