Review of Migration, Research Methods, and Passage for Downstream Migrant Fishes in the Northeast USA

Pre-spawning adults of most northeast diadromous species migrate from the Atlantic Ocean into rivers in March-June. Many adults survive spawning and return downstream to salt water. Thus, for species passed upstream of dams to spawn, both post-spawned adults and early life stages (typically, juveniles) need safe passage when moving downstream past dams and water withdrawals. Many northeast potamodromous fishes (=riverine fish species here) have evolved up- and downstream migrations that occur from March to November. Migrations of the riverine Connecticut River shortnose sturgeon, Acipenser brevirostrum, show the river is a busy highway of up- and downstream movement of various life stages during March-November. These migrations may be typical of long-lived riverine fishes that have evolved in a large open river. Researchers study downstream fish migrations using traps, nets, telemetry, and hydroacoustic techniques. When field studies are not possible, scientists study migration of early life stages in artificial streams. Fish passage in the northeast US is directed by agencies at a few diadromous sport fish species that are the subject of restoration programs, and not at the diverse diadromous and riverine migratory fish community. Target species and life stages are typically adult and juvenile alosids (American shad, Alosa sapidissima, and blueback herring, A. aestivalis), and Atlantic salmon, Salmo salar, smolts. These fish are in the upper part of the water column; so surface bypass systems are effective. At Holyoke Dam, Connecticut River, MA efforts are underway to protect two new diadromous target species that are benthic, i.e., the federally endangered shortnose sturgeon and American eel, Anguilla rostrata, whose populations have declined. To date, no bypass system for benthic species has been developed. Screens are commonly used in the western US to protect fish with mixed success, but are uncommon in the Northeast because agencies protect surface migrants mainly using bar racks with 25-mm clear spacing that extend from the surface to 3 m deep. While this effort has been successful for a few surface-oriented species, it does not protect small fish of any species or benthic species. Many northeast rivers have been dammed and the riverine fish populations