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North Carolina Department of Environment Quality

NC Department of Environment and Natural Resources
Marine Fisheries - Physical Threats to Habitat

Marine Fisheries

Physical Threats to Coastal Habitats

8-point rule

 
 

Physical habitat loss or degradation occurs with activities that disturb the visible structure of fish habitats.
Those activities include:

Beach Nourishment

Habitats Affected: 

Water columnsoft bottomocean hard bottom

Common Sources: 

Nourishment projects on ocean-facing beaches

Impacts:

  • Partial or complete burial of nearby hard bottom areas with redistributed sediment
  • Increased turbidity in water column
  • Physical disturbance to mining (“borrow”) sites
  • Direct mortality of important food resources for fish and shorebirds, including mole crabs, coquina clams and amphipods.

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Bottom Disturbing Fishing Gear

Habitats Affected:

Shell bottomSAVsoft bottomocean hard bottomwater column

Common Sources: (See table below)

Fishing gear

Water column

Shell bottom

SAV

Soft bottom

Hard bottom

Bay scallop dredge

Low/unsure

Low/unsure

Low/unsure

   

Bull rake

 

Low/unsure Severe    

Clam hand rake

 

Low/unsure

Low/unsure

   

Clam tongs

 

Low/unsure

Moderate

   

Clam trawl (kicking)

Low/unsure

Moderate

Severe

Low/unsure

 

Crab dredge

Low/unsure

Moderate

Severe

Low/unsure

Low/unsure

Crab trawl

Low/unsure

Moderate

Moderate

Low/unsure

Low/unsure

Hydraulic clam dredge

Low/unsure

Moderate

Severe

Low/unsure

 

Long haul seine

 

Low/unsure

Low/unsure

   

Oyster dredge

Low/unsure

Moderate

Severe

Low/unsure

 

Pots

   

Low/unsure

 

Low/unsure

Shrimp trawl

Low/unsure

Moderate

Low/unsure

Low/unsure

Low/unsure

Impacts:

  • Mobile bottom-disturbing gears dig down into the bottom and uproot SAV.
  • Hard bottom and shell bottom structure can be broken apart, killing organisms and reducing habitat value.
  • The vertical profile of subtidal oyster reefs can be lowered, making the shell bottom community more susceptible to low oxygen events.
  • Elevated turbidity can degrade water column, SAV, shell botttom, or hard bottom habitat, depending on the frequency and intensity.
  • Disturbance of soft bottom habitat can alter productivity of benthic microalgae and reduce structural complexity of the bottom.

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Channelization, Ditching, and Filling

Habitats Affected:

Wetlandswater columnsoft bottom

Common Sources:

Flood control, agriculture, urban and suburban development, forestry

Impacts:

  • Reduction in wetland habitat.
  • Loss of wetlands or conversion to uplands reduces system’s ability to filter pollutants and regulate water flows.
  • Loss of riparian vegetation increases loading of non-point source pollutants.
  • Filling and channelization reduces fish access to wetlands.
  • Channelization increases erosion of stream banks and turbidity in the water.
  • Waters adjacent to channelized streams and ditched wetlands support lower abundance and diversity of fish.

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Dredging

Habitats Affected:

Water Column, shell bottom, SAV, wetlands, soft bottom, hard bottom

Common Sources:

Navigation channels, marina boat basins

Impacts:

  • Dredging can directly remove SAV, shell bottom, wetlands, or shallow soft bottom features.
  • Conversion of shallow water habitats to deep habitat results in loss of valuable nursery habitat and alters natural circulation patterns. 
  • Dredging can degrade SAV habitat, shell bottom, and hard bottom by increasing turbidity and sedimentation
  • Increased turbidity in the water column can deter successful recruitment of larvae, clog fish’s gills, reduce ability of visual foraging predators to catch prey, and make toxins in bottom sediments biologically available to fish.

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Flow Regulation and Obstruction

Habitats Affected:

Water column

Common Sources: 

Dams, water withdrawals, road fill, and culverts

Impacts:

  • Dams, road fill, and pipe culverts can obstruct passage of anadromous fish to historical upstream spawning grounds.
  • Surface and ground water withdrawals can significantly alter currents, temperature, and oxygen levels to conditions that deter spawning and egg development of anadromous fish.

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Infastructure

Habitats Affected:

Water column, SAV, wetlands

Common sources:

Construction and operation of bridges, roads, culverts, sewage systems, pipelines, etc.

Impacts:

  • Construction of new bridges may result in loss of SAV or wetlands, while also degrading nearby habitat with increased sediment loading.
  • Fill, impervious surfaces, or culverts placed in wetlands for roadways alters the hydrology of the system, often impacting upstream wetlands, and the ability of fish to migrate upstream to spawning or nursery areas.
  • Installation of submerged pipes or cables across SAV beds or ocean hard bottom can result in destruction of habitats that have long recovery periods

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Marinas, Docks and Piers

Habitats Affected:

Water column, shell bottom, SAV, wetlands, soft bottom

Impacts:

  • Shading by boats and structures reduces light availability for SAV, and to a lesser extent wetlands. Reduced light can cause mortality of SAV or prevent its expansion in otherwise suitable areas.
  • Dredging of marina basins reduces productivity of the soft bottom community.
  • Dredged basins alter circulation patterns and can result in water quality degradation and low oxygen events, which stress or kill fish.
  • Fuel, bottom paint, and other toxins found at marinas and docking facilities can impact recruitment and survival of oyster larvae and degrade water quality.
  • Biological problems associated with docks and piers can be minor individually but can have significant cumulative impacts on coastal fish habitat.

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Mining Operations

Habitats Affected: 

Water column, soft bottom, wetlands

Common Sources: 

As of October 2004, no mining (other than for beach nourishment) occurs in North Carolina estuarine and nearshore ocean waters. However, the potential for mining projects exists in phosphate-rich areas in nearshore ocean waters in Onslow Bay as well as the Pamlico River. In addition, sand mining is common throughout eastern North Carolina, and occasionally mines are dewatered into wetlands or coastal streams.

Impacts:

  • Extraction of minerals could have bottom-disturbing effects similar to that of dredging, such as:
  • Underwater mining activities could lead to the unintentional release of "phosphate mining byproducts" into the water column, including radioactive substances, florides, and other chemicals.
  • Water from sand mines entering wetlands and coastal streams can increase turbidity.

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Shoreline Hardening

Habitats Affected:

Water column, SAV, wetlands, soft bottom

Common Sources:

Bulkheads, jetties, seawalls, groins

Impacts:

  • Increased wave energy on shoreline due to hardened structures accelerates erosion of wetlands and leads to loss of intertidal soft bottom habitat.
  • Increased turbidity in the water column.
  • Deepening of nearshore habitat and elevated turbidity due to hardened structures deters future colonization of wetland or SAV plants.
  • Reduced fish and invertebrate use of hardened shore due to decrease in habitat complexity and toxicity of wood preservatives.
  • Prevents landward migration of wetlands (along estuarine shorelines) or barrier islands (along oceanfront).
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N.C. Division of Marine Fisheries • 3441 Arendell Street • Morehead City, NC 28557 • 252-726-7021 or 800-682-2632

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