The biochemical composition and calorie density of the walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in the Sea of Okhotsk

In tissues of the walleye pollock Theragra chalcogramma the dry matter content averages 18.5%. The lipid content of the raw material is 0.7%, the protein content is 15.3%, carbohydrates are 0.6%, and ash is 1.3%. The average calorie density is 940 cal/g wet weight and 5080 cal/g dry weight. The dry matter content of gonads varies within 14.9–28.0% in females and 14.5–17.0% in males. The lipid content of the raw material is 0.9–3.0% in females and 1.3–1.8% in males; the protein content is 10.2–21.5% and 10.7–13.4%, respectively. The calorie density of female gonads is 702–1537 cal/g wet weight and 4426–5482 cal/g dry weight; for the male gonads it is 760–960 cal/g wet weight and 4952–5641 cal/g dry weight. The dry matter content of the liver varies within 42.2–62.2% for females and 34.4–62.4 for males. The lipid content of the raw material is 25.6–44.5% for females and 16.6–41.3% for males; the protein content is 6.3–9.8% and 8.1–12.3%, respectively. The calorie density of the liver in females varies within 2918–4601 cal/g wet weight and 6370–7395 cal/g dry weight; in males it is 2291–4357 cal/g wet weight and 6392–7492 cal/g dry weight. The minimum calorie density of the liver is observed in juvenile pollock: 963 cal/g wet weight and 2045 cal/g dry weight. The dry-matter content of feces in different size groups varies within 15.0–18.4%. Values of the average lipid content of raw material range from 1.1 to 1.6%; the protein content is from 1.8 to 3.8% and carbohydrates are from 0.9 to 1.4%. The calorie density of feces from variously-sized walleye pollock varies within a narrow range, from 308 to 362 cal/g wet weight. The energy equivalent ranges, depending on body size, from 259 to 2377 cal. The share of energy concentrated in the somatic (muscle) tissue of variously-sized walleye pollock during ontogenesis constitutes 56.5–93.9%; in female gonads it is 0.9–26.6%; in male gonads it is 0.4–7.3%, in the female liver it is 7.9–27.2%, and in the male liver it is 5.7–26.9%. The amount of energy (cal), concentrated in the female liver and gonads is on average 1.5 and 3 times as high as that in the male liver and gonads, respectively. The maximum total energy loss (15–30%) in mature walleye pollock of various-sizes occurs in the spawning period, during the transition from the maturity stage 5 to stage 6. The total amount of energy accumulated during the lifecycle from small juveniles (<17 cm) to very large individuals (>60 cm) averages 1964 kcal for females and 1465 kcal for males. The difference in the amount of energy is explained by the fact that oogenesis requires more energy than spermatogenesis.     

Distribution,Feeding, and Some Physiological Parameters of the Pacific Herring from the Gizhigin and Okhotsk Populations in the North Part of the Sea of Okhotsk in the Spring Season

The distribution of the Pacific herring of various sizes from the Okhotsk and Gizhigin-Kamchatka populations is discussed. The dependence of herring food composition on the condition of the plankton community is demonstrated. In the spring season the feeding rate of juveniles and fattening adult herring depended on the degree of its fatness and on the maturity of the gonads in the prespawning period.     

Benthic-pelagic trophic interactions within the fish assemblage in the western Bering Sea shelf area according to stomach content analysis and ratios of C and N stable isotopes

The composition, abundance, diet and trophic status of zooplankton, bottom invertebrates, fish and nekton were analyzed based on the data collected by the staff of the TINRO-Center during complex bottom trawl catches on the Bering Sea shelf in the fall of 2004. The stomach contents of mass fish species were analyzed and the nitrogen and carbon isotopic composition of 36 mass species of plankton, benthos, nekton and nektobenthos, which together make up the basis of pelagic and bottom communities, was determined. It was found that zooplankton noticeably differ from benthic invertebrates in carbon isotopic composition: δ¹³C values in zooplankton varied from −20.3‰ to −17.9‰; in benthos—from −17.5‰to −13.0‰; and in fish—from −19.2‰ (juvenile walleye pollock) to −15.3‰ (saffron cod). The levels of ¹³C isotope in the tissues of fish depended mostly on the share of pelagic or benthic animals in their diet. δ¹⁵N values in the studied species ranged from 8.6‰ (in sea urchins) to 17.2‰ (in large Pacific cods), which corresponds to a trophic level of 2.8. Obviously the δ¹⁵N values reflect the degree of predation and generally show the ratio of primary, secondary and tertiary consumers in a fish’s diet. Trophic interactions manifest a high degree of interdependence between benthic and pelagic communities (even without taking into account such lower components of the food web as phytoplankton, bacteria, and protozoa) occurring in most nektonic species that depend on both bottom and pelagic food.     

Underyearling pink and chum salmon in the western Bering Sea during the fall season (September and October 2013): Distribution,feeding habits,and growth patterns

The ontogeny of a year class of pink and chum salmon is described for the period after the redistribution of underyearling individuals from coastal waters to deep-sea areas of the western Bering Sea in September and October, 2013. The intensity of their feeding was high; their diet included hyperiids, pteropods, and juvenile euphausiids. The metabolic costs of growth reached only 20% of the consumed food, which indicates significant energy costs for locomotion; moreover, as the body size increases, the level of metabolic functions rises at a decreasing rate, which causes the body growth to slow down and food consumption to decrease. The main items in the diet of underyearling salmon are characterized by a low content of dry matter, low lipid content, and, consequently, a low calorie content, i.e., underyearlings mainly consume protein-rich food with a low fat content. The chemical composition of the tissues almost did not differ between underyearling pink and chum salmon. Both species typically had a low fat content in their muscles. Thus, fat is not accumulated at this stage of ontogeny; all energy that is obtained with food, after being used for locomotion and metabolism, is spent for linear growth.     

The population characteristics and trophic status of herring in the pelagic layer of the northern Okhotsk Sea

The trophic status of Okhotsk and Gizhiga-Kamchatka herring populations is defined more accurately through the analysis of their diet and ratios of stable nitrogen and carbon isotopes based on materials of trawl catches in the Sea of Okhotsk for the period from 2003 to 2010. The possibility of applying isotope analysis to the study of the stock characteristics of herring in the northern Sea of Okhotsk is evaluated.     

Assessment of the consumption of walleye pollock eggs by nekton and jellyfish in the northern Sea of Okhotsk in the spring

In the northern Sea of Okhotsk, nekton and jellyfish consumed as many as 831 × 10⁹ walleye pollock eggs per day in 2011. The nekton exerted the highest pressure, viz., 98.3% of the overall predation on pollock egg by aquatic animals. Of the entire quantity of consumed eggs, 55.9% were eaten by herring, 35.9% by walleye pollock, 6.5% by Sakhalin sole, and 1.7% by jellyfish. Among jellyfish, scyphomedusae Cyanea capillata and Chrysaora melonaster, as well as the hydromedusa Tima sachalinensis consumed the largest quantities of eggs. The total consumption of pollock egg by aquatic animals in 2011 was estimated at 42.4 × 10¹², or 11.4% of the entire quantity of eggs that were spawned by walleye pollock in the waters of the northern part of the sea. The total amount of pollock eggs that were eaten by herring and pollock together for 51 days in 2011 amounted to 38.9 × 10¹², which was 5.7 times as much as that in 2002. Thus, a significant growth of predation on pollock eggs by their main consumers, viz., herring and walleye pollock, was observed in 2011. This was caused by an increase in the populations of both species during the recent years and also by a higher concentration of pollock eggs.