Some Effects of Groundwater on Brown Trout Redds

Abstract

A field study investigating the role of groundwater in trout spawning was conducted on Poplar Creek in northern Lower Michigan during 1969-1971. Seventy-eight natural brown trout (Salmo trutta) redds were instrumented with Mark VI standpipes during the study. Three Vibert boxes, each containing 100 fertilized brown trout eggs, were buried near each standpipe. Periodic measurements were made of gravel permeability, apparent water velocity, dissolved oxygen, temperature, and sand content of the redd gravels. Extensive measurements showed temperatures of 8.5 to 10 C and dissolved oxygen contents of 2 to 8 mg/liter in the groundwater at considerable depth beneath the streambed. The density of redds was the same in areas with or without groundwater inflow. Where there was groundwater inflow, the trout preferred zones of intermediate surface-groundwater mix, but avoided zones of undiluted groundwater inflow. Redds had higher and less variable temperatures as the percentage of groundwater increased. This resulted in earlier egg hatching. However, eggs survived in all redds regardless of the presence or absence of groundwater. Redds without groundwater inflow had temperatures closely approximating the generally colder surface water. There were no measurable changes in intragravel permeability, velocity, dissolved oxygen, or sand content of the redds as groundwater inflow increased.