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Second International Symposium on the Effects of Climate Change on the World's Oceans (cont.)

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Apr-May-June 2012
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Anne Hollowed gave an oral presentation titled "Modeling Fish and Shellfish Responses to Climate Change: Trade-offs in Model Complexity." She recognized that the marine science community has applied numerous techniques to project the effects of climate change on marine ecosystems and the responses of fishery dependent communities to these ecosystem changes.

Considerable progress has already been made in coupling nutrient, phytoplankton and zooplankton into physical models using the existing Global Climate Model and Earth System Models. There is considerable interest in extending this capability to include commercially exploited fish and shellfish. Fish and shellfish exhibit complex responses to changes in the distribution and abundance of prey, competitors, and predators. Incorporation of these complex processes will come at a high computational cost.

She compared the costs and benefits of different methods for modeling fish and shellfish responses to climate change on a global scale. A variety of different modeling approaches were considered including: minimally realistic trophic energy transfers, size spectrum models, single species and multispecies stock assessment models, whole ecosystem food web models, spatially explicit coupled-biophysical models (e.g. NEMURO-FISH), and spatially explicit gradient tracking models.

Paul Spencer and Teresa A'mar also gave oral presentations in Session 4. Their abstracts follow:


Management strategy evaluation for the Gulf of Alaska walleye pollock (Theragra chalcogramma) fishery: How persistent are the environmental-recruitment links?  (Z. Teresa A'mar and Martin W. Dorn)

A management strategy evaluation for the Gulf of Alaska walleye pollock fishery was performed based on data through 2005. One of the sources of error and uncertainty in the previous analysis included links between environmental indices and age-1 recruitment. The results suggested that winter precipitation and summer sea surface temperature (SST) had a positive impact and spring and autumn SST had a negative impact on recruitment when the normalized indices were included to account for some recruitment variability; these findings matched results from other studies.

It is useful to reexamine these environmental recruitment relationships after new data have been collected to assess how robust they are. This study includes six additional years of stock assessment and environmental data and examines whether the environmental recruitment links, suggested previously, have persisted. This study also extends the previous operating model configurations by considering additional local- and basin-scale environmental covariates which were available for the historical period and can be obtained or calculated from downscaled IPCC model output. Environmental recruitment relationships were evaluated with cross-validation outside of the operating model, and a set of parsimonious models which explained a considerable amount of the recruitment variance were included in the operating model to generate future recruitment based on IPCC model output.


Projected spatial distributions for eastern Bering Sea arrowtooth flounder under simulated climate scenarios, with implications for predation  (Paul D. Spencer, Nicholas A. Bond, Anne B. Hollowed and Franz J. Mueter)

Empirical relationships between the extent of the eastern Bering Sea shelf summer "cold pool" (bottom water < 2°C) and maximum sea ice extent and sea level pressure allow projections of cold pool area from global climate model simulations. The present study uses these projections to predict future spatial distributions of arrowtooth flounder in the Bering Sea, assuming these distributions are controlled primarily by the cold pool.

An inverse relationship between the area occupied by arrowtooth flounder and the cold pool area has been observed from 1982 to 2010. Small cold pool areas and large arrowtooth flounder areas were observed in the warm years of 2003-05, whereas the colder years of 2006-10 have exhibited larger cold pool areas and smaller arrowtooth flounder areas. Projections of cold pool area from 2010 to 2050 based upon 15 International Panel on Climate Change (IPCC) model runs show a wide range of variability but an overall decreasing trend, resulting in the median arrowtooth flounder area across the 15 IPCC models increasing from 140,000 km2 in 2010 to 160,000 km2 in 2050.

Changes in the spatial distribution of arrowtooth flounder relative to other species can affect their consumption of prey, of which age-1 and -2 walleye pollock comprise a large portion. The relationship between the area occupied within various EBS subareas and cold pool extent will be examined for arrowtooth flounder and walleye pollock in order to project future spatial distributions and assess the potential impact of arrowtooth predation on pollock.

By Anne Hollowed, Teresa A'mar, and Paul Spencer
 

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