SALMON TRAP: Department of Marine Resources technician Josh Noll, right, releases an alewife Tuesday as his colleague, Derik Lee, checks the interior of an auger trap anchored beneath the dam on the Sheepscot River at Head Tide Village in Alna. The scientists were sampling fish species to determine how many Atlantic salmon are migrating through the passage. So far, they have collected about a 100 juveniles since March, according to Noll, and five adult fish.