• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.1
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• pp.80-89
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• 2021

In Korea, marine fish landed at ports are randomly sampled on a periodic basis (e.g., daily or weekly), and body sizes (e.g., lengths and weights) of those sampled fish are measured. The motivation for our study is whether or not such measurements reflect the size distribution, especially the length distribution of fish landed (= a population), because such length measurements are key data for a length-based assessment model. The current sampling method is to sample fish landed at ports by body size group (e.g., very small, small, medium, large, very large), using the sampling weights as the number of boxes by body size group. In this study, we showed that length composition data about fish sampled by the current method did not represent the length frequency distribution of the fish landed, and suggested that an alternative sampling method should be applied of using the sampling weights as the number of fish landed by body size group. We also introduced a method for determining an appropriate sample size.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.4
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• pp.265-275
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• 2005

A prerequisite for deriving the abundance estimates from acoustic surveys for commercially important fish species is the identification of target strength measurements for selected fish species. In relation to these needs, the goal of this study was to construct a data bank for converting the acoustic measurements of target strength to biological estimates of fish length and to simultaneously obtain the target strength-fish length relationship. Laboratory measurements of target strength on 15 commercially important fish species were carried out at five frequencies of 50, 70, 75, 120 and 200 kHz by single and split beam methods under the controlled conditions of the fresh and the sea water tanks with the 389 samples of dead and live fishes. The target strength pattern on individual fish of each species was measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down aspect) to $+45^{\circ}$ (head up aspect) in $0.2^{\circ}$ intervals, and the averaged target strength was estimated by assuming the tilt angle distribution as N $(-5.0^{\circ},\;15.0^{\circ})$. The TS to fish length relationship for each species was independently derived by a least-squares fitting procedure. Also, a linear regression analysis for all species was performed to reduce the data to a set of empirical equations showing the variation of target strength to a fish length, wavelength and fish species. For four of the frequencies (50, 75, 120 and 200 kHz), an empirical model for fish target strength (TS, dB) averaged over the dorsal sapect of 602 fishes of 10 species and which spans the fish length (L, m) to wavelength (\Lambda,\;m)$ ratio between 5 and 73 was derived: $TS=19.44\;Log(L)+0.56\;Log(\Lambda)-30.9,\;(r^2=0.53)$.

• Fisheries and Aquatic Sciences
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• v.12 no.2
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• pp.152-161
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• 2009

The largehead hairtail (Trichiurus lepturus) is one of the most common fisheries stocks in the East China Sea and the Yellow Sea. The species is caught using a variety of fishing tools, such as a stow net or a long line, as well as jigging and trawling. Scientific investigations have been conducted throughout the world to enable evidence-based estimations for the management and protection of the main fisheries biomass. For example, inshore and offshore hydro acoustic surveys are performed annually using bottom- and mid-water trawls around the Korean Peninsula. However, to date, no acoustic survey has been conducted to estimate fish size distribution, which is necessary to construct a data bank of target strength (TS) relative to fish species, length (L), and frequency. This study describes the frequency and length dependence of TS among fishes in Korean waters for the purpose of constructing such a TS data bank. TS measurements of the largehead hairtail were carried out in a water tank (L 5 m$\times$width 6 m$\times$ height 5 m) at frequencies of 50, 75, 120, and 200 kHz, using a tethering method. The average TS patterns were measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down) to $+45^{\circ}$ (head up) every $0.2^{\circ}$. The length conversion constant ($b_{20}$) was estimated under the assumption that TS is proportional to the square of the length. In addition, in situ TS measurements on live largehead hairtails were performed using a split beam echo sounder.

• Korean Journal of Ichthyology
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• v.32 no.2
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• pp.55-62
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• 2020

The Relative weight index is an index for evaluating nutritional condition of fish by calculating a ratio of observed weight to standard weight. The purpose of this study is estimating standard Length-Weight relationships (standard LWRs) to calculate standard weight for application of relative weight index and analyze frequency distribution of relative weight index of 10 freshwater fish in the South Korea. The standard LWRs for each species was calculated by the Length-Weight data sets from 798 times of captures at 141 sites. The correlation of determination (r²) for all species was over 0.9 and values of parameter b were within the expected range according to Froese (2006). We calculated in increments of 10 from 10 to 90 percentile of relative weight index for each species, and it could be used as a standard for quantitative assessment of nutritional condition of freshwater fish.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.4
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• pp.404-409
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• 1999

The in situ target strengths of, maurolicus muelleri were measured by the split beam echo sounder system at the frequency of 38kHz.Target strengths were measured during the night time in order to obtain the pure separated echoes from the scattered individual. And also it was to establish reasonable threshold due to taking the signals like as the planktons and etc.Since Maurolicus muelleri is a typical micronektonic fish, they mainly consisted of deep scattering layers(DSLs), and had a vertical migration perrodically during daytime and at night.We found that the Maurolicus muelleri occupied about 99% of total catch. Total length ranged from 4.5 to 5.7cm with a mean of 5.2cm and a standard deviation of 0.22cm.The target strengths of Maurolicus muelleir ranged from -60.4 to - 52.7dB and -59.2 to - 52.5 dB in the water layer of 10~30m and 30~50m depth, perspectively. Mean target strength was -57.1dB/fish and -28.5dB/kg. The target strength had the relation with the total length of the fish as, TS=20logL-71.4.

• Korean Journal of Environmental Biology
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• v.31 no.4
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• pp.370-375
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• 2013

Exotic species in aquatic ecosystem generate various problems domestically as well as globally. Largemouth bass (Micropterus salmoides) which is a well-known exotic species globally, acts as a substantial disturbance factor on the native fish communities in Korea due to the high predation pressure and hence designated as a ecologically harmful species by Ministry of Environment. In this study, we investigated the impact of largemouth bass on Korean native fish population, crucian carp (Carassius auratus), to identify responses of the prey fish. Two fish species were collected at seven reservoirs distributed at the Nakdong River catchment area, and changes in length-frequency and length-weight relationship (LWR) were analysed depending on existence of large-mouth bass. At bass absent sites, ratio of under age 1 year individuals were small, and over age two years were dominant. Conversely, normal length-frequency distribution pattern was identified at bass absent sites. The LWR of crucian carp (fish smaller than total length of 160 mm were only considered as it is frequently consumed by bass predation) was different depending upon bass existence. The value of parameter b at bass absent reservoirs was 2.909, which was smaller than that of bass present reservoirs, 3.100. Our results imply that crucian carp at bass present reservoirs presented a different strategy to survive from predation by bass, through relatively rapid growth. We propose that other native species might have similar growth strategies like crucian carp.

• Korean Journal of Ichthyology
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• v.11 no.1
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• pp.72-85
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• 1999

A study on the larval fish assemblage around the front area was conducted in the Korea Strait in August, 1993. The front was found in the shelf break located in $35{\sim}36^{\circ}N$. A total of 125 species were found in the study area. Of these Engraulis japonicus was the most dominant species comprising 84.3% of the total fish larvae collected and followed by Maurolicus muelleri accounting for 7.7%. Gobiidae, Callionymidae and Pomacentridae showed higher frequency of occurrence. These five species can be divided into three groups. First group was comprised in the larval fish species such as E. japonicus and Callionymidae which were found in the whole study area. The second group was comprised of Gobiidae and Pomacentridae which were found in the warm area located in the southern part of the front area. The other species was M. muelleri found in the cold area located in the northern part of the front area including the front area. The assemblage, geological distribution and body length composition of the fish larvae in the Korea Strait would be mainly determined by the spawning ecology of the fishes, and the geological distribution and structure of the front which is formed in the ocean boundary between the Tsushima Current and the East Sea Cold Water.

• Korean Journal of Environment and Ecology
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• v.29 no.6
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• pp.873-883
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• 2015

From August 2012 to April 2013, the ichthyofauna and post-restoration properties of Yangjae stream were investigated. A total of 1,503 fish of 2 forms, 16 species and 5 families were studied during the survey period. A survey of the distribution of freshwater fish inhabiting Yangjae stream after restoration of the stream showed large populations of Zacco platypus and Rhynchocypris oxycephalus. From the frequency distribution of the total length for the Zacco platypus population inhabiting Yangjae stream, it was estimated that there are 4 distinct age groups, with an abundance of the 27-63 mm (Age $0^+$) category accounting for 51.3% of the population. The regression coefficient (b) for the length-weight relationship in Zacco platypus was 3.27, while the slope of the condition factor was positive, demonstrating that stable growth conditions are being maintained. Analysis of tolerance and trophic guilds showed a decrease in the numbers of sensitive species and insectivore species further downstream, and an increase in tolerant species and omnivore species. Principal component analysis using community indices and indices of biotic integrity (IBI) showed that there were differences according to the survey time: the first and second surveys showed major changes on certain single species populations while during the third survey, it was analyzed that the populations of various types of fish had established balance.

• Korean Journal of Environment and Ecology
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• v.30 no.4
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• pp.745-750
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• 2016

Morphological characteristics and population characteristics of the Rhynchocypris kumgangensis were investigated at Taehwa River from April 2014 to April 2015. This is the first record on R. kumgangensis not only from Guksu stream (the upstream region of Taehwa River, Ulsan-si Ulchu-gun Beomseo-eup Kuksu-ri) but also from the stream flowing into the Gangneungnamdae stream, in the southern part of East Sea, Korea. The morphometric characteristics of R. kumgangensis in the Taehwa River and the Han River are very similar except that the population at Taehwa River showed shorter caudal peduncle length than caudal peduncle depth when compared with the population at Han River. In terms of meristic character the population at Taehwa River showed fewer numbers of scales at the lateral line, above the lateral line and below the lateral line. Other than that, the two populations showed the same meristic characters. The fish cohabiting with R. kumgangensis mainly composed of Zacco platypus (25.2%), Rhynchocypris oxycephalus (24.1%) and Zacco koreanus (21.8%). Length frequency distribution analysis indicated that the length of the group ranged between 45~65 mm and the average length was 54.3 mm. Calculation of the length-weight relation of R. kumgangensis showed the value of constant a as 0.000002 and b as 3.34, and the Condition factor (K) was 1.10 an on average.

• Korean Journal of Environmental Biology
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• v.38 no.4
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• pp.667-677
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• 2020

This study was conducted to investigate the fish fauna and characteristics of the Carassius auratus population in the Boryeong Reservoir in Chungcheongnam-do from October 2017 to June 2018. The collected fish were identified as 3,506 individuals of 15 species from a total of nine families. The dominant and subdominant species were H. nipponensis with 1,706 (48.6%) individuals and C. auratus with 1,021 (29.1%) individuals, respectively. The biomass of C. auratus (246,130g), P. fulvidraco(50,610g), C. cuvieri (14,730 g), S. asotus (11,560 g), and C. carpio (10,930 g) was analyzed. The results of the community analysis showed a dominant index value of 0.87 (±0.2), a diversity index value of 0.78 (±0.5), an evenness index value of 0.47 (±0.2), and a richness index value of 0.99 (±0.5). The length-weight analysis of C. auratus showed a regression coefficient b of 3.06, and a condition factor (K) of 0.0004 with a positive slope. The frequency distribution of the total length analysis of the C. auratus population inhabiting the Boryeong Reservoir showed a high distribution of lengths between 140-160 mm and a low distribution between 230-280 mm. The normalized difference water index (NDWI) was analyzed over the Boryeong Reservoir water surface from 2013 to 2014 using Landsat 8 channel data. The areas where the NDWI was decreased were located at the inflow site of Ungcheon Stream.