FISH MIGRATION BARRIERSFish migration barriers are anything in the stream that significantly interferes with the upstream movement of fish. Unimpeded fish passage is especially important for
anadromous fish which live much of their lives in tidal waters but must move into non-tidal rivers and streams to spawn. |
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Anadromous fish species, including American shad, white perch, yellow perch, blueback herring and alewife migrate from the Chesapeake Bay into Maryland rivers and streams in early spring to spawn. Unimpeded upstream movement is also important for resident fish species, many of which also move both up and down stream during different parts of their life cycle. Without free fish passage, some sections in a stream network can become isolated. If a disturbance occurs in an isolated stretch of stream, such as a sewage spill on a small tributary, some or all fish species may be eliminated from that isolated section of stream. With a fish blockage present and no natural way for a fish to repopulate the isolated stream section, the diversity of the fish community in an area will be reduced and the remaining biological community may be out of natural balance. Fish blockages can be cause by man-made structures such as dams or road culverts, and by natural features such as waterfalls or beaver dams. Fish blockages occur for three main reasons. First, there is a vertical water drop such as a dam that it is too high for fish to swim over. A vertical drop of 6 inches may cause fish passage problems for some resident fish species, while anadromous fish can usually move through water drops of up to 1 foot, providing there is sufficient flow and water depth. The second reason a structure may be a fish passage problem is because the water is too shallow. This can often occur in channelized stream sections or at road crossings where the water from a small stream has been spread over a large flat area and the water is not deep enough for fish. Finally, a structure may be a fish blockage if the water is moving too fast. This can occur at road crossings where the culvert pipe has been placed at a steep angle and the water moving through the pipe has a velocity higher than a fish's swimming ability. For more information about fish passage and Maryland Fish Passage Program: /fisheries/recreational/articles/fishpassage02.html If you see a fish barrier you can call Department of Natural Resources at 1-877-620-8DNR and ask for the Fish Passage Program.  Dark Branch fish barrier (After) |
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