| 英文摘要 |
Fishing grounds of scombrids and carangids of Taiwan are mainly located in (1) the waters northeast of Taiwan where the subsurface Kuroshio upwells, (2) the area where counter Kuroshio and slope water of the East China Sea meet to form a front, and (3) the marginal area of continental shelf marked by 200-m bathymetric line southwest of Taiwan.?The major fishing gears for these fisheries are mackerel purse seine and Danish seine; mackerels and carangids are also caught by light and trawl fishings.?Since 1995, the annual product of these fishes has been varied between 40 and 80 thousand metric tons, and valued between 600 and 1400 million NT dollars.?Owing to high costs in labor, fuel, and maintenance of fishing equipment, the substenable operation of mackerel purse seine fishery has become difficult and only three (down from 8 at peak) fleets of these fishing vessels are still operational in 2009.?On the other hand the Danish seine fishery has become the principal fishing method for mackerel-carangid fishery because of its high mobility, low running cost, high efficiency, and characteristically combined with purse seine, trawl net, and light fishing.?From 1982-2009 the major target species of scombrid-carangid fishery in the waters northeast of Taiwan have been Scomber australasicus (spotted chub mackerel), S. japonicus (chub mackerel), Decapterus lajang (slender mackerel scad), D. maruadsi (Japanese scad), D. kurroides (redtail scad), and Trachurus japonicus (Japanese jack mackerel).?Among these fishes, S. australasicus contributed to 70% of the total catch.?In these waters, the spawning ground for S. australasicus is located in the area between Gueishandao Island and Pengchiayu Island of Ilan.?Eggs are laid from January to May, recruitment is from June to December, and body length at recruitment is 20 cm.?Using von Bertalanffy Growth Equation to deduce the growth of specimens caught by the present study, it showed the maximum body size becoming smaller and growth rate higher; and coupled with decreasing trend of CPUE of purse seine fishing vessels, it indicated that the resource of S. australasicus is facing overfishing problem.?Furthermore, when we analyzed our samples with yield-per-reerat (Y/R) model (Chen ＆ Gordon, 1977), we found the fishing mortality to be Fcurrent = 1.29/yr, smaller than maximum fishing mortality Fmax = 1.47/yr, but larger than 0.8 Fcurrent = 1.03/yr, an indication that enforcement of the resource management for the scombrid-carangid fishery is indeed in need. |