Stock assessment and management implications of sailfin sandfish () caught by multiple fishing gears with different selectivity in Korean waters.

The yield per recruit (YPR) model developed by Berverton & Holt in 1957 is widely used to determine the optimal age at first capture ( ) and optimal fishing intensity ( ) for the sustainable use of fish stocks. The YPR model is mainly applied to fishing gears, including trawlers and Danish seines, as individual gear types. In practice, fishery resources are predominantly harvested using multiple fishing gears rather than using a single fishing gear, with selectivity differing among the various gears employed. Therefore, management reference points, such as or , should be derived from stock assessments that account for multiple fishing gears and their respective selectivity. In this study, the traditional (single-gear) YPR and spawning biomass per recruit (SBPR) models were modified into multi-gear YPR and SBPR models to assess the stock status of fish species caught using multiple fishing gears with different selectivities. The modified models were applied to sailfin sandfish () stocks, primarily caught by the East Sea mid-sized Danish seine and coastal gillnet fisheries in Korean waters. The results showed that the optimal fishing intensities ( , ) were higher for the multi-gear model than those for the single-gear model. The optimal fishing intensities of the multi-gear model considered the different selectivities and fishing intensities of multiple fishing gears; therefore, the estimation results of this model provided a more accurate assessment of the stock status of the sandfish. The optimal fishing intensity derived from the traditional (single-gear) model was underestimated because it considered only one fishing gear. Consequently, employing this fishing intensity for resource management poses a risk of overfishing. In the sensitivity analysis of the main parameters used in the multi-gear models, the natural mortality () and growth () coefficients resulted in YPR exhibiting greater sensitivity than SBPR in response to variations in and . Furthermore, YPR demonstrated a greater sensitivity to variations in than those in .