Jung-Hwa Choi

Acoustical backscattering strength characteristics and density estimates of Japanese common squid distributed in Yellow Sea

), which was distributed in East Sea, was recently caught in Yellow Sea during asummer season from 2006. The fishery resources density research was carried out in Korea-ChinaProvisional Water Zone using trawl fishing gear and acoustics in National Fisheries Research &Development Institute in Korea. This paper showed the analysis on the acoustical backscattering strength bytwo frequencies(38kHz, 120kHz) for Japanese common squid by acoustical scattering theoretical modelbased on size distribution for survey period, and estimate the density distribution for squids integrated layerwhich was extracted from any scatterers distributed in water column using two frequency difference methodwhich has been used to distinguish fish shoals or specific target scatterers from sound scattering layer whichis composed of various zooplankton. Furthermore, the entire range of their density estimation was suggestedusing by Monte Carlo simulation under considering each uncertainty such as size distributions or swimmingangle and so on in survey area.Key words : Japanese common squid, Todarodes pacificus, Acoustical scattering theoretical model, DWBA,Density estimates

Seasonal Variation of Species Composition in Marine Organisms at Oryukdo in the Southeastern waters off Korea

Seasonal variation of species composition in marine organisms around Oryukdo of Busan was investigated using a gill net between 2009 and 2011. A total of 82 species, 52 families, and 6 taxa were collected during the sampling periods. Species were included two species in Cnidaria, one in Urochordata, 12 in Mollusca, 12 in Crustacea, seven in Echinodermata, and 48 in Pisces. The dominant species were Crepidula onyx, Asterina pectinifera, Ceratostoma burnetti, Asterias amurensis, Anthocidaris crassispina, and Trachurus japonicus. These six species accounted for 48.4% in the total number. Diversity indices were highest in spring 2009 (2.77) and lowest in spring 2011 (1.66). Seasonal variation of species composition and abundance in marine organisms corresponded with the water temperature.

Population Dynamics of Smoothshell Shrimp, Parapenaeopsis tenella from the Coastal Area of Geomun-do, Korea

Parapenaeopsis tenella occurs widely on the south and west coasts of Korea. Sex ratio showed seasonal variations, with a mean value of 48.6% for the females. The species produces one cohort a year, with the ovaries ripening from July to August. Insemination took place from July to August, as more than half of the females sampled in the study over 14 mm CL were inseminated. Gonadosomatic index (GSI) reached the maximum between July and August. The smallest mature female was 11 mm CL. Size at 50% sexual maturity (), determined from both mature females and inseminated females, was 12.53 mm and 12.28 mm CL, respectively. The life span of females appeared to be 14-15 months according to size frequency distributions, while that of the male was 13-14 months. Population growth was estimated by the modified von Bertalanffy growth function incorporating seasonal variation in growth. Based on the growth parameters (K

Forecasting common mackerel auction price by artificial neural network in Busan Cooperative Fish Market before introducing TAC system in Korea

Using artificial neural network (ANN) technique, auction prices for common mackerel were forecasted with the daily total sale and auction price data at the Busan Cooperative Fish Market before introducing Total Allowable Catch (TAC) system, when catch data had no limit in Korea. Virtual input data produced from actual data were used to improve the accuracy of prediction and the suitable neural network was induced for the prediction. We tested 35 networks to be retained 10, and found good performance network with regression ratio of 0.904 and determination coefficient of 0.695. There were significant variations between training and verification errors in this network. Ideally, it should require more training cases to avoid over-learning, which leads to improve performance and makes the results more reliable. And the precision of prediction was improved when environmental factors including physical and biological variables were added. This network for prediction of price and catch was considered to be applicable for other fishes.

New extension range and complementary description of Eurytemora americana (Calanoida: Temoridae) in northern Korea

BackgroundThe brackish calanoid, Eurytemora americana Williams, 1906, is reported in the northern part of Korea. It is found to be an important copepod in the mesozooplankton community structure from the estuarine and shallow waters. The range extension and of E. americana is reported additionally to previously known distributional range from brackish waters of the South Atlantic Ocean, United Kingdom, Canada, English Channel, Iceland, the North Atlantic Ocean, the North Pacific Ocean (Japan, Korea, and Russia), and the North Sea. In this study, both sexes of E. americana are redescribed and illustrated including their undescribed mouthparts.ResultsThe most important characters that have been overlooked in the previous descriptions are: shape of the last pedigerous somite in female, structure of the genital double-somite, and ornamentation of the fifth leg in both sexes.ConclusionThe distributional range of E. americana is now given with its northern and southern hemisphere limit as 70 to 37°N in the North Pacific and 38°S in the Southwest Atlantic.

Target-strength Measurements of Sandfish Arctoscopus japonicus

The goal of this study was to estimate the target strength (TS) of the sandfish Arctoscopus japonicus using in-situ and ex-situ methods with an echosounder. For the in-situ TS measurement, the survey was conducted by taking hydroacoustic measurements at 38 and 120 kHz and using a coastal gill net, in Goseong, in the northeastern sea of Korea in early December 2009. Ex-situ measurement of TS used live specimens and the tethering method, and was conducted at 120 kHz. The distribution of fork length (FL) was bimodal: 14.6–19.8 cm (n = 241 individuals, mean = 17.0 cm) for males and 16.3–24.5 cm (n = 105 individuals, mean = 19.6 cm) for females. The in-situ TS ranged from −79.8 to −59.1 dB (mean = −74.3 dB for males and −64.1 dB for females) at 38 kHz and −79.9 to −56.2 dB (mean = −74.3 dB for males and −64.1 dB for females) at 120 kHz. The mean TS of females was approximately 10 dB higher than that of males at each dominant frequency. The female ex-situ TS values ranged from 68.5 to −54.6 dB, and those of males was from −67.7 to −59.3 dB. The mean TS value for females was 2.9 dB higher than that of males. These results may be used in echo-integration surveys of sandfish to estimate their abundance and seasonal distribution.

Korean-Russian Surveys of Cephalopods in the East/Japan Sea in November and December 1993 and 1994

We examined the distribution and biology of cephalopods collected during joint Korean-Russian surveys of the East/Japan Sea in 1993 and 1994. A total of six species of cephalopods belonging to five families were collected during the surveys: one sepiid squid, four teuthid squids, and one octopus.