Rainbow Smelt
Osmerus mordax
Profile / Morphology 2
The rainbow smelt is a schooling species that lives in the ocean and/or fresh water. Sea-dwelling populations are anadromous, migrating from the ocean to spawn in fresh water, while some populations are found entirely in fresh water. They are slender and elongate with a silvery color on their entire body.
Diet 3
Rainbow smelt are voracious feeders of amphipods, mysids, euphausiids, shrimps, and marine worms; and as they grow, any small fishes that are available
Average lifespan in the wild 3
5-6 years
Size / Weight 3
This is a small, slender, elongated fish averaging 6 to 8 inches (15 to 20 cm) in length. They weigh no more than a pounds
Habitat 3
Rainbow smelt are a schooling species. They usually remain close to shore and in shallow water, and some spend the entire year in the estuaries (Collette and Klein-MacPhee 2002). Summer habitat varies with water temperature. Smelt leave the harbors and estuaries of Massachusetts Bay for slightly deeper and cooler offshore water during the summer. Farther north, east of Penobscot Bay, Maine, they remain in harbors, bays, and river mouths all summer (Collette and Klein-MacPhee 2002). Rainbow smelt overwinter in nearshore waters prior to making their spawning runs in late-winter or spring.
Range 3
They naturally occur in the Northeast U.S. and around Alaska, but have been introduced widely into freshwater systems in the northeastern and central U.S., including the Great Lakes (Buckley 1989). The Atlantic and Pacific populations are different subspecies. There is evidence of migrations while in the ocean; however, little is known about this part of the smelt life history.
Reproductive / Life span 3
Most rainbow smelt are anadromous and migrate from adult ocean habitat into freshwaters to spawn. Spawning takes place in late winter or early spring in the southern portion of their range and in mid-spring farther north. Anadromous populations can migrate over 100 km (62 miles) upstream to spawn. Spawning is believed to be triggered by length of daylight period rather than water temperature (Collette and Klein-MacPhee 2002). A female smelt can produce 7,000 to over 75,000 eggs at a time, depending on size (Collette and Klein-MacPhee 2002).
The rainbow smelt is relatively short-lived, living for up to 7 years, though generally they only live 3-4 years.
Relatives 3
Rainbow smelt are in the smelt family that includes the endangered delta smelt of San Francisco Bay and the proposed endangered eulachon of the Pacific Coast. Rainbow smelt are also distantly related to salmon and have the same adipose fin as salmon (the fleshy little fin without bony supports on the back near the tail).
Found in the following Estuarine Reserves 3
Wells (ME), Great Bay (NH), Waquoit Bay (MA), Narragansett Bay (RI), Kachemak Bay (AK)and historically in Hudson River (NY), Jacques Cousteau (NJ)
Water quality factors needed for survival 3
•Water Temperature: moderate (4-16oC)
•Turbidity: low to moderate
•Water Flow: low
•Salinity: 0 to 35 ppt
•Dissolved Oxygen: moderate to high
Threats 3
Spawning habitat degradation
•Acid precipitation
•Excessive fishing
•Dams and blocked culverts
This is a NOAA Fisheries Species of Concern in the Northeast U.S. During the last 15 to 20 years there has been a region-wide trend of declining smelt populations in Massachusetts Bay (Chase and Childs 2001). However, the current status of rainbow smelt populations for the majority of the Gulf of Maine is not well known, especially east of the Kennebec drainage. Many inland populations appear to be declining.
The species is thought to have declined largely because of habitat degradation, apparently due in part to the impacts of poor water quality, acid precipitation, and dams and blocked culverts. Dams and other impediments to fish movement are particularly critical in Massachusetts Bay. Chase and Childs (2001) note that fishing mortality is not suspected to be a major influence in smelt population dynamics in Massachusetts, due to the absence of a commercial fishery and very little catch and effort involved in the sport fishery.
In Maine, they are a prized food fish harvested in three distinct fisheries. They are eagerly pursued along the coast and also during spawning migrations to rivers and estuaries (Collette and Klein-MacPhee 2002). Recreational fishermen use dip nets to catch them in one fishery. In the fall, a riverine and coastal bay hook and line fishery occurs. During the winter months, smelt support a large recreational ice fishery in all of the larger rivers. For over 100 years smelt supported a successful commercial fishery. Commercial landings declined in the mid-20th century to a low in 1988 of 1.3 mt landed. In the early 1990s, landings increased slightly to a high of 27.1 mt in 1992. However, a declining trend has again been evident, and landings have averaged only 0.14 mt since 1998. In 2001, total U.S. landings were 0.1 mt with all fish reported as being landed from New Hampshire waters. Fishing and natural mortality rates of smelt are not known (Chase and Childs 2001).
Conservation notes 3
Importance to Humans and Estuaries
Rainbow smelt are fished recreationally throughout their range and have been the target of commercial fisheries as well. In many areas they occurred in high numbers, and because of their migratory lifestyle, they were a significant source of nutrients being brought into and out of estuaries where they served as prey for many larger predators, including striped bass, bluefish and a variety of birds.
How to Help Protect This Species
Because this species uses estuaries and freshwater areas they are susceptible to water pollution and damage to and alteration of stream channels and riparian zones. Therefore, efforts to protect the species include:
•Minimize runoff of neighborhood pollutants, fertilizer, and sediment into local streams are helpful to this species, and other estuary dwelling species.
•Join a stream or watershed advocacy group in your area to protect your local estuary ecosystems.
•Support restoration of more natural water flow regimes.
•Support research into the ecology of the species including poorly studied areas of the marine phase and better knowledge of spawning, rearing, and other river habitat needs and surveys to establish population sizes in poorly studied river systems.
The states of Maine, New Hampshire and Massachusetts have a large NOAA grant to conserve and restore wild populations. In Massachusetts the fishery is closed by regulation from March 15th to June 15th to protect spawning fish.
Sources and Credits
- (c) NOAA Great Lakes Environmental Research Laboratory, some rights reserved (CC BY-NC), http://www.flickr.com/photos/noaa_glerl/4045899707/
- Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Osmerus_mordax
- (c) GTMResearchReserve, some rights reserved (CC BY-SA)
