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The Effects of Dredge Harvesting

Dredge harvesting is a process for collecting clams, oysters, crustaceans and other bottom-dwelling organisms from the bottoms of rivers, streams and oceans. In dredging, fishermen drag large, heavy nets along the bottom of a body of water to catch shellfish. Unfortunately, the dredging technique can cause problems to the marine ecosystem, causing short-term and long-term damage.

  1. Bycatch

    • As the huge nets pass over the ocean or river floor, they often ensnare many nontarget species -- this unintentional catch is known as bycatch. These organisms tend to be of little to no commercial value, and often die by the time fishermen throw them back into the water. In frequently dredged rivers, this can lead to the partial or even total depletion of a species. When this occurs with one or more species, the biodiversity of the entire region suffers.

    Plant Disturbance

    • Although dredge nets don't pick up all bottom-dwelling plants, the act of dredge harvesting can still damage or kill many aquatic plants. Without these plants filtering the water and undergoing photosynthesis, water quality can decrease rapidly. The reduced rate of photosynthesis can cause a decreased concentration of dissolved oxygen in the water, which can make the habitat unsuitable for certain organisms. This too can cause a loss of biodiversity in the area.

    Loss of Rugosity

    • One key element of many aquatic ecosystems is the rugosity of the habitat. Rugosity is the complexity of the river bottom or seafloor; a more complex surface allows more niches for various organisms. When dredge harvesting occurs, the seafloor is often scraped clean, removing rocks, plants, logs and other objects that may have provided a habitat for marine creatures. Without that maze of shelters for protection from predators and strong tides, many species cannot survive.

    Turbidity

    • Whenever anything is dragged along the sediment-covered seafloor, it causes dirt, sand and silt to become suspended in the water. This causes the water to appear brown and cloudy. Dredging can cause temporary turbidity, which can disorient many marine organisms and cause them to have trouble absorbing oxygen. Turbidity can also lead to reduced light infiltration into the water, which can decrease the photosynthetic activity of leafy plants or phytoplankton, causing lower dissolved oxygen concentrations.

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