Assessing the abundance of Bristol Bay belugas with genetic mark‐recapture methods

The Bristol Bay stock of beluga whales (Delphinapterus leucas) is genetically distinct and resides in Bristol Bay year‐round. We estimated the abundance of this population using genetic mark‐recapture, whereby genetic markers from skin biopsies, collected between 2002 and 2011, were used to identify individuals. We identified 516 individual belugas in two inner bays, 468 from Kvichak Bay and 48 from Nushagak Bay, and recaptured 75 belugas in separate years. Using a POPAN Jolly‐Seber model, abundance was estimated at 1,928 belugas (95% CI = 1,611–2,337), not including calves, which were not sampled. Most belugas were sampled in Kvichak Bay at a time when belugas are also known to occur in Nushagak Bay. The pattern of genetic recaptures and data from belugas with satellite transmitters suggested that belugas in the two bays regularly mix. Hence, the estimate of abundance likely applies to all belugas within Bristol Bay. Simulations suggested that POPAN estimates of abundance are robust to most forms of emigration, but that emigration causes negative bias in both capture and survival probabilities. Because it is likely that some belugas do not enter the sampling area during sampling, our estimate of abundance is best considered a minimum population size.     

Satellite telemetry reveals population specific winter ranges of beluga whales in the Bering Sea

At least five populations (stocks) of beluga whales (Delphinapterus leucas) are thought to winter in the Being Sea, including the Bristol Bay, Eastern Bering Sea (Norton Sound), Anadyr, Eastern Chukchi Sea, and Eastern Beaufort Sea (Mackenzie) populations. Belugas from each population have been tagged with satellite‐linked transmitters, allowing us to describe their winter (January–March) distribution. The objectives of this paper were to determine: (1) If each population winters in the Bering Sea, and if so, where? (2) Do populations return to the same area each year (i.e., are wintering areas traditional)? (3) To what extent do the winter ranges of different populations overlap? Tagged belugas from all five populations either remained in, or moved into, the Bering Sea and spent the winter there. Each population wintered in a different part of the Bering Sea and populations with multiple years of data (four of five) returned to the same regions in multiple years. When data were available from two populations that overlapped in the same year, they did not occupy the shared area at the same time. Although our sample sizes were small, the evidence suggests belugas from different populations have traditional winter ranges that are mostly exclusive to each population.     

KILLER WHALES, ORCINUS ORCA, IN THE SOUTHEASTERN BERING SEA: RECENT SIGHTINGS andPREDATION ON OTHER MARINE MAMMALS

An unusual number of killer whales appeared in inshore waters of the southeastern Bering Sea in summer 1989 and 1990. Multiple sightings occurred in Bristol and Kuskokwim bays where killer whales had been seen only rarely in previous years. Three animals became stranded on mud flats in Kuskokwim Bay but were able to free themselves on a high tide. Killer whales were observed interacting with salmon, harbor seals, Steller sea lions, walruses, and beluga whales. Detailed observations were made of killer whales attacking belugas in the Naknek River. Local conditions and behavioral adaptations may reduce the susceptibility of belugas to killer whale predation. Continued killer whale activity in this area would be unlikely to affect fish resources, but might have some influence on beluga whales.     

Beluga (Delphinapterus leucas) habitat selection in the eastern Beaufort Sea in spring, 1975�C1979

An understanding of the adaptability of belugas (Delphinapterus leucas) to changing ice conditions is required to interpret and predict possible changes in habitat selection in response to projected loss of sea ice throughout the circumpolar Arctic. We analyzed beluga observations made during spring aerial surveys for ringed seals conducted from 1975 to 1979 in the eastern Beaufort Sea. Despite inter-annual variability in the extent and distribution of sea ice, belugas consistently selected areas with water depths of 200–500 m and heavy ice concentrations (8/10 to 10/10) while areas of open water to light ice concentrations (0/10 to 1/10) were not selected. Belugas were also found in proximity to regions with ≥0.5 degrees seafloor slope which include the continental slope and other areas with the potential for oceanographic upwellings. In most years (4 of 5), fast-ice edges and coastal areas were not selected. In the lightest ice year analyzed, belugas showed less specificity in habitat selection as their distribution expanded and shifted shoreward to fast-ice edges. The observed distribution is discussed in terms of predator–prey relationships particularly with reference to beluga feeding on polar cod (Boreogadus saida). More research is required to examine and compare possible changes in distribution since the late 1970s and to investigate the factors driving the patterns described.     

River discharge predicts spatial distributions of beluga whales in the Upper Cook Inlet, Alaska, during early summer

In the Cook Inlet, a subarctic estuary in Alaska, the endangered population of beluga whales (Delphinapterus leucas) has not recovered despite regulation of hunting and the reason is not well understood. To examine the potential roles of habitat and food availability, we compared spatial data on distribution and abundance from aerial surveys undertaken during the seasonal transition into early summer, with corresponding data for river discharge and salmon abundance. Principal component regression indicated strong relationships with rates of river discharge that explained over 90 % of the inter-annual variability of beluga abundances recorded in the Susitna Delta. Belugas moved away from the Susitna Delta when flow rate from the Susitna River was low relative to rivers draining into the Knik Arm and Turnagain Arm. Using only three principal components describing shape, river discharge during May explained 86 % of the inter-annual variability in abundances recorded in the Susitna Delta. In years of reduced abundance in the Susitna Delta, movement was toward the Knik Arm until 2003, transitioning thereafter to the Turnagain Arm including Chickaloon Bay. In contrast, escapements of Chinook salmon in the Deshka River (a tributary of the Susitna River) showed an inverse relationship with beluga abundance in the Susitna Delta, suggesting that escapements were dependent on beluga abundance. These results demonstrated the influence of highly dynamic habitat availability on the distribution of belugas and the importance of the physical environment in structuring the activity of higher predators on prey species.     

Key Factors Determining the Distribution of Beluga Whales, <Emphasis Type="Italic">Delphinapterus leucas</Emphasis> (Pallas, 1776), in River Estuaries of Western Kamchatka

The results of observations on the distribution of beluga whales, Delphinapterus leucas (Pallas, 1776), in three large rivers of western Kamchatka in the summer and autumn seasons are discussed. In the summer, the number of beluga whales in the Khairyuzova, Belogolovaya, and Moroshechnaya rivers reaches 111–250 individuals. Most of the belugas enter the rivers during the flood tidal phase: the number of animals in the estuaries increases along with the rising water level to the maximum value at spring tide. The belugas do not move upstream out of the estuaries and tend to remain in the zone of mixing riverine and marine waters, where 20 species of fish and three species of invertebrates have been identified. At ebb tide, the belugas leave for the sea; however, during a large run of salmon some individuals remain in the estuaries and continue hunting in deep-water areas. The main issue that causes beluga whales to form summer aggregations in Kamchatkan rivers is the hunt for salmon. The distribution of beluga whales in river estuaries is defined by the dynamics and intensity of salmon spawning runs. The preference of beluga whales for these rivers can be explained by the channel type of their estuaries.     

Seasonal migrations of Sea of Okhotsk beluga whales (<Emphasis Type="Italic">Delphinapterus leucas</Emphasis>) of the Sakhalin-Amur summer aggregation

Seasonal migrations of beluga whales from the Sakhalin-Amur aggregation in the Sea of Okhotsk were investigated with the use of satellite telemetry. Satellite tags were attached to four females captured near Chkalova Island, Sakhalin Bay, in August 2007. At 5 weeks after tagging, the belugas left the Chkalova Island area and moved to the Nikolaya and Ul’banskii Bays in the Shantar Sea. The animals stayed in these bays (mainly in Nikolaya Bay) until the end of autumn and then traveled northward to deeper waters. In winter and spring, they preferred to stay in the regions with dense ice cover or close to the ice edge. During the winter migration, the tagged whales, as a rule, did not keep together, although they followed the same course with a little time lag. The female whose tag transmitted the longest (9.5 months) returned to Chkalova Island in late May and thus completed the seasonal migration cycle. Based on the data on the migration routes of the tagged belugas, we suggest that the Sakhalin-Amur and Shantar aggregations interact in autumn. It is also possible that they have similar winter migratory paths     

Indirect effects of sea ice loss on summer‐fall habitat and behaviour for sympatric populations of an Arctic marine predator

Aim

Climate change is fundamentally altering habitats, with complex consequences for species across the globe. The Arctic has warmed 2–3 times faster than the global average, and unprecedented sea ice loss can have multiple outcomes for ice‐associated marine predators. Our goal was to assess impacts of sea ice loss on population‐specific habitat and behaviour of a migratory Arctic cetacean.

Location

Arctic Ocean.

Methods

Using satellite telemetry data collected during summer‐fall from sympatric beluga whale (Delphinapterus leucas) populations (“Chukchi” and “Beaufort” belugas), we applied generalized estimating equations to evaluate shifts in sea ice habitat associations and diving behaviour during two periods: 1993–2002 (“early”) and 2004–2012 (“late”). We used resource selection functions to assess changes in sea ice selection as well as predict trends in habitat selection and “optimal” habitat, based on satellite‐derived sea ice data from 1990 to 2014.

Results

Sea ice cover declined substantially between periods, and Chukchi belugas specifically used significantly lower sea ice concentrations during the late than early period. Use of bathymetric features did not change between periods for either population. Population‐specific sea ice selection, predicted habitat and the amount of optimal habitat also generally did not change during 1990–2014. Chukchi belugas tracked during 2007–2012 made significantly more long‐duration and deeper dives than those tracked during 1998–2002.

Main conclusions

Taken together, our results suggest bathymetric parameters are consistent predictors of summer‐fall beluga habitat rather than selection for specific sea ice conditions during recent sea ice loss. Beluga whales were able to mediate habitat change despite their sea ice associations. However, trends towards prolonged and deeper diving possibly indicate shifting foraging opportunities associated with ecological changes that occur in concert with sea ice loss. Our results highlight that responses by some Arctic marine wildlife can be indirect and variable among populations, which could be included in predictions for the future.

     

Decadal shifts in autumn migration timing by Pacific Arctic beluga whales are related to delayed annual sea ice formation

Migrations are often influenced by seasonal environmental gradients that are increasingly being altered by climate change. The consequences of rapid changes in Arctic sea ice have the potential to affect migrations of a number of marine species whose timing is temporally matched to seasonal sea ice cover. This topic has not been investigated for Pacific Arctic beluga whales (Delphinapterus leucas) that follow matrilineally maintained autumn migrations in the waters around Alaska and Russia. For the sympatric Eastern Chukchi Sea (‘Chukchi’) and Eastern Beaufort Sea (‘Beaufort’) beluga populations, we examined changes in autumn migration timing as related to delayed regional sea ice freeze‐up since the 1990s, using two independent data sources (satellite telemetry data and passive acoustics) for both populations. We compared dates of migration between ‘early’ (1993–2002) and ‘late’ (2004–2012) tagging periods. During the late tagging period, Chukchi belugas had significantly delayed migrations (by 2 to >4 weeks, depending on location) from the Beaufort and Chukchi seas. Spatial analyses also revealed that departure from Beaufort Sea foraging regions by Chukchi whales was postponed in the late period. Chukchi beluga autumn migration timing occurred significantly later as regional sea ice freeze‐up timing became later in the Beaufort, Chukchi, and Bering seas. In contrast, Beaufort belugas did not shift migration timing between periods, nor was migration timing related to freeze‐up timing, other than for southward migration at the Bering Strait. Passive acoustic data from 2008 to 2014 provided independent and supplementary support for delayed migration from the Beaufort Sea (4 day yr^?1) by Chukchi belugas. Here, we report the first phenological study examining beluga whale migrations within the context of their rapidly transforming Pacific Arctic ecosystem, suggesting flexible responses that may enable their persistence yet also complicate predictions of how belugas may fare in the future.     

Exchange of “signature” calls in captive belugas (Delphinapterus leucas)

Belugas (Delphinapterus leucas) produce echolocation clicks, burst pulses, and whistles. The sounds of 3 captive belugas were recorded using 2 hydrophones at the Port of Nagoya Public Aquarium. There were stable individual differences in the pulse patterning of one type of pulsed sounds (PS1 call), suggesting that belugas use these as “signature” calls. Eighty-eight percent of PS1 calls initiated PS1 calls from other animals within 1 s. PS1 calls repeated by the same individual occurred primarily when other belugas did not respond within 1 s of the first call. Belugas delayed successive PS1 calls when other belugas responded with a PS1 call within 1 s. There was no clear temporal pattern for whistles. It appears that the time limit for responding to calls is 1 s after the initial call. If other individuals do not respond to the PS1 call of a beluga within 1 s, belugas tend to repeat the call and wait for a response. The results of this study suggest that the belugas exchange their individual signatures by using PS1 calls, in a manner similar to that of signature whistles used by bottlenose dolphins.     

AIRCRAFT SOUND AND DISTURBANCE TO BOWHEAD AND BELUGA WHALES DURING SPRING MIGRATION IN THE ALASKAN BEAUFORT SEA

Short‐term behavioral responses of bowhead whales (Balaena mysticetus) and beluga whales (Delphinapterus leucas) to a Bell 212 helicopter and Twin Otter fixed‐wing aircraft were observed opportunistically during four spring seasons (1989–1991 and 1994). Behaviors classified as reactions consisted of short surfacings, immediate dives or turns, changes in behavior state, vigorous swimming, and breaching. The helicopter elicited fewer detectable responses by bowheads (14% of 63 groups) than by belugas (38% of 40). Most observed reactions by bowheads (63%) and belugas (86%) occurred when the helicopter was at altitudes ≤150 m and lateral distances ≤250 m. Belugas reacted significantly more frequently during overflights at lateral distances ≤250 m than at longer lateral distances (P= 0.004). When the helicopter was on the ice with engines running, 7 of 14 groups of belugas reacted, up to 320 m away, sometimes with small‐scale (≤100 m) diversion; only 1 of 8 groups of bowheads reacted. For the fixed‐wing aircraft, few bowheads (2.2%) or belugas (3.2%) were observed to react to overflights at altitudes 60–460 m. Most observed reactions by bowheads (73%) and belugas (70%) occurred when the fixed‐wing aircraft was at altitudes ≤182 m and lateral distances ≤250 m. However, the proportions reacting, especially to low‐altitude flights (e. g., ≤182 m), were underestimated for both species because observation opportunities were brief. Even so, reactions were more common when the aircraft was low (≤182 m): P= 0.009 for belugas, P= 0.06 for bowheads. There was little if any reaction by bowheads when the aircraft circled at altitude 460 m and radius 1 km. Aircraft sounds measured underwater at depths 3 m and 18 m showed that a Bell 212 helicopter was 7–17.5 dB noisier than a Twin Otter (10–500 Hz band). Bell 212 sound consisted mainly of main rotor tones ahead of the helicopter and tail rotor tones behind it. Twin Otter sound contained fewer prominent tones. Peak sound level as received underwater was inversely related to aircraft altitude, and received levels at 3 m depth averaged 2.5 dB higher than at 18 m depth. The dominant low‐frequency components of aircraft sound are presumed to be readily audible to bowheads. For belugas, these components may be inaudible, or at most only weakly audible. Mid‐frequency sound components, visual cues, or both, are probably important in eliciting beluga reactions to aircraft.     

Characteristics of the spawning stock of chinook salmon <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis> from the Apuka River (northeastern Kamchatka)

Biological features of chinook salmon Oncorhynchus tshawytscha from the Apuka River, the largest river of the northeastern Kamchatka inflowing Olyutorskii Bay of the Bering Sea, are studied. Chinook salmon from the Apuka River spend mainly a year in the river before downstream migration to the sea. The fish live in the sea for 1–4 years. The spawning migration of chinook salmon into the Apuka River begins in late May just after ice melting, and it continues until early August. The main part of the spawners enters the river during June. A hypothesis on the occurrence of two seasonal races in the Apuka River is proposed.     

山东半岛南部海湾底栖动物群落生态特征及其与水环境的关系

2006-2007年对山东半岛南部4个海湾(荣成湾、桑沟湾、靖海湾和五垒岛湾)19个站位的底栖动物群落结构特征进行了研究,并对14个环境因素和底栖动物群落生态特征分别进行主成分分析和Spearman相关分析。结果显示,荣成湾、桑沟湾和靖海湾的底栖动物种类中,多毛类所占比例最高,而五垒岛湾仅秋、冬季多毛类所占比例最高。根据聚类分析和非度量多维标度方法分析,4季底栖动物群落均可分为2个群落,春、冬季的第一聚群为靖海湾和五垒岛湾,第二聚群为荣成湾和桑沟湾。秋季荣成湾、桑沟湾、靖海湾组成第一聚群,第二聚群由五垒岛湾构成。夏季,底栖动物Shannon-Wiener多样性指数(H')与采样深度和总碱度呈显著正相关,与水温呈极显著的负相关关系。秋季,与硝酸盐呈负相关关系,说明富营养化对山东半岛南部4个海湾大型底栖动物群落产生了一定负面影响。ABC曲线法分析显示,荣成湾和桑沟湾底栖动物的丰度优势度曲线与生物量优势度曲线相交,表明荣成湾和桑沟湾大型底栖动物群落处于中度干扰状态,密集的养殖活动可能对其生态系统带来了巨大影响,加强海水养殖管理,强化生态健康养殖理念,合理利用海洋生物资源,对大型底栖动物群落的稳定性具有重要意义。     

Distribution of the Beluga Delphinapterus leucas in the Anadyr Estuary in 2000

The results of stationary observations of the beluga Delphinapterus leucas Pall. 1776 conducted in Anadyr Estuary in 2000 were compared with literature and unpublished data. The belugas were found to occur in Anadyr Estuary almost throughout the ice-free period, from the first half of June until mid-November. The largest schools usually concentrated during the spawning migration of salmon in the bottleneck of Anadyr Estuary and in waters near the city of Anadyr.     

Winter distribution and migrations of beluga whales (<Emphasis Type="Italic">Delphinapterus leucas</Emphasis>) in the White Sea based on satellite tracking data

Based on satellite tracking of eight beluga whale males in the White Sea, their habitats in the autumn, winter, and spring periods have been identified. A correlation between the distribution of beluga whales, ice dynamics, and migration of Atlantic salmon has been revealed. It has been found than beluga whale males do not leave the White Sea during the entire ice period. The results obtained confirm the hypothesis that the White Sea population of beluga whales is isolated.     

An estimate of the fraction of belugas (<Emphasis Type="Italic">Delphinapterus leucas</Emphasis>) in the Canadian high Arctic that winter in West Greenland

Five belugas, or white whales (Delphinapterus leucas), were tracked by satellite from Creswell Bay, Somerset Island, in the Canadian high Arctic towards West Greenland in autumn 2001. After 1 October, three of the whales stayed in the North Water polynya and the other two whales moved to West Greenland. One of the whales that moved to Greenland migrated south along the west coast, following a route and timing similar to another beluga tracked in 1996. The belugas that moved towards West Greenland from Canada did so before or near 1 October. The movements of both these whales followed a similar timing and assumed migratory route of belugas hunted in autumn in West Greenland. In Greenland, the hunt begins in September, where the first whales are taken in the northernmost community of Qaanaaq. Hunting takes place farther south in Upernavik in October, and finally in November and December, belugas are taken even farther south in Uummannaq and Disko Bay. The whales that remain in the North Water after 1 October most likely do not contribute to the harvest in West Greenland. Based on the total number of belugas satellite-tracked in Canada between 1995 and 2001 with tags that lasted beyond 1 October, approximately 0.15 (95% CI 0.06-0.35; n=26) of the summering stock of belugas in the Canadian high Arctic move to West Greenland for the winter. Genetic studies have indicated that belugas moving east through Lancaster Sound are significantly differentiated from belugas taken in the autumn hunt in West Greenland. These conflicting results suggest molecular genetics cannot be solely relied on to reveal the stock identity of these belugas.     

Using stable isotopes to understand changes in ringed seal foraging ecology as a response to a warming environment

Trends toward increased temperatures, reduced sea ice extent, and longer open water seasons have resulted in changing Arctic ecosystem dynamics. Expected changes include shifts in distribution and abundance of prey species for seabirds and marine mammals. Using stable isotope analysis, we studied spatial and interannual variation in ringed seal (Pusa hispida) feeding ecology in Hudson Bay in relation to environmental variables, between 2003 and 2010. Ringed seal muscle and hair samples collected from Arviat and Sanikiluaq, Nunavut, were analyzed for stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C). Seals from western Hudson Bay (Arviat) had higher δ¹⁵N and lower δ¹³C than seals from eastern Hudson Bay (Sanikiluaq), and stable isotope ratios varied interannually within each region. Peak δ¹⁵N occurred in years with spring air temperatures between approximately ?5°C and ?2°C. This temperature range was characteristic of warm years in western Hudson Bay and cool years in eastern Hudson Bay. We hypothesize that the high δ¹⁵N observed in ringed seals is indicative of greater importance of capelin (Mallotus villosus) in ringed seal diet. A comparison of ringed seal isotopic niche widths indicated greater dietary differences between western and eastern Hudson Bay with warming, suggesting a possible ecological divergence related to climate change.     

Changes in scale circulus spacings of an endangered Atlantic salmon Salmo salar population: evidence of a shift in marine migration?

Post‐smolt scale circulus spacing patterns for two Atlantic salmon Salmo salar populations from the Southern Upland (SU) of Nova Scotia, Canada, were compared with spacings from two endangered populations from the inner Bay of Fundy (iBoF) Nova Scotia and New Brunswick, to determine if growth patterns differed among these populations, and if growth patterns had changed as the abundance of these populations declined. An analysis of numbers of marine circuli from scales of post‐smolts and one‐sea‐winter adults of known age indicated that circuli were deposited at a rate of about one circulus per week in summer and slowed to one every 2 weeks in winter. During the summer and the autumn, mean circulus spacing in the iBoF populations, known to have occupied the outer Bay of Fundy during these seasons, was lower than in the SU populations, which are known to migrate to the North Atlantic. Similar circulus spacing patterns within SU populations is suggestive of a common marine distribution for these populations. In contrast, a cluster analysis revealed that within the geographically intermediate Big Salmon River (iBoF), some individuals exhibited wider spacing patterns that resemble the distant migrating SU populations, while others exhibited narrower spacing similar to other iBoF S. salar. Within the Big Salmon River, the relative abundance of the wider and the narrower spacing patterns varied in the earlier years, but all fish sampled since 1999, exhibited wider spacings similar to distant migrating SU S. salar. The apparent disappearance of the narrower pattern, characteristic of localized migration and indicative of historical iBoF populations, suggests that local migration may not presently be a successful strategy for these populations.     

Persistence of bacterial and archaeal communities in sea ice through an Arctic winter

The structure of bacterial communities in first‐year spring and summer sea ice differs from that in source seawaters, suggesting selection during ice formation in autumn or taxon‐specific mortality in the ice during winter. We tested these hypotheses by weekly sampling (January–March 2004) of first‐year winter sea ice (Franklin Bay, Western Arctic) that experienced temperatures from ?9°C to ?26°C, generating community fingerprints and clone libraries for Bacteria and Archaea. Despite severe conditions and significant decreases in microbial abundance, no significant changes in richness or community structure were detected in the ice. Communities of Bacteria and Archaea in the ice, as in under‐ice seawater, were dominated by SAR11 clade Alphaproteobacteria and Marine Group I Crenarchaeota, neither of which is known from later season sea ice. The bacterial ice library contained clones of Gammaproteobacteria from oligotrophic seawater clades (e.g. OM60, OM182) but no clones from gammaproteobacterial genera commonly detected in later season sea ice by similar methods (e.g. Colwellia, Psychrobacter). The only common sea ice bacterial genus detected in winter ice was Polaribacter. Overall, selection during ice formation and mortality during winter appear to play minor roles in the process of microbial succession that leads to distinctive spring and summer sea ice communities.     

Juvenile sockeye salmon distribution, size, condition and diet during years with warm and cool spring sea temperatures along the eastern Bering Sea shelf

Interannual variations in distribution, size, indices of feeding and condition of juvenile Bristol Bay sockeye salmon Oncorhynchus nerka collected in August to September (2000–2003) during Bering–Aleutian Salmon International Surveys were examined to test possible mechanisms influencing their early marine growth and survival. Juvenile sockeye salmon were mainly distributed within the southern region of the eastern Bering Sea, south of 57°0' N during 2000 and 2001 and farther offshore, south of 58°0' N during 2002 and 2003. In general, juvenile sockeye salmon were significantly larger ( P < 0·05) and had significantly higher indices of condition ( P < 0·05) during 2002 and 2003 than during 2000 and 2001. The feeding index was generally higher for age 1.0 year sockeye salmon than age 2.0 year during all years. Among-year comparisons suggested that Pacific sand lance Ammodytes hexapterus were important components of the juvenile sockeye salmon diet during 2000 and 2001 (20 to 50% of the mean wet mass) and age 0 year walleye pollock Theragra chalcogramma were important components during 2002 and 2003 (50 to 60% of the mean wet mass). Warmer sea temperatures during spring and summer of 2002 and 2003 probably increased productivity on the eastern Bering Sea shelf, enhancing juvenile sockeye salmon growth.