The Crystal Darter is an endangered fish species, and as such is difficult for water monitoring crews to find while sampling lakes and streams. But positive news of the Crystal Darter’s existence and reproduction has emerged during recent sampling events, including the summer of 2017.
Darters are a relatively unknown species of fish to most people in Minnesota, but are found in streams, rivers, and lakes throughout the state. Of the roughly 140 darter species found in North America, 14 exist in Minnesota, with the Crystal Darter being perhaps the rarest and least known. Crystal Darters are small, slender fish colored a pale yellow with several dark bars along their sides. Once fully grown their length is typically 3-4 inches, rarely growing past 5 inches.
Little is known about the life history of the Crystal Darter within Minnesota. Specimens have been collected from rivers in southeastern Minnesota, in moderate to large water bodies with clean water and active flows. These rivers include the St. Croix, the Mississippi just north of Red Wing, the Zumbro, and the Root.
Crystal darters are typically found near sand and/or gravel substrates, which they use to their advantage by burying their bodies while keeping their eyes exposed and ambushing prey as it swims or drifts by.
Due to their rare existence, unknown life history, and relatively low sampled populations, they were initially designated a species of special concern within Minnesota in 1984. However, after targeted surveys and analysis, the designation was elevated to endangered in 2013.
Minnesota Dept. of Natural Resources (DNR) crews found Crystal Darters when sampling fish near Folsom Island in the St. Croix River in August 2014 and June 2015. John Waters, DNR invasive carp fisheries coordinator, and his crew found one Crystal Darter during each sampling event.
Then, in late 2017, four additional Crystal Darters were sampled in the same general area. Each darter was found over sandy substrate in about 5-8 feet of water.
Similarly, Konrad Schmidt, a retired Minnesota DNR biologist, found a single Crystal Darter over sand/gravel substrate in roughly 3 feet of water using a seine.
Crystal Darter populations are very susceptible and sensitive to environmental changes such as:
- Habitat degradation and modification
- Flow alteration
- Lack of connectivity
Populations are dependent on clean gravel/sand substrates for reproduction and foraging, which makes them sensitive to siltation often arising from erosion, logging, or agriculture.
Moderate to fast-flowing streams where the Crystal Darters reside often have enough current to keep substrates clean. However, flow alterations such as dams, slow the flow of streams allowing sediments to settle to the bottom. Flow alterations often prohibit fish passage, negatively affecting the darter’s (and other fish species’) ability to disperse and establish new populations.
“Although Crystal Darters are a small, relatively unknown fish to most in Minnesota, there is no denying their uniqueness, not only in appearance but as well as lifestyle. In order to ensure this unique species does not become extinct in Minnesota, care should be given to reduce sediments entering streams and limit blockages to fish passage where known populations exist,” said Tony Dingmann, MPCA biologist.
For more information on the Crystal Darter and other rare fish species in Minnesota, visit the DNR website.