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Spatial Patterns of Arrowtooth Flounder

Figure 1, see caption
Figure 1.  Proportional numbers of walleye pollock found in arrowtooth flounder stomachs at sampled trawl stations in the eastern Bering Sea during summer 2007.  Small dots indicate stations where sampled arrowtooth flounder stomachs contained no pollock.

A new postdoctoral project to analyze spatial patterns of arrowtooth flounder (Atheresthes stomias) population growth, predation, and dynamic habitat characteristics in the eastern Bering Sea (EBS) was started in October 2007. Multiple lines of evidence suggest that changes in the EBS climate are leading to distributional shifts and changes in recruitment of fish populations. For example, the estimated biomass of arrowtooth flounder has quadrupled since the early 1980s in the EBS, in contrast to other groundfish species there.

Recently, recommended catches for EBS walleye pollock (Theragra chalcogramma) have been reduced, in part due to concerns about the growing threat of arrowtooth flounder predation on juvenile pollock. Thus, one goal of the study is to improve our understanding of the impact of arrowtooth flounder to commercial fisheries in the EBS. To meet this goal, physical and biological habitat characteristics, specifically dynamic characteristics associated with water temperature and foraging, that are correlated with arrowtooth flounder biomass trends at individual trawl stations sampled in the EBS are being identified, and spatial variations in arrowtooth flounder diet and length classes analyzed.Early data exploration has shown that the distribution of arrowtooth flounder is extremely sensitive to bottom temperatures; they are rarely found in waters with bottom temperatures colder than 0C. Annual changes in arrowtooth flounder distribution are negatively correlated with the extent of the cold pool of bottom water over the EBS shelf, thereby potentially affecting their overlap with prey, such as juvenile pollock.

Additional data exploration has indicated that while increasing in overall biomass, arrowtooth flounder have expanded their range to the northwest and that this expansion has been dominated by larger individuals. In addition, consumption of pollock by arrowtooth flounder appears to be greatest in the northwest portion of their range (Fig. 1). This analysis will provide information about the potential for arrowtooth flounder to further increase their distribution and abundance in the EBS and help to predict future responses to climate and fisheries management actions.

By Stephani Zador

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