Alosa to detect ultrasound (at frequencies above 20 kHz, which is the limit of human hearing). This was first discovered by fisheries biologists studying a type of shad known as blueback herring, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid dolphins that find prey using echolocation. "Alosa" species are generally pelagic. They are mostly anadromous or semianadromous with the exception of strictly freshwater landlocked species. "Alosa" species are generally migratory and schooling fish. Males usually mature about a year before females; they spawn in the late spring to summer.
Fish Hook River Fish Hook River is considered to begin in the city of Park Rapids, at a dam forming the Fish Hook River Reservoir, which was constructed to supply hydropower at the site of rapids on the river. From Park Rapids the Fish Hook River flows south-southeastwardly through Todd, Straight River, and Hubbard townships, collecting the Straight River from the west. It flows into the Shell River from the north in Hubbard Township. The Fish Hook River Reservoir flows from Fish Hook Lake, which collects the river's northern watershed. The Portage and Potato rivers flow short distances to the lake from Portage