• Journal of Environmental Science International
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• v.26 no.12
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• pp.1341-1353
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• 2017

This study aimed to identify the aquatic and riparian factors associated with the presence/absence of the Eurasian otter in the Nakdong river basin, where the species is relatively more abundant than other otter species. Environmental factors and presence records were collected. Geographical Information System technology and chi-square test were used to compare environmental gradients in aquatic and riparian factors between presence and absence sites. Aquatic habitat attributes were evaluated with natural riverside sandbars and channel crossing artificial structures, the ratio of channel width to alluvial plain width, riverbed substrate, and flow diversity. Riverbank characteristics, bank materials, man-made embankment types, and land use/land cover of inland and riverside areas were selected as riparian habitat attributes. Compared to the aquatic attributes, riparian attributes were highly significant when assessing otter presence and absence sites, suggesting that conservation of suitable riparian areas to provide maternity and resting areas for otter species is essential in the Nakdong river basin. None of the aquatic attributes examined were statistically significant when evaluating otter presence or absence. These results indicate that the presence of suitable riparian area for resting and reproduction habitats is more critical to the presence of Eurasian otter than food availability in aquatic areas. To inform implementation of effective conservation actions, broad-scale factors, such as watershed attributes, would be needed to further assess habitat conditions of the Eurasian otter.

• Journal of Environmental Impact Assessment
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• v.14 no.6
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• pp.377-385
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• 2005

The Eurasian otter(Lutra lutra) is listed as No. 330 in natural monument. To manage and conserve habitat for otters, it is critical to understand which habitat components are important for otters. The objectives of this study were to analyze otter habitat characteristics in accordance with land-cover map. We investigated otter spraints and sprainting site in Geoje Island from January to December, 2004. with GPS coordinates. The analysis of otter habitat use pattern was used by Arcview ver. 3.2 with 1: 25,000 Topology Map and field data. Otter habitat use was strongly related to sites in riparian vegetation riparian(dam or river) structures. In this study, Gucheon was a site with high coverage of riparian vegetation and unconfined channels, thus recording higher number of spraint densities than those of Yeonchocheon. Yeonchocheon was under construction at lower stream areas so that otter habitat use was limited. This study suggests that securing suitable forests and riparian vegetation zone is essential for conservation of otters.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.4
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• pp.333-340
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• 1990

The authors carried out a visiualizational model test by the hydrogen bubble method to examine the pattern of the fluid flow besides the simple camber type and plane type otter board in circulation water channel. The experimental conditions are velocity of flow 0.05 and 0.1m/sec, angle of attack 0$^{\circ}$~45$^{\circ}$(5$^{\circ}$step). The results obtained are as follows: 1. In the case of the simple camber type otter board located angle of attack 25$^{\circ}$, vortex at the leading edge was geneated at 1/2 of chord length. 2. Size of the vortex generated in the trailing edge was about 2~3 times larger then that of the leading edge. 3. In the case of the simple camber type otter board located angle of attack 30$^{\circ}$, separation of stream-line at leading edge was generated at 1/3 of chord length. 4. Nearest stream-line in the back side of the simple camber type otter board was bent in the direction of otter board when the angle of attack was 25$^{\circ}$ and 30$^{\circ}$, and in the case of plane type otter board was expanded outside of the flow direction. 6. Area separated of the simple camber type otter board at the angle of attack 30$^{\circ}$ was smaller then that of plane type otter board. 7. Flow speed in the back side of the simple camber type otter board was about 1.4 times faster then that in the front side, and in the case of the plane otter board about 1.2 times faster.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.49-55
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• 1986

The authors carried out an experiment to determine the horizontal opening of the mid water trawl gear, which is the same as was used in the foreward experiment concerned to the attitude and opening efficiency of otter board. The trawl net .used in the experiment was designed to have a square sectional four-seamed body with two three-sepenlted wings. Each wing tip was rigged with a net pendant of 70 m long and the fore ends of the pendants were directly jointed to the otter pendant without inserting hand rope, and a front weight of 200 kg weigh was rigged with in front of the lowest wing tip. To determine the opening between otter boards ani between wing tips, two 50 KHz fish finders were set sideways on the otter board and on the port middle wing tip so as to detect the distance froa the finders to the starboard otter board and to the wing tip respectively, and the informations were transmitted to the indicators onboard the ship through water-tight cables. The results obtained can be summarized as follows: 1. The openings between otter borads were 43-45 m in case of the warp 100 m, 53-55 m in the war;> 150 m and 54-59 m in the warp 200 m. It was increased in linear according to the increase of towin; speed in the range of 1. 1-1. 8 mlscc. 2. The determined values of the openings between otter boards were greater than the estimated values. which were calculated by the opening between warps at the gallows of the ship and the length of tt~ warp, assuming that the warps from the top rollers to the otter boards were straight. The rates of the determined values to the estimated values were 1. 23-11. 0 in case of the warp 100 m, 1. 23-1. 12 in the warp 150 m and 1. 23-1. 15 in the warp 200 m respectively. The rates were almost the same at the slow towing speed of 1. 3 mlscc or so, then the higher the speed, the less the rate, and the longer the warp, the greater the rate. 3. The rates of the openings between otter boards to the total length of net pendant and the net (excluded cod end) showed 43-43% in case of the warp 150-200 m. It was a little smaller than th~ standard. which is 50%. in the common bottom trawl. 4. The determined openings between wing tips were 18-19 m in case of the warp 100m, 21-22 m in the warp 150 rn, They showed that the higher the speed, the greater the openings even though its range was no more than 1 m or so. 5. The rates of openings between otter boards to th~ openings betwee:l wing tips were almost invariably 38%. 6. The rates of openigs b2tween otter boards to the lenth of h~ad rope were 60-65% in cas': of th~ warp lOa-150m. It were much larg2r than th~ standard. which is 50%. in the common botto:n trawl.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.2
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• pp.113-121
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• 2005

How to extimate the angle of attack of a vertical V-type cambered otter board was described. A three-dimensional semi-analytic treatment of a towing cable system was applied to the field experiments of a midwater trawl obtained by the Scanmar system. Also the equilibrium condition of the horizontal component and vertical component of forces and moment around the otter board was used. When the warp length was 300m long and the towing speed was between 2.61 and 3.86 knots, the estimated angle of attack of the otter board was ranged between $24.7^{\circ}$ and $26.2^{\circ}$, though the maximum lift force was at the angle of attack $22^{\circ}$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.286-292
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• 1991

The authors propose to use the vortex generators in order to improve of the efficiency for the cambered otter boards. The equipments and testing method of this model test was the same as the previous report. This study was tested for 6 models such as the single cambered, the V-shaped cambered and the slotted cambered otter board without and with vortex generators. The results obtained are as follows: \circled1 C sub(L) of the single cambered model otter board with vortex generators was increased about 10% in comparison with that of model without vortex generators, C sub(D) decreased 2%, and L/D increased 5~20%. \circled2 L/D of the V-shaped cambered model otter board with vortex generators was increased 10~20% in comparison with that of model without vortex generators. \circled3 C sub(L) of the two slotted cambered model otter board with vortex generators was increased about 20% within an angle of attack 25$^{\circ}$ in comparison with that of without vortex generators, C sub(D) increased 5~20%, and L/D was higher than prototype within an angle of attack 20$^{\circ}$. \circled4 The separation point of the model otter boards with vortex generators was removed back ward a little in comparison with that of the model without vortex generators. \circled5 Flow speed difference of the back side to the front side of model otter boards with vortex generators was increased a little in comparison with that of the models without vortex generators. \circled6 The size of separation zone in case of the model otter boards with vortex generators was decreased about 10% in comparison with that of the models without vortex generators.

• Journal of Veterinary Clinics
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• v.26 no.4
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• pp.395-399
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• 2009

Radiotelemetry device was surgically implanted in the abdomen of a Eurasian river otter (Lutra lutra). Behaviors of the otter, hospitalized after surgical implantation were also observed. The surgical techniques involved an incision in the paralumbar fossa to introduce a radiotelemetry device into the abdominal cavity. Thirteen behaviors of the otter during hospitalization following abdominal surgery were observed and the time budget of each behavior and the times at which each behavior seems to appear most frequently were measured. This report could provide surgical techniques involving intra-abdominal implantation in otter and basic information associated with otter's behaviors during hospitalization.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.278-285
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• 1991

The authors propose to use the slot system in order to improve of the efficiency for the cambered otter boards. The experiment is divided into 2 parts, one is the efficiency model test, and the other is the visualization model test. The hydrodynamic characteristics of the model otter boards were tested by efficiency model test to measure the shearing, drag force of the models and visualization test using hydrogen bubble method to observe the streak-line and time-line of flow around the models, and milk spout method to observe the separation zone in the wake behind the models. This study tested for 5 models such ad without slot, slot position 0.2C, 0.4C, 0.6C and 0.8C. The results obtained are as follows: \circled1 The maximum C sub(L) of model otter board with slot position 0.6C in attack angle 27$^{\circ}$ was the highest of all models, it's value was 1.59. \circled2 In general, the L/D ratio of the one slot otter boards were 16~28% higher than otter board without slot. \circled3 The slot position 0.6C was better than any other slot position, and it's conformed by visiualization. \circled4 As to the model otter board with slot position 0.6C, flow speed of the back side was faster 1.3 to 1.7 times than in the front side. \circled5 The size of the separated zone in case of the model otter board with 0.6C was smaller than that of any other models.

• Spatial Information Research
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• v.16 no.3
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• pp.343-357
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• 2008

Hongdo and Huksando belong to the Dadohae national park parks in Korea and are famous sightseeing spots in Shinahn-gun. One of the keystone species in this area is otter (Lutra lutra). We accomplished field works for finding its present habitat and condition analyses for the potential habitat in the area via spatial analyses with digital elevation model and satellite imagery. Isolated condition with coastal cliffs was one of the superior conditions over habitat in the main land, but the road kills of small animals were also observed. Three underground eco-corridors were suggested for the protection of otter habitat in the Shinahn-gun area. Regional development strategies of Shinahn-gun should be focused on the protection of safe and pristine habitat for otter population.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.53 no.4
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• pp.337-348
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• 2017

The tension of warp from trawler and sea-floor contact can generate tilt and wake turbulence around otter boards. Preliminary measurements of otter board tilt and 3-D flow velocity during bottom trawl operations were taken using a vector instrument to investigate the effects of wake turbulence at the trailing edge of the otter board. Tilt data (i.e., yaw, pitch, and roll) at 1 Hz and flow data (velocities in the towing, lateral, and vertical directions) at 16 Hz were analyzed to determine their periods and amplitudes using global wavelet and peak event analyses. The mean period (${\pm}standard$ deviation) of the tilt from the peak event analysis ($5{\pm}2s$) was longer or double than that of flow velocity ($3{\pm}2s$). The two periods also had a significant linear relationship. The turbulence rate of flow was 30-50% at the trailing edge and was closely related to roll deviation. The frequency of phase difference ratios (i.e., peak time differences between tilts and flow periods) was significantly different from random occurrence in two trials, possibly due to side tidal effects. However, in the other trials, flow peaks were random, as shown by the even peak times between tilts and flows. Future studies should focus on reducing tilt variation, wake turbulence, and bottom contact to stabilize otter board motion.