UNDERSTANDING PROCESSES IN THE 2007–2013

Distributions of Bering Sea Forage THE MOVING MIDDLE OF THE Forage fish, which include cape- How We Did It biological, and/or climate factors lin, , and the young life stages At sea, we used echosound- on forage fish distributions. Models of and Pacific , ers and trawling to map distri- varied by species but, in general, are food for many fish, birds, and butions of forage fish between temperature, bottom depth, and/or mammals in the Bering Sea. These BASIS (Bering Aleutian prey were important predators are ecologically important, International Survey) survey sta- predictors of forage fish presence commercially valuable, and the focus tions in 2008-2010. The analysis and density. Interestingly, annual of traditional harvest. Evidence sug- was expanded to include existing variables, such as storminess in June gests that forage fish distributions acoustic data from 2006-2007. In and sea ice, were sometimes as or (vertically within the 2008, age-0 pollock were primar- more predictive than local condi- and horizontally across the Bering ily found in the surface water, less tions at a station. Sea) can change from year to year, than 35 m deep (Figure 1). In both and yet we don’t fully understand 2009 and 2010, highest densities Why We Did It why. Knowing that climate change were found in dense schools in the Environmental conditions (e.g., may impact the available for midwater, more than 35 m deep temperature, salinity), the avail- forage fish, it is necessary to under- (Figure 2). Both age-0 ability of zooplankton prey, and stand the where, how many, and why and had high densities in continued on page 2 of fish distribution to predict how the surface in 2010 as compared to changes may affect forage fish popu- 2009 (Figures 3 and 4), but no or lations and the predators that count low densities in the midwater. We The Big Picture on them as prey. evaluated the influence of physical, Forage fish are the critical middle of aquatic food webs throughout the world. Fig. 1 Changes in forage fish densities or distribu- tions can affect forage fish recruitment, nesting/breeding success of birds, and/ or movements of fish or predators that are important for commercial or traditional harvest. Understanding how forage fish distribute themselves is critical when evaluating potential impacts of cli- mate change, and to fulfill the requirements of ecosystem-based approaches to management. Our baseline information can inform Bering Sea models that predict biological responses to climate change and improve methodologies for future Acoustic echograms showing differences in vertical distribution of age-0 pollock in 2008, 2009, and 2010. Bottom abundance estimate surveys. depth shown is ~80 m in 2008, ~110 m in 2009, and ~150 m in 2010.

ICHTHYOPLANKTON SURVEYS A component of the BEST-BSIERP Bering Sea Project, funded by the National Science Foundation and the North Pacific Research Board with in-kind support from participants. vulnerability to predators can all and our ability to obtain informa- Sandra Parker-Stetter, University of Washington (UW) influence survival of forage fish. tion on forage fish distributions John Horne, UW Distributions may result from a from existing surveys will also Ed Farley, National Oceanic and Atmospheric Administration, combination of selection of pre- change. A comprehensive analysis Alaska Center ferred conditions and the influ- that included physical, biological, ence of water movement in the and climate factors was needed to The Bering Sea Project is a partnership between Bering Sea. If forage fish vertical understand what affects forage fish the North Pacific Research Board’s Bering Sea Integrated Ecosystem Research Program and the or horizontal distributions change distributions. National Science Foundation’s Bering Ecosystem with environmental conditions, Study. www.nprb.org/beringseaproject then food availability for predators

Fig. 2 Fig. 3

Distribution of age-0 pollock in the surface (left) and midwater (right) Distribution of age-0 Pacific cod in the surface waters in 2009 (left) in 2009. Larger dots show higher densities. Bottom temperature (ºC) and 2010 (right). Larger dots show higher densities. High densities was an important predictor of midwater pollock density and is shown of age-0 Pacific cod were observed in 2010 in regions that had low on the midwater figure (red is warmest). Although there were few age-0 densities in 2009. pollock in the surface zone in 2009, there were regions of high densities in the midwater zone. Bottom temperature data courtesy of Bob Lauth (NOAA-AFSC).

Fig. 4 Sandra Parker-Stetter Forage fish, , and jellyfish from a surface trawl catch on the R/V Oscar Distribution of capelin in the surface waters in 2009 (left) and 2010 (right). Dyson in 2010. Larger dots show higher densities. Capelin were found in the same regions in both years, but densities were higher and more continuous along tran- sects in 2010.

ICHTHYOPLANKTON SURVEYS A component of the BEST-BSIERP Bering Sea Project, funded by the National Science Foundation and the North Pacific Research Board with in-kind support from participants.