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Status of Stocks & Multispecies Assessment Program

International Symposium on the Effects of Climate Change on the World’s Oceans(continued)

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Spring 2015
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Carey McGilliard presented "Quantitative tools for predicting fish population dynamics and evaluating alternative harvest strategies under climate change for marine fisheries in Alaska"

Recruitment and other population processes of groundfish in the Gulf of Alaska and Bering Sea-Aleutian Islands have well-documented linkages to indices of environmental forcing and variability, such as the Pacific Decadal Oscillation (PDO), sea surface temperature and height, and sea ice extent. Quantifying scientific uncertainty due to future climate conditions and identifying management strategies that are most robust to climate uncertainty are, therefore, key parts of providing scientific advice to fisheries managers in these regions. Management Strategy Evaluation (MSE) is a powerful simulation tool for such explorations. In an MSE, fish population dynamics, and the process of harvesting, sampling fish populations, assessing the status of fish populations, and specifying and implementing assessment-based management is simulated over a number of years. Linkages between fish population dynamics and environmental variables can be incorporated into MSEs. An MSE was developed with application to Alaska groundfish species to examine the performance of an alternative management strategy that quantifies scientific uncertainty, including uncertainty about future climate conditions, and incorporates estimates of the magnitude of uncertainty into harvest regulations. Results were compared to long-term outcomes of continuing to use the current harvest regulations. The probability of extinction, or the probability of the population falling below a biomass threshold, long-term catch, and variability in catch were calculated. Future research will expand the population dynamics in the analyses to include multiple species, linked through technical interactions.

Paul Spencer presented "How might environmentally-driven changes in the distribution of arrowtooth flounder affect eastern Bering Sea walleye pollock predation mortality and population projections?"

Arrowtooth flounder (Atheresthes sp.) are an important predator of juvenile walleye pollock in the eastern Bering Sea shelf, and their avoidance of the summer “cold pool” (bottom water ≤ 2°C) has resulted in variability in their spatial distribution. Spatially-resolved predation mortality rates were estimated within the age-structured walleye pollock stock assessment population model, based upon spatial information on diet and abundance (from trawl surveys). Estimates of predation mortality attributed to arrowtooth flounder have increased due to the increase in arrowtooth flounder abundance. Empirical relationships between the extent of the eastern Bering Sea shelf summer “cold pool” and maximum sea ice extent and sea level pressure allow projections of cold pool area from global climate model simulations and can be used to predict future spatial distributions of arrowtooth flounder and pollock. Projections of cold pool area to 2050 based upon 15 International Panel on Climate Change model runs show a wide range of variability but an overall decreasing trend, resulting in a projected increasing trend in the area occupied by arrowtooth flounder. The projected impact of arrowtooth flounder predation upon walleye pollock is expected to be small because the changes in spatial distributions largely affect areas with limited juvenile pollock abundance. However, increased predation would be expected if arrowtooth flounder shift their distribution northward. An age-structured population model will be used to evaluate how projections of pollock abundance and yield are affected by information on projected spatial distributions and predator-prey overlap.

Anne Hollowed presented "A framework for evaluating IPCC AR5 projected climate change impacts on Bering Sea (AK) fish and fisheries"

Climate change is a global issue affecting marine ecosystems and species that span multiple international boundaries. To address this challenge scientists have developed global climate and earth system models (GCM and ESM, respectively) to project future conditions. These models are being tested regionally and discussed globally. In several regions, GCM or ESM output has been used to force regional ocean circulation models with coupled nutrient, phytoplankton, and zooplankton dynamics; however, the methods differ regionally and internationally. In preparation for the next IPCC assessment, scientists have initiated an international collaborative effort to provide quantitative estimates of the status and trends of commercial fish and fisheries worldwide by 2019. Of particular interest are models that extend regional models to include projections of climate impacts on the distribution and abundance of commercial fish and fisheries. A variety of different models could be employed ranging from minimally realistic single-species climate enhanced stock projection models with detailed treatment of process error, measurement error and model misspecification to whole ecosystem models with complex treatment of ecosystem interactions and only modest treatment of uncertainty. The proliferation of modelling improvements and global projections creates a dilemma for regional ocean modelers and fisheries scientists as the number of possible permutations that could be explored rapidly can become too large to manage. Identifying a reasonable range of representative futures (with sufficient contrast in scenarios) and biological models allows analysts to compare projections and report on the relationship between model complexity, efficiency, and the computational costs of increased ecological realism in models. This paper presents a proof-of-concept implementation of a Management Strategy Evaluation (MSE) framework for the eastern Bering Sea for evaluating the performance of resource management strategies under different climate change scenarios.

Ivonne Ortiz presented "Fish movement and distribution drivers in a climate to fisheries model for the Bering Sea"

We use results of multi-year simulations of an end-to-end model including oceanography, lower trophic levels, fish dynamics and fisheries (FEAST model), and compare them to survey data to evaluate fish movement, distribution, and responses to environmental conditions. In particular, we focus on results for walleye pollock, Pacific cod, and arrowtooth flounder. Fish move following gradients based on potential growth (in weight) and least predation mortality (numbers of fish), with distributions differing by age and season depending on their diet, prey availability and vulnerability as prey. Temperature limitation is intrinsic to the underlying bioenergetics regulating fish growth. The model closely reproduces the extent of the cold pool in the eastern Bering Sea shelf (waters less than 2ºC), a feature shown to influence the latitudinal and longitudinal distribution of walleye pollock and arrowtooth flounder. Our results show fish responding to the extent of the cold pool (warm and cold conditions) and showing a distribution pattern similar to that from the survey, but differing in the marginal distribution and or center of distribution. We focus on the sources of error and potential factors causing the discrepancies, such as distribution of prey fields, feedback to the lower trophic levels, and the number of fish removed by fisheries. Challenges going forward include refining the underlying seasonal dynamics of zooplankton and prey preferences in diets, but most importantly—improving recruitment and implementing a fleet dynamics model to forecast the distribution fishing effort.


Submitted by Alan Haynie, Anne Hollowed, Carey McGilliard, Ivonne Ortiz, and Paul Spencer

 

 

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