Improvement on the Effectiveness of Marine Stock Enhancement in the Artificial Reef Area by a New Cage-Based Release Technique

The release technique, affecting the survival rate of fish species released for stock enhancement, plays a vital role in the effectiveness of the enhancement. In order to improve the probability of released fish settling down to bottom, a new cage-based release technique was designed and tested via a water tank with artificial reef models. Two coral reef fish species, Sebastes schlegelii and Paralichthys olivaceus were assessed using this technique. Fish behavior and distribution in water tank were recorded and compared with the traditional release release techniques. Results showed that in the case of cage-based release technique: 1) when the release process is just finished, the distribution index (DI) of juveniles S. schlegelii and P. olivaceus were 97.8% and 98.9% at reef area, 40% and 71.1% at release point, respectively, which was higher than those using two alternative techniques; 2) its impact duration was less than that in the other two conditions, where the DI within 4 hours was higher after releasing, especially for S. schiegelii. These findings indicated that the new cage-based technique could release the fish into the specified location, and has a potential to mitigate the stress reaction of fish caused by releasing process.