Fish, Seafood, and Aquaculture: What Are You Eating? (Part I: Environmental Impacts)

More and more people are making conscious decisions to purchase quality food or personal care products.  I notice many people choose to eat organic produce and meats, avoid GMOs, or avoid crops known for high pesticide contamination. In some instances red meat is avoided for healthier options such as fish or chicken.  As with many other foods, fish and seafood also have their downside. Many fish species are contaminated with mercury and other contaminants due to continuous polluting of the oceans, lakes, and rivers.  Additionally, many fish and seafood stocks across the world have crashed from overfishing, which has increased the popularity of aquaculture, or farmed fish and seafood.

Aquaculture

The oceans have long been a source of food for various populations across the world.  As the world population has increased to seven billion people and demand for fish and other aquatic food sources has increased, various aquatic populations have crashed due to overfishing.  It can take several years, even decades for a collapsed fish population to recover.  A classic case of a collapsed fishery is that of northwest Atlantic cod, which collapsed in 1992 and has yet to fully recover 22 years later.  Factors such as a continuously cooling North Atlantic are suspected to be contributors to the slow recovery.  The ecological consequences of collapsed fisheries within aquatic ecosystems are also vast due to a loss of key species in the food web.  Farming has gained increasing prominence because it can serve as a method to relieve natural aquatic ecosystems of the stresses of overfishing.

Aquaculture, or farming of aquatic species, involves breeding, raising, and harvesting of species in controlled environments (oceans, lakes, rivers, and ponds) until they are large enough for consumption (FishWatch).  Presently the most commonly farmed fish species are carp, salmon, tilapia, and catfish.  Shrimp and various mollusk species including clams and mussels are farmed, as well as aquatic plant species and sea vegetables.  Though farming does help to alleviate overfishing of targeted species in the wild, it does have several negative impacts on environment and human health.

Impacts of Aquaculture

Approximately half of all seafood (including fish) consumed by humans is from aquaculture (NOAA).  In the United States 91 percent of all fish and seafood is imported, of which 45.5% is farmed (FishWatch).  The remaining 9 percent is supplied by wild caught fish and U.S. based aquaculture (lowest contributor).  Most of the imported farmed fish and seafood comes from   Asia (89 percent), with China being the largest producer (62%) (FishWatch).  Regulatory standards for farmed seafood in China, Thailand and other Asian countries are not as stringent as they are in the U.S., which results increased environmental pollution, risk of disease, and increased contamination in some instances.

Environmental

Many aquaculture pens are in coastal regions near oceans.  The coastal areas are home to estuaries, mangroves, and tidal creeks, which often become depleted as they become converted to aquaculture ponds or pens (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012).  Impacts of aquaculture in coastal areas include but are not limited to habitat loss/modifications, introduction of exotic species, over harvesting of wild seed/spawners and damage to bycatch, misuse of chemicals and antibiotics, release of wastes, interactions with wild populations, and dependence on wild fisheries (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012).  Mangroves are also accumulation sites for contaminants, nitrogen, carbon, and sediments, and offer protection against erosion (Martinez-Porchas and Martinez-Cordova 2012).  The aforementioned impacts have been observed in southeast Asia (Vietnam and Philippines) where mangroves have been depleted in order to create shrimp ponds (farms).  As of 2006, an estimated 35 percent of global mangroves have been lost due to shrimp farming (Primavera 2006).  Similar trends have been observed in Thailand, Indonesia, Ecuador, Bangladesh and Madagascar, with Thailand converting almost half of its 312,700 hectares of mangroves and wetlands to shrimp farms (Martinez-Porchas and Martinez-Cordova 2012).  Mangrove degradation leads to loss of essential ecosystem services such as  fish/crustacean nurseries, wildlife habitat, flood control, sediment trapping, water treatment and coastal protection (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012).  Loss of such protection in countries such as the Philippines may exacerbate vulnerability and damage from typhoons.  Fish pens also contribute to deteriorating coastal habitats (Primavera 2006).

Aquaculture also impacts the biogeochemistry of surrounding areas.  Wide spread use of antibiotics and chemicals can contribute to the salinization and acidification of soils near aquaculture farms (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012).  Unconsumed fish feed leads to eutrophication, the over-enrichment of nutrients, in conjunction with overfertilization, decomposition of dead organisms, and lixiviation (separation of a substance into soluble and insoluble constituents) of feed (Martinez-Porchas and Martinez-Cordova 2012).  An estimated 20 to 50% of feed is retained by farmed species as biomass, with the remainder eventually become incorporated into the water column or sediment, and discharging to nearby ecosystems causing phytoplankton blooms, death of benthic (bottom) species, and the dispersal of pathogens (Martinez-Porchas and Martinez-Cordova 2012).  An estimated 5.5 million tons of organic matter, 360,000 tons of nitrogen, and 125,000 tons of phosphorus are discharged into ecosystems annually from shrimp farming alone, which accounts for only 8 percent of all aquaculture (Martinez-Porchas and Martinez-Cordova 2012).

Close quarters for farmed aquatic species and introduction of exotic species also contribute to the spread of diseases, which are then treated with antibiotics and other chemicals (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012).  Parasites from farmed fish can spread to wild species, such as the spread of sea lice which may result in a collapse in pink salmon populations and possible cause extinction of a specific local population (Martinez-Porchas and Martinez-Cordova 2012).  Low to high levels of antibiotics, hormones, steroids and other pharmaceuticals have been detected in soils, surface waters, and groundwater (Martinez-Porchas and Martinez-Cordova 2012).  The implications of widespread antibiotic and chemical use can also impact human health.

Part II will discuss the Public Health impacts of Aquaculture.

Sources:

FishWatch.  n.d.  “Farmed Seafood.”  FishWatch U.S. Seafood Facts.  <http://www.fishwatch.gov/farmed_seafood/index.htm>

FishWatch.  n.d.  “Outside the U.S.”  FishWatch U.S. Seafood Facts.  <http://www.fishwatch.gov/farmed_seafood/outside_the_us.htm>

Martinez-Porchas, M. and L.R. Martinez-Cordova.  2012.  “World aquaculture: environmental impacts and troubleshooting alternatives.”  The Scientific World Journal.  

Primavera, J.H.  2006.  “Overcoming the impacts of aquaculture on the coastal zone.”  Journal of Ocean & Coastal Management.  49: 531-545.

NOAA.  n.d.  “Basic Questions about Aquaculture.”  Office of Aquaculture.<http://www.nmfs.noaa.gov/aquaculture/faqs/faq_aq_101.html>

No images in this post are my own, no copyright infringement intended.

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