Fishing Capacity and Conditions of Light Fishery under Different Fishing Light Intensity

Abstract

A total of 116 nets of halogen light fishing under 6 classes of light intensity were conducted in the northern waters of Taiwan during June 19 to October 28, 2003. The average CPUE of 6 classes of light intensity showed that the CPUE was increased by the increasing intensity of fishing light and reached a peak under 80 kw condition. Cluster analysis indicated that the species composition from the 116 fishing nets could be divided into five major groups-A (squid group), B (hair-tail fish group), C (squid and hair-tail fish mixed group), D (file fish group), and E (multi-species group). The relationship between CPUE and light intensity was quite different in each group, probably due to the different species composition under different light intensity. In group A, the average CPUE of squid was not increased by increasing intensity of fishing light, it had the higher fishing capacity under 20 kw and 80 kw. In groups B and D, the average CPUE was increased by increasing intensity of fishing light. In group C, the average CPUE of hair-tail fish was also increased by increasing intensity of fishing light, but the average CPUE of squid was decreased by increasing intensity of fishing light, probably due to the aggregation of squid was discouraged by the presence of more hair-tail fish, a predator of squid, under higher light intensity. In group E, there is no relationship between CPUE and light intensity, due to the complexity in its species composition. Compared with the distribution of dorsal mantle length (ML) of squid, which was the major target spices of light fishery in Taiwan, we found that the smaller squid (ML＜ 80 mm) had higher CPUE at lower fishing light intensity (below 40 kw) than at higher intensity (above 60 kw). Conversely, for the larger squid (ML ＞80 mm), CPUE is better at higher capability of fishing light intensity. This result suggested that the CPUE of squid was influenced not only by the physical factor (capability of fishing light), but also by the biological factor such as body size, presence of predator, and so on.