• Ocean and Polar Research
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• v.39 no.2
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• pp.73-84
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• 2017

The probability distribution of ichthyoplankton is important for enhancing the precision of sampling while reducing unnecessary surveys. To estimate the ichthyoplankton detection proportion (IDP) and its margin of error (ME), the monitoring information of the chub mackerel's (Scomber japonicus) ichthyoplankton presence-absence sampling data has been were collected over approximately 30 years (from 1982 to 2011) in the Korean coastal seas. Based on the computed spatial distributions of the mackerel's IDP and ME, the confidence interval (CI) range, defined as 2 ME, decreases from approximately 80% to 40% as the sample size n increases from 4 to 24 and the ME is approximately 40% in the typical (seasonal survey) case n = 4 per year. The IDP and ME off Jeju Island are relatively high at the 0.5-degree smoothing level. After increasing the spatial smoothing level to 1.0-degree, the ME decreased, and the spatial distribution pattern also changed due to the over-smoothing effects. In this study, the 0.5-degree smoothing is more suitable for the distribution pattern than the 1.0-degree smoothing level. The area of the high IDP and the low ME on the mackerel's ichthyoplankton was similar to the estimated spawning ground in the Korean peninsula. This information could contribute to enhancing for the spawning ecology surveys.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.4
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• pp.498-507
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• 2021

Ichthyoplankton (fish eggs and larvae) were collected seasonally collected from 2017 to 2019 to clarify whether Dokdo serves as a fish spawning and/or nursery ground. Fish eggs were identified and classified into 16 species. The dominant fish egg species were Engraulis japonicus, Maurolicus japonicus, and Parajulis poecilepterus. Fish larvae were identified and classified into 15 species. The dominant fish larvae species were E. japonicus, M. japonicus, and Sebastes owstoni. A cluster analysis similarity percentages revealed two distinct groupings according to sample location (stations) with E. japonicus and M. japonicus as the main group influencers. E. japonicus was the dominant species off Dokdo. The species diversity and abundance peaked in summer. The diversity index, richness index, and evenness index fluctuated seasonally. There were no predominant species variations among the years. Sedentary species such as P. poecilepterus, Semicossyphus reticulatus, and Glyptocephalus stelleri occurred in the inshore stations. E. japonicus, M. japonicus, and Trachipterus trachypterus occurred in the offshore stations. Our results show these species use Dokdo as spawning and nursery grounds.

• Korean Journal of Environment and Ecology
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• v.34 no.6
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• pp.551-557
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• 2020

This study surveyed the ecological characteristics of Ladislabia taczanowskii at Songcheon Stream from March to November 2019. The species inhabited upstream, where the riverbed structure was mostly covered with boulders and cobbles. The water depth was 31-148 cm, and the stream velocity was fast at 0.94±0.23 (0.51-1.39) m/sec. The gender ratio of females to males was 1 : 0.89. The age according to the total length frequency distribution indicated that the group with 38-70 mm below in total length was one year old, the group with 70-100 mm was two years old, the group with 100-120 mm was three years old, and the group over 120-128 mm was over four years old. The total length of sexually mature fishes was 70 mm for females and 75 mm or more for males. The spawning season was from May to August, and the water temperature was 15.5-20.1℃ during the period. The prosperous spawning season was from June to July, and the water temperature was 15.8-17.2℃ during the period. The spawning ground was where the riffle began in the pool, and its bottom was formed of sand and gravel. The width was about 150 cm, and the water depth was 20 to 50 cm. The average number of eggs in the ovaries was 821 (401-1,314) per matured female, and the matured eggs were yellowish and spherical with a mean diameter of 1.62±0.02 (1.43-2.01) mm. The live foods of L. taczanowskii Cyanophyta, Chlorophyta, Bacillariophyta, Ephemeroptera, and Diptera. The feeding habit of L. taczanowskii is omnivorous, but more than 90% of the stomach content was attached algae.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.17 no.1
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• pp.68-80
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• 1984

Garolim Bay is not only important fishing ground but also expected area for the tidal power plant. The construction and operation of tidal power plant will make change the ecosystem of this bay. Therefore, the actual fisheries stocks should be precisely understood for the effect estimation and overall utilization of the bay after the construction of the tidal power plant. During the study period from January through December in 1981, forty-six adult fishes species, 3 species of fish egg and 25 fishes larvae species have occurred in the bay. Considering the result on monthly distribution of eggs and larvae, the inner area of the bay seems to be important as nursing ground of larvae spawned at the outside bay in winter, e. g., Ammodytes personatus, and Enedrias sp. This inner bay is also major spawning ground for many species spawning in spring and summer, e. g., Gobiidae, Konosirus punctatus, Engraulis japonica, etc. Taking into consideration the annual mean production for three years($1978{\sim}1980$), there are two major fishing seasons. The one is in May-June for Enedrias larvae stock, and the another in October-November for big eyed herring stock. For the mariculture stocks, short necked clam, oyster and laver are important species. After construction of the tidal power plant, the migratory species, i. e., larvae of Enedrias and Ammodytes personatus, Mugil cephalus, Konosirus punctatus, etc. will be directly damaged by the interuption of migration route. On the otter hand, the change of physico-chemical factors of seawater will also affect the ecosystem of the bay. Consequently, for the overall utilization of the bay after construction, the actual ecosystem including the fisheries stocks, must bs precisely revealed, and the mechanical designs, e. g., sluice position and its demension, should be also considered with these biological characters of the bay.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.238-246
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• 1991

In order to make clear the mechanism forming the fishing ground of anchovy drag net in connection with water temperature, catch and oceanographic data for the years of 1970-1988 in the Southern Sea of Korea were analyzed. The annual catch of anchovy drag net was about 21,000M/T in 1970 but it was increasing largely so far 100,000M/T in recent years. The fishing season of anchovy drag net is the whole year beside the prohibition season established in aims to protect the spawning group of anchovy, and then in the best season of the period from July to December, the fishing ground is made up in the coastal area joining Yosu, Namhaedo and Bangeojin. There were some evidences that the fishing condition was controlled by the oceanographic condition, especially water temperature, that is, when there was large difference in water temperature between the south area of the Eastern Sea and the west area of the southern Sea and the thermocline is formed strongly in the larger less than 20m, the fishing condition was good. On the other hand, there was a very effective correlation between the catch(X) of anchovy spawning group in Spring by other fishing gears, mainly drift net and that(Y) of the little size of anchovy by drag net in Autumn, expressed by the relative equation, Y=62,246+1.3X, r=0.63.

• Journal of Aquaculture
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• v.21 no.4
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• pp.331-338
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• 2008

Monthly changes in the gonadosomatic index (GSI) and hepatosomatic index (HSI) of wild river puffer Takifugu obscurus, and water quality environment in spawning area during breeding season were investigated from March 1995 to February 1996. Monthly changes in GSI and HSI of T. obscurus, that was cultured in low salinity, were calculated. The external morphology of the gonads, germ cell differentiation during gametogenesis and the reproductive cycle with the gonad developmental phases were investigated by histological analysis. The optimum water quality environment in Ganggyung, Choongcheongnam-do, where is spawning ground of wild T. obscurus, was $15-20^{\circ}C$ (water temperature) and 0 psu (salinity). Monthly changes in the GSI in females and males reached a maximum in May, and then rapidly decreased. Therefore, it is assumed that in the natural condition the spawning period of wild T. obscurus is May to June. In females and males, it showed a negative correlationship between the GSI and HSI. The external morphology of the gonads in female and male T. obscurus, that was cultured in low salinity, is composed of a pair of saccular structure. Based on monthly changes in the GSI, it is assumed that in female T. obscurus, that was cultured in low salinity, spawn from March through May. Therefore, it showed a negative correlationship between changes in the GSI and HSI. On the whole, in females and males, it showed a similar pattern between wild and cultured T. obscurus. The reproductive cycle with the gonad developmental phases can be classified into successive five stages in females: the early growing stage, late growing stage, mature stage, ripe and spent stage, and recovery and resting stage. In males, that can be divided into successive four stages: the growing stage, mature stage, ripe and spent stage, and recovery and resting stage. In case of wild T. obscurus, the spawning period has once a year, however, those cultured in the high water temperature ($20-27^{\circ}C$) - low salinity (under 3.3 psu) condition have reproductive characteristics having possibilities of discharge of eggs and sperms year-round as a multiple spawner.

• Ocean and Polar Research
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• v.24 no.4
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• pp.443-448
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• 2002

A study on the ichthyoplankton assemblage was conducted around Dokdo in the East Sea in September 1999 and May 2000. Sixteen species of fish larvae including eggs were collected during the surveys. Anchovy (Engraulis japonicus) eggs and larvae were comprised of 2.0% and 94.5% of total samples in number, respectively. Muller's pearlside (Maurolicus muelleri) eggs and larvae were comprised of 95.0% and 3.2%, respectively. The other species mostly composed of warm water species were less than 2% of total samples in number. The number of species and abundance of the fish lawae and eggs were higher in September than in May. Although there were limited data on the ichthyoplankton around Dokdo in summer and winter, this study area seems to be used for the spawning or nursery ground of fishes.

• Korean Journal of Ichthyology
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• v.13 no.2
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• pp.123-128
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• 2001

The reproductive ecology of Gobiobotia brevibarba was investigated at Hongchen River of Bangokri, Seomyon, Hongcheongun, Kangwondo, from March 1999 to February 2000. The favorite habitat was a stretch of river with fast flow and a stream bed mostly covered with cobbles and pebbles. The spawning ground was a riffle area 20~50 cm deep, with a current velocity of 0.6~1.3 m/sec, and a bottom consisting of cobble and boulder. The sex ratio of female to male was 1 : 0.86. Peak spawning season was May when water temperatures rose to $18{\sim}20^{\circ}C$. Male and females became sexually mature when they attained more than 40 mm and 50 mm in body length, respectively. The average number of eggs in the ovary was $2,040{\pm}400.57$ and the egg diameter was $1.98{\pm}0.06\;mm$. The matured eggs were demersal, spherical, and dimmed light yellow in color.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.2
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• pp.173-179
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• 2012

The common squid $Todarodes$ $pacificus$ is a dominant species in Korean waters, where it is captured preponderantly by the angling fishery. The spawning and nursery grounds of $T.$ $pacificus$ extend from the southern East Sea to the northern East China Sea. Consequently, the environmental conditions in this area during the spawning and nursery seasons might affect the abundance of $T.$ $pacificus$. This study, analyzed the relationship between the distribution of zooplankton and the abundance of $T.$ $pacificus$ and variation in the squid angling fishing grounds in Korean waters. There was a positive relationship between the fluctuations in zooplankton and the catch per unit effort (CPUE; $kg{\cdot}day^{-1}{\cdot}person^{-1}$) of the angling fishery in the East Sea of Korea. The main fishing season is from July to December and the CPUE was closely related to the zooplankton biomass in April in the East Sea. Recently, the center of the squid jigging ground has moved drastically from the area around Ulleung Island to the northern East Sea. We postulate that the fishing grounds of the squid angling fishery will move farther north with climate change.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.4
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• pp.527-534
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• 2015

The twenty six specimens of leptocephali (15.8-32.6 mm TL) of the family Congridae, collected from southeastern waters offshore of Jeju Island during August 2014, and were identified by means of morphology and genetics. Those specimens were identified as belonging to the family Congridae based on various combinations of morphological characters. An analysis of the partial 12S rRNA sequences (886 base pairs) of mitochondrial DNA showed that our specimens must be Gnathophis nystromi, because their sequences were concordant with those of G. nystromi adult (genetic distance= 0.001), furthermore their total myomeres being consistent with those of G. nystromi adult. Catch rates of G. nystromi leptocephali were higher in the offshore regions than coastal regions of Jeju Island. The smallest leptocephali (< 20 mm TL) were collected offshore from Jeju Island. We hypothesize that one of the spawning grounds of G. nystromi is located offshore in the Jeju Island. In conclusion, the hatched preleptocephali of G. nystromi might have been transported from offshore near Jeju Island to the Korea Strait by the Kuroshio Current and Tsushima Warm Current.