금강 용담댐 하류의 어류군집 특성과 조사어구별 채집어종의 차이, 멸종위기어종의 서식양상을 밝히기 위해 2023년 5월부터 8월까지 족대와 투망, 일각망, 통발을 이용하여 5개 지점을 2회 조사하였다. 조사결과 11과 35종 2,010개체가 채집되었으며, 우점종은 참갈겨니(Zacco koreanus, 비교풍부도 30.1%), 아우점종은 돌고기(Pungtungia herzi, 11.9%), 그 다음으로 칼납자루(Acheilognathus koreensis, 8.6%), 긴몰개(Squalidus gracilis majimae, 7.4%), 눈동자개 (Pseudobagrus koreanus, 6.0%) 등의 순으로 우세하였다. 출현종 중 환경부지정 멸종위기야생생물은 I급의 감돌고기 (Pseudopungtungia nigra), II급의 돌상어(Gobiobotia brevibarba), 꺽저기(Coreoperca kawamebari) 등 3종이 출현하였고, 한국고유종은 칼납자루, 줄납자루(A. yamatsutae), 감돌고기, 쉬리(Coreoleuciscus splendidus), 참중고기(Sarcocheilichthys variegatus wakiyae), 긴몰개, 돌상어, 돌마자(Microphysogobio yaluensis), 참갈겨니, 참종개(Iksookimia koreensis), 눈동자 개, 금강자가사리(Liobagrus geumgangensis), 꺽지(C. herzi), 동사리(Odontobutis platycephala), 얼록동사리(O. interrupta) 등 15종(고유화율 42.9%)이, 외래어종은 생태계교란 생물로 지정된 배스(Micropterus salmoides)와 블루길(Lepomis macrochirus) 2종이 출현하였다. 군집분석 결과, 비교적 우점도(0.38~0.57)와 균등도(0.66~0.78)는 낮고 종 다양도 (2.01~2.52), 종 풍부도(2.98~3.94)는 높게 나타났다. 하천건강성평가(FAI)는 지점별 87.5~100.0으로 모두 매우좋음(A)으로 평가되었다. 어구별 출현결과를 보면 족대는 8과 23종 294개체, 투망은 6과 19종 627개체, 일각망은 8과 25종 824개체, 통발은 9과 20종 265개체로 나타나, 종수와 개체수는 일각망이 가장 높았고, 종수는 투망이, 개체수는 통발이 가장 적었다. 어구별 채집 특성을 보면, 투망은 표층성 유영어류가, 족대는 소형 저서성 어류가 많이 채집되었고 일각망은 종수와 개체수가 가장 풍부하게 채집된 어구이며, 통발은 이입어종인 꺽저기가 많이 채집되어 주목되었다. 출현 어류 중 멸종위기종 I급인 감돌고기는 비교적 안정적으로 서식하고 있었고, II급의 돌상어는 소수 서식이 확인되었으며, 꺽저기는 국내도입종으로 많은 개체가 서식하고 있어 주목되었다. 교란요인으로 조사기간 중 일부 구간이 하천공사로 어류 서식지가 교란되고 있었고, 생태계교란생물로 지정된 배스와 블루길이 각각 17개체 출현하여 우려되었다. 따라서 본 구간에서 안정적인 어류 서식을 위해서는 무분별한 하천공사는 지양해야 하고, 배스와 블루길의 개체수를 감소시킬 수 있는 구제방안이 필요하며, 최근 도입된 꺽저기의 서식범위 및 양상, 생태계에 미치는 영향 등에 대한 연구가 요구되었다.

River estuaries are dynamic and productive ecosystems with high regional biodiversity. Environmental DNA (eDNA) has become a useful approach to assessing biodiversity in aquatic ecosystems. This study was conducted to investigate fish community characteristics and species diversity in two river estuary ecosystems, the Taehwa River and Changwon Stream. We further compared conventional and eDNA metabarcoding analyses of the fish communities. The conventional survey was performed in May, July, and October 2022, while the eDNA analysis was conducted only in May. We observed various fish species with different life histories, including carp, goby, and marine fish. We also found that migratory fish, such as dace Tribolodon hakonensis, sweetfish Plecoglossus altivelis, and eel Auguilla japonica, occurred in the Taehwa River, suggesting high river connectivity. Marine fish species were predominant in the Changwon Stream, as this river is located close to the sea. The diversity indices showed that the Taehwa River generally had higher species richness, evenness, and diversity values than the Changwon Stream. A total of 9-19 species were detected in the conventional survey for the three sites, whereas 11-18 species were found from eDNA analysis. The findings indicate that the sensitivity of eDNA was similar to or higher than that of the conventional method. Our study findings suggest the efficiency and efficacy of eDNA-based fish community monitoring, although with some shortcomings in applying the genetic marker to Korean fish, including no clear-cut distinction for Korean endemic species and/or genetically closely related species groups.

In order to investigate the cause and magnitude of scale effect occurring in the model experiments of fishing nets, five pairs of Nylon pyramid nets and one pair of PE ones in which all the two nets paired were equal each other in the factors determining their flow resistance, i. e., the ratio d/l of diameter d to length l of bars, the angle f between two adjacent bars, the attack angle q of nettings to the water flow, and the wall area S of nets, and different in the values of d and l were prepared. Then, the nets were attached to the circular steel frame alternately and their flow resistances with shapes in water were measured on the sea ascribing no turbulent flows by using the tension meter made of a block bearing for the experiment. All the Nylon nets were spreads out easily in water to form a circular cone at relatively low velocity of water and showed the resistance smaller a little in the nets with larger d and l than them with smaller d and l, because the filtration of water through meshes become easier in nets especially with larger l. But PE nettings were not spread out sufficiently on account of their small flexibility and showed higher resistance especially in them with thicker twines. Therefore, the difference in bar length or mesh size and flexibility of nettings between prototype and model nets are regarded to become factors ascribing scale effect. Especially the influence of the difference in mesh size may become large significantly in actual model experiments because the mesh size of model nets is decided at much larger value than that given by scale ratio and so the difference of mesh size between the two nets become much larger than that between nets used in this experiment.

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×lO-4kg/m3 in the 1994 survey area and 1.3636×lO-4kg/m3 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.