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The yield per recruit (YPR) model developed by Berverton & Holt in 1957 is widely used to determine the optimal age at first capture ( t c ) and optimal fishing intensity ( F 0.1 ) 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 F 0.1 or F 40% , 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 ( Arctoscopus japonicus ) 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 ( F 0.1 , F 40% ) 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 ( M ) and growth ( K ) coefficients resulted in YPR exhibiting greater sensitivity than SBPR in response to variations in M and K . Furthermore, YPR demonstrated a greater sensitivity to variations in K than those in M .

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for high-risk fishing gear, such as trawls. We experimented with two BRD types (guiding nets) attached in front of codend at 30° and 45° angles, and catch losses and mesh size selectivity were investigated. Experimental fishing operations were conducted along the East Coast of South Korea where whales and dolphins are commonly sighted. The catch was classified according to fishing location, BRD type, codend, and covernet, with measurements recorded for body length, maximum girth, and weight. The average selectivity for each haul was analyzed using the ‘selfisher’ package. The catch loss rates with the BRD attached at tilt angles of 30° and 45° were 11% and 29% for common flying squid, 6% and 28% for sailfin sandfish, and 5% and 8% for pearlside. While the mesh selectivity rates for common flying squid and pearlside remained at 0.2–0.5 across all lengths and tilt angles, the mesh selectivity curve for sailfin sandfish was estimated. There were significant differences in catch loss between 30° and 45° angles, with the 30° angle being more effective in catch loss. We observed a masking effect in the codend.