||This research was conducted in the area with the boundaries from 21°50’ N to 23°60’ N and from118°00’ E to 120°70’ E, located in the Southwestern Waters off Taiwan. The analytical data were collected from the landings and the track of Voyage Data Recorder (VDR) of Kezailiao, Mituo, and Tongkang implemented in 2014. The purpose of this research is to capture the operating characteristics of trawlers, the locations of fishing ground, and the species distribution in fishing ground using the analytical results of (1) the estimation of fishing speed, (2) the calculation of Landing Per Unit Effort (LPUE), and (3) overlay analysis. The methodology of the above three analyses implemented by using Geographic Information Systems (GIS) is capable of displaying the distribution of landings, effort, and LPUE in each month of all fish species, economic fish species, trash species, etc..|
This research results demonstrate several conclusions as follows. (1) The fishing speed in Kezailiao and Mituo was 2 to 5 knots (of otter trawl) and 1.5 to 5 knots in Tongkang (of shrimp trawl) using the method of estimation of fishing speed. (2) After a further analysis with incorporating the data of ship heading into the operation types employed in the previous researchers, it was found that the major part of the operation types within otter trawl and shrimp trawl was quite different. The fishing boats of otter trawl were operated around the same waters but the ones of shrimp trawl were mainly operated along a fixed direction instead of around the same waters. (3) According the statistics of landings, the major percentages of landings from otter trawl in Kezailiao and Mituo were 10% of Loliginidae, 9% of Priacanthus macracanthus, 7% of Sepia esculenta, 7% of Trichiurus spp., 7% of Trachurus japonicas, 5% of Psenopsis anomala, and 2% of Atrobucca nibe; however, the major percentages of landings from shrimp trawl in Tongkang were 62% of Sergestes lucens, 35% of Acetes intermedius, and 3% of Palinuridae. (4) The spatial range with high LPUE values of economic fish species was narrower in the period of May to August than in the rest of the year. The highest LPUE value and widest spatial distribution of trash species occurred in July and the LPUE values obtained in the period of July to December were higher than the ones in the period of January to June. Higher LPUE values of Priacanthus macracanthus were found in April, November, and December. Higher values of Psenopsis anomala happened in the period of January to March, November, and December. Higher LPUE values with wide spatial ranges of Trachurus japonicas were found in March, May, and July. The spatial range of higher LPUE values in each month of Loliginidae was wider than the ones of the rest of all species. The fishing grounds of Sergestes lucens, Acetes intermedius, and Palinuridae were mostly located around Gaoping Canyon and Fangliao Canyon. Higher LPUE values of Sergestes lucens in May occurred less than the rest of the year. Higher landings of Palinuridae were found when the landings of Sergestes lucens were relatively lower. Higher LPUE values of Acetes intermedius happened in September and above 150-m isobaths.
The established model of operation types (coupled with ship heading data) using the above research results can be employed by government and researchers to increasingly verify the collected operation data in the field and formulate more suitable official policy for trawl fishery. In addition, it was found in this research that the rich period in Southwestern Waters off Taiwan for all species was from September to February and the higher LPUE values of trash fish occurred in the period of June to December. Therefore, implementing a fishery moratorium in the period of June to October is helpful and advisable to improve the sustainable development of offshore fisheries in the southwestern waters off Taiwan.