1.Introduction
About 72 % of marine accident have been occurring in fishing vessels and 81 % of collision have been associated with fishing vessels. Consequently, an effort to reduce fishing vessel accident has been continuously required (KMST, 2012).
Studies on merchant vessels have been actively studied from various angles through AIS trajectory analysis, such as on vessels sheltering, vessel encountering, etc (Makino et al., 2012; Van Iperen, 2015). On the other hand, studies on fishing vessels have been limited to the ones that have proposed the personnel on board and the training, by reviewing the legal aspects, such as the Seaman’s Act and the Ship Officer’s Act due to the difficulty of securing fishing location data (Jeong, 2014; Park et al., 2014; Chong, 2015; Chong, 2016). Thus, studies that have analyzed the traffic flow based on the trajectory of fishing vessels are still insufficient.
Nowadays, fishing gears are made by putting the light emitting material in them to be identified even during the day as well as at night. But the emitting material is useless in the night and restricted visibility. Therefore, navigators of merchant vessels are inquiring into the location of fishing gears with other merchant vessels on Very High Frequency (VHF) channel 16 to navigate away the gill nets in the West Sea. The navigators rely on previous navigating experiences and intuition due to the absence of quantitative data. Besides, the fishing vessel calls the merchant vessel navigating to the fishing gear, and recommends or instructs it to navigate avoiding its away on the VHF channel 16. An emotional conflict over the issue between the merchant vessel and the fishing vessel is frequent.
Recently, the number of fish species with major catch such as pomfret has been reduced sharply in the West coastal. As the decline in coastal regions, the waters of installing gill nets tend to increasingly go to the offshore. In this situation, such fishing gears crisscross with the main routes of merchant vessels and are frequently damaged. And, if the wire rope of fishing gear is interwound with the screw or propeller of merchant vessels, they cannot navigate any longer.
Therefore, this study attempted to present the density index to spatially figure out the distribution of the inshore gill netters in the West sea. If a navigator of merchant vessel is aware of the temporal and spatial distribution of the inshore gill netters, the data will be able to contribute to the protection of fishing gears damage and the propeller failure.
2.Method
This study was conducted using the transmitting device of fishing location (V-Pass) for one year in 2014. The study area is the West sea at the latitude 34° ~ 37.5°, longitude 123° ~ 127°.
The V-Pass is a device for automatically transmitting the location to ensure the safe operation of the fishing vessel pursuant to the Fishing Vessel Act. It will be installed even to small fishing vessels less than 1 ton until December 31, 2016. As of 2014, of the entire 68,417 ships registered, 37,567 (54.9 %) ships were installed with V-Pass. And of the total registered 13,674 inshore gill netters, 7,456 (54.5 %) ships were installed with V-Pass.
The grid intervals are 30 minute × 30 minute (latitude × longitude) based on the section of the sea. It is because the base of data on fishing conditions is a unit per the section of the sea. A total of 56 section of the sea from the section no. 148 to the section no. 213 were analyzed by constructing a grid.
Fig. 1 shows this research flow. The data collected through V-Pass were grouped for each month. Then, the inshore gill netters in this study area were extracted in each section of the sea. Of them, area with the speed less than 3 knots was regarded as location of fishing operation. The density distribution of inshore gill netters was analyzed in each section of the sea. The density index was analyzed in relation to the main routes of merchant vessels and location of fishing gears damage.
3.Status of inshore gill netter
3.1.Characteristics of gill netter
A gill netter install an elongated rectangular net on the surface of water as seen in Fig. 2. A gill netter operate by casting and hauling gill nets. A gill netter move forward at low speed and cast fishing gear at the stern. The cast fishing gear moves slowly along the tidal current together with gill netter. After a certain period of time, gill netter set the main engine clutch in neutral and haul the net. In consideration of this characteristics of gill netter, the speed less than 3 knots was deemed as fishing operation.
Fig. 3 shows the sample of trajectories according to speed in the section no. 194. Trajectories with speed more than 5 knots represent high possibility of navigating from port to fishing operation site. Trajectories with speed between 3 and 5 knots are deemed as movement around fishing operation site. On the other hand, trajectories with speed less than 1 knots and trajectories with speed between 1 and 3 knots were almost identical. Therefore, the speed less than 3 knots was assumed as fishing operation in this study.
3.2.Number of registered inshore gill netter
Table 1 shows the number of registered fishing vessels for inshore gill netters in each region. A total of 13,674 gill netters were registered, accounting for 32.4 % of the whole number of inshore fishing vessels (MOF, 2015). 6,322 inshore gill netters are registered in the West coast. Of them, the data of 2,194 ships (34.7 %) with V-Pass were analyzed.
3.3.Difficulty in navigation due to fishing gear
Fig. 4 shows a sample of trajectory of a merchant vessel as a gill netter that had installed its fishing gears asked the merchant vessel to detour.
In the case of the merchant vessel, its route plan is to navigate in the direction of about 170 degrees. However, it has navigated altering course in the port side after in the starboard side. As seen in this case, the fishing vessel calls the merchant vessel to protect its fishing gears and require the merchant vessel to navigate in recognition of the presence of the fishing gears. But merchant vessels navigating the waters prefer the route that they have always used, rather than navigate detour the fishing gears to save time and cost. For that reason the vessels navigate facing many risks.
Of the total inshore gill netters enrolled, only 1,659 vessels are equipped with radio equipment (MOF, 2015). Therefore, it is difficult to request avoiding the fishing gears by calling the merchant vessels. Even if the radio equipment has been installed, it is difficult to communicate. Also, the noise of radio equipment is serious. For this reason it is turned off.
Fig. 5 shows the locations of 34 fishing gear damage for the year of 2014. Of the 34 cases, 29 (85 %) took place at night time (20:00 ~ 08:00 in the next morning). Even if the fishing gears are made by putting the light emitting material, the material is useless in the night and restricted visibility.
The followings are recent propeller failure caused by the fishing gear damage to make navigating impossible; in March 2016, cargo vessel ‘C’ (3,763 ton); April, tug boat ‘S’ (113 ton); May, and cargo vessel ‘E’ (1,510 ton) became unable to navigate due to fishing gear entangled with their propellers (MPSS, 2016a; MPSS, 2016b; MPSS, 2016c).
Fig. 6 shows the actual trajectory of the cargo vessel ‘C’ in March 2016. The propeller of the vessel was entangled with fishing gear to become unable to start the engine and made a distress call. The cargo vessel ‘C’ couldn’t navigate for 7 hours until a diver arrived at the site and removed the ropes.
4.Result and Discussion
To indicate the monthly density distribution of gill netters by section of the sea, the average number of gill netters and the hours of fishing operation per day were analyzed. To differently apply the hours of fishing operation only for 10 minutes in spite of numerous gill netters and the hours of fishing operation for 10 hours in spite of less gill netters, density was defined as the index considering the number of gill netters and the hours of fishing operation. The general formula is as seen in the formula (1).
where, ρi : the average density index of fishing operation per day according to the i(i=1,2,3,...,56) section of the sea
Ni : the average number of gill netters per day according to the i section of the sea
Hi : the average hours of fishing operation per day according to the i section of the sea
4.1.Number of gill netter
Fig. 7 shows the average number of gill netters per day according to the section. To display the legend, 15 sections with higher number of fishing vessels were marked. The area of the highest number of gill netters was the section no. 194, the Imjado Island ~ Wido Island coastal sea, with 123 ships on average daily in August, followed by the section no. 194 with 118 ships and the section no. 5154 with 115 ships.
The sections of the sea where more than 100 gill netters have engaged in fishing were the section no. 154 in September and October, the section no. 5154 in May, September and October, and the section no. 194 from July through September. These sections were found that the number of gill netters rapidly increased more than 2 times from February through May. Besides, the number of gill netters in three sections reached the peak between August and October.
4.2.Hours of fishing operation
Fig. 8 shows the average hours of fishing operation per day according to the section. To display the legend, 15 sections with higher hours of fishing operation were marked.
The longest hours of fishing operation was 16.7 hours in the section no. 194 in December, followed by 16.7 hours in the same section in July, and 15.9 hours in the section no. 203 in July. The section no. 194 was found to be about for 12 hours in fishing, regardless of the season. The section no. 202 and 203 sections were observed to reach about more than 11 hours in fishing.
4.3.Density index
Fig. 9 shows the monthly density index according to the section of the sea. To display the legend, 15 sections with higher density index of fishing operation were marked.
The highest density index was 81.3 in the section no. 194 in August, followed by 73.6 in the same section in September. This section showed an higher density index than other section from May through September. This section was analyzed for more than 85 vessels to fish for more than 14 hours per day from May through September.
The 15 sections with the high density index coincide with 15 sections with the numerous fishing vessels. Based on this finding, it is analyzed that the number of fishing vessels had a relatively larger impact on the density index rather than hours of fishing operation.
4.4.Consideration of the realation between the density index and the main routes of merchant vessels
To investigate the density index of fishing operation from the perspective of merchant ships, location of fishing operation and fishing gear damage were marked on the main routes of merchant vessels as in Fig 10. For merchant vessels, based upon AIS data, grid was established with 0.1 nautical mile intervals to indicate accumulated trajectory distribution and identify main routes. The main routes of merchant vessels were found to depart from the Incheon/Pyeongtaek/Daeshin port toward the section no. 173→183 →193→203.
Fig. A-1 and Fig. A-2 in Appendix show monthly 3-day location of the gill netters upon 3-day accumulated trajectory of the merchant vessels. Fig. B-1 and Fig. B-2 in Appendix present monthly enlarged figures of sections with frequent fishing gear damage.
The section no. 194 with the highest density index showed no case of fishing gear damage, rather the section no. 193 with relatively lower density index showed more of such damage. The section no. 193 with relatively frequent fishing gear damage is part of the main route of merchant vessels. That’s why, the fishing gears were set in the section result in more frequent damage accident.
Fig. B-1 and B-2 in Appendix show that between December and March, the gill netters are not in the main route of the merchant vessels. On the other hand, between May and September, they seem to have no more place to install own gill nets in the section no. 194. Thus, they tend to move farther into the section no. 193 to cast their nets. Accordingly, their fishing gear is placed in the way of merchant vessels to be damaged more often. Based on this analysis, it is deemed that the fishing gears are not damaged in proportion to density index but damage risk exists according to the route of merchant vessels.
Concerning the number of the gill netters in the sections of 173, 183, 193, and 203; from May to September, the section no. 173 and 183 are found to have only about 5 gill netters on daily average. On the other hand, the sea section no. 193 and 203 were found to have about 30~40 ships in operation on daily average.
Therefore, special caution is necessary for the fishing gear installed in the section no. 193 and 203 between May and September. Accordingly, if the merchant vessels have to navigate in the section no. 193 and 203, the area of 34.5° ~ 35.5° at latitude and 125.5° ~ 125.67° at longitude is recommended for the safe navigation. The recommeded route takes account of the traffic flow of North Maemul traffic separation scheme as in Fig 11.
Smaller vessels such as tug boats navigating the section no. 194 with the highest density index, though not included in the main routes of merchant vessel, are required to take extra caution. To prevent fishing gear damage, day-time navigation is required than night-time.
The section with the density index more than 10 is very dangerous. Because the density index of the section no. 193, which is frequent fishing gear damage, is more than 10 from May through September. Table C-1 in Appendix shows the section of density index more than 10. The density index 10 means more than 20 gill netters engage in fishing more than 8 hours per day. Each gill netter is deemed to set up an average of 3~4 gill net frames (length of 1 gill net frame is more than 300 meter) or over. If more than 20 gill netters operate, they would set up about 60 frames or, that is, 10-nautical mile long fishing gears in the sea separately.
5.Conclusions
This study yielded a density index to help identify the monthly distribution of the gill netters for the safety of the merchant vessels navigating in the West Sea. The density index of the inshore gill netters according to the section were derived.
The results revealed that the section no. 194, the Imjado Island ~ Wido Island coastal sea, showed the highest number of gill netters and the longest hours of fishing operation. This section was analyzed for more than 85 gill netters to fish for more than 14 hours per day from May through September.
However, the section no. 194 with the highest density index showed no fishing gear damage accident. But the section no. 193 with a relatively lower density index showed more frequent fishing gear damage accident. The section no. 193 is included in the main route of the merchant vessels. Thus, the fishing gears installed in the section were damaged often.
For the safety of the merchant vessels, it is necessary to alert vessels to take extra care in navigating the section no. 193 and 203. Notifying the section no. 193 and 203, the specific area of 34.5° ~ 35.5° at latitude and 125.67° ~ 126° at longitude, as a navigational warning area from May through September, will prevent marine accident, such as propeller failure and fishing gear damage. If the merchant vessels have to navigate in the section no. 193 and 203, the area of 34.5° ~ 35.5° at latitude and 125.5° ~ 125.67° at longitude is recommended for the safe navigation.
Accordingly, the navigators passing through the sections have to recognize the monthly distribution of gill netters in advance. Additionally, they should set a offshore route from 125.67° at longitude in the sections to avoid potential marine accident such as propeller failure and fishing gear damage.
This study is significant in that it presented the useful utilization of the accumulated V-Pass data. This study seems to present the value as a basis for future research. The data on the fishing vessels may provide the basic materials to set the coastal Vessel Traffic Services (VTS) area to be installed in the future and be used as a feasibility evidence for the maritime safety audit scheme such like the development of an offshore wind power complex composition.
This study investigated 2,194 ships with V-Pass but, in fact, 6,322 inshore gill netters are registered in the western coast. Therefore, if gill netters without V-Pass are considered as well, the actual installed fishing gears in the sections is expected to be far more than those in the research findings. Also, this study investigated inshore fill netters only. If offshore gill netters are also included in subsequent study, more practical density index would be produced. Furthermore, an analysis of more detailed section, grid intervals are 10 minute × 10 minute (latitude × longitude) based on the small section, makes it possible to present more detailed findings.
