Application of hydroacoustics to investigate the distribution,diel movement, and abundance offish on Zhubi Reef, Nansha Islands, South China Sea

摘要

A combination of traditional fish sampling methods (hand-line and gill net) and modern hydroacoustic techniques were used to study fish community structure,distribution,and diel movements of fish on Zhubi Reef to enhance understanding of the ecosystem.We collected 126 individuals from 29species,20 genera,17 families,three orders,and two classes using traditional gear.Perciforms were the dominant group in terms of species richness and biomass.The acoustic data indicated that very small (target strength [TS],dB) ＜-60 dB) and small (-60 dB≤TS＜-45 dB) fish contributed the most to abundance and species richness on the coral reef,and that the proportion of medium-sized (-45 dB≤TS＜-35 dB) and large-sized (-35 dB≤TS) fish increased gradually as depth increased.The single-target detection method revealed two distinct size classes during the day in the 12-16 and 16-20-m layers.One group consisted of very small-sized fish (TS＜-60 dB) and the other consisted of medium and large-sized fish (TS＞-55 dB).The number of single-target detections was significantly higher during the night than during the day (P＜0.05).The single-target TS frequency distribution during the day was significantly different than during the night at depths of 4-8,8-12,12-16,and 16-20 m.Significant differences were observed among the 4-8,8-12,12-16,and 16-20-m-depth layers during day and night.Diel vertical movement was evidenced as fish began to spread and move upward just before sunset and began to assemble and descend shortly (15 min) after sunrise.