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At least 1,297 records · Page 72Linked to original sources
USGS2009

Warmwater fish in rivers

Large warmwater rivers are complex ecosystems and often contain numerous species and habitats. We loosely define a large river as having a drainage area greater than 50,000 km2 and a stream order great than six. Further, these rivers typically have mean discharges greater than 1,500 m3/s. Channel patterns are highly variable among and within large rivers, generally forming a meandering pattern. Currently, many large rivers are confined by bank stabilization and are characterized by a straight channel because of anthropogenic alterations. Further, most large rivers in North America have altered hydrographs because of main-stem dams or dams within the drainage area. Large rivers that have been modified to reduce meandering and flooding present challenges for deployment and operation of fish sampling gear. Water temperature in large rivers is highly variable across North America and varies longitudinally within a river. For example, the Missouri River originates in the Rocky Mountains and terminates at the confluence with the Mississippi River near St. Louis, Missouri. Thus, mean water temperature in the headwaters is considerably different than the confluence. As a result, we defined warmwater by the dominant fish assemblage found in the river. Most fish species can be categorized into broad categories, such as coldwater, coolwater, or warmwater, based on water temperature in the natural environments where they occur. We define warmwater rivers as rivers that were naturally void of coldwater fishes such as trouts, salmons, and ciscoes. This is appropriate because it disregards zoogeographic boundaries that may limit the inclusion of rivers in the warmwater category. For example, the Colorado River is in a different zoogeographic subdivision than the Ohio River (Moyle and Cech 2000), but both rivers contain warmwater fish assemblages.

Book chapter↗
USGS2009

Coldwater fish in large standing waters

Large coldwater lakes are defined here as standing freshwater bodies with surface area greater than 200 ha that support coldwater fishes such as trouts and salmons throughout the year. These large water bodies can be exposed to extensive wind fetch, which will affect the timing, mobility, and safety of personnel and gear. These considerations become important constraints for deploying, locating, and retrieving sampling gear. Wind and wave energy affect the timing, duration, and stability of thermal stratification, and they can create transient upwellings, thermal fronts, seiches, and other internal waves that affect vertical and horizontal thermal structure and dissolved oxygen availability. Thermal stratification affects seasonal distribution and productivity patterns for most aquatic organisms. When waters are destratified, movements and distributions of fishes can vary considerably, particularly during thermocline formation in spring and destratification during autumn. During thermal stratification, species with similar thermal responses tend to concentrate more predictably within certain depth-temperature strata, and segregate from species with different thermal responses. In mesotrophic and eutrophic lakes, hypoxia below the thermocline (sometimes encroaching into the thermocline) forces coldwater fishes into shallower, warmer depths than they would otherwise inhabit. Seasonal and diel changes in light and turbidity conditions affect the activity levels, behaviors, and distributions of fishes (e.g., schooling, diel vertical or horizontal migrations, refuge-seeking) and influence their ability to detect and evade certain types of sampling gear, such as gill nets and trawls. Major tributaries and outlets can form habitat conditions that differ considerably from the rest of the littoral zone. Tributary mouths form shallow sand-silt deltas with perceptible flow-through channels and groundwater inflows. Localized thermal pockets can develop if the temperature from incoming surface plumes or groundwater differs substantially from the lake water. Inlets are also point sources for recruitment and for delivering turbidity or prey generated from stream, riparian, or terrestrial sources. Because these habitat features tend to attract fishes, inlets and outlets should generally be considered distinct strata in a lake sampling program.

Book chapter↗
USGS2009

Coldwater fish in wadeable streams

Standardizing sampling methods for fish populations across large regions is important for consistent measurement of large-scale effects of climate or geography. In addition, pooling samples creates larger sample sizes and can facilitate data sharing among scientists and land managers. Sampling freshwater fish has largely not been standardized due to the diversity of fish and habitats. USGS aquatic ecologist Jason Dunham and co-authors contributed a chapter about sampling coldwater fish in wadeable streams to a new book that details common methods, protocols, and guidelines for sampling fish across North America. Topics include three common sampling methods: electrofishing, snorkeling, and nest counts. Each method provides complementary information about different species and life stages. The information will be useful for initiating new or fine-tuning ongoing sampling programs.

Book chapter↗
USGS2024

Indices for common North American fishes

One of the greatest advantages to the standardization of fisheries sampling methods is the comparable data they produce (Bonar et al. 2017). Following American Fisheries Society (AFS) standardized sampling methods, fisheries professionals can more easily compare their data with standardized data collected across North America to address both small- and large-scale fisheries questions. For example, access to standardized data can allow fisheries managers to evaluate if a fish species is within an expected range for weight or length in a particular water body, providing them with valuable information about the baseline health of their fish population. Additionally, given that fish can take years to respond to certain management actions (Meals et al. 2010), access to standardized data over time can be used to assess the effectiveness of these actions. Finally, standardized fisheries data can be analyzed over large geographic regions and provide increased sample sizes to evaluate management actions that cross local or state borders, such as habitat improvements or regulations, as well as the effects of large-scale transformations such as climate change on fish growth or body condition. Ultimately, the use of standardized data enhances the ability of fisheries professionals to address both small- and large-scale threats currently facing freshwater ecosystems and the fishes they support.

Book chapter↗
USGS1939

Migratory fish, a problem of interstate cooperation?

Bobwhite quail chicks, when given a choice of balanced diets in which the essential difference was the protein supplement, showed preferences for one diet containing 49 per cent peanut oil meal, another containing a mixture of 9 per cent meat and bone scraps (50% protein) with 38 per cent soybean oil meal, and a third (control) diet containing a mixture of 16 per cent dried buttermilk with 42 per cent soybean oil meal, in contrast to diets containing sardine meal or menhaden fish meal. ....Feeding tests during the first five weeks of life showed that diets containing 14 per cent sardine fish meal consistently gave high live weights, low mortality, and high efficiency of feed utilization. Diets with 9 to 10 per cent menhaden meal produced nearly as good results....Live weights, survival, and efficiency of feed utilization were markedly better on a diet containing 9 per cent meat and bone scrap (50% protein) than on one with 9 per cent meat scrap (55% protein), but not as good as with diets containing fish meal without meat....The chicks grew and survived more successfully on diets containing either soybean oil meal or peanut oil meal as the sole protein supplement, than on diets containing either linseed oil meal, cottonseed oil meal, or dried buttermilk as the sole protein concentrate. None of these was as satisfactory as the diets containing fish meal.....All chicks died on diets containing either linseed oil meal, cottonseed oil meal, or dried buttermilk as the sole source of protein. All three of these concentrates, however, gave satisfactory results, when used as 10 per cent of the diet. In fact, survival and efficiency of feed utilization were nearly as good on a diet containing 10 per cent dried buttermilk, 10 per cent linseed oil meal, 10 per cent peanut oil meal, and 27 per cent soybean oil meal, as on diets containing fish meal.

Transactions of the North American Wildlife Confer↗
USGS1979

Annotated list of the fishes of the Lake Ontario watershed

This annotated list of the fishes of Lake Ontario and its watershed is based on published distribution records, museum collections, and reports of fish surveys that confirm the occurrence of fish species dating back to the 1850's. It includes 130 forms (129 spp. + the hybrid splake), 20 of which have disappeared or are extremely rare today. Considering species present only in the lake proper, 64 were reported in 1929, and 51 of those remained in 1972-73 (13 having disappeared). Seventeen species and the splake are fishes not known to have occurred in the lake in 1929 or were introduced since then. A list of 86 references pertinent to the study of the fish fauna of the watershed is given. The present list, started in 1972, includes some information from as late as 1976.

Technical Report↗
USGS1998

Contaminant effects on Great Lakes' fish-eating birds: a population perspective

Preventing environmental contaminants from reducing wildlife populations is the greatest concern in wildlife toxicology. In the Great Lakes, environmental contaminants have a history of reducing populations of many species of fish-eating birds. Endocrine effects may have contributed to declines in fish-eating bird populations, but the overriding harm was caused by DDE-induced eggshell thinning. Toxic effects may still be occurring today, but apparently they are not of a sufficient magnitude to depress populations of most fish-eating birds. Once DDE levels in the Great Lakes declined, eggshells of birds began to get thicker and reproductive success improved. Populations of double-crested cormorants (Phalacrocorax auritus) and ring-billed gulls (Larus delawarensis) have increased dramatically since the bans on DDT and other organochlorine pesticides. Bald eagles (Haliaeetus leucocephalus) are still not reproducing at a normal rate along the shores of the Great Lakes, but success is much improved compared to earlier records when eggshell thinning was worse. Other species, such as herring gulls (Larus argentatus) and black-crowned night-herons (Nycticorax nycticorax), seem to be having improved reproductive success, but data on Great Lakes'-wide population changes are incomplete. Reproductive success of common terns (Sterna hirundo), Caspian terns (Sterna caspia), and Forster's terns (Sterna forsteri) seems to have improved in recent years, but, again, data on population changes are not very complete, and these birds face many habitat related problems as well as contaminant problems. Although contaminants are still producing toxic effects, and these effects may include endocrine disfunction, fish-eating birds in the Great Lakes seem to be largely weathering these effects, at least as far as populations are concerned. A lack of obvious contaminant effects on populations of fish-eating birds in the Great Lakes, however, should not be equated with a lack of any harm to these birds or with a conclusion that certain contaminants do not need additional control.

Book chapter↗
USGS1995

Effects of fish density and relative abundance on competition between larval lake herring and lake whitefish for zooplankton

Competition for zooplankton between larval lake herring ( Coregonus artedi ) and lake whitefish ( C. clupeaformis ) was compared in mesocosm experiments in a small lake. Both species were combined in test enclosures at relative abundances of 1:1 or 1:4 lake herring to lake whitefish at densities of 500; 1, 000; and 2, 000 fish per cage, and were allowed to feed ad libitum on available zooplankton. After 60 days, at 500 fish per cage and a 1:1 ratio, lake whitfish were significantly larger than lake herring. At 1, 000 and 2, 000 fish per cage, lake herring and lake whitefish exhibited similar depressed growth rates. Survival was lower (30-50%) in the nets with 2, 000 fish than in the lower fish densities. We suspect that diet similarities of juvenile lake herring and lake whitefish in addition to the larger size and more aggressive behavior of larval lake whitefish resulted in the depressed growth and poorer survival for lake herring.

Book chapter↗
USGS1989

Acid rain publications by the U.S. Fish and Wildlife Service, 1979-1989

Pollution of aquatic and terrestrial ecosystems has been a concern to society since the burning of fossil fuels began in the industrial revolution. In the past decade or so, this concern has been heightened by evidence that chemical transformation in the atmosphere of combustion by-products and subsequent long-range transport can cause environmental damage in remote areas. The extent of this damage and the rates of ecological recovery were largely unknown. "Acid rain" became the environmental issue of the 1980's. To address the increasing concerns of the public, in 1980 the Federal government initiated a 10-year interagency research program to develop information that could be used by the President and the Congress in making decisions for emission controls. The U.S. Fish and Wildlife Service has been an active participant in acid precipitation research. The Service provided support to a number of scientific conferences and forums, including the Action Seminar on Acid Precipitation held in Toronto, Canada, in 1979, an international symposium on Acidic Precipitation and Fishery Impacts in Northeastern North America in 1981, and a symposium on Acidic Precipitation and Atmospheric Deposition: A Western Perspective in 1982. These meetings as well as the growing involvement with the government's National Acidic Precipitation Assessment Program placed the Service in the lead in research on the biological effects of acidic deposition. Research projects have encompassed water chemistry, aquatic invertebrates, amphibians, fish, and waterfowl. Water quality surveys have been conducted to help determine the extent of acid precipitation effects in the northeast, Middle Atlantic, and Rocky Mountain regions. In addition to lake and stream studies, research in wetland and some terrestrial habitats has also been conducted. Specific projects have addressed important sport species such as brook trout (Salvelinus fontinalis), Atlantic salmon (Salmo salar), and striped bass (Morone saxatilis). Trace metal accumulation in fish has been investigated and a symposium sponsored on related work. U.S> Fish and Wildlife Service scientists serve as advisors and participants in research being conducted by industry, nonprofit groups, State and other Federal agencies. Researcher have worked closely with colleagues in Canada, England, Norway, Scotland, the Soviet Union, and Sweden to gain additional understanding of the problem. In 1982, the Service implemented a mitigation research program to provide resource managers with information to help them protect sensitive ecosystems, and rehabilitation methods for resources already affected by acidification. An international workshop was convened to outline the research needs. Several conferences were organized to develop appropriate field and laboratory procedures. Scientists with the mitigation research program are evaluating the ecological effects of liming (addition of base material) surface waters and surrounding watershed to provide buffering against acidic inputs. Through long-term cooperative project with States and other organizations, investigations are studying possible abatement methods for regions most affected by acidic deposition. To date, more than 200 reports the describe these studies have been published. These products include conference proceedings, journal articles, and in-house scientific publications. An education poster describing the effects of acid rain on aquatic ecosystems was developed and distributed to individuals, conservations and State organizations, and the public education system. This annotated bibliography lists current publications by Service authors, cooperators, or contractors on acid rain and related quality. Entire are arranged alphabetically by author surname. For further information about the research program, contact the U.S. Fish and Wildlife Service, Acid Precipitation Section, National Fishery Research Center -- Leetown, Box 700, Kearneysville, WV 25430.

Biological Report↗
USGS2002

Resident fish assemblages in shallow shorelines of a Columbia River impoundment

During May-September 1995, we replicated an earlier (1984-85) study of fishes in shoreline habitats of the John Day Reservoir, Columbia River, to investigate fish assemblage structure at several spatial and temporal scales. A total of 37,400 resident fishes representing 24 taxa was collected in 359 beach seine hauls. Fish catch composition during 1984 and 1985 was very similar, but was greatly different from catch in 1995. During 1984-1985, four native taxa (chiselmouth, northern pikeminnow, suckers, and sand rollers) constituted more than 90% of the combined main-channel catch, with introduced taxa comprising only 1.3% of the main-channel catch. In contrast, during 1995 only 37.7% of the main-channel catch comprised chiselmouth, northern pikeminnow, suckers, and sand rollers, while 33.9% were introduced taxa, primarily sunfishes and yellow perch. This shift in catch composition was greatest in the lower reservoir where the 1995 catch was 61% introduced taxa. Although changes in species composition of near-shore reservoir fish assemblages over the 10-yr period appeared to be substantial, we are unsure of annual variability since we have only one season of sampling for comparison with the earlier study. The differences we observed could be a long-term response to reservoir aging, a short-term reaction to annual differences in hydrologic and thermal regimes, or simply the naturally varying reproductive success of some species.

Northwest Science↗
USGS2005

Historical and current perspectives on fish assemblages of the Snake River, Idaho and Wyoming

The Snake River is the tenth longest river in the United States, extending 1,667 km from its origin in Yellowstone National Park in western Wyoming to its union with the Columbia River at Pasco, Washington. Historically, the main-stem Snake River upstream from the Hells Canyon Complex supported at least 26 native fish species, including anadromous stocks of Chinook salmon Oncorhynchus tshawytscha, steelhead O. mykiss, Pacific lamprey Lampetra tridentata, and white sturgeon Acipenser transmontanus. Of these anadromous species, only the white sturgeon remains in the Snake River between the Hells Canyon Complex and Shoshone Falls. Today, much of the Snake River has been transformed into a river with numerous impoundments and flow diversions, increased pollutant loads, and elevated water temperatures. Current (1993-2002) fish assemblage collections from 15 sites along the Snake River and Henrys Fork contained 35 fish species, including 16 alien species. Many of these alien species such as catfish (Ictaluridae), carp (Cyprinidae), and sunfish (Centrarchidae) are adapted for warmwater impounded habitats. Currently, the Snake River supports 19 native species. An index of biotic integrity (IBI), developed to evaluate large rivers in the Northwest, was used to evaluate recent (1993-2002) fish collections from the Snake River and Henrys Fork in southern Idaho and western Wyoming. Index of biotic integrity site scores and component metrics revealed a decline in biotic integrity from upstream to downstream in both the Snake River and Henrys Fork. Two distinct groups of sites were evident that correspond to a range of IBI scores-an upper Snake River and Henrys Fork group with relatively high biotic integrity (mean IBI scores of 46-84) and a lower Snake River group with low biotic integrity (mean IBI scores of 10-29). Sites located in the lower Snake River exhibited fish assemblages that reflect poor-quality habitat where coldwater and sensitive species are rare or absent, and where tolerant, less desirable species predominate. Increases in percentages of agricultural land, total number of diversions, and number of constructed channels were strongly associated with these decreasing IBI scores.

American Fisheries Society Symposium↗
USGS2004

Fishes of the Missouri national recreational river, South Dakota and Nebraska

Two sections of the Missouri River, one extending 94 km downstream from Gavins Point Dam, and the other extending 62 km downstream from Fort Randall Dam, are legally designated as National Recreational Rivers. An ichthyofaunal list and fish habitat data were needed for conservation planning by states and federal agencies (e.g., National Park Service). We collected fish during three summers from four macrohabitats, using five fish collection techniques, and measured fish habitat characteristics. Temperature, conductivity, and turbidity varied little, but substrate, depth, and velocity differed among macrohabitats (e.g., depth and velocity in the channel exceeded those elsewhere; sand dominated the substrate except in silt-laden tributary mouths and backwaters). We collected 21,699 fish of 53 species and combined our survey with others to compile a list of 92 species. Common recreational species included walleye (Sander vitreum) and catfishes (Ictaluridae). Twenty nonnative species were present. Seventy-two native species have persisted, but the pallid sturgeon (Scaphirhynchus albus) is endangered and a few other species (e.g., native minnows) may be in decline.

Great Plains Research↗
USGS2006

River size and fish assemblages in southwestern South Dakota

We studied relations between river size, fish species diversity, and fish species composition along four major rivers in the Great Plains of southwestern South Dakota to assess patterns of species diversity and composition. We expected diversity to increase with river size and fish composition to change via species addition downstream. Previous surveys of 52 sampling stations provided fish assemblage data, and we used the Geographic Information System (GIS) to determine watershed area by station. Watershed area did not predict species richness or species diversity (Fisher's ??), so species richness of 12 ?? 3.5 SD species and Fisher's ?? of 2.3 ?? 0.87 SD characterized species diversity in the study area. Cluster analysis of faunal similarity (S??rensen's Index) among the 52 sampling stations identified two geographically distinct faunal divisions, so species composition was variable within the study area, but changed via species replacements among faunas rather than species additions downstream. Nonnative species were a minor component of all faunas. Uniform species diversity may be a recent phenomenon caused by impacts of Missouri River dams on native large-river fishes and the unsuitability of rivers in the Great Plains for nonnative species. Variation in faunal composition may also be recent because it was affected by dams. ?? Copyright by the Center for Great Plains Studies, University of Nebraska-Lincoln.

Great Plains Research↗
USGS2006

Fish community structure in freshwater karstic water bodies of the Sian Ka'an Reserve in the Yucatan peninsula, Mexico

We evaluated the relationship between limnetic characteristics and fish community structure (based on species richness, abundance and individual size) in contrasting but interconnected inland aquatic habitats of freshwater karstic wetlands in the Yucatan peninsula, Mexico. In the western hemisphere, freshwater karstic wetlands are found in south-eastern Mexico, northern Belize, western Cuba, Andros Island, Bahamas and the Everglades of southern Florida. Only in the Everglades have fish communities been well described. Karstic wetlands are typically oligotrophic because calcium carbonate binds phosphorus, making it relatively unavailable for plants. Fourteen permanent and seasonally flooded water bodies were sampled in both wet and dry seasons in Sian Ka'an Biosphere Reserve, in the Mexican state of Quintana Roo. Water systems were divided by morphology in four groups: cenotes with vegetation (CWV), cenotes without vegetation (CNV), wetlands (WTL), and temporal cenotes (TPC). Discriminant analysis based on physical characteristics such as turbidity, temperature, depth and oxygen confirmed that these habitats differed in characteristics known to influence fish communities. A sample-based rarefaction test showed that species richness was significantly different between water systems groups, showing that WTL and CWV had higher richness values than CNV and TPC. The most abundant fish families, Poeciliidae, Cichlidae and Characidae, differed significantly in average size among habitats and seasons. Seasonal and inter-annual variation, reflecting temporal variation in rainfall, strongly influenced the environmental differences between shallow and deep habitats, which could be linked to fish size and life cycles. Five new records of species were found for the reserve, and one new record for Quintana Roo state. ?? 2006 by Verlag Dr. Friedrich Pfeil.

Ichthyological Exploration of Freshwaters↗
USGS2007

Diet niches of major forage fish in Lake Michigan

A large complex of coregonine species historically dominated the fish community of Lake Michigan. The current species complex is simplified with one remaining coregonine, bloater (Coregonus hoyi), deepwater sculpin (Myoxocephalus thompsoni), slimy sculpin (Cottus cognatus), and two dominant invaders, alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax). To better understand the diet relationships of the major offshore forage fishes now in Lake Michigan, diets of bloater, alewife, rainbow smelt, deepwater sculpin, and slimy sculpin were compared. The three sites, chosen to represent northern, central, and southern components of the lake, were sampled during spring, summer, and fall in 1994, and spring and fall in 1995. Forage fishes had diverse and variable diets, with niches differentiated by prey type or location. Diporeia hoyi, Mysis relicta, and zooplankton were the major diet items. The index of relative importance showed benthic (slimy and deepwater sculpins) and pelagic (alewife, rainbow smelt) feeding strategies with opportunistic bloaters incorporating both feeding strategies. Highest diet overlaps were between species of sculpin, and between large and small bloaters; both groups partitioned food by size. Though competition for food may be minimized by spatial segregation of potential competitors, the forage fish in Lake Michigan apparently partition food resources. Fishery management models incorporating food habits of pelagic forage fish would need to take into account diet variation associated with location and season. ?? 2007 E. Schweizerbart'sche Verlagsbuchhandlung.

Conference Paper↗
USGS2012

The shallow-water fish assemblage of Isla del Coco National Park, Costa Rica: Structure and patterns in an isolated, predator-dominated ecosystem

Fishes at Isla del Coco National Park, Costa Rica, were surveyed as part of a larger scientific expedition to the area in September 2009. The average total biomass of nearshore fishes was 7.8 tonnes per ha, among the largest observed in the tropics, with apex predators such as sharks, jacks, and groupers accounting for nearly 40% of the total biomass. The abundance of reef and pelagic sharks, particularly large aggregations of threatened species such as the scalloped hammerhead shark (up to 42 hammerheads ha-1) and large schools of jacks and snappers show the capacity for high biomass in unfished ecosystems in the Eastern Tropical Pacific. However, the abundance of hammerhead and reef whitetip sharks appears to have been declining since the late 1990s, and likely causes may include increasing fishing pressure on sharks in the region and illegal fishing inside the Park. One Galapagos shark tagged on September 20, 2009 in the Isla del Coco National Park moved 255km southeast towards Malpelo Island in Colombia, when it stopped transmitting. These results contribute to the evidence that sharks conduct large-scale movements between marine protected areas (Isla del Coco, Malpelo, Galápagos) in the Eastern tropical Pacific and emphasize the need for regional-scale management. More than half of the species and 90% of the individuals observed were endemic to the tropical eastern Pacific. These high biomass and endemicity values highlight the uniqueness of the fish assemblage at Isla del Coco and its importance as a global biodiversity hotspot.

Cocos Island, Isla Del Coco↗
USGS2008

Pathogens associated with native and exotic trout populations in Shenandoah National Park and the relationships to fish stocking practices

Restrictive fish stocking policies in National Parks were developed as early as 1936 in order to preserve native fish assemblages and historic genetic diversity. Despite recent efforts to understand the effects of non-native or exotic fish introductions, park managers have limited information regarding the effects of these introductions on native fish communities. Shenandoah National Park was established in 1936 and brook trout (Salvelinus fontinalis) restoration within selected streams in the park began in 1937 in collaboration with the Virginia Department of Game and Inland Fisheries (VDGIF). An analysis of tissue samples from brook, brown (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) from 29 streams within the park from 1998–2002 revealed the presence of Renibacterium salmoninarum, Yersinia ruckeri, and infectious pancreatic necrosis virus (IPNv). In order to investigate the relationships of the occurrence of fish pathogens with stocking histories we classified the streams into three categories: 1) streams with no record of stocking, 2) streams that are known to have been stocked historically, and 3) streams that were historically stocked within the park and continue to be stocked downstream of the park boundary. The occurrences of pathogens were summarized relative to this stocking history. Renibacterium salmoninarum, the causative agent of bacterial kidney disease, was the most prevalent pathogen found, occurring in all three species and stream stocking categories, and appears to be endemic to the park. Two other pathogens, Yersinia ruckeri and infectious pancreatic necrosis virus were also described from brook trout populations within the park. IPNv was only found in brook trout populations in streams with prior stocking histories. Yersinia ruckeri was only found in brook trout in steams that have never been stocked and like R. salmoninarum, is likely endemic.

Virginia↗
USGS2012

Time-to-event analysis as a framework for quantifying fish passage performance

Fish passage is the result of a sequence of processes, whereby fish must approach, enter, and pass a structure. Each of these processes takes time, and fishway performance is best quantified in terms of the rates at which each process is completed. Optimal performance is achieved by maximizing the rates of approach, entry, and passage through safe and desirable routes. Sometimes, however, it is necessary to reduce rates of passage through less desirable routes in order to increase proportions passing through the preferred route. Effectiveness of operational or structural modifications for achieving either of these goals is best quantified by applying time-to-event analysis, commonly known as survival analysis methods, to telemetry data. This set of techniques allows for accurate estimation of passage rates and covariate effects on those rates. Importantly, it allows researchers to quantify rates that vary over time, as well as the effects of covariates that also vary over time. Finally, these methods are able to control for competing risks, i.e., the presence of alternate passage routes, failure to pass, or other fates that remove fish from the pool of candidates available to pass through a particular route. In this chapter, we present a model simulation of telemetered fish passing a hydroelectric dam, and provide step-by-step guidance and rationales for performing time-to-event analysis on the resulting data. We demonstrate how this approach removes bias from performance estimates that can result from using methods that focus only on proportions passing each route. Time-to-event analysis, coupled with multinomial models for measuring survival, provides a comprehensive set of techniques for quantifying fish passage, and a framework from which performance among different sites can be better understood.

Book chapter↗