Известия ТИНРО (Sep 2018)
New data on the diet of juvenile fish in the eastern Chukchi Sea
Abstract
Data on feeding of underyearlings of arctic cod Boreogadus saida, pacific cod Gadus macrocephalus, saffron cod Eleginus gracilis, sand lance Ammodytes hexapterus, capelin Mallotus villosus, and other fish species were collected in the Chukchi Sea in August-September, 2017 in the framework of Arctic Integrated Ecosystem Survey (Arctic IES). In the time of survey, the eastern Chukchi Sea was free of the sea ice to 72о30′ N. Large aggregations of arctic cod were observed in the surveyed area. The diet of arctic cod juveniles and youngsters of other investigated species included both pelagic and near-bottom zooplankton, mainly copepods, euphausiids, oikoplevres, and juvenile decapods. The copepods Calanus glacialis and Calanus. hyperboreus dominated in the northern part of the surveyed area, being typical for the Arctic Ocean and Beaufort Sea, and the species usual for the Bering Sea, as the copepods Calanus glacialis + Calanus marshallae, Eucalanus bungii, and Neocalanus cristatus, were in predominance in its southern part. Besides of these large-sized species, the species typical for the Alaska coastal waters were presented in the diet of juveniles, as the copepods Pseudocalanus spp., Centropages abdominalis, Acartia longiremis, Podon sp., Tortanus discaudatus, Epilabidocera amphitrites, and Eurytemora herdmani, as well as larvae of Polychaeta, Echinodermata, Cirripedia and veligers of Bivalvia. The arctic cod juveniles used the whole spectrum of prey but consumed mainly smalland medium-sized zooplankton, which biomass was relatively low in 2017: 21.8–243.5 mg/m3 in the southern part of the surveyed area and 5.1–83.0 mg/m3 in its northern part. Correspondingly, their feeding intensity was higher in the south: their stomach fullness was 98.7–67.5 ‱ in the south and 76.9–46.9 ‱ in the north; the mean daily ration was 4.2 % of the body weight in the south and 3.4 % in the north. These values are considered as low or medium, possibly the stock of arctic cod was too high for the feeding base, particularly in the northern area. From the other hand, the diets of arctic cod, saffron cod and sand lance were very similar in the areas of joint habitation, so competitive relations between these species could be assumed.
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