The Effects of Sampling-Site Intervals on Fish Species Richness in Wadeable Rivers: A Case Study from Taizi River Basin, Northeastern China

Fish play an important role in river ecosystems, and the conservation of their diversity is a common goal worldwide. It is still unclear how fish monitoring programs should be developed in order to rationalize the monitoring of fish diversity in rivers. To help address this issue, we conducted a comparative study of fish species richness obtained through three site-interval monitoring programs (SS1: 3 km interval scheme; SS2: 6 km interval scheme; SS3: 9 km interval scheme) in wadeable rivers in northeastern China. Here, a total of 18 fish species and 4 rare species were collected from 3 rivers. The cumulative species-richness curves showed that SS1 had the highest species richness in a single river and in the whole region, and the species richness gradually decreased with increasing site intervals. The results of the cumulative percentage of species richness indicated that SS1 and SS2 could achieve a level of 80% of potential species richness, while only SS1 could achieve a level of 90% of potential species richness in the Lanhe River (where no rare species were present). However, the results of cumulative species richness per unit of effort indicated that SS2 and SS3 had higher input-output benefits. These results suggested that rare species were more susceptible to monitoring programs and that SS2 was more advantageous in terms of obtaining species richness and cost-effectiveness. This study provides a reliable reference for river fish-monitoring program development.