Effects of environment and feeding factors on the distribution of different body lengths of Sebastes schlegelii in the reef areas of Shandong Province

In order to study the impact of environmental and feeding factors on the distribution of rockfish (Sebastes schlegelii) in artificial reef areas, this study used environmental and fishery data of three reef areas in Shandong Province from 2017 to 2018. Fish body length was divided into 10 groups by using the mean of the coefficient of variation, and the interval was 33 mm. Using Bray-Curtis similarity index to compare the similarity of the body length composition of rockfish in different regions, detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to describe the effects of environmental factors on the S. schlegelii distribution of different body length groups; the composition of the food of S. schlegelii was detected by using the stomach contents analyses. The results showed that the body length composition similarity index of Xixiakou and Changdao artificial reef areas was 70.66%. Compared with Xixiakou and Changdao, the Qiansandao artificial reef area has a low similarity index with them, which is 54.94% and 59.46% respectively. The distribution of S. schlegelii with larger body type (299-365 mm) is more correlated with depth, WQI and chemical oxygen demand (COD), and it prefers to live in a deep, nutrient-rich environment. Small body type (35-200 mm) S. schlegelii prefers environment with shallow sea areas and good water quality. The older (2-3 years old) large body length (200-365 mm) S. schlegelii mainly consumes fish, shrimp and crabs, and the dominant bait is fish (IRI, %=65.94). Younger (0-1 year old) small body length (35-200 mm) individuals mainly feed on shrimp and crab, the dominant bait is shrimps (IRI, %=45.69). Consequently, the application of juvenile-fish-protection artificial reefs in shallow water can provide shelter for juvenile S. schlegelii; concentration on fishing in deep water can reduce the bycatch of juvenile S. schlegelii, and then their resources can be proliferated and protected.