Analysis on characteristics of stratified clustering of larvae and juveniles in adjacent waters of Yangtze River Estuary

Based on the stratified survey data of larvae and juveniles in the adjacent waters of the Yangtze River Estuary in spring 2016, we investigated the stratified variation characteristics of species number, abundance, diversity and dominant species of larvae and juveniles and their relationship with temperature and salinity. Altogether 1 548 larvae and juveniles were caught with an average of 55 per net. The variation range of abundance value of each water layer was 80.85−312.03 ind ·km⁻³, with 50 m water layer being the largest, 30 m water layer being the smallest, and 15 m water layer being the smallest. The fish species number varied from 7 to 14, with a continuous increasing trend from 5 m to 50 m water layer. The abundance of larvae and juveniles in the four developmental stages was the highest at 50 m water layer. The species number and richness index showed a continuous increasing trend from shallow water to deep water, while the diversity index and evenness index increased first and then decreased. According to the IRI index, there were three main species at 5 m water layer. There were five main species at each of the other water layers, but there were some differences in their IRI index among different water layers. There was a significant positive correlation between the number of larval and juvenile fish species and their salinity (P<0.05, R=0.86). Thus, with the increase of water depth and salinity, the species number also increased. There was a significant positive correlation between the abundance of juvenile and water temperature in the upper and middle water (P<0.01, R=0.98); there was a significant positive correlation between the abundance of juvenile and salinity in the lower and middle water (P<0.05, R=0.79).