Predicted growth (<i>g</i>⋅<i>g</i>⁻¹⋅<i>d</i>⁻¹) of juvenile walleye pollock interpolated over the range of observed temperatures and prey energy density values across both 2005 and 2010, providing a continuous scale of growth over a broad range of possible environmental and biological scenarios.

<p>The observed fish energy density was higher in 2010 (<i>v₂₀₁₀</i> = 5.29 kJ⋅g⁻¹; used in plot shown); therefore this interpolation demonstrates the range of predicted growth for fish with high energy density. Temperatures included 0–16°C to show possible range under variable climate conditions. The dashed rectangle encompasses the range of temperatures and prey energy density values observed in 2005; solid rectangle encompasses values in 2010. Points are shown for average temperature and prey energy density conditions in 2005 and 2010. Predicted growth above 15°C was not possible (black) because the bioenergetics model has a temperature threshold of 15°C.</p

Summary of sensitivity analyses for the IBM model in 2005 and 2010 showing the minimum (min), mean, and maximum (max) growth potential and depth (m) over all stations.

<p>Base values are predicted growth (<i>g</i>⋅<i>g</i>⁻¹⋅<i>d</i>⁻¹) and depth (m) of juvenile pollock from the base model scenarios (<i>W</i> = 2.5 g, zooplankton prey distributed according to vertical profiles). All other values are predicted changes in growth and depth. Negative changes in depth indicate a shallower distribution; positive values indicate a deeper distribution. Weight is a constant value applied across all station, so varying the parameter acts as a scalar and results in similar spatial patterns across the area. The effect of applying a uniform distribution of zooplankton prey with depth varies across stations.</p

Predicted growth (<i>g⋅g</i>⁻¹⋅d⁻¹) of juvenile walleye pollock from the bioenergetics model.

<p>Top panel (a and b) shows growth under the base model scenarios for 2005 and 2010 (<i>W</i> = 2.5 g, Temp = average temperature in upper 30 m,  = 1.0,  = prey energy density,  = 3.92 kJ⋅g⁻¹;  = 5.29 kJ⋅g⁻¹). Middle panel (c and d) shows changes in predicted growth when temperature is increased by 1 standard deviation (SD). Predicted growth could not be estimated at one station in 2005 (c) in the inner domain under increased temperatures because the water temperature in the upper 30 m was greater than 15°C (<i>T_cm</i> = 15°C in the model). Lower panel (e and f) shows changes in predicted growth when prey energy density is increased by 1 SD. Spatial plots of predicted growth when parameters are decreased by 1 SD are not shown, but can be visualized by subtracting the anomalies (lower two panels) from the base scenario plots (top panel).</p

Conceptual figure of the spatial relationship between juvenile fish abundance (yellow) and zooplankton prey availability (blue).

<p>Where these areas overlap (green), juvenile fish are predicted to have higher growth rates and increased survival. Under warm climate conditions, there is reduced spatial overlap between juvenile fish and prey availability, resulting in lower overwinter survival and recruitment success to age-1. In colder conditions, increased spatial overlap between juvenile fish and prey availability results in increased overwinter survival and recruitment to age-1.</p

Parameter definitions and values used in the bioenergetics model to estimate maximum growth potential (<i>g</i>⋅<i>g</i>⁻¹⋅<i>d</i>⁻¹) of juvenile walleye pollock.

<p>Parameters were used as inputs to the bioenergetics model described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084526#pone.0084526-Ciannelli1" target="_blank">[16]</a>.</p><p>^a<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084526#pone.0084526-Holsman1" target="_blank">[25]</a>; <i>^b</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084526#pone.0084526-Ciannelli1" target="_blank">[16]</a>.</p

Main prey taxa included in the models for 2005 and 2010.

<p>Prey items cumulatively accounting for at least 90% of the diet by % volume and individually accounting for at least 2% of the diet by % volume were included. Prey taxa common to both years are shown in <b>bold</b>.</p><p><i>Neocalanus plumchrus</i> was not identified in the 2010 bongo data, but did occur in the Juday data (small-mesh; not quantitative for large zooplankton taxa). Due to the absence in the bongo data, <i>N. plumchrus</i> was excluded from further analyses.</p

Difference in predicted growth (<i>g</i>⋅<i>g</i>⁻¹⋅<i>d</i>⁻¹) of juvenile walleye pollock between the bioenergetics model and the IBM for 2005 (a) and 2010 (b).

<p>Areas of positive differences indicate where maximum growth potential from the bioenergetics model was higher than predicted growth from the IBM.</p

Summary of sensitivity analyses for the bioenergetics model in 2005 and 2010 showing the minimum (min), mean, and maximum (max) growth potential over all stations.

<p>Base values are predicted maximum growth potential (<i>g⋅g</i>⁻¹⋅<i>d</i>⁻¹) of juvenile pollock from the base model scenarios (<i>W</i> = 2.5 g, Temp = average temperature in upper 30 m,  = 1.0,  = prey energy density,  = 3.92 kJ⋅g⁻¹;  = 5.29 kJ⋅g⁻¹). All other values denote the change in growth rate resulting from indicated changes in inputs; therefore (−) effects indicate that varied conditions resulted in lower predicted growth and vice versa. Pooled standard deviations (SDs) for each parameter were calculated across stations after removing the annual means. <i>W</i> and are constant values applied across all station, so changes (±1 SD) act as a scalar and result in similar spatial patterns across the area. Temperature and vary across stations.</p

Return of warm conditions in the southeastern Bering Sea: Phytoplankton - Fish

<div><p>In 2014, the Bering Sea shifted back to warmer ocean temperatures (+2 ^oC above average), bringing concern for the potential for a new warm stanza and broad biological and ecological cascading effects. In 2015 and 2016 dedicated surveys were executed to study the progression of ocean heating and ecosystem response. We describe ecosystem response to multiple, consecutive years of ocean warming and offer perspective on the broader impacts. Ecosystem changes observed include reduced spring phytoplankton biomass over the southeast Bering Sea shelf relative to the north, lower abundances of large-bodied crustacean zooplankton taxa, and degraded feeding and body condition of age-0 walleye pollock. This suggests poor ecosystem conditions for young pollock production and the risk of significant decline in the number of pollock available to the pollock fishery in 2–3 years. However, we also noted that high quality prey, large copepods and euphausiids, and lower temperatures in the north may have provided a refuge from poor conditions over the southern shelf, potentially buffering the impact of a sequential-year warm stanza on the Bering Sea pollock population. We offer the hypothesis that juvenile (age-0, age-1) pollock may buffer deleterious warm stanza effects by either utilizing high productivity waters associated with the strong, northerly Cold Pool, as a refuge from the warm, low production areas of the southern shelf, or by exploiting alternative prey over the southern shelf. We show that in 2015, the ocean waters influenced by spring sea ice (the Cold Pool) supported robust phytoplankton biomass (spring) comprised of centric diatom chains, a crustacean copepod community comprised of large-bodied taxa (spring, summer), and a large aggregation of midwater fishes, potentially young pollock. In this manner, the Cold Pool may have acted as a trophic refuge in that year. The few age-0 pollock occurring over the southeast shelf consumed high numbers of euphausiids which may have provided a high quality alternate prey. In 2016 a retracted Cold Pool precluded significant refuging in the north, though pollock foraging on available euphausiids over the southern shelf may have mitigated the effect of warm waters and reduced large availability of large copepods. This work presents the hypothesis that, in the short term, juvenile pollock can mitigate the drastic impacts of sustained warming. This short-term buffering, combined with recent observations (2017) of renewed sea ice presence over southeast Bering Sea shelf and a potential return to average or at least cooler ecosystem conditions, suggests that recent warm year stanza (2014–2016) effects to the pollock population and fishery may be mitigated.</p></div

Fish catch.

<p>Catch (circles) of age-0 pollock (number h^-1) as determined from oblique and surface trawling in 2015 (A) and 2016 (C). X indicates a trawl conducted but no catch. Heat map presents bottom temperatures (^oC) over the southeast and Northern Bering Sea shelves. Cold Pool denoted where bottom temperatures <2 ^oC (blue color ramp). Catches of age-0 pollock were low over the southern shelf in 2015, with higher catches that year in the vicinity of the Cold Pool (<2 ^oC). In 2016 trawl catches of age-0 pollock over the southern shelf were higher than in 2015 and reduced in the north relative to the southern shelf. Acoustic backscatter (NASC, m²/nmi²) estimates in 2015 (B) and 2016 (D) indicate higher backscatter in the Cold Pool relative to the shelf in both years.</p