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Pacific herring (Clupea pallasii) plays an important and multifaceted role in the Northeast Pacific as a forage fish in coastal ecosystems, target species for commercial fisheries, and culturally significant subsistence resource for coastal communities. This study comparatively evaluated herring fisheries management strategy performance relative to ecological and socioeconomic objectives. Management strategy evaluation employed a mass-balanced ecosystem operating model and accounted for parameter uncertainty, stock assessment error, and strategy implementation error through Monte Carlo resampling. Results revealed a notable trade-off between stable herring catches and high biomasses of herring and several predators. Herring biomass control point values influenced this trade-off more than harvest control rule form. All British Columbia and Alaska strategies yielded similar ecological and socioeconomic impacts relative to the unfished herring baseline. Precautionary strategies recommended for forage fish combined high ecosystem benefits and socioeconomic costs. Reducing fishing mortality fourfold within an existing strategy suggested a possible compromise solution to this trade-off. However, ecological impacts of all strategies were sensitive to operating model parameter uncertainty, stock assessment error, and strategy implementation error, with the potential for undesirable ecosystem states across all strategies. This study suggests trade-offs among management objectives should be considered in pursuing ecosystem-based fisheries management for forage fish. [ABSTRACT FROM AUTHOR]

Bycatch in fisheries can have profound effects on the abundance of species with relatively low resilience to increased mortality, can alter the evolutionary characteristics and concomitant fitness of affected populations through heritable trait-based selective removals, and can alter ecosystem functions, structure and services through food web trophic links. We challenge current piecemeal bycatch management paradigms, which reduce the mortality of one taxon of conservation concern at the unintended expense of others. Bycatch mitigation measures may also reduce intraspecific genetic diversity. We drew examples of broadly prescribed 'best practice' methods to mitigate bycatch that result in unintended cross-taxa conflicts from pelagic longline, tuna purse seine, gillnet and trawl fisheries. We identified priority improvements in data quality and in understanding ecological effects of bycatch fishing mortality to support holistic ecological risk assessments of the effects of bycatch removals conducted through semi-quantitative and model-based approaches. A transition to integrated bycatch assessment and management that comprehensively consider biodiversity across its hierarchical manifestations is needed, where relative risks and conflicts from alternative bycatch management measures are evaluated and accounted for in fisheries decision-making processes. This would enable managers to select measures with intentional and acceptable tradeoffs to best meet objectives, when conflicts are unavoidable. [ABSTRACT FROM AUTHOR]

This paper analyzes the trophic role of Pacific herring, the potential consequences of its depletion, and the impacts of alternative herring fishing strategies on a Northeast Pacific food web in relation to precautionary, ecosystem-based management. We used an Ecopath with Ecosim ecosystem model parameterized for northern British Columbia (Canada), employing Ecosim to simulate ecosystem effects of herring stock collapse. The ecological impacts of various herring fishing strategies were investigated with a Management Strategy Evaluation algorithm within Ecosim, accounting for variability in climatic drivers and stock assessment errors. Ecosim results suggest that herring stock collapse would have cascading impacts on much of the pelagic food web. Management Strategy Evaluation results indicate that herring and their predators suffer moderate impacts from the existing British Columbia harvest control rule, although more precautionary management strategies could substantially reduce these impacts. The non-capture spawn-on-kelp fishery, traditionally practiced by many British Columbia and Alaska indigenous peoples, apparently has extremely limited ecological impacts. Our simulations also suggest that adopting a maximum sustainable yield management strategy in Northeast Pacific herring fisheries could generate strong, cascading food web effects. Furthermore, climate shifts, especially when combined with herring stock assessment errors, could strongly reduce the biomasses and resilience of herring and its predators. By clarifying the trophic role of Pacific herring, this study aims to facilitate precautionary fisheries management via evaluation of alternative fishing strategies, and thereby to inform policy tradeoffs among multiple ecological and socioeconomic factors. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of estimation of fisheries Maximum Sustainable Yield (MSY) reference points using an ecosystem model built for Mille Lacs Lake, the second largest lake within Minnesota, USA. Data from single-species modelling output, extensive annual sampling for species abundances, annual catch-survey, stomach-content analysis for predatory-prey interactions, and expert opinions were brought together within the framework of an Ecopath with Ecosim (EwE) ecosystem model. An increase in the lake water temperature was observed in the last few decades; therefore, we also incorporated a temperature forcing function in the EwE model to capture the influences of changing temperature on the species composition and food web. The EwE model was fitted to abundance and catch time-series for the period 1985 to 2006. Using the ecosystem model, we estimated reference points for most of the fished species in the lake at single-species as well as ecosystem levels with and without considering the influence of temperature change; therefore, our analysis investigated the trophic and temperature effects on the reference points. The paper concludes that reference points such as MSY are not stationary, but change when (1) environmental conditions alter species productivity and (2) fishing on predators alters the compensatory response of their prey. Thus, it is necessary for the management to re-estimate or re-evaluate the reference points when changes in environmental conditions and/or major shifts in species abundance or community structure are observed. [ABSTRACT FROM AUTHOR]

The recovery of whale populations from historical depletion may have the potential to noticeably affect Northeast Pacific ecosystems and fisheries. Surplus production models based on whaling catch records were used to reconstruct the historical abundances of five large whale species in the waters surrounding Haida Gwaii, British Columbia. The results suggest that the local abundances of all five species were vastly higher before the onset of modern whaling. A comparison of ecosystem models representing the states of the local marine food web before and after full whale recovery indicates that abundant whales could consume large proportions of the annual production of their principal prey, ranging up to 87% for Pacific herring ( Clupea pallasii) and 72% for piscivorous rockfish ( Sebastes spp.). Dynamic modelling of the food web effects of whale recovery, including simulations of simultaneous top-down and bottom-up forcing and a Monte Carlo sensitivity analysis, revealed noticeable (∼6-12%) top-down effects on Pacific herring biomass owing to increased predation by humpback and fin whales. However, these effects cannot explain the magnitude of recent declines in local herring biomass. The dynamic modelling results also suggest that top-down effects of whale recovery could result in reduced biomasses of large rockfish as a result of predation by sperm whales, as well as potential cascading effects on many demersal fish groups. These findings have numerous practical implications for ecosystem-based fisheries management and whale conservation strategies in Northeast Pacific waters. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the ecological plausibility of the “krill surplus” hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the “krill surplus” phenomenon and whaling effects on the food web in the years 1900–2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the “krill surplus” hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975–1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web. [ABSTRACT FROM AUTHOR]

Abstract: An ecosystem model was created for the Hudson Bay region, Canada, for 1970–2009, aiming to identify ecosystem linkages while bringing together research from diverse sources. The model presented here in detail includes 40 functional groups. Using the Ecopath with Ecosim (EwE) modelling framework we are able to provide estimates for previously unknown parameters such as the biomass of fish species. In addition to providing a comprehensive overview of the trophic dynamics within the system, temporal simulations mimic the changes known to occur in the region. The model is fitted to catch data for the Hudson Bay region, along with environmental drivers (sea surface temperature and ice cover). Declines in sea ice and increases in the spring bloom facilitate a shift from benthic to pelagic pathways in lower trophic levels of the model. Polar bears, bearded seals and eastern Hudson Bay belugas demonstrate the greatest declines due to hunting mortality. Additional model scenarios testing the model sensitivity to hunting and environmental pressures indicate higher trophic level organisms (marine mammals) are more responsive to hunting pressures, while lower trophic levels (benthos, zooplankton) are primarily influenced by climate drivers. While marine mammals are the most well studied, the region lacks comprehensive assessments on fish and other mid trophic level organisms. This model captures many patterns present in the system, while identifying gaps in existing data for future research and provides the first step for future research simulating climate change and its impacts on the Hudson Bay ecosystem. [Copyright &y& Elsevier]

Abstract: Simulations testing the future impacts of harvest and climate change to the Hudson Bay marine ecosystem were created utilizing an existing Ecopath with Ecosim model (Hoover et al., 2013). Building on past simulations depicting known changes to the region, a suite of future scenarios was constructed to include a variety of climate change and harvest levels. Previously identified ecosystem shifts favoring pelagic species (zooplankton, planktivorous fish) over benthic species (benthos, benthic feeding fish), are further exaggerated under future climate scenarios. Environmental forcing was incorporated to mimic the declines in sea ice, and increases in temperature causing shifts in the food web from an ice algae–benthos–benthic fish pathway to a spring bloom–zooplankton–planktivorous fish dominated ecosystem. Future simulations indicate some stocks are unable to sustain current harvest levels until the end of the future simulations (2069), and may be extirpated (narwhal, eastern Hudson Bay beluga, polar bears, and walrus). Larger populations of marine mammals (ringed seals and western Hudson Bay beluga) are identified to increase in biomass even under extreme harvest and climate scenarios (a high future climate scenario coupled with a doubling in harvest rates). Harvest mortality is highlighted as an important stressor for some marine mammal stocks and should be investigated further when setting future harvest or conservation targets. [Copyright &y& Elsevier]

In less than a decade after being first noticed in 2005, Zebra mussels ( Dreissena polymorpha ) became fully established in Mille Lacs Lake, Minnesota, USA. To explore the ecosystem-wide impact of this invasion in the premier walleye ( Sander vitreus ) lake, an ecosystem model with 51 functional groups was built using Ecopath and Ecosim (EwE) modelling suite. The model which represents the 1985 ecosystem condition of the lake was tuned to observed time series of fish abundance and fisheries catch data from 1985 to 2006. Zebra mussels were setup with a high initial biomass, and an adequate fishing pressure was applied on it with an aim to neutralize the effect on ecosystem caused by the inclusion of the mussels. At the onset of 2005 (the first year the mussels were observed in the lake), the fishing pressure was released with different trajectories so that we could mimic the non-nutritional challenges the species could have faced during its irruption in the lake. The fitted model was simulated to the year 2036 (30 years). To enhance the credibility of the model prediction, we compared the prediction with the available field data from 2007 to 2012: the model successfully forecasted most of the changes seen in the lake after the period of fitted-data. The simulation results indicated system-wide collapse of major predators including walleye due to the bottom-up trophic control as zebra mussels efficiently filter out the phytoplankton from the system. The result also indicated that the population of zebra mussels in the lake stabilized after attaining the maximum density within few years of the invasion. Furthermore, the model predicted a significant boost in smallmouth bass ( Micropterus dolomieui ) population when the mussels were incorporated in the diet of crayfish; remarkably, the predatory pressure did not cause a large impact on zebra mussels biomass. Our capability to predict the response of Mille Lacs Lake to zebra mussels invasion would largely depend on the dynamics of plankton groups, the response of juveniles of higher trophic fish species like walleye to the changing dynamics of plankton groups, and the response of yellow perch ( Perca flavescens ) population—a major prey in the system. [ABSTRACT FROM AUTHOR]