The First Population Simulation for the Zalophus japonicus (Otariidae: Sea Lions) on Dokdo, Korea

The Japanese sea lion (Z. japonicus) has been regarded as an extinct species since the last report on Dokdo in 1951. Not much ecological information on the Z. japonicus on Dokdo (hereafter Dokdo sea lion) is currently available. Using a discrete time stage-structured population model, we reconstructed the Dokdo sea lion population to explore the effect of human hunting pressure on them. This study provides the first estimate for the Dokdo sea lion population from 1900 to 1951. The reconstructed capture numbers of the Dokdo sea lion and the parameters estimated in this study were well matched with the recorded numbers and ecological parameters reported previously for the Californian sea lion. Based on the reconstructed population, their number rapidly declined after hunting started and it took less than 10 years for a 70% decline of the initial population, which would be considered to be an extinction risk. Since some caveats exist in this study, some caution about our results is necessary. However, this study demonstrates how rapidly human over-hunting can cause the extermination of a large local population. This study will be helpful to raise people's awareness about endangered marine animals such as local finless porpoises in Korea.