DESERTED OCEANS:
Habitat Degradation
Human activities are not only directly threatening marine life through overfishing, but also via indirect impacts to fish habitats. Reducing the quality of fish habitat, places pressure on juvenile individuals as well, resulting in future years of decreased recruitment to the fishery.
Wetlands
are found at the interface of land and water and are an important ecosystem
for commercial fish populations. They provide various important ecosystem
services such as acting as natural filters to improve water quality, and
they are a unique nursery habitat for many juvenile fish species. Throughout
history, wetlands have been filled, drained, or ditched for human use
such as development, flood control, aquaculture, or mosquito control.
Increased levels of urban pollution and sediment retention from dams also
threaten these habitats (Mitsch and Gosselink).
Much like wetlands, seagrass beds are also an important habitat for many commercially valuable fish species. They have many ecological roles including stabilizing sediments and absorbing nutrients to increase water clarity and quality. Algae and various epiphytic invertebrates use seagrass blades as a substrate. These invertebrates and the seagrass are a food source for over 340 marine animals, and provide an important link in mineral and nutrient cycles. They are often found close to coral reefs and provide a nursery habitat for juvenile reef fish species. Adult reef fish also venture into seagrass beds at night to feed on prey. Threats to seagrasses include, land based pollution that causes a decrease in water quality, poor boating practices that cause prop scars, and dredging activities which remove seagrass (Florida Oceanographic Society).
A decline in seagrass habitat also affects coral reefs, which are a primary habitat for many commercial fish species. Coral reefs are the most productive marine ecosystem, and are habitat for over 500 commercial fish species in the US, as well as home for endangered and threatened species. Reef fisheries yield 6 million metric tons of catch annually, with one quarter of the total worldwide fish production in developing countries coming from coral reefs (NOAA-Office of Protected Resources). According to the Global Coral Reef Monitoring Network (GCRMN) over 27% of the world's reefs have been lost, which includes 16% that were recently lost in 1998 due to the climate changes caused by the El Nino event. Human impacts to reefs include increased sedimentation and pollution from coastal development, increased nutrient levels from agriculture, unsustainable fishing practices and overfishing (NOAA-Office of Protected Resources).
Bottom
trawling has been documented as one of the most destructive and wasteful
fishing practices due to the high volumes of bycatch and the degradation
of complex benthic habitat. Bottom trawls are mobile fishing gear made
of large nets that are dragged on the seafloor to catch benthic fish species
such as cod, haddock, flounder, and shrimp. Originally, trawls were used
in shallow water areas of sand or mud, but with technological innovation
to reduce damage to the nets, trawls are now being used on structurally
complex habitats (MCBI). Bottom trawls are use
in various fisheries worldwide and approximately half of the world's continental
shelf is currently scoured. The gear crushes and buries marine structures,
which makes recovery after this disturbance slow because species rely
on structural diversity (Watling and Norse, 1998).