Effect of jet boats on salmon eggs

The passage of jet boats through spawning areas can kill salmon eggs buried in the river bed. By using a jet boat on the Ashley River the pressure gradients created in a redd were determined. At the maximum boat speed investigated (11 m.s^‐1) gradients up to 9.32 kPa.m^‐1 were recorded. The induced water velocities through the gravel were then estimated from the equation of motion and reproduced in a gravel‐filled tube in the laboratory. For the test conditions discharge velocities ranged from 0.18–0.3 m.s‐¹. Studies of the effect of these flows on salmon eggs revealed fatality rates of up to 40% at their most critical stage on the ninth day of development.