Acoustic assessment of silver carp and bighead carp in Qinghe Reservoir: comparing echo-counting and echo-integrating methods

We conducted an acoustic assessment of silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) resources in Qinghe Reservoir in late July of 2009 by using the Simrad EY60 split-beam echosounder. With the software Echoview 4.0, we post-processed the data to analyze the distribution of the species during day and night. Besides, we assessed the resource density by using echo-counting and echo-integrating methods, which were then compared to find out the suitable acoustic investigation method for the two species. The results show that both species gather around 10 m in the reservoir and gather more usually during the day with less single echo but disperse at night with more single echo. Large fish gather in deep water area with relative lower density but small fish in shallow water area with high density. The echo-counting method is more suitable for night assessment, and according to the night data, the estimated density is 0.063 indm-3 and 0.049 indm-3 obtained by echo-integrating and echo-counting methods,