2012 Volume 15 Issue 2 Pages 187-195
To evaluate the effects of weirs on the distribution of diadromous fish species, we surveyed fish fauna below and above the weir located the lowest reaches of two tidal rivers (Takada and Oshi River) draining into the Tone River estuary in summer(July-August) and autumn(October) in 2010. Of 15 fish species captured, 10(66.7 %) were diadromous fish species. One river with lower weir height(50 cm at max) had diadromous fish both below and above the weir. The other river with higher weir height(55 cm + 130 cm) , on the other hand, had no diadromous fish above the weir, and similarity index between below and above the weir was quite low. Physical environmental condition of the tributary was almost similar between below and above the weir, suggesting weir-induced substantial differences in fish fauna of the tributary. To solve the problem, mitigation of the height of weirs (small-scale fishways and creating a ramp of cobbles and gravels downstream of weirs) might allow diadromous fish passing such instream obstructions during high water level is proposed as a valid management action in tidal rivers.
