Juvenile Walleye Pollock Research Articles

Effects of Temperature on the Gastric Evacuation Rate and Maintenance Ration of Adult Pointhead Flounder Cleisthenes pinetorum

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169‐day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q10) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g−1 day−1 at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures.

Estimating the Catch Efficiency of a Framed Midwater Trawl under Different Sampling Conditions Using an Acoustic Method

The authors have developed a method to estimate the catch efficiency of sampling gear using acoustic information. Since different sampling conditions will cause different sampling results, it is necessary to know more details about catch efficiency to quantitatively catch juvenile fish. In this study, we estimated the catch efficiency of a framed midwater trawl (FMT) for juvenile walleye pollock, and investigated differences in the catch efficiency of the FMT due to various influencing factors. To clarify the effects of different sampling conditions on catch efficiency, we investigated changes in catch efficiency by survey time (daytime and nighttime), net color (black and cyan), and towing speed (2 kt, 3 kt, 4 kt). It was quantitatively shown that the catch efficiency was higher at nighttime than during the daytime, the catch efficiency of black net was higher than that of cyan net, and the catch efficiency was higher at the faster towing speed. Comparing the estimated catch efficiency under different conditions, we found that survey time was the most important influencing factor.

Shifting fish distributions impact predation intensity in a sub‐Arctic ecosystem

An abundance of studies in marine systems have documented species range shifts in response to climate change, and many more have used species distribution models to project species ranges under future conditions. However, there is increasing interest in moving beyond a single‐species focus to understand how species redistribution alters ecosystem dynamics via changes in trophic interactions. We employed spatiotemporal models to characterize decadal‐scale changes in spatial overlap between the distribution of juvenile walleye pollock Gadus chalcogrammus and the distributions of four of its groundfish predators: arrowtooth flounder Atheresthes stomias, Pacific cod Gadus macrocephalus, Pacific halibut Hippoglossus stenolepis and adult walleye pollock. These fishes represent ecologically and commercially important species in a rapidly changing sub‐Arctic ecosystem, the eastern Bering Sea, Alaska, USA. We then examined whether changes in spatial overlap corresponded to changes in predation, using spatiotemporal models of predator stomach contents. We found marked shifts in spatial overlap between juvenile pollock and two predators (arrowtooth flounder and Pacific halibut) over 34 years, with changes in overlap corresponding to increases in population‐scale predation pressure. By contrast, we did not find clear relationships between spatial overlap and predation for Pacific cod and adult pollock, the two predators for which juvenile pollock constitute a much smaller diet proportion. Our findings highlight the complexity of predicting predation dynamics for generalist marine species and suggest a need for better process‐based methods for understanding the potential future ecological impacts of coupled species range shifts. However, simple metrics of spatial overlap between relatively specialized predators and their prey offer promise as a means to integrate predictions from species distribution models into ecosystem‐based fisheries management.

Some data about distribution of fry saffron cod <i>Eleginus gracilis</i> and walleye pollock <i>Theragra chalcogramma</i> on the west coast of Кamchatka and species composition in the catches of midwater trawl with a small-meshed insertion

Data of trawl surveys for the period 2010–2017 revealed distribution of fry saffron cod in vicinity of river outlets, while juvenile walleye pollock was dictributed either near the shore or over the deepwater area in the southern part of shelf. In 2017 aggregations of saffron cod individuals with the body length 29.4–70.5 mm (averaged 52.9 mm) were observed in the area between 52° and 53°N at the depth range 14–195 m. The aggregation densities were maximum at the plots of the highest salinity, temperature and turbidity of the water and higher chlorophyll- a concentration. Principal catches of juvenile walleye pollock were in the area between 53° and 54°N at the depth from 20 to 195 m (averaged 68.2 mm). The aggregation densities of juvenile walleye pollock were maximal at the plots of higher salinity and oxygen concentrations. The concentration of chlorophyll- a was mediate at these plots, comparing to values in the area observed. The body length of the fry varied from 44.5 to 74.6 mm (57.8 mm averaged). Besides juvenile saffron cod and walleye pollock, adult and juvenile individuals of 11 bottom and demersal-pelagic species were found in the catches of the midwater trawl.

In situ broadband acoustic measurements of age-0 walleye pollock and pointhead flounder in Funka Bay, Hokkaido, Japan

Measurements of the broadband acoustic backscattering from fish should improve acoustic discrimination between species. The pulse compression processing of broadband systems can be used to measure acoustic backscattering with high range resolution and improve signal-to-noise ratio. This may increase opportunities for in situ target strength (TS) measurements, the preferred method of collecting TS data. To evaluate the availability of TS spectra for acoustic discrimination, three Simrad EK80 wideband transceivers and split-beam transducers of 70, 120, and 200 kHz were used to collect in situ frequency responses of TS from age-0 juvenile walleye pollock and pointhead flounder, a swimbladderless flat-fish, distributed in and around Funka Bay, Hokkaido, Japan. The single echoes were extracted from backscattering data, and the TS spectra of the two species were obtained. However, processing of the broadband acoustic data is under discussion. To ensure the reliability of our data, the TS spectra of standard targets were also calculated. The measured TS spectra of the standard targets were close to the theoretical TS spectra. The individual TS spectra of two species included complex frequency response; however, the mean TS spectrum was relatively stable. The different characteristics of the frequency responses observed for the two species were in good agreement with reported observations. The results available for the acoustic discrimination were similar to the multi-frequency method, which uses two or more single frequencies. The raw TS spectra should aid in not only discriminating between species but also Q3 estimating the size of the fish.

Effects of dietary lipid level on growth performance, feed utilization, fatty composition and antioxidant parameters of juvenile walleye pollock, Gadus chalcogrammus

We evaluated effects of dietary lipid level on growth performance, feed utilization, fatty acid composition, plasma chemistry, and antioxidant responses in juvenile walleye pollock (Gadus chalcogrammus). Two-hundred forty juvenile pollock averaging 4.4 g in weight were randomly distributed between 12 400-L flow-through circular tanks (20 fish per tank). Fish were fed four isonitrogenous experimental diets with crude lipid levels of 8.1%, 12.6%, 16.7%, or 20.8% for 8 weeks. Each diet was assigned to three tanks, and the fish were hand-fed to satiation twice daily. At the end of the trial, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio were increased with increasing dietary lipid up to 16.7%, and then decreased with a further increase in dietary lipid. The hepatosomatic index showed an increasing trend with increasing dietary lipid. The crude lipid content in liver increased with increasing dietary lipid. Saturated fatty acid levels in the muscle and liver decreased, whereas essential fatty acids and polyunsaturated fatty acids in the muscle and monounsaturated fatty acids in the liver increased with increasing dietary lipid. The hematological and antioxidant parameters were not affected by the dietary lipid content. In conclusion, on the basis of a second-order polynomial regression analysis of weight gain, the optimum dietary lipid level for juvenile walleye pollock was estimated to be 15.8%.

Differing prey associations and habitat use suggest niche partitioning by fin and humpback whales off Kodiak Island

FinBalaenoptera physalusand humpbackMegaptera novaeangliaewhales share foraging areas and may compete for the same prey, but little is known about the extent to which they partition prey resources. Visual cetacean surveys and simultaneous acoustic-trawl surveys of prey were conducted around 2 submarine canyons off Kodiak Island, Alaska, in 2004 and 2006. Statistical models were used to examine the associations between sightings of fin and humpback whales and measures of their potential prey and environment. Observations and models indicate that fin whales were disproportionately abundant in areas with the highest observed euphausiid concentrations, while humpback whales were abundant at lower euphausiid concentrations and in areas where juvenile walleye pollock were abundant. Fin whales were abundant in the areas where euphausiid biomass was deepest and in the deepest areas surveyed (>150 m depth). In contrast, humpback whales primarily occurred in shallower areas and near more shallowly distributed euphausiids. The different depth and prey affinities of fin and humpback whales suggest niche and habitat partitioning between these 2 co-occurring species. Abundance models built using acoustic estimates of prey density are a useful tool to further understanding of the abundance, distribution, and behavior of these animals.

Environmental impacts on walleye pollock (Gadus chalcogrammus) distribution across the Bering Sea shelf

Adult and juvenile (age-1) walleye pollock (Gadus chalcogrammus) were sampled by the US NOAA Alaska Fisheries Science Center summer bottom trawl survey in 2010, 2017, 2018, and 2019 in the northeastern and southeastern Bering Sea, with profiles of temperature collected concurrently. Similarly, the Russian Research Institute of Fisheries and Oceanography, Pacific branch, collected adult and juvenile pollock and temperature profiles on summer bottom trawl surveys in the northwestern Bering Sea. Results from these surveys show that adult pollock abundance in recent years (2017, 2018, 2019) has increased in northern regions of the Bering Sea shelf in both the US and Russian sectors. Lower abundances, compared to historic means, were observed in southern regions of the shelf, suggesting the pollock moved directionally from the south to the north. We relate changes in pollock distribution in recent intermediate (2017) and warm, low-ice years (2018–2019) to a prior cold, high-ice year (2010) and describe how these observations relate to our longer time series. We link temperature data from bottom trawl surveys (US and Russian), sea-ice indices (retreat timing and extent), as well as model-based estimates of ocean circulation to changes in pollock distribution and examine potential environmental factors driving the observed changes. Changes in sea-ice and bottom temperature (e.g., reductions in ice extent and shrinking of the cold pool), and changes in circulation (stronger northward currents over the northeastern shelf in warmer years, particularly in 2018) led to changes in distributions of adult and age-1 pollock. Adult pollock were concentrated north of St. Lawrence Island and had larger longitudinal distributions in warm years, 2017–2019; whereas they had a more southerly and narrow distribution over the outer shelf in the cold year, 2010. Age-1 pollock had higher densities over the inner eastern shelf in 2017–2019 compared to 2010. Northward flow around St. Lawrence Island (particularly in the spring) alternated between stronger flow on the west side of the island in 2010 and 2017 and stronger flow on the east side of the island in 2018 and 2019; variations in flow may have impacted the location of prey and movement of feeding pollock to the Chukchi Sea. Size structure comparisons between NW, NE and SE sections of the Bering Sea shelf suggest that movement of fish between US and Russian waters may have been highest in 2019, one of the two warmest years, and lowest in 2010, the coldest year. Spatial comparisons of distributions and size structure across the Bering Sea help provide a comprehensive view of factors affecting the movement of this highly important commercial fish species.

Interannual variation in the coastal distribution of a juvenile gadid in the northeast Pacific Ocean: The relevance of wind and effect on recruitment

AbstractDrift of propagules occurs within many populations inhabiting flow fields. This affects the number of propagules that rejoin their source population (recruitment) and plays a role in adaptive spatial redistribution. We focus on the cause and consequence of interannual variation in geographic distribution of population density among five cohorts of young‐of‐the‐year (age‐0) juvenile walleye pollock Gadus chalcogrammus in the western Gulf of Alaska (GOA). The coastal GOA is a wind‐driven advective system. Walleye pollock spawn during spring and their eggs and larvae drift southwestward; by late summer, age‐0 juveniles are variously distributed over the shelf. We found that high population densities of age‐0 juveniles (ca. 6 months old) near the southwestward exit of the Alaska Coastal Current from the GOA corresponded with high abundance of larvae from the major spawning area upstream, but did not translate into high abundance at older ages. Further, offshore and upwelling‐favorable winds were associated with the high downstream abundance and presumed export. In contrast, downwelling‐favorable (northeasterly) wind during and shortly after spawning (April–May) was associated with high recruitment at age 1. Finally, we found that recruitment also increased with apparent retention of age‐0 juveniles in favorable habitat upstream near the main spawning area. We hypothesize that wind‐related retention in superior upstream habitat favors recruitment. Our results argue for including wind‐driven transport in future walleye pollock recruitment models. We encourage more work on the juvenile stage of marine fishes aimed at understanding how transport and species‐specific habitat suitability interact to affect population response to large‐scale forcing.

Determination of optimum dietary protein level for juvenile walleye pollock, Gadus chalcogrammus Pallas 1811

An 8-week feeding trial was conducted to investigate the effects of dietary protein level on growth performance, feed utilization, body composition, plasma chemistry and antioxidant parameters of juvenile walleye pollock (Gadus chalcogrammus). Two-hundred and forty juvenile pollock, averaging 4.5 g, were randomly distributed between 12 400-L flow-through circular tanks (20 fish per tank). Four experimental diets with increased crude protein levels (40, 45, 50, and 55 %) were formulated, and referred to as the P40, P45, P50, and P55 diets, respectively. Each diet was assigned to three tanks and the fish were hand-fed to satiation twice daily. At the end of feeding trial, weight gain and specific growth rate increased with increasing dietary protein up to 50 %, and then decreased with further increase in dietary protein. The feed intake of the fish fed the lowest protein diet (P40) was greater than those of fish fed the higher protein diets (P45, P50 and P55). The feed efficiency was the lowest in the P40-fed fish. The protein retention tended to increase with dietary protein, from P40 to P45, and then decline when the dietary protein level was further increased to P55. The whole-body composition, except for the crude protein content, was not affected by the dietary protein content. Antioxidant response was also not affected by the dietary protein content. In conclusion, based on a second-order polynomial regression analysis of weight gain, the optimum dietary protein level for juvenile pollock was estimated to be 48.2 %.

Acoustic discrimination between juvenile walleye pollock and pointhead flounder

When using acoustic methods to investigate fish biomass, it is important to distinguish the target species from other organisms. Previous limitations to acoustic information in surveys meant it was not possible to discriminate juvenile walleye pollock from their predator, pointhead flounder, in Funka Bay, Japan, possibly leading to overestimates in population size. Thus, here, an acoustic method was developed to distinguish the two species based on relative frequency response. This method was used to survey juvenile walleye pollock to evaluate capture potential around Funka Bay, Japan, where pointhead flounder is reportedly its most abundant predator. Volume backscattering strength of pointhead flounder was highest at 200 kHz, while that of juvenile walleye pollock was highest at 38 kHz. Therefore, the relative frequency response at 38 kHz and 200 kHz was successfully used to distinguish between the two species. This method could be more extensively applied to other species in other aquatic environments globally.

A review of methods for quantifying spatial predator–prey overlap

AbstractBackgroundStudies that attempt to measure shifts in species distributions often consider a single species in isolation. However, understanding changes in spatial overlap between predators and their prey might provide deeper insight into how species redistribution affects food web dynamics.Predator–prey overlap metricsHere, we review a suite of 10 metrics [range overlap, area overlap, the local index of collocation (Pianka's O), Hurlbert's index, biomass‐weighted overlap, asymmetrical alpha, Schoener's D, Bhattacharyya's coefficient, the global index of collocation and the AB ratio] that describe how two species overlap in space, using concepts such as binary co‐occurrence, encounter rates, spatial niche similarity, spatial independence, geographical similarity and trophic transfer. We describe the specific ecological insights that can be gained using each overlap metric, in order to determine which is most appropriate for describing spatial predator–prey interactions for different applications.Simulation and case studyWe use simulated predator and prey distributions to demonstrate how the 10 metrics respond to variation in three types of predator–prey interactions: changing spatial overlap between predator and prey, changing predator population size and changing patterns of predator aggregation in response to prey density. We also apply these overlap metrics to a case study of a predatory fish (arrowtooth flounder, Atheresthes stomias) and its prey (juvenile walleye pollock, Gadus chalcogrammus) in the Eastern Bering Sea, AK, USA. We show how the metrics can be applied to understand spatial and temporal variation in the overlap of species distributions in this rapidly changing Arctic ecosystem.ConclusionsUsing both simulated and empirical data, we provide a roadmap for ecologists and other practitioners to select overlap metrics to describe particular aspects of spatial predator–prey interactions. We outline a range of research and management applications for which each metric may be suited.

External and internal grouping characteristics of juvenile walleye pollock in the Eastern Bering Sea

Size and shape patterns of fish groups are collective outcomes of interactions among members. Consequently, group-level patterns are often affected when any member responds to changes in their internal state, external state, and environment. To determine how groups of fish respond to components of their physical and ecological environment, and whether the response is influenced by a component of their external state (i.e., fish age), we used a multibeam system to collect three-dimensional grouping characteristics of 5 age categories of juvenile walleye pollock (age 1, age 2, age 3, mixed ages 1 and 2, and mixed ages 2 and 3) across the eastern Bering Sea shelf over two consecutive years (2009–2010). Grouping data were expressed as metrics that described group size (length, height), shape (roundness, spread), internal structure (density, internal heterogeneity), and position (depth, distance above bottom). Physical data (water temperature measurements) were collected with temperature-depth probes, and ecological data (densities of predators and prey − adult walleye pollock and euphausiids, respectively) were collected with an EK60 vertical echosounder. Juvenile pollock maintained a relatively constant shape, size-dependent density (number fish/mean body length3), and internal horizontal heterogeneity among age categories and in the presence of predators and prey. There were changes to group structure in the face of local physical forcing. Groups tended to move towards the seafloor when bottom waters became warmer, and groups became vertically shorter, denser, and had more variation in horizontal internal density as group depth increased. These results are explored in relation to the value and limitations of using multibeam data to describe how external and internal group structure map onto environmental influences.

Study on acoustic characteristics of pointhead flounder Cleisthenes pinetorum and juvenile walleye pollock Gadus chalcogrammus

In this study, the acoustic differences between the pointhead flounder and the juvenile walleye pollock were examined using a quantitative echo-sounder around the Funka Bay, Japan and the acoustic characteristics of the pointhead flounder have been surveyed. Acoustics data of the fish were monitored using a Simrad EK60 (38, 120, 200 kHz) split-beam echo sounder in the field. The target strength (TS) and swimming angle of free swimming pointhead flounders were measured in a seawater tank (length: 10 m, width: 5 m, and height: 6 m). As the result, pointhead flounder schools presented a patch shaped echo on the echograms, whereas the distribution patterns of the juvenile walleye pollock schools were layered. The volume backscattering strength (SV) of the target schools extracted from the echograms showed that the pointhead flounder presented a higher SV at high frequency. In contrast, the juvenile walleye pollock showed higher SV at a low frequency. For pointhead flounder, the distribution of pitch angle was measured both by camera and echo-sounder at the experiments in the tank and shown the same distribution pattern. The TS of pointhead flounder is large bigger than other bladderless fish.

Transported zooplankton from the Okhotsk Sea facilitate feeding and growth of juvenile walleye pollock on a continental shelf along the Oyashio Current, western subarctic Pacific

The advective transport of zooplankton provides an important source of energy on continental shelves. On a continental shelf along the Oyashio Current, western subarctic Pacific (42°30′N, 144°00′E), the extant water mass is replaced biannually by inflows of water masses from the highly productive Okhotsk Sea. These inflows and accompanying zooplankton are hypothesized to enhance biological production on the shelf. In this study, seasonal feeding and growth of a juvenile planktivorous fish, walleye pollock (Gadus chalcogrammus), on the shelf were examined in relation to water mass exchanges from September 2003 to June 2005. Zooplankton were sampled from February to April in 2004 and 2005, and in April 2014 and 2015. Juvenile pollock frequently consumed an Arctic copepod, Calanus glacialis, and a boreal euphausiid, Thysanoessa inermis, after January when the shelf was occupied by cold water masses that originated from the southwestern Okhotsk Sea. Juvenile pollock whose diet contained higher contributions of these energy-rich prey items exhibited positive growth in February–March 2005, whereas fish with lower proportions of these prey exhibited little growth during this period in 2004. The winter distributions of the copepod and euphausiid extended from a continental slope area in the southwestern rim of the Okhotsk Sea to the shelf along the Oyashio Current. Together, these results suggest the transport of zooplankton from the Okhotsk Sea likely influences the biological production of the coastal Oyashio ecosystem by enhancing the availability of energy-rich prey for juvenile pollock.

Otolith chemistry of juvenile walleye pollock Gadus chalcogrammus in relation to regional hydrography: evidence of spatially split cohorts

Otolith chemistry of juvenile walleye pollock Gadus chalcogrammus in relation to regional hydrography: evidence of spatially split cohorts

Broadband target strength measurements of juvenile walleye pollock (Theragra chalcogramma)

Walleye pollock (Theragra chalcogramma) is one of very important fisheries resources in Japan. The acoustic-net surveys have been conducted around Hokkaido since 1995. To improve the present resource management, the estimation of the standing stock of juvenile walleye pollock is necessary. The target strengths of juvenile walleye pollock at 38 kHz have been well-studied through measurement. However, there are little knowledge of the target strengths at frequencies other than 38 kHz. In this study, therefore, the target strengths at other frequencies were measured. The acoustic system was consist of a broadband transducer and commercially available equipment. The calibration of the system was performed by using a 20.6-mm-diameter tungsten carbide sphere. The transmitting signal was 20-160 kHz linear frequency modulated signal. The target strengths of nine specimens were measured and their fork lengths were ranged from 6.9 to 12.1 cm. Each individual specimen was anesthetized and tethered in a tank (5 m x 5 m x 5 m) with a thin fishing line. Orientation angles of the specimen were varied between −50 to 50 degrees and the target strengths were measured at each angle. Orientation and length dependences of the target strengths are presented and discussed.

Distributional factors of juvenile Walleye Pollock in the Musashi Bank area, northern Japan Sea

Most of juvenile walleye pollock (Gadus chalcogrammus) in the northern Japan Sea migrate to the bottom layer with 150-200 m depth of Musashi bank area in summer. Clarification of distribution factors of nursery area after the migration is important for resource management. We examined the factors of juvenile pollock after migration to bottom in summer 2014 and 2015. The distribution of density of juvenile pollock was obtained by quantitative echo sounder. The distribution of bottom sediment was discriminated by the side scan sonar. The bottom backscattering strength and sediment data were jointed to analyze bottom sediment of quantitative echo sounder survey transect line based on the Roxann method. In the result, bottom sediment was separated into clay, sand, and boulders. Distribution density of juvenile pollock was high in boulders area. Additionally, the density of juvenile pollock was higher at northward upslope than gentle landform and else way upslope in all boulders area. It is considered that northward ocean flow collided with the northward upslope of boulders make upward flowing and stagnate water, and the water forms the retention space of prey plankton that is favorable for juvenile pollock.

Modelling spatially dependent predation mortality of eastern Bering Sea walleye pollock, and its implications for stock dynamics under future climate scenarios

Abstract Arrowtooth flounder (Atheresthes stomias) are an important predator of juvenile walleye pollock (Gadus chalcogramus) in the eastern Bering Sea (EBS) shelf and have increased 3-fold in biomass from 1977 to 2014. Arrowtooth flounder avoid the summer “cold pool” (bottom water ≤2°C) and variability in cold pool size and location has affected their spatial overlap with juvenile walleye pollock. Developing a method to account for the relationship between climate change and pollock mortality can highlight ecosystem dynamics and contribute to better assessments for fisheries management. Consequently, spatially resolved predation mortality rates were estimated within an age-structured walleye pollock stock assessment population model (based on spatial information on diet and abundance from trawl surveys), along with the effect of sea surface temperature (SST) on pollock recruitment. Projections of SST and cold pool area to 2050 were obtained (or statistically downscaled) from nine global climate models and used within an age-structure population model to project pollock abundance given estimated relationships between environmental variables and predator and prey spatial distributions, pollock recruitment, and maximum rate of arrowtooth flounder consumption. The climate projections show a wide range of variability but an overall trend of increasing SST and decreasing cold pool area. Projected pollock biomass decreased largely due to the negative effect of increased SST on pollock recruitment. A sensitivity analysis indicated that the decline in projected pollock biomass would be exacerbated if arrowtooth flounder increased their relative distribution in the EBS northwest middle shelf (an area of relatively high density of juvenile pollock) in warm years.

Variation in annual production of copepods, euphausiids, and juvenile walleye pollock in the southeastern Bering Sea

We synthesize recent research on variation in annual production of copepods (Calanus spp.), euphausiids (Thysanoessa spp.), and juvenile walleye pollock (Gadus chalcogrammus) in the southeastern Bering Sea. We reach five conclusions: 1) the timing of the spring bloom is more important than the amount of annual primary production for the transfer of primary to secondary production (i.e., timing matters); 2) summer and fall, not just spring, matter: organisms must maximize energy intake devoted to somatic growth and storage of lipids and minimize energy expenditures during each season; 3) stored lipids are important for the overwinter survival of both zooplankton and age-0 walleye pollock; 4) variation in ice extent and timing of ice retreat affect the spatial distributions of phytoplankton, zooplankton, and age-0 walleye pollock; when these spatial distributions match in late-ice-retreat years, the annual production of copepods, euphausiids, and juvenile walleye pollock often increases (i.e., location matters); 5) if years with late ice retreat, which favor copepod, euphausiid, and juvenile walleye pollock production, occur in succession, top–down control increases. These conclusions help to explain annual variation in production of copepods, euphausiids and juvenile walleye pollock. Copepods and euphausiids often are more abundant in cold years with late ice retreat than in warm years with early ice retreat due to bloom timing and the availability of ice algae during years with late ice retreat. As a consequence, age-0 walleye pollock consume lipid-enriched prey in cold years, better preparing them for their first winter and their overwinter survival is greater. In addition, there is a spatial match of primary production, zooplankton, and age-0 walleye pollock in cold years and a mismatch in warm years.