Abstract
Feeding of fish juveniles in the eastern Bering Sea is investigated for the periods of 2003-2006 considered as relatively «warm» and 2007-2012 considered as relatively «cold». Small- and medium-sized zooplankton was the dominant prey in the 2003-2006, in particular copepods prevailed in the food of walleye pollock (41.5 %), pacific herring (48.3 %), and sand lance (71.7 %) juveniles, which in turn were the prey for pollock, herring and cod yearlings and other predators. On the contrary, large-sized zooplankton was more abundant in the 2007-2012, so arrowwarms ( Sagitta sp.), large-sized copepods (in particular Calanus marshallae ), euphausiids (mainly Thysanoessa raschii ), hyperiids, and pteropods were the prey for young fish: C. marshallae - for juveniles of pollock (40-45 % by weight) and capelin (32-34 %), Th. raschii - for yearlings of pollock (51 %) and herring (36-46 %), cold-water hyperiid T. libellula - for adult pollock (24 %), juvenile cod (9-18 %) and juvenile herring (9-11 %), whereas portion of fish in the diets was insignificant. In the warm period (2003-2006), juvenile pollock, herring, sand lance and capelin were zooplankton-eaters with the diets similarity 67 %, while yearlings of pollock and juveniles of cod, herring, sandfish, and atka mackerel were fish-eaters preying upon pollock juveniles. In the cold period (2007-2012), the diets of juvenile pollock, juvenile and adult capelin, and juvenile sand lance were also similar at 85-70 % but they preferred large-sized copepods and euphausiids ( C. marshallae and Th. raschii ), while yearlings of pollock, yearlings and adults of herring, and juveniles of sand fish and cod had the diets of 70 % similarity with Th. raschii prevalence. Feeding intensity was high for all species: the mean stomach fullness was 150-200 ‱ for pollock juveniles and yearlings, 200-250 ‱ for cod juveniles, 200-258 ‱ for sand lance juveniles, 302 ‱ for herring juveniles, and 178-250 ‱ for juvenile atka mackerel. The fullness had diurnal rhythm with three peaks: at noon - up to 179 ‱, in evening - up to 213 ‱, and at night - up to 204 ‱ (the data for walleye pollock juveniles in «cold» years only). Daily food ration of juvenile pollock is estimated as 6.7 % of its body weight in the «warm» years and 7.0 % in the «cold» years.
Highlights
Feeding of fish juveniles in the eastern Bering Sea is investigated for the periods of 2003–2006 considered as relatively «warm» and 2007–2012 considered as relatively «cold»
Small- and medium-sized zooplankton was the dominant prey in the 2003–2006, in particular copepods prevailed in the food of walleye pollock (41.5 %), pacific herring (48.3 %), and sand lance (71.7 %) juveniles, which in turn were the prey for pollock, herring and cod yearlings and other predators
Large-sized zooplankton was more abundant in the 2007– 2012, so arrowwarms (Sagitta sp.), large-sized copepods, euphausiids, hyperiids, and pteropods were the prey for young fish: C. marshallae — for juveniles of pollock (40–45 % by weight) and capelin (32–34 %)
Summary
Исследования по питанию рыб в восточной части Берингова моря проводились в теплый период (2003–2006 гг.) и в холодный (2007–2012 гг.). У сеголеток минтая (5–10 см) на долю копепод приходилось 41,5 % массы пищи, сельди — 48,3 %, песчанки — 71,7 %. В то же время сеголетки минтая, песчанки, мойвы являлись пищей для годовиков минтая (75 % массы пищи), сельди (55–82 %), трески (40–79 %) и других рыб. Высокие средние ИНЖ были также у сеголеток трески — 200–250 ‱, песчанки — 200–258, сельди — 302, молоди северного одноперого терпуга — 178–250 ‱. В этот период были собраны материалы по питанию не только лососей, но и молоди минтая, который является массовым компонентом экосистемы на юго-восточном шельфе Берингова моря (Moss et al, 2009), а также молоди трески, мойвы, песчанки и др., встречающихся в этом районе. Цель настоящего исследования — оценка особенностей питания вышеперечисленных рыб в различных климато-океанологических условиях
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