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Study on the target strength ofsakura shrimp Lucensosergia lucens

Başlık çevirisi mevcut değil.

  1. Tez No: 717124
  2. Yazar: BURAK SAYGILI
  3. Danışmanlar: Belirtilmemiş.
  4. Tez Türü: Doktora
  5. Konular: Deniz Bilimleri, Denizcilik, Çevre Mühendisliği, Marine Science, Marine, Environmental Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2021
  8. Dil: İngilizce
  9. Üniversite: Tokyo University of Marine Science and Technology
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 137

Özet

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Özet (Çeviri)

The goal of this study is to develop the acoustic-trawl method for estimating sakura shrimp resources, thus contributing to the resource management and the sustainable fisheries of this species. Especially, this study focused on the TS of sakura shrimp, which is essential for the use of the acoustic-trawl method. In order to determine the TS, the density contrast and sound speed contrast (which are essential for TS pattern prediction by a theoretical scattering model) and orientation angle distribution (which is essential for averaging the TS pattern) were determined for the first time. The g (density contrast) values of live sakura shrimp were determined from the body densities obtained by the density-bottle method. The body density measurement was conducted five times, thus providing the seasonal g values of the shrimp. The mean g was revealed as 1.053 ± 0.005. The g values of the sakura shrimp were close to those of euphausiids, but a slight fluctuation in the shrimps' g values was observed which is thought to be caused by seasonal changes. The g values were slightly changed (1.052–1.058) by the seasons. There is no length dependence of the body density (r = −0.20)and the g (r = −0.21). The h (sound speed contrast) values of live sakura shrimp were inferred from the measured TS spectra by using a theoretical scattering model. A new broadband TS measurement system was constructed to measure the TS spectra of live sakura shrimp. The applicability of the system for weak backscattering animals was confirmed, and then the TS 105 spectra of live sakura shrimp were successfully measured. The measured TS spectra were compared with the predicted TS spectra which have the explanatory variable of h, and the best-fitted h value was determined for each sample. The mean h was 1.010 ± 0.012, which is close to those of euphausiids (strictly speaking, E. pacifica). The orientation angle distribution of sakura shrimp was inferred as N(29°, 3°) by comparing ΔTSs and ΔSVs. The ΔTSs were estimated for the frequency pairs 70–38 kHz and 120–38 kHz by using the theoretical scattering model, and the ΔSVs were obtained for the same frequency pairs from the acoustic trawl survey. The orientation angle distribution showed that the sakura shrimps were swimming head-up in the survey, which is similar to that of other fluid-like animals such as Antarctic krill. Length dependence of target strength The length dependence of the TS of sakura shrimp was calculated at 38, 70, and 120 kHz for the lengths from 10 to 45 mm (Fig. 5.1). The TS patterns were predicted using the means of the h and g values determined in this study. The TS patterns were averaged over the orientation angle distribution N(29°, 3°). The TS values at 38 and 70 kHz increase as length increases; however, the TS values at 120 kHz fluctuate if the length is >24 mm. The length dependence of the TS can be used for determining the mean TS used to convert recorded echo data into abundance data (Fig. 1.6). In addition, the length dependence of TS will enable the length estimation and echo identification of sakura shrimp in acoustic-trawl surveys. This study's finding will thus 106 contribute to the management of standing stock and sustainable fishing of sakura shrimp. Fig. 5.1 Length dependence of TS of sakura shrimp at 38 kHz (solid line), 70 kHz (broken line), and 120 kHz (gray line). The shape of Sample 3 (Fig. 4.7), density contrast g = 1.053 and sound speed contrast h = 1.010 were used for the prediction of the TS patterns by using the DWBA-DCM. The orientation angle distribution N(29°, 3°) was used for averaging the predicted TS patterns. Broadband target strength measurement system The newly developed broadband TS measurement system has the following features. The system can measure TS spectra at the frequency range below 200 kHz, which is similar to the measurement by scientific echosounders. The use of a 50-ms-long LFM signal in a small tank is unique. The results of the system's evaluation demonstrated that the system is useful for TS spectra measurements of weakly scattering animals. The new system can be 0 5 10 15 20 25 30 35 40 45 50 Body length (mm) -120 -115 -110 -105 -100 -95 -90 -85 -80 T S (d B) 38 kHz 70 kHz 120 kHz 107 can be applied to the TS spectra measurement of other species. Future work There are likely to be individual differences and seasonal and time dependences of the parameters g, h, and orientation angle distribution, and it is therefore necessary to continue similar studies and update the parameters if new findings are obtained. Direct measurements of h by the time-of flight method are needed, and comparisons of those results with the inferences obtained herein are merited. Regarding the orientation angle distribution, target tracking methods with cast platforms and split-beam echosounders (e.g., Sawada et al., 2009) for in situ behavior observations should be evaluated. Simultaneously, in situ TS measurements should be challenged and the length dependence of TS illustrated in Fig. 5.1 should be verified.

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