Methodologies for recommending instream flows for protecting lotic ecosystems are evolving amid constructive criticism. During this period of change it is important that all concerned parties are aware of the ecological factors that control stream ecosystems and fish populations. Ecological factors relating to stream ecology, population dynamics, energetics, predation, and competition are reviewed to explain why indices of microhabitat availability are not expected to be consistent predictors of fish population density. Implications of these concepts for development and application of instream flow-habitat models for recommending instream flow regimes are discussed. Current ecological theory and empirical studies support the hypothesis that microhabitat availability may limit fish populations but not continuously. Therefore, assessments must consider the limiting habitat events as well as temperature and water quality constraints. Also, invertebrates and non-game fishes must be considered in instream flow assessments because of their importance in stream ecosystems.

The index of biotic integrity (IBI) integrates 12 measures of stream fish assemblages for assessing water resource quality. Initially developed and tested in the Midwest, the IBI recently was adapted for use in western Oregon, northeastern Colorado, New England, the Appalachians of West Virginia and Virginia, and northern California. The concept also was extended to Louisiana estuaries. In regions of low species richness, the IBI proved difficult to apply and often required extensive modification. Adapting the 1BI to those regions required that metrics be replaced, deleted, or added to accommodate regional differences in fish distribution and assemblage structure and function. Frequently replaced metrics include: proportion of individuals as green sunfish (Lepomis cyanellus), proportion of individuals as insectivorous cyprinids, proportion of individuals as hybrids, and number and identity of sunfish and darter species. The proportion of individuals as top carnivore metric was often deleted. Metrics added include total fish biomass and the number and identity of minnow species. These modifications generally followed the original IBI concept and its theoretical underpinnings. Problems remain in establishing tolerance rankings and scoring criteria, and adjusting scoring criteria for gradient differences in streams of similar size. The IBI holds promise for direct biological monitoring because of its strong ecological foundation and flexibility. Vermont, Tennessee Valley Authority, Ohio, Kentucky, and Illinois have incorporated the IBI into their monitoring or standards programs. The IBI thus serves as a quantitative, biological goal for water resource management.

We examined habitat‐use patterns in a fish assemblage in a large warmwater stream in West Virginia. Fish species and life stage composition and densities differed among habitat types, and five habitat‐use guilds (edge pool, middle pool, edge channel, riffle, and generalist) were proposed. Larger centrarchids used deep habitats with slow velocities, whereas young centrarchids used shallower habitat. Juvenile and adult smallmouth bass Micropterus dolomieui were nearly ubiquitous in the habitats of the study area, although densities were highest among snags. Minnows and darters used shallower areas, but the range of velocity used differed among species and life stages. Vegetated and channel edge habitats served as nursery areas. Total fish densities were highest in edge pool, backwaters, snags, edge riffles, and riffles. Nearshore, structurally complex habitats seem important in influencing the assemblage structure of fishes of large streams.

No abstract

No abstract

No abstract

Native to the central USA, the Blue Catfish Ictalurus furcatus and the Flathead Catfish Pylodictis olivaris have been widely introduced into many Atlantic slope rivers and are now found in several drainages of the Chesapeake Bay. Fisheries managers are concerned that these large, long‐lived catfish species may be contributing to observed declines in anadromous species, such as the American Shad Alosa sapidissima, Blueback Herring A. aestivalis, and Alewife A. pseudoharengus, all of which once comprised major U.S. fisheries. We assessed spatiotemporal variability and selectivity in the diets of Blue Catfish and Flathead Catfish during the spawning migration of these alosines. Catfish stomachs were collected during March–May in nontidal freshwater, tidal freshwater, oligohaline, and mesohaline portions of the James River. Diet contents were extracted from 2,495 catfish, 69.86% of which had prey items present in their foreguts (N = 1,743). We used DNA barcoding to identify degraded fish prey; nearly 30 taxa that would have otherwise gone undetected were identified in this manner. Blue Catfish had broad, omnivorous diets, whereas Flathead Catfish fed solely on other fish. Alosines were found in 4.46% of Blue Catfish stomachs and 16.67% of Flathead Catfish stomachs. Flathead Catfish selectively preyed on American Shad and, to a lesser degree, river herring. Alosines were consumed more frequently in nontidal freshwater areas, particularly in the high‐gradient reach between Bosher Dam and the 14th Street Bridge, and predation on alosines peaked in April. Our results suggest that Flathead Catfish are likely to have a greater per capita impact on depleted alosines. Furthermore, dams and other obstacles to fish movement may increase alosines’ vulnerability to predation by large catfish.

No abstract