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.
Rachel Carson National Wildlife Refuge have extensive vernal pool habitat that would benefit several Species of Concern. Coastal marshes, bays, tidal creeks, and rivers support diverse shellfish and finfish populations. Sunfish ("Lepomis" species), creek chub ("Semotilus atromaculatus"), cunner ("Tautogolabrus adspersus"), golden shiner ("Notemigonus crysoleucas"), common mummichog ("Fundulus heteroclitus"), American eel ("Anguilla rostrata"), and white sucker ("Catostomus commersoni") abound. Brook trout ("Salvelinus fontinalis") and brown trout ("Salmo trutta") are stocked in rivers and estuaries each year. The Ogunquit River sustains alewife ("Alosa pseudoharengus"), blueback herring ("Alosa aestivalis"), pollock ("Pollachius virens"), bluefish ("Pomatomus saltatrix"), longhorn sculpin ("Myoxocephalus octodecimspinosus"), and winter flounder ("Pleuronectes americanus"). The Webhannet River has