Accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys / David A. Demer

Public ISBD Faire une suggestion d'achat Titre : Accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys Type de document : texte imprimé Auteurs : David A. Demer, Auteur Importance : pp. 1664-1674 Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : Multibeam echosounders can improve the efficiency and the precision of acoustic-survey estimates by providing greater sampling volumes than single-beam echosounders. For a multibeam echosounder, the target strength of fish can vary with its pitch, roll, and yaw. Here, normalized, acoustic backscatter patterns from fish schools are modelled by beam-incidence angle, 0-180, considering the scattering-directivity patterns of each fish. Variation of pitch angle causes a decrease in the mean and an increase in the variance of the backscatter in the vertical beam, but has no effect on the backscatter in the outer beams. Conversely, variation of the yaw causes a decrease in the mean and an increase in the variance of the backscatter in only the outer beams. Because the fish-scattering model predicts different backscatter at dorsal- vs. lateral-incidence angles, backscatter did vary with roll angle. In the hypothetical case of fish avoiding a vessel, the backscatter decreases strongly the outer beams. The results of the model were compared with multibeam measurements of fish schools. In general, the measured mean backscatter vs. beam-incidence angle was nearly uniform. The methods described here provide an approach to accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys. Accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys [texte imprimé] / David A. Demer, Auteur . - [s.d.] . - pp. 1664-1674. Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : Multibeam echosounders can improve the efficiency and the precision of acoustic-survey estimates by providing greater sampling volumes than single-beam echosounders. For a multibeam echosounder, the target strength of fish can vary with its pitch, roll, and yaw. Here, normalized, acoustic backscatter patterns from fish schools are modelled by beam-incidence angle, 0-180, considering the scattering-directivity patterns of each fish. Variation of pitch angle causes a decrease in the mean and an increase in the variance of the backscatter in the vertical beam, but has no effect on the backscatter in the outer beams. Conversely, variation of the yaw causes a decrease in the mean and an increase in the variance of the backscatter in only the outer beams. Because the fish-scattering model predicts different backscatter at dorsal- vs. lateral-incidence angles, backscatter did vary with roll angle. In the hypothetical case of fish avoiding a vessel, the backscatter decreases strongly the outer beams. The results of the model were compared with multibeam measurements of fish schools. In general, the measured mean backscatter vs. beam-incidence angle was nearly uniform. The methods described here provide an approach to accounting for scattering directivity and fish behaviour in multibeam-echosounder surveys.

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Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch / Mooney, T. Aran

Public ISBD Faire une suggestion d'achat Titre : Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch Type de document : texte imprimé Auteurs : Mooney, T. Aran, Auteur Importance : pp. 1324-1332 Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : Small cetaceans are incidental bycatch in gillnet fisheries. Dolphin and porpoise bycatch has been reduced by the use of barium sulphate-enhanced gillnets. This decreased entanglement is likely the result of either higher acoustic reflectivity or greater stiffness for barium nets. To address these variables, our study quantified the acoustic reflectivity and stiffness of six net types including barium sulphate, iron oxide-enhanced and control demersal gillnets of sizes which typically target cod (Cactus morhua) and monkfish (Lophius americanus). Acoustic reflectivity, or target strength (IS), was assessed using dolphin and porpoise-like sonar signals from to 40. TS values were used to calculate likely detection ranges. Barium sulphate- and iron oxide-enhanced nets showed increased reflectivity compared with control nets, with the barium sulphate nets generating the highest TS values. Dolphins should detect these nets in time to avoid contact, but porpoises, with typically lower source levels, may not detect nets at a range great enough to avoid entanglement. Barium sulphate line was significantly stiffer than comparable nylon line. All lines lost stiffness when soaked in seawater for 24 h. Barium sulphate nets proved stiffer and more acoustically reflective, and both factors are likely important in reducing harbour porpoise bycatch. Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch [texte imprimé] / Mooney, T. Aran, Auteur . - [s.d.] . - pp. 1324-1332. Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : Small cetaceans are incidental bycatch in gillnet fisheries. Dolphin and porpoise bycatch has been reduced by the use of barium sulphate-enhanced gillnets. This decreased entanglement is likely the result of either higher acoustic reflectivity or greater stiffness for barium nets. To address these variables, our study quantified the acoustic reflectivity and stiffness of six net types including barium sulphate, iron oxide-enhanced and control demersal gillnets of sizes which typically target cod (Cactus morhua) and monkfish (Lophius americanus). Acoustic reflectivity, or target strength (IS), was assessed using dolphin and porpoise-like sonar signals from to 40. TS values were used to calculate likely detection ranges. Barium sulphate- and iron oxide-enhanced nets showed increased reflectivity compared with control nets, with the barium sulphate nets generating the highest TS values. Dolphins should detect these nets in time to avoid contact, but porpoises, with typically lower source levels, may not detect nets at a range great enough to avoid entanglement. Barium sulphate line was significantly stiffer than comparable nylon line. All lines lost stiffness when soaked in seawater for 24 h. Barium sulphate nets proved stiffer and more acoustically reflective, and both factors are likely important in reducing harbour porpoise bycatch.

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Acoustic backscatter by schools of adult Atlantic mackerel / Gorska, Natalia

Public ISBD Faire une suggestion d'achat Titre : Acoustic backscatter by schools of adult Atlantic mackerel Type de document : texte imprimé Auteurs : Gorska, Natalia, Auteur Importance : pp. 1145-1151 Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : The extent of acoustic backscatter by schools of adult Atlantic mackerel (Scomber scombrus) is investigated to improve biomass estimates. Previous studies involving modelled scattering from individual mackerel showed that backscattering at high frequencies is dominated by the contribution from the backbone. Accurate predictions of the scattering spectra require consideration of back-scattering from the entire skeleton, including details of the bone shapes and their acoustic properties. Here, the backscattering cross-sections from mackerel flesh and backbone are estimated theoretically from 18 to 364 kHz and averaged over fish size and tilt angle, then compared with in situ measurements of volume backscattering from mackerel schools. Based on the comparisons, some gross features of the observed relative frequency response are explained, and recommendations for further studies suggested. Acoustic backscatter by schools of adult Atlantic mackerel [texte imprimé] / Gorska, Natalia, Auteur . - [s.d.] . - pp. 1145-1151. Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : The extent of acoustic backscatter by schools of adult Atlantic mackerel (Scomber scombrus) is investigated to improve biomass estimates. Previous studies involving modelled scattering from individual mackerel showed that backscattering at high frequencies is dominated by the contribution from the backbone. Accurate predictions of the scattering spectra require consideration of back-scattering from the entire skeleton, including details of the bone shapes and their acoustic properties. Here, the backscattering cross-sections from mackerel flesh and backbone are estimated theoretically from 18 to 364 kHz and averaged over fish size and tilt angle, then compared with in situ measurements of volume backscattering from mackerel schools. Based on the comparisons, some gross features of the observed relative frequency response are explained, and recommendations for further studies suggested.

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Acoustic characterization of seafloor habitats on the western continental shelf of India / Chakraborty, Bishwajit

Public ISBD Faire une suggestion d'achat Titre : Acoustic characterization of seafloor habitats on the western continental shelf of India Type de document : texte imprimé Auteurs : Chakraborty, Bishwajit, Auteur Importance : pp. 551-558 Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : This is a study of the interaction effects of the dual-frequency (210 and 33 kHz) backscatter signal with seafloor sediment and benthic biota along a transect in water 27-83 m deep offshore of the Goa region of India's central west coast. Estimation of the power-law exponent using seafloor topographic data provided equivalent values even when using dual high-frequency systems for different grain-size sediments. Backscatter signals corrected from system-related gain, etc., reveal better correlations with sedimentary and benthic parameters than the estimated coherence parameters (using echo peaks). Statistically, correlations are significant for the 210kHz backscatter signal with sand and calcium carbonate (CaCO3) sediment content. Also, correlations are higher for macro-benthic biomass {wet weight) and population density with a 210 kHz backscatter strength, emphasizing the dominant seawater-seafloor interface scattering process. For 33 kHz backscatter strength, the absence of such correlations indicates a different scattering process, i.e. dominant sediment volume scattering attributable to the comparatively lower signal attenuation. Additionally, to validate the results, the backscatter signals from other locations in the vicinity of this transect were considered. Acoustic characterization of seafloor habitats on the western continental shelf of India [texte imprimé] / Chakraborty, Bishwajit, Auteur . - [s.d.] . - pp. 551-558. Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : This is a study of the interaction effects of the dual-frequency (210 and 33 kHz) backscatter signal with seafloor sediment and benthic biota along a transect in water 27-83 m deep offshore of the Goa region of India's central west coast. Estimation of the power-law exponent using seafloor topographic data provided equivalent values even when using dual high-frequency systems for different grain-size sediments. Backscatter signals corrected from system-related gain, etc., reveal better correlations with sedimentary and benthic parameters than the estimated coherence parameters (using echo peaks). Statistically, correlations are significant for the 210kHz backscatter signal with sand and calcium carbonate (CaCO3) sediment content. Also, correlations are higher for macro-benthic biomass {wet weight) and population density with a 210 kHz backscatter strength, emphasizing the dominant seawater-seafloor interface scattering process. For 33 kHz backscatter strength, the absence of such correlations indicates a different scattering process, i.e. dominant sediment volume scattering attributable to the comparatively lower signal attenuation. Additionally, to validate the results, the backscatter signals from other locations in the vicinity of this transect were considered.

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Acoustic estimates of mesopelagic fish / O'Driscoll, Richard L.

Public ISBD Faire une suggestion d'achat Titre : Acoustic estimates of mesopelagic fish : as clear as day and night? Type de document : texte imprimé Auteurs : O'Driscoll, Richard L., Auteur Importance : pp. 1310-1317 Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : The pelagic ecosystem on the Chatham Rise east of New Zealand has been monitored annually using acoustic surveys since 2001. Mos of the acoustic backscatter comes from diurnally migrating mesopelagic fish, which are the major prey of hold (Macwronu: novaezelandiae) and other valuable commercial species. Mesopelagic schools and layers typically occur at 100-400 m deptr during the day and migrate above 200 m depth at night. Previous acoustic estimates of the biomass of mesopelagic fish on the Chatham Rise were based only on night-time estimates from the upper 200 m and may significantly underestimate actual biomass Paired day-night comparisons found that an estimated 20% of the total daytime backscatter migrates to depths of 0-14 m al night, where it is too shallow to be detected by hull-mounted acoustic instruments. In contrast, there is a positive bias associated with acoustic estimates of mesopelagic organisms during the day because they can occur close to the bottom mixed with demersal fish. Two alternative approaches for estimating biomass of diurnally migrating mesopelagic species are suggested. The first applies a correction based on the estimated proportion of backscatter migrating into the surface deadzone to night-time estimates of back-scatter in the upper 200 m. The second uses night-time estimates of demersal backscatter, which remains deeper than 200 m at night, to correct daytime estimates of total backscatter. Both methods gave similar estimates of abundance and demonstrated that there was no statistically significant trend in mesopelagic fish biomass on the Chatham Rise over the past seven years. Acoustic estimates of mesopelagic fish : as clear as day and night? [texte imprimé] / O'Driscoll, Richard L., Auteur . - [s.d.] . - pp. 1310-1317. Langues : Anglais (eng) Index. décimale : 508 Voyages et relevés scientifiques. Histoire naturelle Résumé : The pelagic ecosystem on the Chatham Rise east of New Zealand has been monitored annually using acoustic surveys since 2001. Mos of the acoustic backscatter comes from diurnally migrating mesopelagic fish, which are the major prey of hold (Macwronu: novaezelandiae) and other valuable commercial species. Mesopelagic schools and layers typically occur at 100-400 m deptr during the day and migrate above 200 m depth at night. Previous acoustic estimates of the biomass of mesopelagic fish on the Chatham Rise were based only on night-time estimates from the upper 200 m and may significantly underestimate actual biomass Paired day-night comparisons found that an estimated 20% of the total daytime backscatter migrates to depths of 0-14 m al night, where it is too shallow to be detected by hull-mounted acoustic instruments. In contrast, there is a positive bias associated with acoustic estimates of mesopelagic organisms during the day because they can occur close to the bottom mixed with demersal fish. Two alternative approaches for estimating biomass of diurnally migrating mesopelagic species are suggested. The first applies a correction based on the estimated proportion of backscatter migrating into the surface deadzone to night-time estimates of back-scatter in the upper 200 m. The second uses night-time estimates of demersal backscatter, which remains deeper than 200 m at night, to correct daytime estimates of total backscatter. Both methods gave similar estimates of abundance and demonstrated that there was no statistically significant trend in mesopelagic fish biomass on the Chatham Rise over the past seven years.

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Acoustic observations of micronekton fish on the scale of an ocean basin / Kloser, Rudy J.

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Acoustic seabed classification / Anderson, John T.

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Acoustic species identification of schooling fish / Korneliussen, Rolf J.

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Advances in herring biology / Geffen, Audrey J.

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Age and growth of bluemouth, Helicolenus dactylopterus, from the Portuguese continental slope / Sequeira, Vera

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Age, growth, and condition of European eel (Anguilla anguillo) from six lakes in the river havel system (Germany) / Simon, Janek

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Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific / Licandeo, Roberto

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Age, growth, and reproductive season of bluefish (Pomatomus saltatrix) in the Marmara region, Turkey / Ceyhan, Tevfik

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Aggregata octopiana (Protista a picomplexa) a dangerous pathogen during commercial Octopus vulgaris ongrowing / Gestal, Camino

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An altered carrying capacity of the benguela upwelling ecosystem for African penguins (Spheniscus demersus) / Crawford, Robert J. M.

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