The number of rainbow smelt has plummeted in recent decades, even in streams that once hosted abundant runs each spring. The diminishing numbers have become evident in the Gulf of Maine. Historically, rainbow smelt had a geographic range from Virginia to the Canadian Maritimes, but now the species is believed to have disappeared from waters south of Massachusetts. Recognizing the plight of the rainbow smelt, the U.S. government listed it in 2004 as a federal Species of Concern.

Many Potential Causes

A clear explanation for the rainbow smelt’s decline is not yet known, but the species faces three broad types of potential threats:

  1. Loss of suitable spawning habitat
  2. Unfavorable changes in ocean conditions such as water temperature or predation
  3. Fishing pressure

What Makes a Good Spawning Place?

Rainbow smelt tend to deposit their eggs in shallow riffles just upstream from the meeting of salt and fresh water.


Some Human Activities Harm Spawning Areas

People have degraded many of the rainbow smelt’s spawning sites in Massachusetts, New Hampshire, and Maine.

Dams and poorly designed culverts block rainbow smelt from spawning grounds.
Sediment from construction sites, road maintenance, and other sources smothers eggs.
Faulty septic systems, fertilizers, and other sources of nutrients enhance growth of algae in streams, which can degrade spawning habitat and affect egg survival.
Pavement and other impervious surfaces promote runoff of pollutant-laden rainwater.