@article{oai:ir.kagoshima-u.ac.jp:00004841,
 author = {松野, 保久},
 issue = {2},
 journal = {鹿児島大学水産学部紀要=Memoirs of Faculty of Fisheries Kagoshima University},
 month = {2016-10-28},
 note = {It has been confirmed that the 'ultrasonic scattering layers' give significant effects not only upon the biological workings in the formation of fishing ground but upon the planning, researching and using of the various underwater acoustic instruments - those which are concerned with navigation, fisheries and investigations ; including oceanic life, oceanophysics, submarine resources, and so on. Owing the fact that the researches of the ultrasonic scattering layers have been performed by the oceanographically advanced countries, a great
number of information have been obtained, concerning both biological and physiological issues. However, about such important issues as ① the relationship between the ultrasonic scattering layers and the fisheries, ② composition organisms in the layers, ③ ultrasonic scattering characteristics, and so on, no accurate information have been obtained, yet. Accordingly, with the intention of clarifying the oceanic state as it is, the author carried out
some investigations on the Kagoshima bay where no existence of the ultrasonic scattering layers having diurnal vertical migration had been confirmed, yet.
Firstly, some information about the ultrasonic scattering layers were obtained by means of the 50 kHz fish finder - in other words, a number of records were fixed continuously, day and night, on board the Training ship Nansei maru belonging to the Faculty of Fisheries, Kagoshima University, at both the innermost, and the middle, areas of the Kagoshima bay, in the respective seasons of spring, summer, autumn and winter. Both vertical and horizontal
towings were carried out by the closing plankton net and the Isaacs-Kidd midwater trawl net for the purpose of ascertaining the composition organisms of each layer. On the other hand, for the elucidation of the ultrasonic scattering characteristics, the scattering strengths of the respective
layers were measured, and, in order to ascertain the physical features in the ocean, the vertical distributions of the water temperature from the sea surface to the sea bottom were observed by DBT (digital bathythermo graph) ; with the performed confirmation of the submarine illumination by an under water illuminometer., The number of the ultrasonic layers having diurnal vertical migration was fixed to be 'three', being unvaried through the whole year, both at the innermost and the middle, areas of the Kagoshima bay. Occasionally, only 'two' layers were recorded during the period from autumn to winter. Although more or less complicated phases were noted in the vertical migrations of the
respective layers, in the outlined patterns, a close resemblance was noted. It was ascertained that there was a close relationship between the cause of the vertical migration, the depth where the respective layers were situated, and the degree of the submarine illumination. The optimum submarine illumination was fixed as in the following : the 1st layer, 10^[-7] lux ~ 10^[-9] lux ; the
2nd layer, 10^[-4] lux ~ 10^[-7] lux, and in case of the 3rd layer, 10^[0] lux ~ 10^[-2] lux. No direct
relationship was noted between the vertical distribution of water temperatures and the cause of
vertical migration ; however, the depth of the ultrasonic scattering layer showing no vertical
migration agreed quite well with the depth of thermocline. The mean value of the maximum
velosity of the vertical migration at each layer was as follows : the 1st layer 2.5 m/min., the 2nd layer 2.0 m/min., and the 3rd layer 0.8 m/min. respectively. The mean value of the
scattering strength of each layer was as follows : the 1st layer, -39.1 dB, the 2nd layer, -34.7 dB and the 3rd layer, -36.0 dB. The composition organisms of each layer were as follows
: the 1st layer, Pollichthys maulli, Maurolicus japonicus, Lophogaster japonicus ; the 2nd layer,
Bemthosema pterotu, and the 3rd layer, Pilchard., Secondly, considerations were made on a measuring theory applicable for the estimation of
organism abundance in the ultrasonic scattering layers. With the use of frequency 50 kHz, at
the indoor 50 tons water tank of the Kagoshima prefectural cultural fishery center, were carried
out 2 sorts of experimental workings : － the measuring of the target strength of one individual
in the four kinds of organisms composing the ultrasonic scattering layers, and the workings to
examine the influence of the secondary radiation on the scattering strength. The target-movements were processed by a personal computer,
with the employment of the general purpose
signal analyser in processing the acoustic signal.
Through the considerations of the measurement theory, a formula 8-34 described in the thesis
and the approximate expression 8-63 indicated in the following :
10 log n = SV - 10 log (Tse + n・Tsm^[2])
were obtained. The target strengths of the individual organisms composing the ultrasonic
scattering layers were as follows, respectively : Bemthosema pterotu, -48.4 dB, Pollichthys maulli, -49.3 dB, Maurolicus japonicus, -50.0 dB, and Lophogaster japonicus, -52.9dB. In
the target strength pattern, there was a strong similarity between the above mentioned fishes
and the crustacea in the roll plane, but in the pitch plane, there was a large difference between
these two.
Lastly, the distribution of the organism abundance composing the ultrasonic scattering
layers in the Kagoshima bay was estimated by making use of the following three issues,
ascertained : namely, ① the target strength of the individual organisms obtained by the
measurements in water tank, ② the scattering strength of each ultrasonic scattering layer
obtained by the measurements on board the Nansei maru, and ③ the results of the organism
collections obtained by towing the Isaacs-Kidd midwater trawl net., The approximate 'organisum abundance' composing the ultrasonic scattering layers (1st layer, 2nd layer) was estimated in all the areas of the Kagoshima bay (excluding entrance area), the results obtained was as it follows : Bemthosema pterotu 115,000 tons, Pollichthys maulli 6,000 tons, Maurolicus japonicus 5,000 tons, and Lophogaster japonicus 13,000 tons, with
the confirmed result showing 140,000 tons total amount. While the total fish catches by
fishermen in all the areas of the Kagoshima bay were noted to be about 3,450 tons. Hence the
assumption that, due to the fact that the total abundance of the organisms composing ultrasonic
scattering layers was big enough, compared with the total fish catches, the ever lasting
importance of the ultrasonic scattering layers in the Kagoshima bay was reasonably confirmed.},
 pages = {227--377},
 title = {鹿児島湾における超音波散乱層に関する研究},
 volume = {36},
 year = {}
}