Search

Eutrophication and climate warming are profoundly affecting fish in many freshwater lakes. Understanding the specific effects of these stressors is critical for development of effective adaptation and remediation strategies for conserving fish populations in a changing environment. Ecological niche models that incorporated the individual effects of nutrient concentration and climate were developed for 25 species of fish sampled in standard gillnet surveys from 1,577 Minnesota lakes. Lake phosphorus concentrations and climates were hindcasted to a pre-disturbance period of 1896–1925 using existing land use models and historical temperature data. Then historical fish assemblages were reconstructed using the ecological niche models. Substantial changes were noted when reconstructed fish assemblages were compared to those from the contemporary period (1981–2010). Disentangling the sometimes opposing, sometimes compounding, effects of eutrophication and climate warming was critical for understanding changes in fish assemblages. Reconstructed abundances of eutrophication-tolerant, warmwater taxa increased in prairie lakes that experienced significant eutrophication and climate warming. Eutrophication-intolerant, warmwater taxa abundance increased in forest lakes where primarily climate warming was the stressor. Coolwater fish declined in abundance in both ecoregions. Large changes in modeled abundance occurred when the effects of both climate and eutrophication operated in the same direction for some species. Conversely, the effects of climate warming and eutrophication operated in opposing directions for other species and dampened net changes in abundance. Quantifying the specific effects of climate and eutrophication will allow water resource managers to better understand how lakes have changed and provide expectations for sustainable fish assemblages in the future. [ABSTRACT FROM AUTHOR]

Freshwaters are being transformed by multiple environmental drivers, creating uncertainty about future conditions. One way of coping with uncertainty is to manage for resilience to unanticipated events while facilitating learning through adaptive management. We outline the application of these strategies to freshwater recreational fisheries management using a case study in Wisconsin, USA, where black bass (Micropterus spp.) populations are increasing, while Walleye (Sander vitreus) populations are decreasing. Managing for heterogeneity in functional groups (e.g., age classes and prey species of sport fishes), fishery objectives, and regulations can increase resilience, although heterogeneity must be balanced with replication to facilitate learning. Monitoring designed to evaluate management objectives and inform about critical uncertainties, when combined with heterogeneity, creates opportunities for adaptive management, another critical resilience strategy. Although barriers exist to implementing resilience strategies, management designed to accommodate uncertainty and illuminate its consequences is needed to maintain critical fisheries in a rapidly changing world. Los cuerpos de agua dulce están siendo transformados por múltiples factores ambientales, lo que genera incertidumbre sobre lo que sucederá en el futuro. Una forma de enfrentar esta incertidumbre es el manejo de la resiliencia con respeto a eventos no anticipados y, simultáneamente, facilitar el aprendizaje a través del manejo adaptativo. En este trabajo se muestra la aplicación de estas estrategias en el manejo de pesquerías recreativas de agua dulce tomando un caso de estudio en Wisconsin, en el que las poblaciones de la lobina negra (Micropterus spp.) están incrementándose, en tanto que las de la lucioperca americana (Sander vitreus) están disminuyendo. El manejo enfocado en la heterogeneidad de grupos funcionales (p.e., ciertas clases de edad y presas de peces de pesca deportiva), en los objetivos y en las regulaciones de la pesquería pueden aumentar la resiliencia, no obstante atender la heterogeneidad debe equilibrarse usando réplicas que faciliten el aprendizaje. El monitoreo diseñado para evaluar los objetivos del manejo e informar acerca de imprecisiones importantes que, al combinarse con la heterogeneidad, generan oportunidades para el manejo adaptativo, representa otra estrategia crítica para incrementar la resiliencia. Aunque existen obstáculos para implementar las estrategias enfocadas en la resiliencia, se necesita un manejo que incorpore la incertidumbre y que advierta sobre sus consecuencias, con el fin de mantener vivas importantes pesquerías en un mundo que está en constante cambio. [ABSTRACT FROM AUTHOR]

We developed and evaluated an alternative method (rapid assessment or RA) for assessment of larval sea lampreys, Petromyzon marinus. We determined that using RA would result in at least as many, if not more, sea lampreys being killed than would using the current assessment method (quantitative assessment sampling or QAS) to select streams for lampricide treatment. Both assessment methods were carried out simultaneously throughout the entire Great Lakes basin from 2005 to 2007. RA required fewer resources than the current method and thus allowed for the chemical treatment of additional streams with lampricides, given a fixed overall budget for control. Population estimates generated from the QAS surveys showed that using RA would result in approximately equal numbers of metamorphosing lamprey and greater numbers of larval lamprey killed than by using QAS. Mark–recapture results indicated that prioritizing streams for treatment using RA may result in higher numbers of metamorphosing and larval lampreys killed than by using QAS. RA is currently being adopted throughout the Great Lakes as the method for assessing larval sea lamprey populations. Other fishery management programs may benefit from examining the value of their assessment programs relative to other uses of resources. [ABSTRACT FROM AUTHOR]

Fishery management is often characterized by trade-offs among conflicting objectives. One important tradeoff exists between investments in assessment (reducing uncertainty) and in implementation of management actions in system. Resource-intensive assessment programs are often used to inform decision makers, and we argue that the value of these assessments should be measured not only in terms of the information they provide, but also relative to other management actions that could be funded in their place. In this article, we illustrate the importance of accounting for all aspects of the value of information using examples drawn from three critical areas of fishery management: invasive species control, commercial fisheries stock assessments, and marine protected area design. We discuss how experts have judged the value of assessment programs in the past, and provide suggestions as to how these methods could be expanded to examine the value of information in a more holistic manner. [ABSTRACT FROM AUTHOR]

Reply to letters to the editor on two studies are presented including the perception about the failure in fisheries management and concern over the utilization of hydrologic units and the removal of economic and population growth as causes of danger for fishes.

Successful management of natural resources requires local action that adapts to larger‐scale environmental changes in order to maintain populations within the safe operating space (SOS) of acceptable conditions. Here, we identify the boundaries of the SOS for a managed freshwater fishery in the first empirical test of the SOS concept applied to management of harvested resources. Walleye (Sander vitreus) are popular sport fish with declining populations in many North American lakes, and understanding the causes of and responding to these changes is a high priority for fisheries management. We evaluated the role of changing water clarity and temperature in the decline of a high‐profile walleye population in Mille Lacs, Minnesota, USA, and estimated safe harvest under changing conditions from 1987 to 2017. Thermal–optical habitat area (TOHA)—the proportion of lake area in which the optimal thermal and optical conditions for walleye overlap—was estimated using a thermodynamic simulation model of daily water temperatures and light conditions. We then used a SOS model to analyze how walleye carrying capacity and safe harvest relate to walleye thermal–optical habitat. Thermal–optical habitat area varied annually and declined over time due to increased water clarity, and maximum safe harvest estimated by the SOS model varied by nearly an order of magnitude. Maximum safe harvest levels of walleye declined with declining TOHA. Walleye harvest exceeded safe harvest estimated by the SOS model in 16 out of the 30 yr of our dataset, and walleye abundance declined following 14 of those years, suggesting that walleye harvest should be managed to accommodate changing habitat conditions. By quantifying harvest trade‐offs associated with loss of walleye habitat, this study provides a framework for managing walleye in the context of ecosystem change. [ABSTRACT FROM AUTHOR]

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short-term management goals with long-term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long-term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on fishes and fisheries through creating resilient management and ecological systems. [ABSTRACT FROM AUTHOR]