New data on the diet of juvenile fish in the eastern Chukchi Sea

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.

Chukchi Sea, eastern Chukchi Sea, feeding, arctic cod, pacific cod, saffron cod, diet

1. Volkov, A.F., Technique of collecting and processing the samples of plankton and the samples on nekton feeding (step-by-step instructions), Izv. Tikhookean. Nauchno–Issled. Inst. Rybn. Khoz. Okeanogr., 2008, vol. 154, pp. 405–416.

2. Volkov, A.F. and Murphy, J.M., Plankton and diet of fish in the Chukchi Sea and the northern Bering Sea, Byull. no. 2 realizatsii “Kontseptsii dal’nevostochnoi basseinovoi programmy izucheniya tikhookeanskikh lososei” (Bull. No. 2 Implementation “Concept of the Far Eastern Basin Program for the Study of Pacific Salmon”), Vladivostok: TINRO-Tsentr, 2007, pp. 70–80.

3. Efimkin, A.Ya., Feeding of arctic cod Boreogadus saida in the Bering and Chukchi Seas, Izv. Tikhookean. NauchnoIssled. Inst. Rybn. Khoz. Okeanogr., 2013, vol. 173, pp. 184–192.

4. Kuznetsova, N.A. and Slabinsky, A.M., Hydrobiological studies in the western Bering and Chukchi seas and the Pacific waters off the Commander Islands in 2007 by the BASIS program, Byull. no. 2 realizatsii “Kontseptsii dal’nevostochnoi basseinovoi programmy izucheniya tikhookeanskikh lososei” (Bull. No. 2 Implementation “Concept of the Far Eastern Basin Program for the Study of Pacific Salmon”), Vladivostok: TINRO-Tsentr, 2007, pp. 282–293.

5. Napazakov, V.V., Chuchukalo, V.I., Kuznetsova, N.A., Radchenko, V.I., Slabinsky, A.M., and Nadtochy, V.A., Feeding and some features of ecology of Gadidae fish in the western part of Bering Sea in the summerautumn season, Izv. Tikhookean. Nauchno–Issled. Inst. Rybn. Khoz. Okeanogr., 2001, vol. 128, pp. 907–928.

6. Chuchukalo, V.I. and Volkov, A.F., Rukovodstvo po izucheniyu pitaniya ryb (Guide to the Study of Diet of Fish), Vladivostok: TINRO, 1986.

7. Slabinsky, A.M. and Figurkin, A.L., Structure of planktonic community in the southern part of the Chukchi Sea in summer period, Izv. Tikhookean. NauchnoIssled. Inst. Rybn. Khoz. Okeanogr., 2014, vol. 178, pp. 135–147.

8. Chuchukalo, V.I., Some methods of determination of fish daily ration, Izv. Tikhookean. NauchnoIssled. Inst. Rybn. Khoz. Okeanogr., 1996, vol. 119, pp. 289–305.

9. Chuchukalo, V.I., Pitanie i pishchevye otnosheniya nektona i nektobentosa v dal’nevostochnykh moryakh (Diet and Feeding Interactions of Nekton and Nektobenthos in the Far Eastern Seas), Vladivostok: TINRO-Tsentr, 2006.

10. Eisner, L., Hillgruber, N., Martinson, E., and Maselko, J., Pelagic fish and zooplankton spe¬cies assemblages in relation to water mass characteristics in the northern Bering and southeast Chukchi seas, Polar Biol., 2013, no. 36, pp. 87–113. doi 10.1007/s00300-012-1241-0

11. Gann, J.C., Eisner, L.B., and Danielson, S., How do oceanographic characteristics in the northern Bering Sea relate to juvenile salmon biomass?, NPAFC Tech. Rep., 2013, no. 9, pp. 83–89.

12. Moss, J.H., Murphy, J.M., Farley, E.V., Eisner, L.B., and Andrews, A.G., Juvenile pink and chum salmon distribution, diet, and growth in the northern Bering and Chukchi Seas, North Pac. Anadromous Fish Comm. Bull., 2009, no. 5, pp. 191–196.