•Modeling stressors singly can produce misleading estimates if the stressor modelled is not the dominant system stressor.•Expected temperature increase is indicated as the dominant stressor in the ...Chesapeake Bay system.•Full-system ecosystem models can be essential tools to identify non-additive and unexpected effects of system change.•Ecosystem modelling tools like Atlantis are useful to test effects of single factors confounded in nature and not separable in the laboratory.
Many external stressors influence marine and coastal ecosystems. Understanding effects of these stressors is important for managers concerned with living marine resources (LMR). Historically, analytical methods for understanding these effects have been limited to a relative few stressors being modelled. Recent work has shown that multiple stressors may commonly have non-additive or cumulative effects, so accounting for the interactions of such stressors on LMR populations may be important. Coastal and marine ecosystems, which are often important for early life stages of many LMR populations, have a wide variety of stressors, yet analytical approaches accounting for the dynamics of multiple stressors have been used infrequently in these types of systems. For this work, we simulate the effects of individual and multiple stressors on a complex estuarine system, the Chesapeake Bay (USA), to demonstrate the range of conclusions about the effects of stressors on LMR populations that might be reached if stressors are considered singly versus in combination. Temperature increase has the greatest effect on productivity in our simulations, and appears to be the dominant stressor currently affecting this system. Consequently, we suggest it may be important for future work focusing on the effects of other factors to also consider the effects of expected temperature increase in this system, or important non-additive trends could be missed. With recent improvements in processing speed, full system models like Atlantis have become effective tools to provide resource managers with the information regarding non-additive effects of multiple stressors that they need for sound decision making.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Harvests from recreational fishing are increasingly as important as commercial harvest to populations of popularly fished marine recreational species. However, it has yet to be determined whether the ...increasing importance of recreational fishing is a general trend of marine fisheries in the US or whether such a trend is limited to only those species recognized as popular recreational fishes. 71% of marine species in the US have experienced an increase in the proportion of total harvest from the recreational sector during the time harvest data are available for both sectors. Species demonstrating an increase in the proportion of harvests by the recreational sector included those generally regarded as commercial, bait, and bycatch species, as well as those considered recreational species. Marine species categorized as overfished could not be predicted from either fishery characteristics or life history characteristics in a PCA analysis of available data for fished species in the US. Consequently, there appears to be little to predict vulnerability of populations to fishing efforts save that all fished species can be made vulnerable to overexploitation. Well-developed yield-based strategies, designed for commercial fisheries, are not likely to be effective in managing populations as the diverse recreational fishing sector continues to increase in its importance. Thus, new management strategies for US marine fisheries are needed. Some possible alternative strategies are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The Chesapeake Bay is the largest, most productive, and most biologically diverse estuary in the continental United States.•Pressures from human population growth and agricultural intensification ...have led to excessive nutrient and sediment inputs.•The Chesapeake Bay program partnership has been developing and applying a complex modeling system as a planning tool to inform management decisions and Bay restoration efforts.•This paper provides a description of the modeling system along with specific recommendations that emerged from a 2018 workshop designed to inform future model development.
The Chesapeake Bay is the largest, most productive, and most biologically diverse estuary in the continental United States providing crucial habitat and natural resources for culturally and economically important species. Pressures from human population growth and associated development and agricultural intensification have led to excessive nutrient and sediment inputs entering the Bay, negatively affecting the health of the Bay ecosystem and the economic services it provides. The Chesapeake Bay Program (CBP) is a unique program formally created in 1983 as a multi-stakeholder partnership to guide and foster restoration of the Chesapeake Bay and its watershed. Since its inception, the CBP Partnership has been developing, updating, and applying a complex linked modeling system of watershed, airshed, and estuary models as a planning tool to inform strategic management decisions and Bay restoration efforts. This paper provides a description of the 2017 CBP Modeling System and the higher trophic level models developed by the NOAA Chesapeake Bay Office, along with specific recommendations that emerged from a 2018 workshop designed to inform future model development. Recommendations highlight the need for simulation of watershed inputs, conditions, processes, and practices at higher resolution to provide improved information to guide local nutrient and sediment management plans. More explicit and extensive modeling of connectivity between watershed landforms and estuary sub-areas, estuarine hydrodynamics, watershed and estuarine water quality, the estuarine-watershed socioecological system, and living resources will be important to broaden and improve characterization of responses to targeted nutrient and sediment load reductions. Finally, the value and importance of maintaining effective collaborations among jurisdictional managers, scientists, modelers, support staff, and stakeholder communities is emphasized. An open collaborative and transparent process has been a key element of successes to date and is vitally important as the CBP Partnership moves forward with modeling system improvements that help stakeholders evolve new knowledge, improve management strategies, and better communicate outcomes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Ecosystem-based management (EBM) of the ocean considers all impacts on and uses of marine and coastal systems. In recent years, there has been a heightened interest in EBM tools that allow testing of ...alternative management options and help identify tradeoffs among human uses. End-to-end ecosystem modelling frameworks that consider a wide range of management options are a means to provide integrated solutions to the complex ocean management problems encountered in EBM. Here, we leverage the global advances in ecosystem modelling to explore common opportunities and challenges for ecosystem-based management, including changes in ocean acidification, spatial management, and fishing pressure across eight Atlantis (atlantis.cmar.csiro.au) end-to-end ecosystem models. These models represent marine ecosystems from the tropics to the arctic, varying in size, ecology, and management regimes, using a three-dimensional, spatially-explicit structure parametrized for each system. Results suggest stronger impacts from ocean acidification and marine protected areas than from altering fishing pressure, both in terms of guild-level (i.e., aggregations of similar species or groups) biomass and in terms of indicators of ecological and fishery structure. Effects of ocean acidification were typically negative (reducing biomass), while MPAs led to both 'winners' and 'losers' at the level of particular species (or functional groups). Changing fishing pressure (doubling or halving) had smaller effects on the species guilds or ecosystem indicators than either OA or MPAs. Compensatory effects within guilds led to weaker average effects at the guild level than the species or group level. The impacts and tradeoffs implied by these future scenarios are highly relevant as ocean governance shifts focus from single-sector objectives (e.g., sustainable levels of individual fished stocks) to taking into account competing industrial sectors' objectives (e.g., simultaneous spatial management of energy, shipping, and fishing) while at the same time grappling with compounded impacts of global climate change (e.g., ocean acidification and warming).
Until recently, marine fisheries managers have predominately interacted with a single user group—commercial fisheries. However, changes in participation in fisheries and progress toward ...ecosystem‐based approaches have introduced new stakeholders into the management process. Yet, there are few examples of successful approaches of how to engage the spectrum of stakeholders interested in management policy and decisions. Here we describe one such approach that was used in the fisheries for king mackerel (Scomberomorus cavalla) along the U.S. southeast coast. The approach combined consensus building in facilitated workshops and decision analysis in which stakeholders could compare the consequences of alternative management options on trends in the king mackerel population and the fisheries it supports. The process resulted in a workgroup of stakeholders that developed a clear vision for its desired future of king mackerel fisheries and several alternative management options. Decision analysis was used to select the best options that were then recommended to the South Atlantic Fisheries Management Council (SAFMC). These options were more conservative than the council's own recommendations. Additional benefits of the process included stakeholder education, both in stock assessment methodology and in an understanding other stakeholder positions, and the development of closer cooperation among stakeholders and managers.
hasta hace poco tiempo, los administradores de las pesquerías marinas habían interactuado principalmente con grupos individuales de usuarios– de pesquerías comerciales. Sin embargo, los cambios en cuanto a participación en las pesquerías y progreso hacia el enfoque de manejo basado en el ecosistema, han introducido a un mayor número de participantes interesados en el proceso de manejo. Aun así, existen pocos ejemplos de enfoques exitosos acerca de cómo comprometer el espectro de interesados en las decisiones y política de manejo. Aquí se describe uno de estos enfoques, que fue utilizado en la pesquería del peto (Scomberomorus cavalla) a lo largo de la costa sureste de los Estados Unidos de Norteamérica. El enfoque combina el consenso logrado en talleres y análisis de decisión en los que las partes interesadas pudieron comparar las consecuencias de distintas opciones de manejo en las tendencias poblacionales del peto y en las pesquerías que este recurso sostiene. El proceso dio como resultado un grupo de interesados que desarrolló una clara visión de su futuro esperable con respecto a las pesquerías del peto y numerosas opciones alternativas de manejo. El análisis de decisión se utilizó para seleccionar las mejores opciones que después fueron transmitidas al Consejo de Manejo Pesquero del Atlántico Sur (CMPAS). Estas opciones resultaron más conservativas que las recomendaciones del propio consejo. Beneficios adicionales del proceso incluyeron la educación de las partes involucradas, tanto en las metodologías de evaluación de los stocks y en el entendimiento de la postura de otros interesados, como en el desarrollo de una cooperación más estrecha entre involucrados y administradores.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The index‐removal method provides estimates of abundance, exploitation rate, and catchability coefficient. Estimates from the original method suffer from poor precision. Recent work has improved the ...precision of model estimates; however, the method still includes the strong assumption of constant survey catchability over years and seasons. This assumption is not tenable in many fisheries. This work introduces a new multiyear model, 2qIR, that allows catchability to differ between surveys of the same year. Simulations were performed to examine the effects of variability in (1) the exploitation rate among years, (2) survey catchability, and (3) the number of years of data on model performance. The 2qIR model estimates were always more accurate and precise than those of the other models examined and other model scenarios in which there was moderate contrast in exploitation among years, regardless of the seasonal difference between survey catchability coefficients. The ratios of survey catchability tested ranged from 0.1 to 10, but the model worked best at catchability ratios greater than 0.3. The 2qIR model performance improved slightly when a third year was added to the data set, but performance was similar with 3 or 5 years of data. In all types of simulations, the 2qIR model estimates were usable (i.e., not negative, infinite, or made with a convergence error) a greater proportion of the time than were annual model estimates. The 2qIR model produced reasonable results when applied to data from a population of southern rock lobster Jasus edwardsii in Tasmania, whereas the models that assume constant catchability among surveys sometimes predicted exploitation rates exceeding 100%. The results from both the simulations and the lobster data suggest that the 2qIR model can be reliably applied in more situations than models that assume constant survey catchability.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aging structures for spotted seatrout Cynoscion nebulosus have been compared for the first time by using sectioned pectoral fin rays, sectioned dorsal fin spines, scales, and whole and sectioned ...otoliths from 50 fish of 300 to 731 mm total length. We considered the following criteria: processing time, reader confidence, reader agreement (precision), agreement of mark counts between structures, and growth with presumed age. Processing time—more than 1 h per fish—was unreasonably high for sectioned pectoral fin rays, so we did not evaluate their use further. Sectioned dorsal fin spines were clear and easy to read, but mark counts disagreed with those of other structures and were not significantly related to the growth of the fish or that of the aging structure. Scale marks often were inconsistent, which led to low confidence and low agreement between readers. Scale ages also showed systematic disagreement with sectioned‐otolith ages. Reader confidence was relatively low for whole‐otolith age readings in comparison with sectioned readings of the same otolith, and whole‐otolith ages showed systematic disagreement with sectioned‐otolith ages. Sectioned otoliths were far superior to all other structures in all criteria: marks were clearest, reader confidence was highest, agreement was 100% both within and between readers, and both fish size and structure size increased significantly with presumed age. Consequently, we recommend that sectioned otoliths be the preferred structure for determining the age of spotted seatrout.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Annual otolith incremnet deposition has not been validated for spotted seatrout populations north of Florida. To validate the marks on sectioned otoliths of Chesapeake Bay spotted seatrout, a ...size-stratified subsample (n = 683) was randomly selected from a total of 2763 fish collected
from June 1996 to March 1999. Monthly marginal increment frequency plots and monthly frequency of 0 marginal increment plots showed that presumed annual marks -interpreted as the distal edge of the translucent margin- formed once a year, during March and April, thus validating
the sectioned otolith method in spotted seatrout of ages 1-5 for the Chesapeake Bay region.
The index-removal method estimates abundance, exploitation and catchability coefficient, given surveys conducted before and after a known removal. The method assumes a closed population between ...surveys. Index-removal has seldom been applied due to its strong assumption of constant survey catchabilities. This work generalizes the method to allow multiple years of data to be incorporated, and the assumptions of the original model to be relaxed. If catchability is constant across years, precision can be improved by analyzing multi-year data simultaneously. Two multiple-year models were developed: the first, 1qIR, assumes constant catchability within and among years; the second, 2qIR, allows catchability to change between surveys within years, but assumes survey-specific catchability constant across years. The new models were tested by Monte Carlo simulation then applied to data from two southern rock lobster (Jasus edwardsii) populations. The 1qIR model produced reasonable estimates in one application, but the 2qIR model was required to produce reasonable estimates for the second population. A likelihood ratio test found 1qIR to be the most parsimonious model, even when, the assumption of constant survey catchability appeared to be violated. In that case, diagnostic plots suggested that the 2qIR model provided the most reliable estimates. However, when the constant catchability assumption is tenable, the 1qIR model offers the greatest precision for parameter estimates. Size- and sex-specific heterogeneity of catchability introduces bias in model estimates. Field experiments were performed to test whether the catchability of small lobster was constant for southern rock lobster during two seasons when fishing occurs. No evidence of heterogeneous catchability was observed during the spring. However, significantly more small lobster were caught in control traps and traps seeded with one large adult male lobster than were caught in traps seeded with one large adult female during the summer, when females are preparing to molt and reproduce in Tasmania. Because heterogeneous catchability occurred during the summer, but not the spring, an index of recruitment based on the catch of lobsters one molt size below legal size might be developed for the spring, however, more sampling is needed to resolve the annual timing of sex- and size-specific catchability changes.
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