Marine Fisheries Research and Development Department, Fisheries Research Agency, Yokohama, Kanagawa 220-6115, Japan
This paper investigates the length distribution of red tilefish Branchiostegus japonicus in catch and the fishing grounds of bottom and vertical longline fisheries in the East China Sea. Monthly data of landed red tilefish were taken by category stratified by fish size at the Nagasaki fish market. Information about the fishing grounds of the landing boats was also taken from fishermen. Experimental fishing with the standard gear commercially used by two fisheries was conducted in several fishing areas, in order to investigate the effect of gear and fishing ground on the length distribution. From the results, the Likelihood Ratio (LR) test using frequency of the size categories in catch showed a significant difference (5% significance level) of the frequency between the fisheries. The LR test using data of length distribution from the experimental catch rejected the effect of the fishing gear (5%). On the other hand, according to the information from the fishermen, two longline fisheries usually covered different fishing areas, and the LR test using data of length distribution by areas supported the effect of the area (5%). The difference of operating area is likely to be the main cause of the length distributions.