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At least 289 records · Page 16Linked to original sources
USGS2009

Applications of a broad-spectrum tool for conservation and fisheries analysis: Aquatic gap analysis

Natural resources support all of our social and economic activities, as well as our biological existence. Humans have little control over most of the physical, biological, and sociological conditions dictating the status and capacity of natural resources in any particular area. However, the most rapid and threatening influences on natural resources typically are anthropogenic overuse and degradation. In addition, living natural resources (i.e., organisms) do not respect political boundaries, but are aware of their optimal habitat and environmental conditions. Most organisms have wider spatial ranges than the jurisdictional boundaries of environmental agencies that deal with them; even within those jurisdictions, information is patchy and disconnected. Planning and projecting effects of ecological management are difficult, because many organisms, habitat conditions, and interactions are involved. Conservation and responsible resource use involves wise management and manipulation of the aspects of the environment and biological communities that can be effectively changed. Tools and data sets that provide new insights and analysis capabilities can enhance the ability of resource managers to make wise decisions and plan effective, long-term management strategies. Aquatic gap analysis has been developed to provide those benefits. Gap analysis is more than just the assessment of the match or mis-match (i.e., gaps) between habitats of ecological value and areas with an appropriate level of environmental protection (e.g., refuges, parks, preserves), as the name suggests. Rather, a Gap Analysis project is a process which leads to an organized database of georeferenced information and previously available tools to examine conservation and other ecological issues; it provides a geographic analysis platform that serves as a foundation for aquatic ecological studies. This analytical tool box allows one to conduct assessments of all habitat elements within an area of interest. Aquatic gap analysis naturally focuses on aquatic habitats. The analytical tools are largely based on specification of the species-habitat relations for the system and organism group of interest (Morrison et al. 2003; McKenna et al. 2006; Steen et al. 2006; Sowa et al. 2007). The Great Lakes Regional Aquatic Gap Analysis (GLGap) project focuses primarily on lotic habitat of the U.S. Great Lakes drainage basin and associated states and has been developed to address fish and fisheries issues. These tools are unique because they allow us to address problems at a range of scales from the region to the stream segment and include the ability to predict species specific occurrence or abundance for most of the fish species in the study area. The results and types of questions that can be addressed provide better global understanding of the ecological context within which specific natural resources fit (e.g., neighboring environments and resources, and large and small scale processes). The geographic analysis platform consists of broad and flexible geospatial tools (and associated data) with many potential applications. The objectives of this article are to provide a brief overview of GLGap methods and analysis tools, and demonstrate conservation and planning applications of those data and tools. Although there are many potential applications, we will highlight just three: (1) support for the Eastern Brook Trout Joint Venture (EBTJV), (2) Aquatic Life classification in Wisconsin, and (3) an educational tool that makes use of Google Earth (use of trade or product names does not imply endorsement by the U.S. Government) and Internet accessibility.

Gap Analysis Bulletin↗
USGS2011

Estimating age from recapture data: Integrating incremental growth measures with ancillary data to infer age-at-length

Estimating the age of individuals in wild populations can be of fundamental importance for answering ecological questions, modeling population demographics, and managing exploited or threatened species. Significant effort has been devoted to determining age through the use of growth annuli, secondary physical characteristics related to age, and growth models. Many species, however, either do not exhibit physical characteristics useful for independent age validation or are too rare to justify sacrificing a large number of individuals to establish the relationship between size and age. Length‐at‐age models are well represented in the fisheries and other wildlife management literature. Many of these models overlook variation in growth rates of individuals and consider growth parameters as population parameters. More recent models have taken advantage of hierarchical structuring of parameters and Bayesian inference methods to allow for variation among individuals as functions of environmental covariates or individual‐specific random effects. Here, we describe hierarchical models in which growth curves vary as individual‐specific stochastic processes, and we show how these models can be fit using capture–recapture data for animals of unknown age along with data for animals of known age. We combine these independent data sources in a Bayesian analysis, distinguishing natural variation (among and within individuals) from measurement error. We illustrate using data for African dwarf crocodiles, comparing von Bertalanffy and logistic growth models. The analysis provides the means of predicting crocodile age, given a single measurement of head length. The von Bertalanffy was much better supported than the logistic growth model and predicted that dwarf crocodiles grow from 19.4 cm total length at birth to 32.9 cm in the first year and 45.3 cm by the end of their second year. Based on the minimum size of females observed with hatchlings, reproductive maturity was estimated to be at nine years. These size benchmarks are believed to represent thresholds for important demographic parameters; improved estimates of age, therefore, will increase the precision of population projection models. The modeling approach that we present can be applied to other species and offers significant advantages when multiple sources of data are available and traditional aging techniques are not practical.

Loango National Park↗
USGS2026

Disease-associated mortality drives reduction in Yukon River Chinook salmon escapement: A novel method for quantifying the negative impacts of ‘misfit’ parasites to improve fisheries management

Parasites can suppress host populations through parasite-induced mortality. However, the negative effects of parasites are difficult to measure in wild populations and we have few tools for quantifying the magnitude of parasite-induced mortality. This is especially true for many ‘misfit’ parasites that do not fit into standard classifications (e.g. fungal-like parasites and myxozoans). As such, we are limited in our ability to include the effects of parasites in fish and wildlife management strategies. Chinook salmon ( Oncorhynchus tshawytscha ) are a species of immense cultural and ecological significance but populations are declining across much of their range. In the Yukon River, Alaska, USA, episodic outbreaks of the ichthyosporean parasite Ichthyophonus have been linked to declines, but population-level effects of Ichthyophonus on Yukon Chinook salmon remain largely unknown. We developed a novel model that leverages changes in parasite intensity distributions to quantify the magnitude of disease-induced mortality occurring in host populations. We used it to address two questions to inform management of Yukon Chinook salmon: (i) Is parasite-induced mortality occurring in Chinook salmon and at what magnitude? (ii) What are the drivers of spatio-temporal variability in parasite-induced mortality? Using 3 years of surveys, we quantified the evidence for the presence, magnitude, and variability in Ichthyophonus -induced mortality in Chinook salmon. Our model predicted that Ichthyophonus was responsible for between 8% and 15% mortality of the migrating Chinook salmon population prior to reaching the Canadian border and could describe nearly 35% of unaccounted for mortality at the border. The model predicted that variability in mortality among years could largely be explained by differences in parasite acquisition in the marine environment rather than differences in infection dynamics in the river. Synthesis and applications . Alaska Department of Fish and Game is implementing an annual monitoring program at the mouth of the Yukon River where our model will estimate the proportion of fish at risk from parasite-induced mortality to inform annual management. Moreover, the model is broadly applicable to other fungal-like and myxozoan parasites of conservation concern, where improved estimates of parasite-induced mortality could be used to predict parasite suppression of wild and managed host populations.

Alaska↗
USGS2022

FishStan: Hierarchical Bayesian models for fisheries

Fisheries managers and ecologists use statistical models to estimate population-level relations and demographic rates (e.g., length-maturity curves, growth curves, and mortality rates). These relations and rates provide insight into populations and inputs for other models. For example, growth curves may vary across lakes showing fish populations differ due to management actions or underlying environmental conditions. A fisheries manager could use this information to set lake-specific harvest limits or an ecologist could use this information to test scientific hypotheses about fish populations. The above example also demonstrates how populations exist within hierarchical structures where sub-populations may be nested within a meta-population. More generally, these hierarchical structures may be both biological (e.g., different lakes or river pools) and statistical (e.g., correlated error structures). Currently, limited options exist for fitting these hierarchical models and people seeking to use them often must program their own implementations. Furthermore, many fisheries managers and researchers may not have Bayesian programming skills, but many can use interactive languages such as R. Additionally, programs such as JAGS often require long run times (e.g., hours if not days) to fit hierarchical models and programs such as Stan can be more difficult to program because it is a compiled language. We created fishStan to share hierarchical models for fisheries and ecology in an easy-to-use R package.

Journal of Open Source Software↗
USGS2019

Restoration of Lake Trout in Lake Superior through Interagency Cooperative Management

The lake trout is a keystone species in the Laurentian Great Lakes that supported valuable fisheries throughout the basin. However, lake trout populations declined to near extirpation in nearly all of the lakes because of the combined effects of over-fishing, sea lamprey predation, and habitat degradation. To restore self-sustaining lake trout populations in Lake Superior, state, provincial, federal, and tribal agencies agreed to an interjurisdictional management framework that allowed them to articulate and institute: (1) clear and common goals and actions for recovery; (2) early and intensive lake-wide stocking of hatchery-reared lake trout to enhance failing stocks; (3) early and effective lake-wide controls on mortality caused by sea lampreys and fisheries; and (4) standardized lake-wide evaluations of population trajectories and performance. Stocking was initiated in Lake Superior in 1950 and expanded after 1953, prior to effecting sea lamprey or fishery controls, thereby introducing large numbers of hatchery-origin fish that grew to maturity shortly after mortality was reduced. Abundant suitable nearshore spawning habitat was widely available for naïve lean hatchery-origin lake trout, and native lean lake trout persisted in some areas. The sea-lamprey-selective pesticide TFM (3-trifluoromethyl-4-nitrophenol) was applied first in Lake Superior in 1958, because of the presence of remnant native lake trout populations, which set the stage for closure of fisheries and good survival of newly stocked and remnant wild fish. As a consequence of these four factors, stocked fish exceeded historical density of wild fish by the 1980s in many areas, and thereby generated enhanced reproductive potential when combined with remnant wild fish. Lake trout recovery in Lake Superior is an extraordinary example of agency cooperation toward a common goal for managing recovery of an ecologically important shared resource.

Lake Superior↗
USGS2011

Ecosystem approach to inland fisheries: Research needs and implementation strategies

Inland fisheries are a vital component in the livelihoods and food security of people throughout the world, as well as contributing huge recreational and economic benefits. These valuable assets are jeopardized by lack of research-based understanding of the impacts of fisheries on inland ecosystems, and similarly the impact of human activities associated with inland waters on fisheries and aquatic biodiversity. To explore this topic, an international workshop was organized in order to examine strategies to incorporate fisheries into ecosystem approaches for management of inland waters. To achieve this goal, a new research agenda is needed that focuses on: quantifying the ecosystem services provided by fresh waters; quantifying the economic, social and nutritional benefits of inland fisheries; improving assessments designed to evaluate fisheries exploitation potential; and examining feedbacks between fisheries, ecosystem productivity and aquatic biodiversity. Accomplishing these objectives will require merging natural and social science approaches to address coupled social-ecological system dynamics. ?? 2010 The Royal Society.

Conference Paper↗
USGS2010

Large reservoirs: Chapter 17

Large impoundments, defined as those with surface area of 200 ha or greater, are relatively new aquatic ecosystems in the global landscape. They represent important economic and environmental resources that provide benefits such as flood control, hydropower generation, navigation, water supply, commercial and recreational fisheries, and various other recreational and esthetic values. Construction of large impoundments was initially driven by economic needs, and ecological consequences received little consideration. However, in recent decades environmental issues have come to the forefront. In the closing decades of the 20th century societal values began to shift, especially in the developed world. Society is no longer willing to accept environmental damage as an inevitable consequence of human development, and it is now recognized that continued environmental degradation is unsustainable. Consequently, construction of large reservoirs has virtually stopped in North America. Nevertheless, in other parts of the world construction of large reservoirs continues. The emergence of systematic reservoir management in the early 20th century was guided by concepts developed for natural lakes (Miranda 1996). However, we now recognize that reservoirs are different and that reservoirs are not independent aquatic systems inasmuch as they are connected to upstream rivers and streams, the downstream river, other reservoirs in the basin, and the watershed. Reservoir systems exhibit longitudinal patterns both within and among reservoirs. Reservoirs are typically arranged sequentially as elements of an interacting network, filter water collected throughout their watersheds, and form a mosaic of predictable patterns. Traditional approaches to fisheries management such as stocking, regulating harvest, and in-lake habitat management do not always produce desired effects in reservoirs. As a result, managers may expend resources with little benefit to either fish or fishing. Some locally expressed effects, such as turbidity and water quality, zooplankton density and size composition, or fish growth rates and assemblage composition, are the upshot of large-scale factors operating outside reservoirs and not under the direct control of reservoir managers. Realistically, abiotic and biotic conditions in reservoirs are shaped by factors working inside and outside reservoirs, with the relative importance of external factors differing among reservoirs. With this perspective, large reservoirs are viewed from a habitat standpoint within the framework of a conceptual model in which individual reservoir characteristics are influenced by both local- and landscape-scale factors (Figure 17.1). In the sections that follow, how each element of this hierarchical model influences habitat and fish assemblages in reservoirs is considered. Important in-reservoir habitat issues and reservoirs as part of larger systems, where reservoir management requires looking for real solutions outside individual reservoirs are described.

Book chapter↗
USGS2001

The introduction of nonnative fish into wilderness lakes: Good intentions, conflicting mandates, and unintended consequences

Because they have the potential to provide the best remaining standards of relatively unmodified landscapes, protected areas in North America (such as wilderness areas and national parks) have tremendous ecological and scientific value (Cole and Landres 1996). Although the montane ecosystems of western North America are particularly well represented in this complex of protected lands, aquatic habitats within these protected areas are often subject to management practices that are inconsistent with the goal of maintaining natural processes. The most prevalent of these practices is the introduction of salmonid fishes (such as trout) into historically fishless ecosystems to create recreational fisheries.

Ecosystems↗
USGS2007

Potential strategies for recovery of lake whitefish and lake herring stocks in eastern Lake Erie

Lake Erie sustained large populations of ciscoes ( Salmonidae : Coregoninae ) 120 years ago. By the end of the 19 th century, abundance of lake whitefish ( Coregonus clupeaformis ) had declined drastically. By 1925, the lake herring (a cisco) population (Coregonus artedii) had collapsed, although a limited lake herring fishery persisted in the eastern basin until the 1950s. In the latter part of the 20 th century, the composition of the fish community changed as oligotrophication proceeded. Since 1984, a limited recovery of lake whitefish has occurred, however no recovery was evident for lake herring. Current ecological conditions in Lake Erie probably will not inhibit recovery of the coregonine species. Recovery of walleye ( Sander vitreus ) and efforts to rehabilitate the native lake trout ( Salvelinus namaycush ) in Lake Erie will probably assist recovery because these piscivores reduce populations of alewife ( Alosa psuedoharengus ) and rainbow smelt ( Osmerus mordax ), which inhibit reproductive success of coregonines. Although there are considerable spawning substrates available to coregonine species in eastern Lake Erie, eggs and fry would probably be displaced by storm surge from most shoals. Site selection for stocking or seeding of eggs should consider the reproductive life cycle of the stocked fish and suitable protection from storm events. Two potential sites in the eastern basin have been identified. Recommended management procedures, including commercial fisheries, are suggested to assist in recovery. Stocking in the eastern basin of Lake Erie is recommended for both species, as conditions are adequate and the native spawning population in the eastern basin is low. For lake herring, consideration should be given to match ecophenotypes as much as possible. Egg seeding is recommended. Egg seeding of lake whitefish should be considered initially, with fingerling or yearling stocking suggested if unsuccessful. Spawning stocks of whitefish in the western basin of Lake Erie could be utilized.

Journal of Great Lakes Research↗
USGS2023

Accounting for spatiotemporal sampling variation in joint species distribution models

Estimating relative abundance is critical for informing conservation and management efforts and for making inferences about the effects of environmental change on populations. Freshwater fisheries span large geographic regions, occupy diverse habitats and consist of varying species assemblages. Monitoring schemes used to sample these diverse populations often result in populations being sampled at different times and under different environmental conditions. Varying sampling conditions can bias estimates of abundance when compared across time, location and species, and properly accounting for these biases is critical for making inferences. We develop a joint species distribution model (JSDM) that accounts for varying sampling conditions due to the environment and time of sampling when estimating relative abundance. The novelty of our JSDM is that we explicitly model sampling effort as the product of known quantities based on time and gear type and an unknown functional relationship to capture seasonal variation in species life history. We use the model to study relative abundance of six freshwater fish species across the state of Minnesota, USA. Our model enables estimates of relative abundance to be compared both within and across species and lakes, and captures the inconsistent sampling present in the data. We discuss how gear type, water temperature and day of the year impact catchability for each species at the lake level and throughout a year. We compare our estimates of relative abundance to those obtained from a model that assumes constant catchability to highlight important differences within and across lakes and species. Synthesis and applications : Our method illustrates that assumptions relating indices of abundance to observed catch data can greatly impact model inferences derived from JSDMs. Specifically, not accounting for varying sampling conditions can bias inference of relative abundance, restricting our ability to detect responses to management interventions and environmental change. While our focus is on freshwater fisheries, this model architecture can be adopted to other systems where catchability may vary as a function of space, time and species.

Journal of Applied Ecology↗
USGS2017

Isotopic structure of Lake Whitefish in Lake Huron: Evidence for regional and local populations based on resource use

Lake Whitefish Coregonus clupeaformis is the most commercially valuable species in Lake Huron. The fishery for this species has historically been managed based on 25 management units (17 in Canada, 8 in the USA). However, congruence between the contemporary population structure of Lake Whitefish and management units is poorly understood. We used stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N), food web markers that reflect patterns in resource use (i.e., prey, location, habitat), to assess the population structure of spawning-phase Lake Whitefish collected from 32 sites (1,474 fish) across Lake Huron. We found large isotopic variation among fish from different sites (ranges: δ 13 C = 10.2‰, δ 15 N = 5.5‰) and variable niche size and levels of overlap (standard ellipse area = 1.0–4.3‰ 2 ). Lake Huron contained spawning-phase fish from four major isotopic clusters largely defined by extensive variation in δ 13 C, and the isotopic composition of fish sampled was spatially structured both within and between lake basins. Based on cluster compositions, we identified six putative regional groups, some of which represented sites of high diversity (three to four clusters) and others with less (one to two clusters). Analysis of isotopic values from Lake Whitefish collected from summer feeding locations and baseline prey items showed similar isotopic variation and established spatial linkage between spawning-phase and summer fish. Our results show that summer feeding location contributes strongly to the isotopic structure we observed in spawning-phase fish. One of the regional groups we identified in northern Georgian Bay is highly distinct based on isotopic composition and possibly ecologically unique within Lake Huron. Our findings are congruent with several previous studies using different markers (genetics, mark–recapture), and we conclude that current management units are generally too small and numerous to reflect the population structure of Lake Whitefish in Lake Huron.

Lake Huron↗
USGS2017

The fishery resources of the Mississippi River: A model for conservation and management

The Mississippi River is a multijurisdictional and multiuse resource that has been variously altered and is foremost managed for navigation and flood control throughout much of its 3,734‐km passage from its origin at Lake Itasca, Minnesota, to its outlet at the Gulf of Mexico. Despite alterations summarized herein, the native fish fauna remains largely intact and only five nonnative species have colonized segments of the river. Diverse habitats still remain, but loss of habitat, declining habitat suitability, and reduced floodplain functionality warrant concern. Fisheries monitoring and assessment, ecological research, and habitat rehabilitation vary from adequate in the upper reaches of the river to minimal in the lower reaches of the river, and these efforts parallel the recreational use, local values, and visibility of the river. A conceptual model is proposed to depict the value of the social, economic, and many ecosystem services the Mississippi River ecosystem offers that can be used to achieve the social and economic support needed to conserve and restore this valuable fishery resource.

Mississippi River↗
USGS2016

Misapplied survey data and model uncertainty result in incorrect conclusions about the role of predation on alewife population dynamics in Lake Huron: a comment on He et al. (2015)

Drastic recent and ongoing changes to fish populations and food webs in the Great Lakes have been well-described ( Riley et al. 2008 ; Barbiero et al. 2009 ; Nalepa et al. 2009 ; Fahnenstiel et al. 2010 ; Evans et al. 2011 ; Gobin et al. 2015 ), and uncertainty regarding their potential effects on fisheries has caused concern among scientists and fishery managers (e.g., Dettmers et al. 2012 ). In particular, the relative importance of “bottom-up” (e.g., lower trophic level changes) versus “top-down” (e.g., predation) factors to fish community changes in the Great Lakes have been widely debated (e.g., Barbiero et al. 2011 ; Eshenroder and Lantry 2012 ; Bunnell et al. 2014 ). In Lake Huron, recent ecosystem changes have been particularly profound, and populations of alewife ( Alosa pseudoharengus ), an offshore pelagic prey fish, collapsed in 2003 and have yet to recover ( Riley et al. 2008 , 2014 ). He et al. (2015) recently used a series of linked ecological models to assess the role of predation in the dynamics of the offshore prey fish community in Lake Huron. While we believe that they provide a novel method for combining bioenergetics and stock assessment modeling, we question the validity of their conclusions because of the misapplication of survey data and the lack of critical interpretation of their modeling efforts. Here we describe how He et al. (2015) have misapplied bottom trawl data from Lake Huron, and we provide examples of how this has resulted in erroneous conclusions regarding the importance of predation to the population dynamics and collapse of alewife in Lake Huron.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2010

Assessing the response of the Pamlico Sound, North Carolina, USA to human and climatic disturbances: Management implications

The Pamlico Sound (PS) with its sub-estuaries is the largest lagoonal ecosystem in the United States. It exhibits periodically strong salinity stratification and an average freshwater residence time of 1 year for the sound proper. This relatively long residence time promotes effective use and cycling of nutrients, allowing the system to support high rates of primary and secondary production, and serve as a vitally important fisheries nursery. This hydrologic characteristic also makes the system highly sensitive to nutrient over-enrichment and eutrophication. The PS is experiencing ecological change in response to increasing human activity and climatic perturbations. Human impacts include a rise in nutrient, sediment, and other pollutant loads that accompany urbanization and agricultural and industrial growth in its watersheds and airsheds. Since the mid-1990s, the PS has witnessed a sudden rise in tropical storm and hurricane impacts, with eight hurricanes and four tropical storms having made landfall in the PS watershed during the 1996 to 2007 period. Each of these storms had unique hydrologic, nutrient, and other pollutant loading effects. In addition, since the early 2000s, the region has experienced record droughts, which are continuing. Variable freshwater discharges from storms and droughts have caused large oscillations in nutrient enrichment, reflected ultimately in differential phytoplankton production, biomass, and community compositional responses. Floodwaters from the two wettest hurricanes, Fran (1996) and Floyd (1999), and from Tropical Storm Ernesto (2006) exerted long-term (months) effects on hydrology, nutrient loads, and algal production. Windy but relatively dry hurricanes, like Irene (1999) and Isabel (2003), caused strong vertical mixing, storm surges, but relatively minor changes in river flow, flushing, and nutrient loads. These contrasting effects are accompanied by biogeochemical (hypoxia, nutrient cycling) and habitat alterations, and associated food web disturbances. Each storm type influenced algal growth and compositional dynamics; however, their respective ecological impacts differed substantially. Changes in hydrologic and wind forcing resulting from changes in frequency and intensity of storms and droughts strongly influence water and habitat quality. These changes must be integrated with nutrient loading/dilution effects when assessing and predicting ecological responses to nutrient and hydrologic variability on this and other large lagoonal ecosystems.

North Carolina↗
USGS2025

Forecasting sea otter recolonization: Insights from isotopic analysis of modern and zooarchaeological populations

Retrospective datasets offer essential context for conservation by revealing species’ ecological roles before industrial-era human impacts. We analysed isotopic compositions of pre-industrial and modern sea otters ( Enhydra lutris ) to reconstruct pre-extirpation ecology and offer insights for management. Our study focuses on southeast Alaska (SEAK), where sea otters are recolonizing, and northern Oregon, where translocations are being considered. We measured bulk bone collagen δ 13 C and δ 15 N values and essential amino acid δ 13 C values of extirpated sea otters from archaeological contexts, and bulk isotopic values from vibrissae of modern SEAK sea otters. We compare these results with published isotopic data of potential prey and additional archaeological datasets. In SEAK, our data show pre-industrial sea otter populations consumed infaunal bivalves and used soft-sediment (33%) and kelp forest habitats (67%), with sub-regional variation. We anticipate current populations will expand into this historical niche, and conflict with regional traditional/subsistence bivalve fisheries will persist. In northern Oregon, isotopic data from extirpated sea otters indicate past consumption of low trophic level invertebrates and a stronger reliance on kelp forests (88%) rather than soft-sediment habitats, highlighting the importance of kelp forests for future translocations. Our work exemplifies the value of historical ecology in informing conservation strategies for recovering species.

Alaska, Oregon↗
USGS2013

Broad-scale patterns of Brook Trout responses to introduced Brown Trout in New York

Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta are valuable sport fish that coexist in many parts of the world due to stocking introductions. Causes for the decline of Brook Trout within their native range are not clear but include competition with Brown Trout, habitat alteration, and repetitive stocking practices. New York State contains a large portion of the Brook Trout's native range, where both species are maintained by stocking and other management actions. We used artificial neural network models, regression, principal components analysis, and simulation to evaluate the effects of Brown Trout, environmental conditions, and stocking on the distribution of Brook Trout in the center of their native range. We found evidence for the decline of Brook Trout in the presence of Brown Trout across many watersheds; 22% of sampled reaches where both species were expected to occur contained only Brown Trout. However, a model of the direct relationship between Brook Trout and Brown Trout abundance explained less than 1% of data variation. Ordination showed extensive overlap of Brook Trout and Brown Trout habitat conditions, with only small components of the hypervolume (multidimensional space) being distinctive. Subsequent analysis indicated higher abundances of Brook Trout in highly forested areas, while Brown Trout were more abundant in areas with relatively high proportions of agriculture. Simulation results indicated that direct interactions and habitat conditions were relatively minor factors compared with the effects of repeated stocking of Brown Trout into Brook Trout habitat. Intensive annual stocking of Brown Trout could eliminate resident Brook Trout in less than a decade. Ecological differences, harvest behavior, and other habitat changes can exacerbate Brook Trout losses. Custom stocking scenarios with Brown Trout introductions at relatively low proportions of resident Brook Trout populations may be able to sustain healthy populations of both species within their present range.

New York↗
USGS2016

Pelagic nekton abundance and distribution in the northern Sacramento–San Joaquin Delta, California

Knowledge of the habitats occupied by species is fundamental for the development of effective conservation and management actions. The collapse of pelagic fish species in the Sacramento–San Joaquin Delta, California, has triggered a need to better understand factors that drive their distribution and abundance. A study was conducted in summer–fall 2014 in an attempt to identify physical and biological habitat conditions that drive the abundance and distribution of pelagic species in the northern region of the system. The study was conducted in the three largest channels in the northern Sacramento–San Joaquin Delta by dimension, volume, and flow capacity. The pelagic community was dominated by three nonnative species, Siberian prawn Exopalaemon modestus , which comprised 56% of the total number of organisms, and two fish species, Threadfin Shad Dorosoma petenense and Mississippi Silversides Menidia audens , which together comprised 43% of the total number of organisms. Total fish and total shrimp abundance were sensitive to the most extreme values of turbidity and temperature encountered and positively associated with total zooplankton biomass. The results suggested that habitat conditions in terminal channels, historically a common feature on the landscape, support higher abundances of pelagic species and zooplankton than open-ended channels. These results provide resource managers with useful information on the habitat associations of pelagic species and on how the future distribution and abundance of pelagic species will likely change in response to climate or other ecological factors.

California↗
USGS2024

Synthesizing professional opinion of Lake Whitefish and Cisco recruitment drivers across the Great Lakes

Disentangling the suite of ecological drivers that explain recruitment variability for Lake Whitefish Coregonus clupeaformis and Cisco C. artedi is of critical importance for their conservation, management, and stewardship in the Laurentian Great Lakes. However, recruitment is inherently variable and can be regulated by many interacting processes, the relative importance of which can vary spatially, temporally, and ontogenetically. Given this complexity, comparisons across lakes and species that identify overarching hypotheses could efficiently guide future research. Using facilitated deliberations among fishery professionals (n = 57) with expertise in Great Lakes Coregonus spp., we synthesized current knowledge regarding (1) which biophysical processes are most important for driving contemporary recruitment between species, among lakes, and across life stages and (2) mechanisms by which those drivers regulate recruitment at key life stages. Participants affirmed the hypothesis that many drivers interact in complex ways to regulate Lake Whitefish and Cisco recruitment. Large-scale climatic processes affecting early life-stage growth and survival were consistently considered important. Other drivers were only deemed influential in certain lakes, highlighting perceived context-dependent recruitment dynamics. Notably, recruitment in Lakes Superior, Michigan, and Huron was considered limited during larval and early juvenile life stages by low productivity, whereas spawning-habitat degradation and reduced metapopulation diversity were hypothesized to limit recruitment during embryonic and larval stages in Lakes Erie and Ontario. Several drivers were hypothesized to similarly impact Lake Whitefish and Cisco during early life stages, while drivers acting on post-larval life stages were typically distinct between species. The hypotheses synthesized herein can guide future research on Lake Whitefish and Cisco recruitment dynamics in the Great Lakes.

Great Lakes↗