Simulated ghost fishing experiment on size selectivity of red queen crab traps

Abstract

  To investigate size selectivity of lost traps for the red queen crab Chionoecetes japonicus, a comparative fishing experiment was conducted west of the Oki islands in the Sea of Japan, in which commercially-used traps having a mesh size of 150 mm, traps having circular escape vents with a 90,100 and 110 mm inner diameter, and traps having a small mesh size (34 mm) were utilized. A soaking time of approximately six months was used to evaluate the size selectivity when traps were lost. The size selectivity curves of these traps were estimated by the SELECT model using the likelihood of a multinomial distribution from the proportions taken in the experimental traps catch to the total catch of each carapace width class. The 50 percent retention carapace width of commercially-used traps and the selection range (difference from 75% to 25% retention carapace width) were estimated to be 100.8 mm and 3.4 mm, respectively. The majority of the crabs of carapace width smaller than 99 mm escaped from the commercially-used traps. Ghost fishing does not occur for females because most of the females are smaller than 90 mm carapace width. However, the male crabs of carapace width larger than 103 mm would be retained in the commercially-used traps, then isolated from the population.