The demand for seafood is expected to rise substantially as both the standard of living and human population size continue to increase. Stock enhancement programs will likely help fill some of the projected gap in supply as well as replenish severely depleted or recruitment-limited fisheries. At present, stock enhancement programs have been widely implemented in the coastal waters of the Yellow Sea and Bohai Sea, China, including a program to enhance populations of the swimming crab (Portunus trituberculatus). However, little effort has been made to evaluate the effectiveness of these stock enhancement programs, particularly for species that are not suitable for physical tagging, such as the swimming crab. We conducted a quantitative analysis to assess the recapture rates of swimming crabs using survey data collected in May, June, July, and August of 2010 and 2011. We compared survey results before and after the release of swimming crabs in the waters off southern Shandong Peninsula. The wild population was relatively rare: only 0.9 individuals were caught per site per hour prior to release of cultured crabs in late May, 2010. Capture rates increased to 26.08 individuals per site per hour 10 days after the release of ~110.15 million seedling swimming crab, and the supplemented stock accounted for 96.55% of the total catch. The stock density was 1.70 individuals per site per hour during surveys in August, and the age-0 swimming crabs accounted for 64.29% of the total catch. The total yield of swimming crab was 3 108 tons in 2010, the average body weight was 232.3 g, and the recapture rate was 7.54%. In 2011, the density of the wild population of swimming crab was 1.70 individuals per site per hour before supplementation in late May, but increased to 29.14 individuals per site per hour 10 days after release of ~131.32 million seeding swimming crab, of which the supplemented stock accounted for 94.17% of the total catch. In August, the density had declined to 1.00 individual per site per hour and age-0 individuals represented 70.00% of the total catch. The total annual yield was 2 896 tons, the average body weight was 226.0 g, and the recapture rate was 6.43%. Our results suggest that the stock enhancement effort was more successful in 2010 than 2011. Our results also suggest that the water quality (temperature, transparency, salinity, nutrient composition and concentration) and food supply off southern Shandong Peninsula were suitable for stock enhancement of swimming crab, evidenced by the high recapture rates in 2010 and 2011. However, the poor water quality in Jiaozhou Bay and Huangjiatang Bay was associated with relatively low recapture rates