Interannual variability in growth of walleye pollock, Theragra chalcogramma, in the central Bering Sea

Interannual variability in growth of walleye pollock, Theragra chalcogramma, was examined. Adult walleye pollock were collected from the central Bering Sea (Aleutian Basin) from 1978 to 1999. Average fork lengths were found to be approximately 47 cm during the 1970–80s, this increased to 56 cm in the late 1990s. Age was determined for 4805 individuals using the otolith break and burn method. Ages ranged from 5–23 years and the year classes of 1978 and 1989 were dominant in the 1980s and the 1990s, respectively. Fish had significantly larger length-at-age in the 1990s compared to the 1970–80s, and interannual variability in age–length relationship was clearly observed. Taking into consideration a recent decrease of the walleye pollock biomass in the central Bering Sea, density-dependent growth was supported as one possibility of the growth variability. At the same time, we could not rule out the possibility that oceanographic variability affected the growth of walleye pollock in the area.     

Characterization of fast skeletal myosin from white croaker in comparison with that from walleye pollack

ABSTRACT:   Enzymatic and structural properties of white croaker fast skeletal muscle myosin were determined and compared with those of walleye pollack counterpart. Ca²⁺-ATPase activity of white croaker myosin was decreased to approximately 70% of the original activity during 1 day of storage at 0°C and pH 7.0 in 0.5 M KCl and 0.1 mM dithiothreitol, whereas that of walleye pollack was decreased to approximately 20% under the same condition. The activation energy ( E _a) for inactivation of white croaker myosin calculated by the Arrhenius plot for inactivation rate constant (K_D) was 1.2-fold higher than that of walleye pollack. While Ca²⁺-ATPase showed a similar KCl-dependency for the two species, the maximal activity was observed at pH 6.2 and 6.3 for white croaker and walleye pollack, respectively. Actin-activated myosin Mg²⁺-ATPase activity of white croaker was approximately half that of walleye pollack at 0.05 M KCl and pH 7.0, although the two myosins showed a similar affinity to F-actin with K _m of 1.7 and 1.4, respectively. Limited proteolysis with α-chymotrypsin cleaved heat-denatured white croaker myosin mainly at heavy meromyosin/light meromyosin (HMM/LMM) junction, whereas walleye pollack myosin was cleaved at several sites in LMM as well as at the HMM/LMM junction.     

Variations in larval walleye pollock feeding and condition: a synthesis

There was a strong association among concentrations of microzooplankton prey sampled from the walleye pollock, Theragra chalcogramma , larval habitat, gut contents of larvae, and their nutritional condition. Subsequently, hypothesized survival potentials linked to food availability were validated by independently determined mortality rates. We present evidence that a significant number of walleye pollock larvae were starving in 1991 but that fewer were starving in 1992. At some stations where prey levels were anomalously low in 1991, up to 40% of the larvae were in poor condition. There appears to be a 2-week period after first feeding when walleye pollock are vulnerable to starvation.     

Predation on walleye pollock (Theragra chakograrnma) eggs and yolk-sac larvae by pelagic crustacean invertebrates in the western Gulf of Alaska

Immunological detection of yolk protein was used to assess predation by pelagic amphipods (gammarid and hyperiid), mysids, and euphausiids on eggs and yolk-sac larvae of walleye pollock Theragra chalcogramma during 1988 and 1989. Consumption estimates were made on the basis of frequency of positive immunoassays, assay detection times (gut clearance time), predator abundance, and spatial overlap of predators and prey. From our results gammarid amphipods and euphausiids were important predators on eggs and yolk-sac larvae, respectively. Gammarid amphipods alone consumed about 14% of the standing stock of pollock eggs in 1989. These results were compared with those from clearance rate experiments of predators feeding on pollock eggs in 300-1 bags. In general, clearance rate estimates of egg consumption were lower than those determined from gut contents.     

Application of NaLA,a fishing net configuration and loading analysis system,to bottom gill nets

ABSTRACT:   The net-shape and loading analysis system (NaLA) was developed to determine fishing net configuration and load in a previous study. The system has since been applied to general gill nets and aquaculture nets, and its validity has been proven through model experiments in tanks. In this study, the system was applied to estimate the dynamic behavior of a bottom gill net for walleye pollock, to test the system's applicability of the system to gear operations in the field. To obtain in situ data, four bottom gill net operations were performed in February 2004 off the coast of Sawara, Hokkaido, Japan. During operations, vertical displacements of the bottom gill net's float and sinker lines were measured as representative values of gear behavior, and ocean current direction, and speed at the gear position were observed simultaneously. Then, bottom gill net behavior was simulated using NaLA, incorporating observed environmental conditions and gear specifications. The resulting calculated behavior was compared to measured behavior in terms of the relationship between net height and environmental or setting conditions. Agreement between the calculated and measured net behavior was found. Thus, it is believe that our NaLA calculation model has the potential to simulate the dynamic behavior of bottom gill nets in situ .     

Changes in yellow perch (Perca flavescens) growth associated with the establishment of a walleye (Stizostedion vitreum) population in Canadarago Lake, New York (USA)

Abstract – Piscivorous fish can affect prey growth in two ways: directly by reducing prey density and indirectly by inducing predator-avoidance behaviors. We investigated these two pathways in yellow perch ( Perca flavescens ) growth responses to walleye ( Stizostedion vitreum ) stocking in Canadarago Lake, New York (USA) using a 25-year time series. Before walleye stocking, yellow perch growth rate was low and independent of body size. As walleye abundance increased, yellow perch growth increased and became size-dependent. The switch to size-dependent growth occurred in 1 year, indicating a rapid behavioral response to predators. Mean growth rate increased more gradually and was linearly related to walleye density, indicating a slower numerical effect of walleye on yellow perch densities. Although the net effect was an increase in perch growth, small perch growth initially decreased as walleye became established. Therefore, the combination of numerical and behavioral effects produced a complex pattern of size-dependent changes in growth of yellow perch.     

Cohort survival patterns of walleye pollock, Theragra chalcogramma, in Shelikof Strait, Alaska: a critical factor analysis

A series of age-specific life tables for walleye pollock ( Theragra chalcogramma ) in the western Gulf of Alaska was compiled for the 1980-91 year classes. The life tables were utilized to perform an exploratory key factor analysis to examine the timing of critical periods in the recruitment process, evidence of density-dependence at different stages and trends in mortality rates. Early larval mortality was significantly correlated with generational mortality (In recruits/spawning bio-mass), but patterns in juvenile mortality also were similar to generational mortality and in some years were clearly dominant in determining the fate of a cohort. Density-dependent mortality, based on the correlation between mortality and initial abundance, was indicated only for the late larval to early juvenile stage. Time trends were marginally significant for juvenile mortality. It is speculated that the observed increase in juvenile mortality is associated with increasing abundance of arrowtooth flounder. Weaknesses in the data base are discussed; these along with the short time series involved make our conclusions tentative and subject to further study. We hypothesize that pollock recruitment levels can be established at any life stage depending on sufficient supply from prior stages, a type of dynamics which can be termed supply dependent multiple life stage control.     

Contribution of the polymerization of protein by disulfide bonding to increased gel strength of walleye pollack surimi gel with preheating time

ABSTRACT: To clarify the contribution of polymerization of myosin heavy chain (MHC) by disulfide bonding to increased gel strength of cooked gel via preheating, the pastes of walleye pollack surimi (SS and C grades) were preheated at 25°C and 40°C for a variety of hours prior to heating at 80°C for 20 min. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) patterns of cooked gels were analyzed with and without reducing the samples, which were solubilized in 8 M urea–2% SDS solution. The formation of polymers by disulfide bonding in cooked gels was almost constant in each of the SS and C grade surimi gels despite the period of preheating. Therefore, it was suggested that polymerization by disulfide bonding occurred during cooking at 80°C and not during preheating.     

Inhibiting effect of polymerization and degradation of myosin heavy chain during preheating at 30°C and 50°C on the gel-forming ability of walleye pollack surimi

ABSTRACT: To confirm the contribution of polymerization and degradation of myosin heavy chain (MHC) during preheating to the gel-forming ability of fish meat paste, walleye pollack surimi paste was preheated at 30°C and 50°C prior to heating at 80°C in the presence of various inhibitors. At 30°C, ethyleneglycol bis(2-aminoethyl ether) -N,N,N ', N '-tetraacetic acid (EGTA) and ethylenediaminetetraacitic acid (EDTA) inhibited gel formation as well as the polymerization of MHC, whereas dithiothreitol (DTT) and leupeptin promoted gel formation, which was accompanied by the enhancement of MHC polymerization and decreased MHC degradation, respectively. At 50°C, leupeptin inhibited MHC degradation and improved gel strength, whereas EGTA, EDTA and DTT had no effect on MHC polymerization and degradation and did not affect gel formation. The results demonstrate that the gel strength of cooked gel (80°C) is not affected by preheating at 30°C and 50°C and does not inhibit polymerization and degradation. Results suggest that the gel strength of cooked gel is dependent on the polymerization and degradation of MHC during preheating.     

Heat-induced structural changes and aggregation of walleye pollack myosin in the light meromyosin region

Heat-induced structural changes and aggregation properties of walleye pollack myosin, light meromyosin (LMM) and heavy meromyosin (HMM) were investigated. According to the circular dichroism (CD) measurement, the α-helix content of the pollack myosin and LMM were estimated to be 72% and 90% at 5°C but decreased to 22% and 21% by increasing the temperature to 60°C with two transitions at 35°C and 50°C, respectively. In contrast, that of HMM decreased gradually from 37% to 33% by increasing the temperature from 5°C to 40°C, and decreased steeply to 20% above 50°C. These results indicate that the decrease in the α-helix content in the myosin molecule upon heating was attributable mainly to the decrease in the α-helix content in the LMM region. In contrast, 1-anilinonaphthalene-8-sulfonate (ANS) fluorescence and light scattering intensity of both myosin and HMM were remarkably increased above 25°C and 35°C, respectively, while those of LMM showed only a slight change even above 60°C. Although LMM alone formed no aggregates detectable by the light scattering measurement, it formed coprecipitates with myosin but not with HMM upon heating at 40°C for 10 min. These facts suggest that LMM bind to the LMM region of the myosin. Further, it was found that myosin gel formed in a test tube by the same heating conditions was significantly weakened by coexistence of LMM. These results suggest that the association of the LMM region of myosin molecules is essential for the heat-induced gelation of myosin.