Evaluating the Fish Aggregation Effect of Wind Turbine Facilities by using Scientific Echo Sounder in Nanlong Wind Farm Area, Western Taiwan

Abstract

During the stages of construction and operation of the wind power facilities, fishery and fishery resources in the wind farm areas will certainly be changed greatly. One of the major concern is the aggregation effect of wind turbines facility. We use scientific echo sounder together with scuba diving to survey fish aggregations in the wind farm areas. In order to obtain echoes very near the facility, we use tilt beam angle instead of traditional vertical one. Variation of target strength varies while using tilted beam angle were discussed both by ex-situ and in-situ experiment. In ex-situ experiment, we measured TS of sample fish in different attacking beam angle in three different rotation planes, and conducted by setting four different beam angles to detect free-swimming fishes in a cage. We found that fish length estimated by different title angle varied greatly, but maintained linear relationship with target strength at tilt angle of 30 degrees and 60 degrees. In in-situ experiment, we developed a special trackline for acoustic survey using 60 degrees tilt beam angle together with scuba diving observation to evaluate fish aggregation effect among two wind turbines, a wind tower and a neighboring artificial reefs in the Nanlong wind farm. The results showed that in the core area (<20 m) near the facilities the target strength distribution patterns and values were consistent with the fish length distribution from scuba diving data. In the joint surveys, we observed that the wind turbines had relatively better fish aggregation effect than nearby neighboring wind towers and artificial reefs.