Pattern and scale in latitude–production relationships for freshwater fishes

Reservoir ecosystems support large pools of fish biomass

Humans increasingly dominate Earth's natural freshwater ecosystems, but biomass production of modified ecosystems is rarely studied. We estimate potential fish total standing stock in USA reservoirs is 3.4 billion (B) kg, and approximate annual secondary production is 4.5 B kg y-1. We also observe varied and non-linear trends in reservoir fish biomass over time, thus previous assertions that reservoir fisheries decline over time are not universal. Reservoirs are globally relevant pools of freshwater fisheries, in part due to their immense limnetic footprint and spatial extent. This study further shows that reservoir ecosystems play major roles in food security and fisheries conservation. We encourage additional effort be expended to effectively manage reservoir environments for the good of humanity, biodiversity, and fish conservation.

Probabilistic risk assessment of sustainable fish consumption at sediment sites

A probabilistic risk assessment (PRA) using a range of sustainable usual fish consumption rates (SUFCRs) was performed to evaluate the potential health risks from consuming resident fish at two contaminated sediment sites. The analysis focused on the Portland Harbor Superfund Site, a large river in Oregon, and Koppers Pond, a small pond in New York. At both sites, the sediment cleanup remedy is driven by PCBs in resident fish. The PRA fit probability distributions to inputs used to develop a distribution of SUFCR, the long-term fish consumption rate sustainably supported by a fishery, and other exposure parameters to calculate the range and likelihood of cancer risks and noncancer hazards for adult anglers. At the 95th percentile, which is often considered a reasonable maximum exposure (RME), the SUFCRs calculated using site-specific inputs are six- to ten-fold lower than the point estimate fish consumption rates used in the deterministic baseline human health risk assessment conducted for each site. The combination of sustainable fish consumption rates and probabilistic methods results in a range of risks and thereby provides more information than the more commonly used deterministic approach. For over 99% of the resident fish-consuming population, the potential cancer risks and noncancer hazards calculated in the PRA are below the deterministic estimates for the RME adult consumer at each site. The combination of PRA with the estimation of SUFCRs is a novel application of these techniques at contaminated sediment sites that provides critical information for risk management decision-making. Integr Environ Assess Manag 2023;19:830-843. © 2022 AECOM Technical Services, Inc and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

The spatial synchrony of species richness and its relationship to ecosystem stability

Synchrony is broadly important to population and community dynamics due to its ubiquity and implications for extinction dynamics, system stability, and species diversity. Investigations of synchrony in community ecology have tended to focus on covariance in the abundances of multiple species in a single location. Yet, the importance of regional environmental variation and spatial processes in community dynamics suggests that community properties, such as species richness, could fluctuate synchronously across patches in a metacommunity, in an analog of population spatial synchrony. Here, we test the prevalence of this phenomenon and the conditions under which it may occur using theoretical simulations and empirical data from 20 marine and terrestrial metacommunities. Additionally, given the importance of biodiversity for stability of ecosystem function, we posit that spatial synchrony in species richness is strongly related to stability. Our findings show that metacommunities often exhibit spatial synchrony in species richness. We also found that richness synchrony can be driven by environmental stochasticity and dispersal, two mechanisms of population spatial synchrony. Richness synchrony also depended on community structure, including species evenness and beta diversity. Strikingly, ecosystem stability was more strongly related to richness synchrony than to species richness itself, likely because richness synchrony integrates information about community processes and environmental forcing. Our study highlights a new approach for studying spatiotemporal community dynamics and emphasizes the spatial dimensions of community dynamics and stability.

Estimating Sustainable Fish Production: Effect on Fish Consumption Rates Used to Develop Remediation Goals at Contaminated Sediment Sites

The long-term fish consumption rate (also referred to as the "usual fish consumption rate" [UFCR]) is a critical assumption in the derivation of human health remedial goals for contaminated sediments. At many sites, remedial goals are established using fish consumption rates based on information available from surveys of the general population or of specific highly exposed populations. To be protective of human health, remedial goals are often established using those high-end fish consumption rates. However, high-end fish consumption rates may overestimate the amount of fish that can be sustainably harvested and consumed and, thus, lead to remedial goals that may not be representative of long-term consumption from the contaminated portion of a water body. This paper presents a methodology to estimate the amount of edible fish that can be harvested sustainably from a contaminated sediment site. The methodology requires 1) estimating the total fish productivity of the area of contaminated sediments, 2) estimating the portion of total productivity that can be harvested sustainably, and 3) determining the portion of the sustainable harvest that is edible fish tissue. Estimates of total fish production rate (TFPR) and the proportion of such harvest that can be harvested sustainably rely primarily on available compilations of TFPR and harvest measurements across a range of water bodies throughout the world. Estimates of the fraction of whole fresh fish that is consumed rely on information available from the United States Environmental Protection Agency (USEPA). The methodology is used to develop sustainable UFCRs for 4 hypothetical water bodies with distinct characteristics and to compare the UFCRs to commonly used default fish consumption rates. Estimates of sustainable production provide risk managers valuable perspective about the benefits realized by cleanup of contaminated sediment sites. Integr Environ Assess Manag 2021;17:584-596. © 2020 SETAC.

The interactive effects of climate change and land use on boreal stream fish communities

Ongoing and projected climate change is likely to greatly alter co-occurring stressor mechanisms, yet these potential interactions remain poorly understood in natural freshwater systems worldwide. As the global biodiversity crisis deepens, successful conservation efforts will hinge on developing mechanistic multiple stressor frameworks that have been ground-truthed in natural systems containing complex species dynamics and ecological processes. Our study examined the combined and interacting effects of potential climate and land use stressors on boreal stream fishes using data from over 300 catchments across a broad 250,000 km² region. To characterize boreal fish community health, we examined four indicators including species richness, total catch per unit effort, the proportion of lithophilic spawners (fish sensitive to sedimentation), and the assemblage tolerance index which provides a measurement of the overall community tolerance to disturbance. Land use stressors included total anthropogenic land use area and linear disturbance at multiple watershed scales as well as two site-specific habitat degradation indicators (dissolved oxygen and the proportion of fine substrate). Overall community richness and productivity were not negatively related to land use changes indicating potential compensatory dynamics (e.g. where intolerant species are replaced with more tolerant species as habitat quality degrades). In contrast, we observed declines for sensitive species, including highly valued salmonids, that varied depending on interactions between local climate, land use, and stream type. Sensitive species declines were concentrated in regions experiencing increased land use and warming, whereas increases were observed in cooler regions consistent with a subsidy-stress response. In addition, lithophilic spawners declined in watersheds experiencing warmer and wetter conditions owing to potential indirect effects on spawning habitat quality. Results from our study provide novel insight into complex climate and land use interactions occurring across a broad, real-world landscape, and highlight the potential for amplified species declines under future warming and land use scenarios.

Production dynamics reveal hidden overharvest of inland recreational fisheries

Recreational fisheries are valued at $190B globally and constitute the predominant way in which people use wild fish stocks in developed countries, with inland systems contributing the main fraction of recreational fisheries. Although inland recreational fisheries are thought to be highly resilient and self-regulating, the rapid pace of environmental change is increasing the vulnerability of these fisheries to overharvest and collapse. Here we directly evaluate angler harvest relative to the biomass production of individual stocks for a major inland recreational fishery. Using an extensive 28-y dataset of the walleye (Sander vitreus) fisheries in northern Wisconsin, United States, we compare empirical biomass harvest (Y) and calculated production (P) and biomass (B) for 390 lake year combinations. Production overharvest occurs when harvest exceeds production in that year. Biomass and biomass turnover (P/B) declined by ∼30 and ∼20%, respectively, over time, while biomass harvest did not change, causing overharvest to increase. Our analysis revealed that ∼40% of populations were production-overharvested, a rate >10× higher than estimates based on population thresholds often used by fisheries managers. Our study highlights the need to adapt harvest to changes in production due to environmental change.

Biodiversity and ecosystem functioning in naturally assembled communities

Approximately 25 years ago, ecologists became increasingly interested in the question of whether ongoing biodiversity loss matters for the functioning of ecosystems. As such, a new ecological subfield on Biodiversity and Ecosystem Functioning (BEF) was born. This subfield was initially dominated by theoretical studies and by experiments in which biodiversity was manipulated, and responses of ecosystem functions such as biomass production, decomposition rates, carbon sequestration, trophic interactions and pollination were assessed. More recently, an increasing number of studies have investigated BEF relationships in non-manipulated ecosystems, but reviews synthesizing our knowledge on the importance of real-world biodiversity are still largely missing. I performed a systematic review in order to assess how biodiversity drives ecosystem functioning in both terrestrial and aquatic, naturally assembled communities, and on how important biodiversity is compared to other factors, including other aspects of community composition and abiotic conditions. The outcomes of 258 published studies, which reported 726 BEF relationships, revealed that in many cases, biodiversity promotes average biomass production and its temporal stability, and pollination success. For decomposition rates and ecosystem multifunctionality, positive effects of biodiversity outnumbered negative effects, but neutral relationships were even more common. Similarly, negative effects of prey biodiversity on pathogen and herbivore damage outnumbered positive effects, but were less common than neutral relationships. Finally, there was no evidence that biodiversity is related to soil carbon storage. Most BEF studies focused on the effects of taxonomic diversity, however, metrics of functional diversity were generally stronger predictors of ecosystem functioning. Furthermore, in most studies, abiotic factors and functional composition (e.g. the presence of a certain functional group) were stronger drivers of ecosystem functioning than biodiversity per se. While experiments suggest that positive biodiversity effects become stronger at larger spatial scales, in naturally assembled communities this idea is too poorly studied to draw general conclusions. In summary, a high biodiversity in naturally assembled communities positively drives various ecosystem functions. At the same time, the strength and direction of these effects vary highly among studies, and factors other than biodiversity can be even more important in driving ecosystem functioning. Thus, to promote those ecosystem functions that underpin human well-being, conservation should not only promote biodiversity per se, but also the abiotic conditions favouring species with suitable trait combinations.