Comparative fishing experiments were conducted in the eastern coastal waters near Uljin, Korea from 2002 to 2004, using the experimental trammel nets to estimate the selectivity for spinyhead sculpin Dasycottus setiger. The inner panels of the nets were made of nylon monofilament with four mesh sizes (82.2, 89.4, 104.8, and 120.2 mm) while its two outer panels were made of twisted nylon multifilament with a mesh size of 510 mm. The SELECT (Share Each Length’s Catch Total) procedure with maximum likelihood method was applied to obtain a master selection curve. The different functional models (normal, lognormal, bi-normal, and logistic model) were fitted to the catch data. The lognormal model with the fixed relative fishing intensity was chosen as the best-fitted selection curve through comparison of model deviance and AIC (Akaike’s Information Criterion). The optimum relative length (the ratio of fish total length to mesh size) with the maximum relative efficiency was obtained as 2.492.

Species composition in the coastal waters off Ulleungdo of Korea were examined based on catches bimonthly collected by trammel net in 2013. A total of 711 individuals and 181.9 Kg were caught and catches were composed of 4 classes 15 orders 27 families 52 species including 44 Pisces, 4 Gastropoda, 3 Cephalopoda, and 1 Echinodermata. The dominant species in biomass were File fish (Thamnaconus modestus), Atka mackerel (Pleurogrammus azonus), and Greenling (Hexagrammos otakii). Data were summarized using hierarchical cluster analysis (HCA) and detrended correspondence analysis (DCA) to examine similarity in species composition for each month, and community structure in Ulleungdo was divided into two groups. Community structures in February, April and December with low temperature and well-mixed surface water were distinguished from those in June, August and October with high temperature and strong stratification, which could be attributed to temporal changes in dominant species. Atka mackerel and Spear squid mainly caught in February and April, disappearing in June, August and October, and File fish outburst was shown in October. Because the water off Ulleungdo has been under low human pressure, it could be a good case study to elucidate effects of climate change on community structure and ecosystem in the East sea. Continuous surveys and further studies are required to demonstrate migration route and distribution of dominant species and long-term changes in community structure in the water of Ulleungdo.

A series of field tests to estimate the size selectivity of monofilament and multifilament gill net for marbled sole, Pleuronectes yokohamae, were carried out 12 times with five different mesh sizes (86.6, 101.0, 121.2, 137.7 and 151.5mm) in the western sea of Korea from 2007 to 2009. The master selection curve was estimated by the extended Kitahara’s method. The total number of catch species was 23 and that of catch was 1,688 in the field tests. Marbled sole of total catch was 1,150 with 68.1 percent. In the monofilament trammel net, the optimum value of total length (TL) per mesh size (m) for 1.0 of retention probability was estimated 0.280 and the values of TL/m were estimated to be 0.187, 0.201, 0.210, 0.218 and 0.226 when the retention probability were 0.1, 0.2, 0.3, 0.4 and 0.5, respectively. In the multifilament trammel net, the optimum value of TL/m for 1.0 of retention probability was estimated 0.307 and the values of TL/m were estimated to be 0.195, 0.211, 0.222, 0.232 and 0.241 when the retention probability were 0.1, 0.2, 0.3, 0.4 and 0.5, respectively.

2005년 6월, 9월, 12월 및 2006년 3월에 동해안의 감포연안에서 저층삼중자망에 어획된 어류 종 조성을 분석하였다. 조사기간 동안 총 21과 32종, 695마리, 180,012.0 g의 어류가 채집되었다. 채집된 어류 가운데, 가장 많이 채집된 종은 망상어 (Ditrema temminckii)로서 채집 개체수의 52.4%, 생체량의 40.4%를 차지하였다. 그 다음 주요 종으로는 쥐노래미 (Hexagrammos otakii), 조피볼락 (Sebastes schlegelii), 쥐치 (Stephanolepis cirrhifer), 탁자볼락 (Sebastes taczanowskii), 용치놀래기 (Halichoeres poecilopterus) 등이었다. 이들 6종은 전체 개체수의 77.6%, 전체 생체량의 77.5%를 차지하였다. 종수, 개체수 및 생체량은 계절에 따라 변동하였다. 종수는 2005년 6월에 가장 많았고 2006년 3월에 가장 적었다. 개체수와 생체량은 2005년 9월에 가장 많았고, 2005년 6월에 가장 낮았다.

Seasonal variation in species composition and abundance of fish assemblage in the north coast (NC: Ayajin) and central coast (CC: Hupo) of the East Sea were calculated using samples collected by trammel net during 2011-2012. A total of 20 species from NC and 17 species from CC were collected. Of the fishes collected, the dominant fish species were Glyptocephalus stelleri and Careproctus rastrinus in the NC, and Dasycottus setiger and G. stelleri in the CC. These 2 fishes accounted for 71.7% and 81.0% of the total number of individuals collected in the NC and CC, respectively. The number of fish species, number of individuals, biomass and species diversity indices fluctuated with the seasons. The cluster analysis and non-metric multidimensional scaling (MDS) based on Bray-Curtis similarity revealed that the fish assemblages classified into north and central groups. Analysis of similarity percentages of species contributions (SIMPER) indicated that most individual of G. stelleri and Gadus macrocephalus contributed to north group, and D. setiger and G. stelleri in central group, whereas 15 species contributed to 90% of the dissimilarity.

To study the catching efficiency of biodegradable trammel net for swimming crab (Portunus trituberculatus), three types (biodegradable, monofilament and multifilament) of trammel nets were used in the field test, and the tests were carried out 16 times with two different mesh sizes (105mm and 160mm) in the Yeonpyeong fishing ground of Korea, 2009~2011. The catching efficiency of three type nets was analyzed by catch in number, catch in weight and average weight per individual of small and large size swimming crab by net types and mesh sizes. Statistical T-test was also carried out to verify the efficiency between the three types of nets. The results are as follows. The catch in number of swimming crab was 24,667 and formed about 81.0% of total catch. Of all swimming crab catch, small swimming crabs with less than 64mm in carapace length which is a prohibited landing size by law formed 48.1%, larger swimming crabs with more than 64mm in carapace length which is a landing size formed 51.9%. In 105mm mesh size trammel net test, the catch share in number of small size swimming crab by biodegradable trammel net was 47.5% in comparison with multifilament trammel net and 74.2% in comparison with monofilament trammel net, so biodegradable trammel net has more protective effects on small size swimming crab than other types of trammel nets. The protective effects for small size swimming crab by biodegradable trammel net was 25.8~52.5% in comparison with other types of trammel nets. The catch share in weight of large size swimming crab by biodegradable trammel net was 98.3% in comparison with multifilament trammel net and 92.3% in comparison with monofilament trammel net, so biodegradable trammel net has a similar catch efficiency to multifilament trammel net. The results of 160mm mesh size trammel net test have shown similar results of 105mm mesh size trammel net test. This study shows that biodegradable trammel net is a more useful fishing gear than multifilament and monofilament trammel net because biodegradable trammel net has lower catch rate than other types of nets in small size swimming crab and similar catch rate than multifilament trammel net which is a well used net by fishermen.

An estimation of the headline height of a bottom trammel net set across under uniform current was achieved numerically from a differential equations describing the forces of the net and compared with the measured value in a flume tank experiment. The analysis on the shape of the bottom trammel net with the headline free was based on the equilibrium equation of the bottom gill net which was modified and slack of the trammel net was varied with net depth as shown in the tank experiment. The differential equations were solved by a forth-order Runge-Kutta method. The estimated headline heights with varied slack was found to be closer than that with constant slack when compared with the actual values.

홑자망과 삼중자망에 의한 어획성능을 파악하기 위하여 한국 남해안의 거문도연안에 시설된 세라믹 어초어장에서 어구 성능시험과 수중 비디오 카메라로 어군 위집상을 조사로 하였다. 흩자망에 의한 폭당 어획량은 삼중자망에 비해 49.2% 많았으나, 어종수는 34.5% 적었는데, 이를 ANOVA로 분석한 결과 5% 유의수준에서 차이가 없었다. 어구별 우점종은 홑자망에서 참돔 1종, 삼중자망에서 참돔, 말쥐치, 홍어 등 3종이었으며, 홑자망에의해 어획된 참돔의 체장범위와 평균체장은 삼중자망에 어획된 참돔보다 다소 적게 나타났다. 홑자망에 의한 어획성능이 삼중자망보다 높았던 원인은 홑자망에 어획되기 쉬운 어종이 군을 형성하고 있었고, 개체의 크기도 홑자망에 적합하였기 때문이라고 판단된다.

삼중자망의 망목 선택성 및 적정망목을 추정하기 위하여 강원도 주문진 해역에서 2000년 8월 10~13일, 11월 9~13일 (18회), 부산 수영만에서 2001년 6월 1일~27일(21회), 시험조업을 행하였다. 또한 주문진 해역에서는 60, 75, 90 105, 135, 150, 180mm의 7가지의 삼중자망으로 조업하였고, 수영만에서는 60, 75, 90mm의 삼중자망과 홑자망으로 비교실험을 행하였다. 망목 선택성 곡선의 분석은 전체 어획량의 약 60%를 차지하는 물가자미(Eopsetta grigorjewi) 를 대상으로 하였으며, Master curve의 다항식이 포함된 Kitahara(1968)방법을 사용하여 작성하였다. 그 결과를 요약하면 다음과 같다. 1. 총 어획미수는 삼중자망이 2,331미였고, 홑자망이 1,433미였으며, 가자미류가 59.8%~60%였다. 2. 최적 l/m값은 삼중자망이 2.56이었으며, 흩자망이 2.47로 삼중자망이 약 0.1 정도 크게 나타났다. 3. 50% 선택구간은 삼중자망이 1.88~3.36(1.48)로 나타났으며, 홑자망은 2.00~3.02(1.02)로 삼중자망이 약 1.5배 정도 넓게 나타났다. 4. 가자미의 최소성숙체장 265mm에 대한 적정망목은 삼중자망이 약 141mm, 홑자망이 약 132mm로 삼중자망이 약 10mm 정도 크게 나타났다. 5. 적정망목을 사용했을 경우 50% 선택 체장범위는 삼중자망이 265mm~474mm, 흩자망이 265mm~398mm로 삼중자망의 체장범위가 76mm 정도 넓은 것으로 나타났다.

서대 3중자망의 망목 선택성을 규명하기 위하여 각각 3가지 종류의 망목(70.5mm, 86.6mm, 101mm)으로 구성 된 자망 및 3중자망을 사용하여 1999년 5월부터 8월까지 전남 여수시 돌산도 연안에서 총 30회의 실험조업을 하고, 그 결과를 분석하였다. 망목 선택성 곡선은 개서대를 대상으로 Kitahara 방법으로 작성되었다. 본 연구에 대한 결과를 요약하면 다음과 같다. 1. 현용어구 규격인 3중자망(내망 망목 70.5mm망)의 어획비율은 39.0%로, 자망 15.8%에 비해서 약 2.5배 높았다. 2. 3중자망의 선택률이 1이 되는 최적 l/m값은 3.51로 자망 3.38에 비해서 약 0.13 높게 나타났다. 3. 3중자망의 낮은 체장계급에서의 선택성은 자망과 비슷하였으나, 높은 체장계급에서의 선택성은 자망에 비해서 떨어졌다. 이 때 3중자 망의 50% 선택 구간은 1.33으로 자망 0.83에 비해 1.5배 넓게 나타났다. 이상의 결과에서 볼 때, 서대의 경우 3중자망은 자망에 비해 어획성능이 우수하고, 망목 크기를 조절함으로서 대상 어종의 어획 체장을 제어할 수 있음을 알 수 있었다.