The Return of Rainbow Smelt to the Megunticook

Rainbow smelt are generally weak swimmers, which prevents them from making it past dams to the headwater streams where they spawn. The steep dams and barrier walls in the Megunticook make it impossible for rainbow smelt to return. In other places, present efforts to scale back the human effect on damming and erosion has assisted the return of rainbow smelt. There is hope that removing the Megunticook dams and returning the river to its natural state will bring the rise of rainbow smelt populations.

Diet

Rainbow smelt are aggressive, and can eat practically any fish they discover. However, in their younger years, rainbow smelt are known to prefer zooplankton and young Ciscoes. Rainbow smelt will eat a variety of small organisms – animals and vegetation – in addition to juvenile fish.

Trophic level

Rainbow smelt are popular among predators; with estimates of up to 72% of adult smelt dying each year. Many species rely on rainbow smelt for a primary food source, including:

• Striped bass

• Bluefish

• Birds

• Marine mammals

Macrohabitat

The rainbow smelt is native to North American watersheds. They are widespread along north Atlantic coastal areas, and also in freshwater lakes and rivers in North America. However, smelt have a preference for rivers, ponds, and lakes, and are capable of completing their life exclusively in freshwater. In their anadromous territories, rainbow smelt spend the summers alongside the coast, usually in shallow waters no more than 1 mile (1.6 km) from shore.

Microhabitat

The rainbow smelt can survive in a broad range of environmental conditions and abiotic factors. Rainbow smelt survival only dropped significantly when dissolved oxygen levels were less than 20% and the pH<5. Smelt were not found in lakes with pH less than 6.0 in several surveys. Otherwise, rainbow smelt can survive in a broad range of other abiotic factors, such as salinity, nitrates, and phosphates. They can survive within a temperature range of -1.8°C to around 20°C., and can also acclimate to extreme cold (<5°) by producing an antifreeze protein, glycerol. However, rainbow smelt prefer clean streams with light flow and light siltation.

Migration

Rainbow smelt are an anadromous species, ascending from saltwater to freshwater to spawn. In their native habitat, they spend most of their lives at sea and migrate into freshwater to spawn. In some instances, it is difficult for them to travel upstream, as rainbow smelt are weak swimmers and cannot overcome most dams and fish ladders. This prevents them from making it past the dams to the headwater streams where they spawn.

Spawning

Rainbow smelt spawn in spring, mainly from early March to early May. They migrate upstream into freshwater, as they prefer clear streams with light movement and light siltation. This is due to the fact that the eggs survive best in fast moving water and on aquatic vegetation. The smelt spawn only at night, and female smelt produce about 60,000 eggs. The adhesive eggs attach to sand or gravel, and hatch in freshwater within 10 to 30 days.

Conservation

In 2004, the National Oceanic and Atmospheric Administration listed the rainbow smelt as a federal Species of Concern. There are currently many plans to attempt to scale back damming and to control erosion, which will aid the smelt in returning to their freshwater natural habitats.