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Kresimir Williams - One of the best experts on this subject based on the ideXlab platform.
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walleye pollock Theragra chalcogramma behavior in midwater trawls
Fisheries Research, 2013Co-Authors: Kresimir Williams, Christopher D. Wilson, John K. HorneAbstract:Abstract Trawls are standard tools for surveying fisheries resources, yet they are selective in what they retain, and thus provide potentially misleading information about fish populations. In order to evaluate the potential for selective retention in a midwater survey trawl used in conjunction with acoustic surveys of walleye pollock, fish behavior was examined using an integrated approach of optical, acoustic and recapture net methods. A stereo-camera system was used to provide length, position and orientation information, and a dual-frequency identification sonar was used to track fish targets in the trawl. Fish escaping the trawl were sampled using recapture, or pocket, nets mounted to the outside of the trawl. Most fish were found to be oriented along the main trawl axis, facing the forward trawl opening. Nearest distance to the trawl panel did not appear to be length-dependent, however, at night when ambient light levels were lower, fish maintained less distance to the trawl panel compared to daytime observations. Consequently, significantly more fish escapes occurred at lower light levels. Trajectories of fish escaping the trawl were highly variable compared with fish that herded into the net, or those whose retention state was unknown. Greatest escapement into pocket nets was observed from the bottom panel of the trawl at night. These findings suggest that survey trawl samples will be less biased due to selectivity when trawls are conducted during the day.
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length selective retention of walleye pollock Theragra chalcogramma by midwater trawls
Ices Journal of Marine Science, 2011Co-Authors: Kresimir Williams, André E. Punt, Christopher D. Wilson, John K. HorneAbstract:Williams, K., Punt, A. E., Wilson, C. D., and Horne, J. K. 2011. Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls. – ICES Journal of Marine Science, 68: 119–129.Midwater trawls are commonly used during acoustic surveys of fish abundance to determine species and length compositions of acoustically sampled fish aggregations. As trawls are selective samplers, catches can be unrepresentative of sampled populations and lead to biased abundance estimates. Length-dependent retention of walleye pollock was estimated using small recapture nets, so-called pocket nets, attached to the outside of the trawl. Experimental haul sets comprising eight hauls each were conducted in the Gulf of Alaska in 2007 and 2008 and in the eastern Bering Sea (EBS) in 2007. Pocket-net catches were then modelled by fitting parameters for selectivity and escapement location along the trawl. Within- and between-haul variability was jointly estimated using hierarchical Bayesian methods. There was significant undersampling of juvenile (<25 cm) pollock, with the length-at-50%-retention (L 50 ) estimated between 13.5 and 26.1 cm among haul sets. In the EBS set, L 50 values were correlated with light level, escapement being greater at night. Trawl selectivity may be a significant source of error in acoustic-survey estimates of the abundance of pollock.
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Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls
Ices Journal of Marine Science, 2010Co-Authors: Kresimir Williams, André E. Punt, Christopher D. Wilson, John K. HorneAbstract:Williams, K., Punt, A. E., Wilson, C. D., and Horne, J. K. 2011. Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls. – ICES Journal of Marine Science, 68: 119–129.Midwater trawls are commonly used during acoustic surveys of fish abundance to determine species and length compositions of acoustically sampled fish aggregations. As trawls are selective samplers, catches can be unrepresentative of sampled populations and lead to biased abundance estimates. Length-dependent retention of walleye pollock was estimated using small recapture nets, so-called pocket nets, attached to the outside of the trawl. Experimental haul sets comprising eight hauls each were conducted in the Gulf of Alaska in 2007 and 2008 and in the eastern Bering Sea (EBS) in 2007. Pocket-net catches were then modelled by fitting parameters for selectivity and escapement location along the trawl. Within- and between-haul variability was jointly estimated using hierarchical Bayesian methods. There was significant undersampling of juvenile (
John K. Horne - One of the best experts on this subject based on the ideXlab platform.
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walleye pollock Theragra chalcogramma behavior in midwater trawls
Fisheries Research, 2013Co-Authors: Kresimir Williams, Christopher D. Wilson, John K. HorneAbstract:Abstract Trawls are standard tools for surveying fisheries resources, yet they are selective in what they retain, and thus provide potentially misleading information about fish populations. In order to evaluate the potential for selective retention in a midwater survey trawl used in conjunction with acoustic surveys of walleye pollock, fish behavior was examined using an integrated approach of optical, acoustic and recapture net methods. A stereo-camera system was used to provide length, position and orientation information, and a dual-frequency identification sonar was used to track fish targets in the trawl. Fish escaping the trawl were sampled using recapture, or pocket, nets mounted to the outside of the trawl. Most fish were found to be oriented along the main trawl axis, facing the forward trawl opening. Nearest distance to the trawl panel did not appear to be length-dependent, however, at night when ambient light levels were lower, fish maintained less distance to the trawl panel compared to daytime observations. Consequently, significantly more fish escapes occurred at lower light levels. Trajectories of fish escaping the trawl were highly variable compared with fish that herded into the net, or those whose retention state was unknown. Greatest escapement into pocket nets was observed from the bottom panel of the trawl at night. These findings suggest that survey trawl samples will be less biased due to selectivity when trawls are conducted during the day.
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Characterizing walleye pollock (Theragra chalcogramma) winter distribution from opportunistic acoustic data
ICES Journal of Marine Science, 2013Co-Authors: Steven J. Barbeaux, John K. Horne, Martin W. DornAbstract:In 2003, acoustic data from 25 000 km of ship track lines were collected from two fishing vessels participating in the eastern Bering Sea walleye pollock (Theragra chalcogramma) fishery. Although these data were not calibrated or collected on a systematic grid, their broad temporal extent combined with high spatial resolution facilitated the examination of the distribution and behaviour of fished aggregations. To demonstrate their scientific applicability, these data were used to identify the spatio-temporal dynamics of pollock aggregations over scales ranging from hundreds of metres to hundreds of kilometres and from minutes to months. The spatial analysis identified three levels of pollock aggregation. The largest regions of high pollock density had an average diameter of 110 km and were comparable with distinct fishing grounds identified by fishers. The next smaller areas of high pollock density had a diameter between 2.5 and 6 km. Within these areas were clusters of pollock at even higher densities. The extent of the smallest aggregations ranged in diameter from 0.1 km in daylight to 0.6 km at night. Time-series analysis identified vertical and horizontal diel changes in pollock distribution and an overall decline in pollock density over the study period.
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length selective retention of walleye pollock Theragra chalcogramma by midwater trawls
Ices Journal of Marine Science, 2011Co-Authors: Kresimir Williams, André E. Punt, Christopher D. Wilson, John K. HorneAbstract:Williams, K., Punt, A. E., Wilson, C. D., and Horne, J. K. 2011. Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls. – ICES Journal of Marine Science, 68: 119–129.Midwater trawls are commonly used during acoustic surveys of fish abundance to determine species and length compositions of acoustically sampled fish aggregations. As trawls are selective samplers, catches can be unrepresentative of sampled populations and lead to biased abundance estimates. Length-dependent retention of walleye pollock was estimated using small recapture nets, so-called pocket nets, attached to the outside of the trawl. Experimental haul sets comprising eight hauls each were conducted in the Gulf of Alaska in 2007 and 2008 and in the eastern Bering Sea (EBS) in 2007. Pocket-net catches were then modelled by fitting parameters for selectivity and escapement location along the trawl. Within- and between-haul variability was jointly estimated using hierarchical Bayesian methods. There was significant undersampling of juvenile (<25 cm) pollock, with the length-at-50%-retention (L 50 ) estimated between 13.5 and 26.1 cm among haul sets. In the EBS set, L 50 values were correlated with light level, escapement being greater at night. Trawl selectivity may be a significant source of error in acoustic-survey estimates of the abundance of pollock.
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Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls
Ices Journal of Marine Science, 2010Co-Authors: Kresimir Williams, André E. Punt, Christopher D. Wilson, John K. HorneAbstract:Williams, K., Punt, A. E., Wilson, C. D., and Horne, J. K. 2011. Length-selective retention of walleye pollock, Theragra chalcogramma, by midwater trawls. – ICES Journal of Marine Science, 68: 119–129.Midwater trawls are commonly used during acoustic surveys of fish abundance to determine species and length compositions of acoustically sampled fish aggregations. As trawls are selective samplers, catches can be unrepresentative of sampled populations and lead to biased abundance estimates. Length-dependent retention of walleye pollock was estimated using small recapture nets, so-called pocket nets, attached to the outside of the trawl. Experimental haul sets comprising eight hauls each were conducted in the Gulf of Alaska in 2007 and 2008 and in the eastern Bering Sea (EBS) in 2007. Pocket-net catches were then modelled by fitting parameters for selectivity and escapement location along the trawl. Within- and between-haul variability was jointly estimated using hierarchical Bayesian methods. There was significant undersampling of juvenile (
Xue Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of concentration ph and ionic strength on the kinetic self assembly of acid soluble collagen from walleye pollock Theragra chalcogramma skin
Food Hydrocolloids, 2012Co-Authors: Bafang Li, Xue ZhaoAbstract:The effects of concentration, pH value and ionic strength on the kinetic self-assembly of acid-soluble collagen from walleye pollock (Theragra chalcogramma) skin were investigated. A two-phase kinetic process was provided which included the formation of nucleus center and nucleus growth, the first phase being the controlled step for collagen self-assembly. Collagen showed marked assembly behavior when concentration reaching and above 0.6 mg/mL, and higher concentration could accelerate collagen self-assembly. Rate constants of the first and second assembly phase both increased with pH to a maximum around pH 7.2 and then decreased, indicating that pH 7.2 was the optimum pH value for collagen self-assembly. The kinetics of collagen self-assembly could be modulated by NaCl concentration. The concentration of NaCl from 30 to 60 mM was more suitable to self-assemble for pollock skin collagen. (C) 2012 Elsevier Ltd. All rights reserved.
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determination of critical aggregation concentration and aggregation number of acid soluble collagen from walleye pollock Theragra chalcogramma skin using the fluorescence probe pyrene
Food Chemistry, 2010Co-Authors: Bafang Li, Xue ZhaoAbstract:The aim of this paper was to investigate the critical aggregation concentration and aggregation number of acid-soluble collagen from walleye pollock (Theragra chalcogramma) skin using the fluorescence probe pyrene. Results showed that pyrene was fit for studying the aggregation behaviour of collagen in sodium phosphate buffer at pH 7.2. The plots of the pyrene l(1)/l(3) ratio, as a function of the logarithm of total collagen concentration, revealed a typical sigmoidal decrease, the critical aggregation concentration (CAC) from which was determined to be at 0.48 mg/ml. The subsequent transient fluorescence decay study indicated that the aggregation number of collagen was not constant, but varied with different concentrations of collagen. The structure of the aggregates tended to be stable, when the collagen concentration exceeded 1.2 mg/ml. (C) 2010 Elsevier Ltd. All rights reserved.
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The scavenging of free radical and oxygen species activities and hydration capacity of collagen hydrolysates from walleye pollock (Theragra chalcogramma) skin
Journal of Ocean University of China, 2009Co-Authors: Yongliang Zhuang, Xue ZhaoAbstract:Fish skin collagen hydrolysates (FSCH) were prepared from walleye pollock (Theragra chalcogramma) using a mixture of enzymes, namely trypsin and flavourzyme. The degree of hydrolysis of the skin collagen was 27.3%. FSCH was mainly composed of low-molecular-weight peptides and the relative proportion of
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Characterization of acid-soluble collagen from the skin of walleye pollock (Theragra chalcogramma)
Food Chemistry, 2008Co-Authors: Mingyan Yan, Yongliang Zhuang, Xue Zhao, Guoyan Ren, Hu Hou, Xiukun Zhang, Li Chen, Yan FanAbstract:Abstract Acid-soluble collagen (ASC) was extracted from the skin of walleye pollock ( Theragra chalcogramma ) and partially characterized. It exhibited a maximum absorbance at 220 nm, but little absorbance near to 280 nm. Amino acid composition and SDS-PAGE suggested that the collagen might be classified as type I collagen. Moreover, FTIR investigations showed the existence of helical arrangements of collagen. The denaturation temperature ( T d ) and shrinkage temperature ( T s ) were 24.6 °C and 47 °C, respectively, both lower than those of mammalian collagens. However, T d of walleye pollock skin collagen was higher than that of cod skin collagen reported previously. These results indicate that walleye pollock skin is a potential source of collagen and provide the theoretical basis for further research.
L S Incze - One of the best experts on this subject based on the ideXlab platform.
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temporal and geographic differences in feeding and nutritional condition of walleye pollock larvae Theragra chalcogramma in shelikof strait gulf of alaska
Marine Ecology Progress Series, 1991Co-Authors: M F Canino, K M Bailey, L S InczeAbstract:Feeding and nutritional condition of first-feeding walleye pollock larvae Theragra chalcogramma were compared to available prey levels measured during early spring (late April- early May) and mid-spring (mid-May) 1989. In early spring, feeding intensity, mean RNNDNA values of larvae, and microzooplankton abundance were higher within a large patch of larvae compared with areas outside the patch. In mid-spring, microzooplankton prey abundance, feedmg levels and RNA/DNA of larvae m and out of the previously defined patch were higher, indicating better overall conditions for growth than in early spring. The results suggest that limiting food densities may occur during spring over spatial and temporal scales that affect feeding and growth of larval pollock.
A.m. Privalikhin - One of the best experts on this subject based on the ideXlab platform.
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First record of intersexuality in walleye pollock Theragra chalcogramma (Pallas, 1814)
Marine Biodiversity Records, 2015Co-Authors: K. Zhukova, A.m. PrivalikhinAbstract:We report the first record of intersexuality in walleye pollock Theragra chalcogramma (Pallas, 1814) caught in the Bering and Okhotsk seas. Prevalence of intersexuality was low (0.0003–0.0016%). We describe intersex gonads at the macro- and microscopic levels (using histological methods).
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New data on distribution of Norwegian (Atlantic) pollock Theragra finnmarchica (Gadidae) in the Barents Sea
Journal of Ichthyology, 2014Co-Authors: K. A. Zhukova, A.m. PrivalikhinAbstract:New data have been acquired on the biology, morphological features and distribution of Norwegian (Atlantic) pollock Theragra finnmarchica in the Barents Sea. Two individuals of this rare species gadoid (Gadidae) were caught in June and July 2012 in the south-eastern part of the Barents Sea, indicating a wider distribution area of this species than previously thought. It has been confirmed that a number of morphological features of Norwegian pollock is different from T. chalcogramma , and that it feeds on macroplankton (Euphausiidae, Hyperiidae).
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On the finding of a rare species—Norwegian pollock Theragra finnmarchica Koefoed, 1956 (Gadidae)—in the Barents Sea
Journal of Ichthyology, 2010Co-Authors: A.m. Privalikhin, G. V. NorvilloAbstract:A description of a rare representative of the family Gadidae—the Norwegian pollock Theragra finnmarchica Koefoed, 1956—is given. The Norwegian pollock caught in November 2004 in the Barents Sea off Nadezhda Island is the first individual of this species officially recorded in Russia. At the present time, reliable information is available about 42 caught individuals of this species. A review was performed of evidence on the history of study and modern concepts of the origin, biology, and distribution of Norwegian pollock.
