Impact of Aquaculture

1
Impact of Aquaculture (Chapter 4)

• Main concern about impacts is the contamination
  of the natural environment with aquacultural
  effluent (waste) other concerns include genetic
  impact of escapees on natural populations,
  introduction of exotics, competition for water
• Topics to be covered
• Land-based aquaculture
• Open system aquaculture (large water bodies)
• General concerns (common to both)
• Wastewater treatment and aquaculture example of
  positive impacts

2
Impact of Aquaculture

• Land-based aquaculture
• This includes aquaculture in coastal regions.
  Environmental impacts associated with extensive
  aquaculture systems are minimal. But as the
  intensity of the operation increases, so does the
  potential impact on the environment. Major
  concerns include
• Eutrophication and sedimentation
• Physical destruction of natural habitats
  forests, mangroves
• Excessive use of resources water, food stuffs,
  electricity
• Negative effects on native fisheries and
  biodiversity (genetics, exotics and invasive
  species)

3
Impact of Aquaculture

• Land-based aquaculture
• Effluent-derived eutrophication this problem
  continues to plague the industry
• The impact of effluent discharge depends on
  species cultured, culture methods, stocking
  density, food composition and feeding techniques,
  and site hydrography
• Results of eutrophication increased oxygen
  demand, reduced DO (critical point downstream)
  increased suspended solids (turbidity), P, and N.
  
• Deterioration in water quality parameters reduces
  quality of habitat for animals and plants e.g.,
  high sediment loads kill mangroves, affect
  benthic species increased turbidity affects sea
  grasses, coral reefs high oxygen demand causes
  anaerobic conditions in sediment with production
  of toxic sulfides et cetera.
• Source of suspended particles uneaten or
  regurgitated food and feces in flow-through
  systems same as well as water-conditioning
  devices in recirculating systems
• Source of N and P feed wastage (by overfeeding
  or poor FCR), feces, respiration, excretion
  depending on species and culture techniques, up
  to 85 of P and 50-95 of N entering the culture
  system may be lost into the environment.

4
Impact of Aquaculture

• Land-based aquaculture
• Destruction of natural habitat
• Large-scale removal of mangroves for coastal
  aquaculture and destruction of forest in mountain
  areas for freshwater aquaculture have been
  documented
• In some countries, environmental issues may take
  second place to food production, out of
  necessity. However, the importance of these
  habitats to the maintenance of other natural
  resources cannot be overestimated.
• Mangroves, for example, are a major natural
  source of coastal productivity and are important
  nursery grounds for many important fishery
  species
• Continued degradation of these habitats is not
  sustainable in the long term because of serious
  environmental and social consequences

5
Impact of Aquaculture

• Open system aquaculture
• Operations of primary concern include fish
  aquaculture using cages or pens and near-shore
  bivalve aquaculture. Environmental effects of
  these operations include
• Cage culture
• Eutrophication and sedimentation (difficult to
  treat)
• Cage culture effects seem to be localized (near
  facilities). Solid waste accumulates on bottom
  under cage and affects sediment quality and
  benthic biota
• Rapid expansion of cage culture (e.g., salmon)
  has promoted use of chemicals (pesticides,
  antibiotics), which add to the chemical waste
  generated
• Cage culture also affects status of wild fish
  populations (feed and substrate availability)

6
Impact of Aquaculture

• Open system aquaculture
• Operations of primary concern include fish
  aquaculture using cages or pens and near-shore
  bivalve aquaculture. Environmental effects of
  these operations include
• Bivalve aquaculture
• Culture structures (racks, etc.) affects
  hydrography and provides substrate upon which
  other epibiota can settle.
• Effects on oxygen demand and nutrient load in the
  vicinity of the culture structures
• Overall very similar effects to cage aquaculture

7
Impact of Aquaculture

• General concerns (Land-based and Open)
• Disease transfer from farm animals to wild, and
  vice versa
• Pathogens obligate (need suitable host) and
  opportunistic (present at all times and become
  harmful when disease resistance of host is
  reduced)
• High-density (intensive) cultures often
  sufficient to allow opportunistic pathogens to
  take hold and form disease reservoir, especially
  when fish may be chronically stressed at high
  densities
• Measures should be taken to minimize disease
  transfer
• Genetic pollution from farm animals to wild
• Culture of inbred strains or species closely
  related to indigenous species carries the risk of
  interbreeding between escapees and native
  populations
• Effects include loss of genetic diversity, loss
  of stock integrity (useful genotypes e.g.,
  disease resistance), sterility

8
Impact of Aquaculture

• General concerns (Land-based and Open)
• Introduction of exotics
• Culture of non-native species carries the risk of
  introduction of exotics into the environment
• Effects include competition for resources and
  displacement of native species, disease transfer,
  changes in trophic structures, habitat
  modification (e.g., grass carp)
• Chemical additions
• Chemotherapeutics (e.g., widespread use of
  antibiotics), vaccines, hormones, food additives,
  disinfectants, water treatment compounds,
  antifoulants (TBT), construction additives
• Predator conflicts
• Predation is day-to-day problem in aquaculture
  large concentrations of prey attract native
  predators

9
Impact of Aquaculture

• General concerns (Land-based and Open)
• Miscellaneous conflicts Relationship between
  aquaculture and capture fisheries
• Depletion of wild stocks could occur due to
  collection of wild seed (e.g., young shrimp and
  juvenile fish) for aquaculture
• As wild fisheries decline and aquaculture grows,
  competition in terms of price and quality of
  product may intensify
• Use of trash fish to provide fish meal for
  aquaculture feeds is viewed as wasteful and
  inefficient. Trend is to use greater amounts of
  plant-based nutrient sources, but 100
  replacement is not yet possible from nutritional
  perspective
• Aquaculture could have positive impact on capture
  fisheries production of young organisms to
  supplement natural stocks. However, genetic
  considerations must be applied.

10
Impact of Aquaculture

• Integrated wastewater treatment and aquaculture
• Integrated aquaculture has been practiced for
  many centuries in Asia
• High system sustainability and minimal
  environmental pollution
• Integration of wastewater treatment and
  aquaculture is a more recent development
• Increasingly recognized that organic waste in
  domestic sewage is not necessarily bad, but can
  be viewed as nutrient source
• Technologies for the recycling of domestic sewage
  through agricultural practices (including
  aquaculture) have been developed in recent times
• Practice is known as waste-fed aquaculture
• It is practiced in several countries such as
  Germany (common carp, tench), Hungary (silver
  carp, common carp), India (several carps),
  Vietnam (tilapias), China (Chinese major carp,
  Indian major carp, tilapia, common carp)
• Concerns about the presence of pollutants in
  wastewater need to be addressed, especially when
  domestic sewage is mixed with industrial
  wastewater.
• Integrated resource management e.g. see figure
  4.10