Estimates of population size of Kichiji rockfish Sebastolobus macrochir from tag recoveries in southern Okhotsk Sea

We tagged and released 3,025 Kichiji rockfish caught in the southern Okhots k Sea. A total of 490 recaptures were reported for seven years after releas e. Assuming the constant fishing and natural mortality rates, we estimated a rapid population decrease from 24 million in 1993 to 8 million in 1999. W e examined effects of the rates of tag shedding and tagging mortality by th e model selection procedure using AIC, and selected the model with the cons tant fishing mortality and changing natural mortality rates at two years af ter release. The exploitation rate after the change point was estimated 0.1 421 +/- 0.0106, and the above population size was found to be overestimated about 30%. The tag reporting rate was very high at 94.3% estimated by the census of the fishermen. However, 40 tags reported from fish brokers strong ly suggested large detection error of tags on fishing boats. The sensitive analysis considering the detection error showed that the population size co uld be overestimated by a maximum of 4.3 times.