The new building was required to cover 8 acres of unstable gravel beds. (totalpolitics.com)
They are carnivorous, and they should be kept in a fairly thick sand / gravel bed where they will «dig in» and extend themselves vertically from the substrate. (petbusiness.com)
Navigating first across the open ocean, and then up rivers, lakes, and streams, they return to the headwater gravel beds of their birth to deposit their own young before dying. (nps.gov)