Posted by Angie Hong | Posted in Aquatic Biology, Wildlife | Posted on 18-09-2014
When it comes to endangered species protection, most people picture a panda, not a tiny little fish in the St. Croix River that only comes out at night. In the conservation world, the term “charismatic megafauna” is used to describe popular animals like elephants, lions and whales that people yearn to protect from extinction. There are eight species of fish in Washington County that are considered threatened or special concern species by the State of Minnesota, and only two – the lake Sturgeon and paddlefish – could, perhaps, be considered charismatic megafauna. Meanwhile, the other six – blue sucker, crystal darter, gilt darter, least darter, pugnose shiner, and southern brook lamprey – are likely doomed to anonymity.
A quick comparison of these eight uncommon fish species shows that they have many similarities in terms of habitat needs and survival threats. The least darter and pugnose shiner, both tiny minnow-sized fish, prefer crystal-clear streams and lakes with an abundance of native aquatic plants such as eelgrass, Canadian elodea, pondweed and muskgrass. The pugnose shiner has disappeared from lakes in Minnesota and other states where people have removed native aquatic plants and scientists suspect that invasive Eurasian milfoil could threaten other populations as well.
The other six rare fish species in our area live in clear-water rivers and streams with sand, gravel, or rubble bottoms. Blue suckers, crystal darters, sturgeon, and paddlefish can be found in both the Mississippi and St. Croix Rivers, whereas crystal darters and southern brook lamprey have only been found in the St. Croix and a few of its tributaries.
Our local rare fish are a strange and varied bunch. The crystal darter is primarily nocturnal and buries itself in sand and gravel with only its eyes protruding while it waits to catch passing midge larvae, mayflies, caddisflies, water scavenger beetles, and nematodes. Minnesota DNR biologists have observed and photographed this species a number of times at night using scuba gear in the St. Croix River downstream of Taylors Falls. The paddlefish has a long paddle-shaped snout, a shark-like tail, and virtually no scales on its body. They live for at least 20 years. In contrast, the southern brook lamprey, which is no more than six inches long when full-grown, spends most of its life in a larval state, known as an ammocoete. When they are three to four years old, they gradually transform into adults, spawn, and then die. During their short-lived adult life, they never eat.
Siltation, sedimentation and turbidity are major threats to threatened and special concern fish species in our area, especially the ones that need clear sand and gravel to lay eggs, find food and hide from predators. Erosion along stream and river banks can bury sandy and gravely areas in shallow water and send dirt and silt further downstream as well. Sediment also washes into streams and rivers from farm fields, construction sites and stormwater pipes. Silt is especially problematic because it is so fine that it can clog the gills and breathing parts of fish, as well as the invertebrates and zooplankton they eat.
Other human changes to local rivers and streams have made it difficult for fish to survive as well. In order for blue suckers, sturgeon or paddlefish to return to historic habitats in the Mississippi and St. Croix River basins, for example, we would have to remove dams or install fish passage features like ladders or lifts. Since the Sandstone Dam was removed from the Kettle River in 1995, lake sturgeon have returned to portions of its upper river. Similarly, streams that have been straightened, realigned or ditched for agriculture and development no longer provide the right habitat for common and uncommon fish. Conservation projects on some of our local streams have helped to recreate rocky riffles and deeper, faster moving water, as well as more natural, meandering pathways some fish species need.
Though they may lack the charisma of a dolphin or a rhino, rare fish species also play an important role in the web of life and their disappearance is emblematic of habitat changes that threaten other plants and animals as well.
To learn more about rare species in Minnesota, go to www.dnr.state.mn.us/rsg/index.html.