Nighttime Visitors by Katrina Mueller Every spring, something very special happens in small freshwater streams that flow into the lower Penobscot River. From about the first of April to the first of June, small, iridescent creatures come in at night, on the high tide when freshwater temperatures are right. They are not strong swimmers and they use the tide to their advantage. These nighttime visitors are sea-run (diadromous) rainbow smelt, and they are looking to spawn. The males may arrive first in some locations, flaunting a full body suit of bumpy "nuptial" tubercles and hoping to attract a silky rainbow female. Some are better suited for spawning later in the season, in different locations that are perhaps farther upriver or close to shore in the Penobscot River itself. This diversity in timing and location enables the population as a whole to persist over time, and is a species' way of putting its eggs in more than one basket. Like other diadromous species, smelt spend portions of their life in freshwater, estuarine and marine environments. Breeding females that come into freshwater to spawn are chock-full of tiny eggs rich in energy derived from amphipods, shrimps and marine worms. After spawning, these eggs cover the streambed like a sticky mat and provide a highly nutritional source of food for the freshwater organisms like aquatic insects and other fish that reside in these streams. In effect, as they travel, smelt and their sea-run counterparts link these different environments together by bringing nutrients they obtained from the estuary and bay into freshwater and vice versa. Successful or not in their quest, the smelt are sensitive to light and temperature; all those looking for a mate must leave as the tide goes out and follow it back to their refuge in the estuary to wait for another night. During the rest of the year, they reside in the Penobscot River estuary, replenishing their energy reserves and providing another very important source of food for post-spawn Atlantic salmon kelts, striped bass, bluefish and a variety of birds. Historically, smelt may have been able to travel up to and perhaps beyond the rock ledges that form the base of the Milford Dam. Today, their passage is blocked by dams located downstream on both the mainstem of the Penobscot River and in tributaries that drain the lower river and estuary. Even seemingly insignificant obstacles, like “perched”, or hanging, road culverts can cut their journey short and have a cumulative effect. With the planned removal of both the Veazie and Great Works dams as part of the Penobscot River Restoration Project, smelt may once again reach 100% of their historic habitat on the mainstem. Current efforts to improve fish passage on smaller tributaries (such as Sedgeunkedunk Stream that flows through the City of Brewer and Town of Orrington) will add up and provide more places where this important (and tasty!) little fish can spawn and be enjoyed by people living in the watershed.  For information about smelt fishing seasons, regulations, and fishing opportunities, visit the Department of Marine Resources website at: http://www.maine.gov/dmr/recreational/rechomepage.html Katrina Mueller is a graduate student from Michigan State University currently housed at the NOAA Fisheries Maine Field Station in Orono, ME.