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USGS2016

Integrating subsistence practice and species distribution modeling: assessing invasive elodea’s potential impact on Native Alaskan subsistence of Chinook salmon and whitefish

Alaska has one of the most rapidly changing climates on earth and is experiencing an accelerated rate of human disturbance, including resource extraction and transportation infrastructure development. Combined, these factors increase the state’s vulnerability to biological invasion, which can have acute negative impacts on ecological integrity and subsistence practices. Of growing concern is the spread of Alaska’s first documented freshwater aquatic invasive plant Elodea spp. (elodea). In this study, we modeled the suitable habitat of elodea using global and state-specific species occurrence records and environmental variables, in concert with an ensemble of model algorithms. Furthermore, we sought to incorporate local subsistence concerns by using Native Alaskan knowledge and available statewide subsistence harvest data to assess the potential threat posed by elodea to Chinook salmon ( Oncorhynchus tshawytscha ) and whitefish ( Coregonus nelsonii ) subsistence. State models were applied to future climate (2040–2059) using five general circulation models best suited for Alaska. Model evaluations indicated that our results had moderate to strong predictability, with area under the receiver-operating characteristic curve values above 0.80 and classification accuracies ranging from 66 to 89 %. State models provided a more robust assessment of elodea habitat suitability. These ensembles revealed different levels of management concern statewide, based on the interaction of fish subsistence patterns, known spawning and rearing sites, and elodea habitat suitability, thus highlighting regions with additional need for targeted monitoring. Our results suggest that this approach can hold great utility for invasion risk assessments and better facilitate the inclusion of local stakeholder concerns in conservation planning and management.

Alaska↗

USGS2013

Conservation status of freshwater gastropods of Canada and the United States

This is the first American Fisheries Society conservation assessment of freshwater gastropods (snails) from Canada and the United States by the Gastropod Subcommittee (Endangered Species Committee). This review covers 703 species representing 16 families and 93 genera, of which 67 species are considered extinct, or possibly extinct, 278 are endangered, 102 are threatened, 73 are vulnerable, 157 are currently stable, and 26 species have uncertain taxonomic status. Of the entire fauna, 74% of gastropods are imperiled (vulnerable, threatened, endangered) or extinct, which exceeds imperilment levels in fishes (39%) and crayfishes (48%) but is similar to that of mussels (72%). Comparison of modern to background extinction rates reveals that gastropods have the highest modern extinction rate yet observed, 9,539 times greater than background rates. Gastropods are highly susceptible to habitat loss and degradation, particularly narrow endemics restricted to a single spring or short stream reaches. Compilation of this review was hampered by a paucity of current distributional information and taxonomic uncertainties. Although research on several fronts including basic biology, physiology, conservation strategies, life history, and ecology are needed, systematics and curation of museum collections and databases coupled with comprehensive status surveys (geographic limits, threat identification) are priorities.

Fisheries↗

USGS2014

Integrated conceptual ecological model and habitat indices for the southwest Florida coastal wetlands

The coastal wetlands of southwest Florida that extend from Charlotte Harbor south to Cape Sable, contain more than 60,000 ha of mangroves and 22,177 ha of salt marsh. These coastal wetlands form a transition zone between the freshwater and marine environments of the South Florida Coastal Marine Ecosystem (SFCME). The coastal wetlands provide diverse ecosystem services that are valued by society and thus are important to the economy of the state. Species from throughout the region spend part of their life cycle in the coastal wetlands, including many marine and coastal-dependent species, making this zone critical to the ecosystem health of the Everglades and the SFCME. However, the coastal wetlands are increasingly vulnerable due to rising sea level, changes in storm intensity and frequency, land use, and water management practices. They are at the boundary of the region covered by the Comprehensive Everglades Restoration Plan (CERP), and thus are impacted by both CERP and marine resource management decisions. An integrated conceptual ecological model (ICEM) for the southwest coastal wetlands of Florida was developed that illustrates the linkages between drivers, pressures, ecological process, and ecosystem services. Five ecological indicators are presented: (1) mangrove community structure and spatial extent; (2) waterbirds; (3) prey-base fish and macroinvertebrates; (4) crocodilians; and (5) periphyton. Most of these indicators are already used in other areas of south Florida and the SFCME, and therefore will allow metrics from the coastal wetlands to be used in system-wide assessments that incorporate the entire Greater Everglades Ecosystem.

Ecological Indicators↗

USGS2011

Comparison of methods for measuring surface area of submersed aquatic macrophytes

The surface area of submersed macrophytes is often viewed from different perspectives such as substrate for colonization by periphyton, or protective cover for fishes. Consequently, several different methods have been used to measure it. We describe a method for measuring that area with an electronic surface area meter, a device that yields, for large samples of macrophytes, measurements in units of square meters of plant surface area per square meter of bottom. Unpreserved macrophytes, pressed gently between plastic sheets, are passed through the sensing head of the meter, which electronically scans and measures their surface area. The technique is several times faster and more precise than previous methods even for plants with finely dissected leaves.

Journal of Freshwater Ecology↗

USGS2022

Native fish need a natural flow regime

Water development has threatened the ecological integrity of riverine ecosystems. Increasing water demand, persistent drought, and climate change exacerbate the effects of habitat degradation and loss in altered systems such as the Colorado River basin. Today, biologists are challenged to identify management actions that benefit native fishes while not hindering water development or management. Herein, we discuss the importance of the natural flow regime for functioning riverine ecosystems and provide examples from four tributaries to the Green River, a major headwater branch of the Colorado River. These tributaries represent a gradient of impacts ranging from water abstraction to the point of complete seasonal desiccation to a relatively natural flow regime, and consequently have maintained different levels of instream habitat complexity and native fish persistence. Despite decades of management, endangered species lack self-sustaining populations and other native species have been extirpated from over half their ranges, which begs the question: can water development and fish conservation be balanced under current water laws and climate change-driven declines in runoff? Given the continued decline in freshwater biodiversity and abundance occurring across the globe, we contend that immediate designation of rivers with natural flow regimes as freshwater conservation areas will enhance native species recovery.

Arizona, Colorado, Utah, Wyoming↗

USGS2024

Refuge identification as a climate adaptation strategy to promote fish persistence during drought

Climate change is leading to global increases in extreme events, such as drought, that threaten the persistence of freshwater biodiversity. Identification and management of drought refuges, areas that promote resistance and resilience to drought, will be critical for preserving and recovering aquatic biodiversity in the face of climate change and increasing human water use. Although several reviews have addressed the effects of droughts and highlighted the role of refuges, a need remains on how to identify functional refuges that can be used in a drought management framework to support fish assemblages. We synthesize literature on drought refuges and propose a framework to identify and manage functional refuges that incorporate species physiological tolerances, behaviours and life-history strategies. Stream pools, perennial reaches and off-channel habitat were identified as important drought refuges for fish. The ability of refuges to improve species resistance and resilience to drought requires careful consideration of the biology of the target species and targeted management to promote persistence, quality and connectivity of refuges. Case studies illustrate that management of drought refuges can be challenging because of competing demands for water, incomplete knowledge of ecological requirements for target species and the increasing occurrence of multi-year droughts. Climate adaptation is increasingly important, and drought refuges can increase fish resistance and resilience to climate-related drought across the riverscape.

Fish and Fisheries↗

USGS2018

Capture versus tagging impacts on chum salmon freshwater spawning migration travel times

The spawning migration travel times of chum salmon, Oncorhynchus keta (Walbaum), fitted with gastrically implanted radio tags vs external spaghetti tags were tested for a short [≈60 river km (rkm)] and long migration route (≈730 rkm) on the Koyukuk River, Alaska, USA. Using a novel application of statistical arrival curve models to infer travel times for uncaptured fish, migrations by chum salmon not directly handled during the study were also assessed. Results demonstrated negligible differences in travel times within migration routes between fish fitted only with spaghetti tags and fish fitted with radio tags, indicating low impacts on migration travel behaviour associated with gastric tags once deployed. Conversely, travel times for unhandled fish as inferred by statistical arrival models may have been 12%–24% shorter than those for fish captured with gillnets for tagging. These results suggest that, if present, chum salmon migration behaviour impacts may be more strongly associated with fish capture than tag deployment.

Fisheries Management and Ecology↗

USGS1993

Organic carbon sources and sinks in San Francisco Bay: variability induced by river flow

Sources and sinks of organic carbon for San Francisco Bay (California, USA) were estimated for 1980. Sources for the southern reach were dominated by phytoplankton and benthic microalgal production. River loading of organic matter was an additional important factor in the northern reach. Tidal marsh export and point sources played a secondary role. Autochthonous production in San Francisco Bay appears to be less than the mean for temperate-zone estuaries, primarily because turbidity limits microalgal production and the development of seagrass beds. Exchange between the Bay and Pacific Ocean plays an unknown but potentially important role in the organic carbon balance. Interannual variability in the organic carbon supply was assessed for Suisun Bay, a northern reach subembayment that provides habitat for important fish species (delta smelt Hypomesus transpacificus and larval striped bass Morone saxatilus). The total supply fluctuated by an order of magnitude; depending on the year, either autochthonous sources (phytoplankton production) or allochthonous sources (riverine loading) could be dominant. The primary cause of the year-to-year change was variability of freshwater inflows from the Sacramento and San Joaquin rivers, and its magnitude was much larger than long-term changes arising from marsh destruction and point source decreases. Although interannual variability of the total organic carbon supply could not be assessed for the southern reach, year-to-year changes in phytoplankton production were much smaller than in Suisun Bay, reflecting a relative lack of river influence.

California↗

USGS2026

Mixed support for the temperature-size rule in wild freshwater fishes

The temperature-size rule states that species living in warmer temperatures will grow faster and mature earlier at smaller sizes. While several studies have documented patterns in average body size consistent with the temperature-size rule in wild populations, a comprehensive test is lacking. Here, we use age and length data of 1.4 million fish across 7 species from 2704 lakes to quantify temperature-related variation in growth across ontogeny. Our results show that no species fully conforms to the temperature-size rule; despite patterns of juvenile growth rate and age at maturity typically aligning with the temperature-size rule, these changes seldom translate to reduced size at maturity or maximum size. We also found evidence that faster life histories in warmer environments are associated with reduced lifespans. A deeper understanding of how temperature shapes growth in natural systems is needed to accurately predict the effects of global warming on wildlife.

Illinois, Indiana, Iowa,Michigan, Minnesota, South↗

USGS2019

Role of recovering river herring population on smallmouth bass diet and growth

Fish assemblages in Atlantic coastal rivers have undergone extensive ecological change in the last two and a half centuries due to human influence, including extirpation of many migratory fish species, such as river herring (Alosa spp.) and introduction of nonnative piscivores, notably Smallmouth Bass Micropterus dolomieu. Recently, dam removals and fish passage improvements in the Penobscot River, Maine, have allowed river herring to return to reaches of the river that have been inaccessible since the late 19th century. Alosine populations have increased and this trend is anticipated to continue. This may increase forage in the system which could potentially increase growth for Smallmouth Bass, the dominant piscivore. We examined the diet and growth of Smallmouth Bass collected from areas of the Penobscot River watershed with and without access to river herring as prey. We collected 765 Smallmouth Bass throughout 2015, examined the stomach contents of 573 individuals, and found notable differences in diet among three river reaches with common seasonal trends. Juvenile river herring composed an average of 19% (SE = ±6%) of stomach contents by mass from Smallmouth Bass collected in the freshwater tidal area but were rarely observed in the diets upstream. We used estimates from von Bertalanffy growth models to examine differences in growth among reaches and found that asymptotic length was the longest (425 mm TL) in the Tidal reach where access to river herring was unrestricted. We then used these data to predict changes to growth associated with increased access to juvenile river herring prey with bioenergetics models. Results indicated that substituting juvenile river herring for less energy-dense prey (e.g.,invertebrates) may lead to increases in seasonal growth throughout the watershed as river herring populations continue to rebound in response to dam removal. Our results provide insight into the diet and growth of Smallmouth Bass in a large New England river, and provide a foundation for future work investigating unfolding changes to these characteristics following recent dam removals.

Maine↗

USGS2007

Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair-1 vs. 1.40 young fledged pair-1) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation. ?? 2007 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗

USGS2017

Ecological impacts of winter water level drawdowns on lake littoral zones: A review

Freshwater littoral zones harbor diverse ecological communities and serve numerous ecosystem functions that are controlled, in part, by natural water level fluctuations. However, human alteration of lake hydrologic regimes beyond natural fluctuations threaten littoral zone ecological integrity. One type of hydrologic alteration in lakes is winter water level drawdowns, which are frequently employed for hydropower, flood control, and macrophyte control, among other purposes. Here, we synthesize the abiotic and biotic responses to annual and novel winter water level drawdowns in littoral zones of lakes and reservoirs. The dewatering, freezing, and increased erosion of exposed lakebeds drive changes in the littoral zone. Shoreline-specific physicochemical conditions such as littoral slope and shoreline exposure further induce modifications. Loss of fine sediment decreases nutrient availability over time, but desiccation may promote a temporary nutrient pulse upon re-inundation. Annual winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects. Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), experience negative effects via indirect pathways like decreased food resources and spawning habitat. We identify eight general research gaps to guide future research that could improve our understanding about the complex effects of winter drawdowns on littoral zone ecology.

Aquatic Sciences↗

USGS2016

Behavior and movements of adult spring Chinook salmon ( Oncorhynchus tshawytscha ) in the Chehalis River Basin, southwestern Washington, 2015

Recent interest in flood control and restoration strategies in the Chehalis River Basin has increased the need to understand the current status and ecology of spring Chinook salmon. Based on the extended period between freshwater entry and spawn timing, spring Chinook salmon have the longest exposure of all adult Chinook salmon life histories to the low-flow and high water temperature conditions that typically occur during summer. About 100 adult spring Chinook salmon were found dead in the Chehalis River in July and August 2009. Adult Chinook salmon are known to hold in cool-water refugia during warm summer months, but the extent to which spring Chinook salmon might use thermal refugia in the Chehalis River is unknown. The movements and temperature exposures of adult spring Chinook salmon following their return to the Chehalis River were investigated using radiotelemetry and transmitters equipped with temperature sensors, combined with water temperature monitoring throughout the basin. A total of 23 spring Chinook salmon were radio-tagged between April and early July 2015; 11 were captured and released in the main-stem Chehalis River, and 12 were captured and released in the South Fork Newaukum River. Tagged fish were monitored with a combination of fixed-site monitoring locations and regular mobile tracking, from freshwater entry through the spawning period. Water temperature and flow conditions in the main-stem Chehalis River during 2015 were atypical compared to historical averages. Mean monthly water temperatures between March and July 2015 were higher than any decade since 1960 and mean daily flows were 30–70 percent of the flows in previous years. Overall, 96 percent of the tagged fish were detected, with a mean of 62 d in the detection history of tagged fish. Of the 11 fish released in the main-stem Chehalis River, six fish (55 percent) moved upstream, either shortly after release (2–7 d, 50 percent), or following a short delay (12–18 d, 50 percent). One fish released in the main-stem Chehalis River remained near the release location for 64 d before moving upstream. The final fates for the seven fish that moved upstream in the main-stem Chehalis River included two fish with unknown fates, two fish with a fate of pre-spawn mortality, and three fish that were assigned a fate of spawner. Four (36 percent) of the radio-tagged Chinook salmon released in the main-stem Chehalis River showed limited movement from their release sites, and were assigned fates of unknown (one fish), pre-spawn mortality (one fish), and spit/mortality (2 fish). The 12 spring Chinook salmon released in the South Fork Newaukum River remained in the South Fork Newaukum River throughout the study period. Five (42 percent) of these fish were actively moving through the spawning period and were assigned a fate of spawner. Seven (58 percent) of these fish were detected for a period following release, but their detection histories ended prior to the spawning period. The fates assigned to these seven fish included two fish with spit/mortality fates and five fish with fates of pre-spawn mortality. Tagged fish in both the Chehalis River and the South Fork Newaukum River showed limited movements during the peak water temperatures in July and August, and were not frequently detected at sites where water temperatures were greater than 21 °C. Pre-spawn mortality due to predation or harvest may be an important factor in the Chehalis River Basin as it was the assigned fate for 27 percent of the fish released in the main-stem Chehalis River and 42 percent of the fish released in the South Fork Newaukum River. This study represents a substantial contribution to the understanding of spring Chinook salmon in the Chehalis River Basin. The water temperatures and flow conditions during the 2015 study period were not typical of the historical conditions in the basin and the numbers of tagged fish monitored was relatively low, so results should be interpreted with those cautions in mind.

Washington↗

USGS2018

Science support for evaluating natural recovery of polychlorinated biphenyl concentrations in fish from Crab Orchard Lake, Crab Orchard National Wildlife Refuge, Illinois

Introduction Crab Orchard Lake in southern Illinois is one of the largest and most popular recreational lakes in the state. Construction of the nearly 7,000-acre reservoir in the late 1930s created employment opportunities through the Works Progress Administration, and the lake itself was intended to supply water, control flooding, and provide recreational opportunities for local communities (Stall, 1954). In 1942, the Department of War appropriated or purchased more than 20,000 acres of land around Crab Orchard Lake and constructed the Illinois Ordnance Plant, which manufactured bombs and anti-tank mines during World War II. After the war, an Act of Congress transferred the property to the U.S. Department of the Interior. Crab Orchard National Wildlife Refuge was established on August 5, 1947, for the joint purposes of wildlife conservation, agriculture, recreation, and industry. Production of explosives continued, but new industries also moved onsite. More than 200 tenants have held leases with Crab Orchard National Wildlife Refuge and have operated a variety of manufacturing plants (electrical components, plated metal parts, ink, machined parts, painted products, and boats) on-site. Soils, water, and sediments in several areas of the refuge were contaminated with hazardous substances from handling and disposal methods that are no longer acceptable environmental practice (for example, direct discharge to surface water, use of unlined landfills). Polychlorinated biphenyl (PCB) contamination at the refuge was identified in the 1970s, and a PCB-based fish-consumption advisory has been in effect since 1988 for Crab Orchard Lake. The present advisory covers common carp ( Cyprinus carpio ) and channel catfish ( Ictalurus punctatus ); see Illinois Department of Public Health (2017). Some of the most contaminated areas of the refuge were actively remediated, and natural ecosystem recovery processes are expected to further reduce residual PCB concentrations in the lake. The U.S. Fish and Wildlife Service sought technical support to understand environmental drivers of current (2017) PCB residues in fish tissue and patterns in PCB residues through time to inform the fish-consumption advisory for Crab Orchard Lake. This project is planned in two phases (Tasks 1 and 2); the first phase is included in this report. Task 1, reported here, includes a review of existing literature and a brief overview focused on environmental and biochemical/physiological processes that drive PCB residues in fish tissue. This review specifically targets processes that are relevant for freshwater lacustrine environments such as those at Crab Orchard Lake. In addition to discussions of environmental fate, metabolism, and accumulation of PCBs, this review includes a brief scientifically based explanation of approaches used to establish fish-consumption advisories. A planned second task (Task 2) will include a compilation and summary of existing data on PCB residues in fish tissue samples from Crab Orchard Lake. This summary will also place Crab Orchard Lake data in a broader geographic context through a comparison with fish data from other Midwestern lakes. When Task 1 and Task 2 are complete, resource managers will have (a) a synthesis of existing literature that characterizes the processes influencing the fate of residual PCBs remaining in systems such as Crab Orchard Lake, (b) a summary of natural PCB attenuation processes for use in risk communication with the public, and (c) a summary of existing data on PCBs in fish tissues from Crab Orchard Lake, including exploratory plots of tissue residues through time. Overall, this project will provide data to help resource managers better understand the ecological and public health consequences of residual PCBs in Crab Orchard Lake.

Illinois↗

USGS2016

Diel diet of fantail darter in a tributary to Lake Ontario, New York, USA

The foraging behavior of benthic fishes in streams is seldom examined but is vital to the health of the aquatic community. We examined the feeding ecology of the fantail darter ( Etheostoma flaballere ) in Trout Brook, a tributary of the Salmon River in central New York, USA. Of the six time periods examined, fantail darters fed most intensely from 1600–2000 h, with ephemeropterans the major prey consumed during all time periods except for 2000 where chironomid larvae were consumed the most. Fantail darter diet composition was similar across all time periods except during the night which appeared to be uniquely different. According to the prey selection analysis, fantail darters appear to prefer dipterans and ephemeropterans but also demonstrated an opportunistic behavior feeding on what was available in the brook.

New York↗

USGS2011

Invasive crayfish in the Pacific Northwest

Invasive species directly threaten freshwater biodiversity, particularly in regions of high aquatic richness like the Pacific Northwest (PNW). Crayfish are among the most impactful of aquatic invasive species. Invasive crayfish are considered ecosystem engineers due to their ability to alter basic wetland properties, such as reducing vegetation and bank integrity and increasing turbidity. In areas where invasion is advanced, crayfish pose major economic and ecological problems. Crayfish have been widely introduced for aquaculture and can become established in a wide range of habitat conditions. They also may be spread by anglers who use them as bait. Several non-native crayfish are established in the PNW, but the extent of their invasion is not well known. At least two groups are known from scattered sites in the PNW, and both have proven problematic for native species in other parts of the world: Red swamp crayfish ( Procambarus clarkii ) and several members of the genus Orconectes . Both groups are native to areas of the eastern United States. Both are identified globally as invasives of high concern and appear on the Oregon Department of Fish and Wildlife's "10 Most Unwanted" and the U.S. Forest Service's "Primary Species of Concern" lists for stream systems in the PNW. Despite the presence of introduced crayfish in the PNW and their high potential for negative effects, the scope of their invasion and effects on aquatic systems are not well known. The U.S. Geological Survey (USGS), along with local groups and state agencies, is working to clarify crayfish distribution and to outline which basins may not yet be invaded. Other goals are to improve understanding of habitat associations of invasive crayfish and their potential effects on native crayfish.

Pacific Northwest↗

USGS2018

Food‐web structure and ecosystem function in the Laurentian Great Lakes—Toward a conceptual model

The relationship between food‐web structure (i.e., trophic connections, including diet, trophic position, and habitat use, and the strength of these connections) and ecosystem functions (i.e., biological, geochemical, and physical processes in an ecosystem, including decomposition, production, nutrient cycling, and nutrient and energy flows among community members) determines how an ecosystem responds to perturbations, and thus is key to understanding the adaptive capacity of a system (i.e., ability to respond to perturbation without loss of essential functions). Given nearly ubiquitous changing environmental conditions and anthropogenic impacts on global lake ecosystems, understanding the adaptive capacity of food webs supporting important resources, such as commercial, recreational, and subsistence fisheries, is vital to ecological and economic stability. Herein, we describe a conceptual framework that can be used to explore food‐web structure and associated ecosystem functions in large lakes. We define three previously recognised broad habitat compartments that constitute large lake food webs (nearshore, pelagic, and profundal). We then consider, at three levels, how energy and nutrients flow: (a) into each basal resource compartment; (b) within each compartment; and (c) among multiple compartments (coupling). Flexible shifts in food‐web structures (e.g., via consumers altering their diet or habitat) that sustain these flows in the face of perturbations provide evidence for adaptive capacity. We demonstrate the conceptual framework through a synthesis of food‐web structure and ecosystem function in the Laurentian Great Lakes, with emphasis on the upper trophic levels (i.e., fishes). Our synthesis showed evidence of notable adaptive capacity. For example, fishes increased benthic coupling in response to invasion by mussels and round gobies. However, we also found evidence of loss of adaptive capacity through species extirpations (e.g., widespread collapse in the abundance and diversity of ciscoes, Coregonus spp., except in Lake Superior). In large freshwater lakes, fishery managers have traditionally taken a top‐down approach, focusing on stocking and harvest policy. By contrast, water quality managers have focused on nutrient effects on chemical composition and lower trophic levels of the ecosystem. The synthesised conceptual model provides resource managers a tool to more systematically interpret how lower food‐web dynamics influence harvestable fish populations, and vice versa, and to act accordingly such that sustainable resource practices can be achieved. We identify key gaps in knowledge that impede a fuller understanding of the adaptive capacities of large lakes. In general, we found a greater uncertainty in our understanding of processes influencing energy and nutrient flow within and among habitats than flows into the system.

Great Lakes↗

USGS2017

The contribution of lakes to global inland fisheries harvest

Freshwater ecosystems provide numerous services for communities worldwide, including irrigation, hydropower, and municipal water; however, the services provided by inland fisheries – nourishment, employment, and recreational opportunities – are often comparatively undervalued. We provide an independent estimate of global lake harvest to improve biological and socioeconomic assessments of inland fisheries. On the basis of satellite-derived estimates of chlorophyll concentration from 80,012 globally distributed lakes, lake-specific fishing effort based on human population, and output from a Bayesian hierarchical model, we estimated that the global lake fishery harvest in the year 2011 was 8.4 million tons (mt). Our calculations excluded harvests from highly productive rivers, wetlands, and very small lakes; therefore, the true cumulative global fishery harvest from all freshwater sources likely exceeded 11 mt as reported by the Food and Agriculture Organization of the United Nations (FAO). This putative underestimate by the FAO could diminish the perceived importance of inland fisheries and perpetuate decisions that adversely affect these fisheries and millions of people.

Frontiers in Ecology and the Environment↗