• Fisheries and Aquatic Sciences
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• 제15권4호
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• pp.337-343
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• 2012

The Korean bottom trawl survey was conducted using a trawl designed by the National Fisheries Research and Development Institute (NFRDI). The capture efficiency and size selectivity of this trawl for snow crab Chionoecetes opilio was investigated by experimental tows. An auxiliary sampling net (underbag) was attached beneath the trawl net to capture crabs escaping under the trawl footrope. Experimental tows were made by the same vessel speed (3.4 knots) as in the bottom trawl survey, but toing time was shortened from the standard 30 min to 10 min to reduce possible trawl distortion due to the high catch rate of mud and debris in the underbag. In averaged over 17 tows conducted between 110-383 m depth, trawl efficiency of both males and females combined increased from about 10% at 20 mm (carapace width) to about 70% at 100 mm, with a width of 50% capture equal to 78 mm.

• 수산해양기술연구
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• 제32권3호
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• pp.257-265
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• 1996

The combined hydroacoustic and bottom trawl surveys were conducted in the Cheju southeastern area by the training ship "KAYA" belong to Pukyong National University in July 1995 and the traning ship "NAGASAKI MARl]" belong to Nagasaki University in April 1994, respectively. The main purpose of the investigations was to provide the basic data for the management and the biomass estimation of commercially important demersal fish stocks in this area. Fish samples were collected by bottom trawling from 10 trawl stations randomly selected in the survey area, and the species and length compositions of trawl catches were examined. The fish school target strength for demersal fish aggregations was related to the catchability of trawl net with a 90 mm mesh codend. The most abundant species in the 1995 trawl stations were Japanese flying squid, sword tip squid and red horsehead and that of the 1994 trawl stations Japanese flying squid and blackmouth goosefish. The average weight per cubic meter of trawl catches collected by bottom trawling in the Cheju southeastern area were $1.0791{\times}lO^-4$kg/$m^3$ in the 1994 survey area and $1.3636{\times}lO^-4$kg/$m^3$ in the 1995 survey area, respectively. The catch data by cover net suggest that the efficiency of trawl net could affect the weight normalized target strength values for demersal fish aggregations. That is, the average target strength per unit of weight dropped from - 33.1 dB/kg using the total catch by codend and cover net to - 30.5 dB/kg using only the catch data by codend, and a change of2.6 dB/kg was observed.ange of2.6 dB/kg was observed.

• 수산해양기술연구
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• 제32권3호
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• pp.266-272
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• 1996

The distribution and abundance of fish in the Cheju southeastern area was studied by the combined hydroacoustic and bottom trawl surveys in April 1994 and in July 1995, respectively. The main purpose of these investigations was to provide the basic data for this management and the biomass estimation of commercially important demersal fish stocks in this area. The hydroacoustic surveys were performed by using a 50 kHz scientific echo sounder system with a microcomputer-based echo integrator. Acoustical measurements of fish abundance and distribution were conducted along the cruise tracks of research vessel and during all trawl hauls by continuous echo sounding. The average weight-normalized target strength for demersal fish aggregations was derived from the relationship between the mean volume backscattering strength for the depth strata of trawl hauls and the weight per cubic meter of trawl catches. The geographical distribution of fish stocks in the 1994 survey area was investigated in relation to oceanographic conditions. The results obtained can be summarized as follows: 1. From the 1994 and 1995 survey data, the relationship between the mean volume backscattering strength (, dB) for the depth strata of trawl hauls and the weight (W, kg/$m^3$) per cubic meter of trawl catches was expressed by the following equation = - 32.8+ lOlog(W) The average weighted-target strength value at 50 kHz derived from this equation was .. 32.8 dB/kg. 2. In 1994 and 1995, both surveys showed a trend of decreasing fish abundance toward the southern area of the Cheju Island with high densities offish along the west coast ofth.e Tsushima Island. The highest demersal concentrations in the southern area of the CheJu Island appeared in bottom waters colder than $12^{\circ}C.$. . 3. From the results of combined bottom trawl and hydroacoustic surveys, the estunated fish densities in the southeastern area of the Cheju Island were 1.5488 x $10^-4$kg/$m^3$ in the 1994 surveyand 1.9498 x $10^-4$kg/$m^3$ in the 1995 survey, respectively.

• 한국수산과학회지
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• 제50권5호
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• pp.594-604
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• 2017

The Korean National Institute of Fisheries Science (NIFS) has biannually (spring and fall, respectively) deployed a bottom trawl survey along the coastal areas for last decade, taking samples on a regular basis (i.e., a systematic sampling). Despite the availability of the survey data, NIFS has not yet officially reported the estimates of the groundfish population sizes as well as has not evaluated uncertainty of the estimates. The objectives of our study were to infer the relative size of a fish population, applying two different sampling techniques (namely simple and stratified sampling) with different observation units to the NIFS survey data, and to compare those two techniques in bias and precision. For demonstration purposes, we used data on Pacific cod (Gadus macrocephalus) collected by the 2011-2015 surveys, and the results of simple and stratified sampling showed that the point estimates and precision varied by observation unit as well as the sampling technique.

• 수산해양기술연구
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• 제52권1호
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• pp.24-35
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• 2016

An acoustic and trawl pilot survey using a small vessel was conducted in Jinhae bay of the South Sea of South Korea on April 13~14, May 11~13 and June 8~10, 2015. During the survey, acoustic data was collected and bottom trawls were conducted at the same time. First, various noises were eliminated by using the Park method based on the Wang method (Wang et al., 2015; Park et al., 2015), the species compositions and catch rate from each bottom trawl were observed, and spatial distribution of fishery resources in the water column and their nautical area scattering coefficient (NASC) were investigated through acoustic data. During the entire survey period, 12 orders, 33 families and 41 species were caught. The most caught species in April, May and June were Okamejei kenojei, Zoarces gilli and Pholis nebulosa, respectively. Fish schools were observed near the line of net mouth height in April. Numerous weak scatters were presented on the echograms in May and June. Many fish schools appeared in between the water surface and 20 m deep in May. The NASC value from entire water columns was the lowest in April ($35.9m^2/n{\cdot}mile^2$) and highest in June ($1541.3m^2/n{\cdot}mile^2$).

• 한국수산과학회지
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• 제48권6호
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• pp.960-968
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• 2015

This study examined the spatiotemporal distribution of demersal fish aggregations in the Northern East China Sea by conducting a trawl survey with hydroacoustic devices. A bottom trawl was used for this survey and fish density was determined from the catch data. Acoustic data were collected at frequencies of 38 and 200 kHz from November to December 2014 and converted into the nautical area scattering coefficient (NASC, $m^2/n{\cdot}mile^2$). In the catch data analysis, the range of catch per unit area by station was $26-8,055kg/km^2$ and for the acoustic data, that of the NASC was $0.45-34.80m^2/n{\cdot}mile^2$. The values were significantly correlated. The combined results of both surveys found that the density was highest at St. 5 ($33^{\circ}$ 10.3', $126^{\circ}$ 23.3') and lowest at St. 8 ($33^{\circ}$ 20.7', $127^{\circ}$ 36.3'). The application of hydroacoustic methods offers a new approach for estimating the biomass of demersal fish aggregations.

• 한국수산과학회지
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• 제48권5호
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• pp.798-804
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• 2015

The distributions of demersal fish along the coast of the South Sea, Korea, were estimated from a hydroacoustic survey and bottom trawl catches in April of 2015. Acoustic data were collected at 38 kHz, and converted into the nautical area scattering coefficient (NASC, m²/n·mile²) for 0.1 n∙mile along eight transects during day and nighttime. Various demersal fish species were collected and the dominant species comprised no more than half of the catch. The estimated acoustic density of demersal fish compared well with the cumulative catch weight from bottom trawl catches in daytime, but showed a low correlation at nighttime. The NASC of pelagic fish determined for anchovy was correlated with water temperature. The combined hydroacoustic and trawl method can be used to understand the spatial/temporal structure and estimate the density of demersal fish in coastal areas.

• 수산해양기술연구
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• 제26권2호
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• pp.143-150
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• 1990

동지나해의 어업자원량을 정량적으로 평가하기 위한 시도로서, 부산수산대학교와 일본 북해도대학이 공동으로 실시한 제1차 동지나해의 저서어족자원조사중에서 계량어군탐지기를 이용하여 수집한 각종의 기초자료를 분석, 검토한 결과를 요약하면 다음과 같다. 1. 동지나해의 24회 조사 Line에서 저층 Trawl에 의해 어획된 어종수는 총 96어종이고, 1시간 예망당 평균어획량은 58.8kg/hour이었다. 2. 저층 Trawl을 행한 수탐층(약 4.5m)에 분포하는 어군의 평균체적산란강도는 25KHz와 100KHz에서 각각 -63.9dB, -67.3dB로서 저주파수의 경우가 고주파수보다 약 3.4dB 더 높았다. 3. 전수탐층(송수파기과 해저간)에 분포하는 어군의 평균체적산란강도는 25KHz와 100KHz에서 각각 -61.9dB, -67.0dB로서 역시 저주파수의 경우가 고주파수보다 약 1.5dB 더 높았다. 4. 저층 Trawl을 행한 수탐층에 분포하는 어군의 평균체적산란강도(SV, dB)와 이 때 어획된 전위제적당의 평균어획량(kg)으로부터 추정한 kg당의 평균반사강도는 25KHz와 100KHz에서 각각 -23.6dB/kg, -26.3dB/kg로서 저주파수의 경우가 고주파수보다 약 2.7dB/kg 더 컸다.

• Fisheries and Aquatic Sciences
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• 제21권8호
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• pp.24.1-24.9
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• 2018

The Korean bottom trawl survey has been deployed on a regular basis for about the last decade as part of groundfish stock assessments. The regularity indicates that they sample groundfish once per grid cell whose sides are half of one latitude and that of one longitude, respectively, and whose inside is furthermore divided into nine nested grids. Unless they have a special reason (e.g., running into a rocky bottom), their sample location is at the center grid of the nine nested grids. Given data collected by the survey, we intended to show how to appropriately estimate not only the survey index of a fish stock but also its uncertainty. For the regularity reason, we applied the systematic sampling theory for the above purposes and compared its results with a reference, which was based on the simple random sampling. When using the survey data about 11 fish stocks, collected by the spring and fall surveys in 2014, the survey indices of those stocks estimated under the systematic sampling were overall more precise than those under the simple random sampling. In estimates of the survey indices in number, the standard errors of those estimates under the systematic sampling were reduced from those under the simple random sampling by 0.23~27.44%, while in estimates of the survey indices in weight, they decreased by 0.04~31.97%. In bias of the estimates, the systematic sampling was the same as the simple random sampling. Our paper is first in formally showing how to apply the systematic sampling theory to the actual data collected by the Korean bottom trawl surveys.

• 수산해양기술연구
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• 제38권3호
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• pp.241-248
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• 2002

황해, 동중국 해역에서 서식하는 어업생물 자원의 평가 및 그 관리에 필요한 기초 자료를 수집하기 위한 시도로서, 1997 년도에 부경대학교와 일본 장기대학이 공동으로 실시한 어업자원조사중에서 주로 계량어군탐지기를 이용하여 수집한 자료를 분석, 고찰한 결과를 요약하면 다음과 같다. 1 황해, 동중국해에 설정한 9개의 조사정점에서 저층트롤에 의한 어획량은 7.7~182.48 kg/hour이었고, 그때 어획된 어종수는 7~34 종이었다. 2. 1997년 5월에 동중국해에 있어서의 어군의 분포는 황해 중부의 저층 냉수역과 동중국해 중앙해역의 저층 고온수역, 또 쿠로시오계의 난류와 황해 냉수 및 대륙 연안수의 사이에 형성된 제주도 남부의 전선역에서 그 어군도가 매우 높았다. 3. 황해, 동중국해의 조사대상해역의 전수층부와 저층부에 대한 어군의 평균 체적산란강도는 각각 -74.57 ㏈, -68.24 ㏈로서 저층부가 전수층부에 비해 5.67 ㏈ 더 높았다. 4. 본 연구의 조사대상해역에 대한 어군의 분포밀도를 추정한 결과, 전수층에 대해서는 6.65$\times$$10^{-5}$ kg/㎥이었고, 저층부에 있어서는 2.86$\times$$10^{-4}$ kg/㎥이었다.