Why is the bridle shiner so rare?
Bryan Windmiller of Grassroots Wildlife Conservation cites several reasons for the bridle shiner’s declining population:
■ Pesticide: Rotenone was used extensively in ponds in Massachusetts in the 1940s and ’50s to kill “trash fish” (mostly native warm-water species), making room for restocked game fish, such as largemouth bass and bluegills, and golden shiners that were added as food for them. Use of rotenone by the state Division of Fisheries & Wildlife is now strictly prohibited, but its earlier widespread use may have wiped out some bridle shiner populations.
■ Introduced fish species: Bridle shiners are not fast swimmers, and are vulnerable to predators such as largemouth bass and bluegills.
■ Decrease in native plants: Bridle shiners are associated with submergent plants such as elodea, which provide cover. They also need open areas to feed. Pollution, exotic invasive plant species, and people removing plants can decrease or eliminate native communities, altering stream or pond characteristics and leading to a decrease in bridle shiner habitat.
■ Turbidity: Bridle shiners are visual foragers, so they need to be able to see the small invertebrates, such as copepods and insect larvae, that are their food. Cloudy water can inhibit the shiners’ ability to see its prey, a particular concern in developed areas like those around Vine Brook in Bedford, where open soil on the edges of roads, parking lots, and construction sites can easily wash into adjacent water bodies.
■ Stream channelization: Straightening of streams by digging ditches to redirect their flow can change the water’s characteristics by altering flow rate, substrate, and vegetation. Vine Brook used to run through the Burlington Mall parking lot, but it was moved out of the way during construction. The rerouted section of the brook has no shiners.