Transcript Aquaculture impact PCB detail

CONSULTANCY AND RESEARCH IN AQUACULTURE AND THE AQUATIC ENVIRONMENT
A Company in the NIVA-group
Environmental impacts of aquaculture
Physical
 physical structures, such as cages, pens, moorings and
jetties, wharves, and with the waves created by boats.
 The nets of the cages, pens and associated moorings
changes the environment by preventing causing friction to
the water currents and changing the current patterns.
 The cages can hamper navigation routes
 Associated impacts include debris and discharges
associated from fish farms, notably fish bags, fish
mortalities, petrol and diesel from outboard motors and even
human faeces
 Nets allowed to drop below the cages.
Aquaculture impacts
 Physical
– Physical structures, cages, pens, jetties
– Visual
– Hazzard to navigation
– Net friction to exchange
– Use of wetlands and mangroves for pond construction
– Saline infiltration
Bolinao north entrance
Dagupan river system - fish pens
Taal Lake
Pond farms in Thailand
Saltwater infiltration
Freshwater pond
Marine pond
Aquaculture impacts
Impacts of aquaculture can be put into 3 categories
 Physical
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Physical structures, cages, pens, jetties
Visual
Net friction to exchange
Use of wetlands and mangroves for pond construction
 Chemical
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Oxygen depletion
Eutrophication
Antifoulants boats and nets
Medications and treatments
 Biological
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Faeces
Excretion
Waste food
Genetics and Biodiversity
Biological
 Aquaculture produces wastes which may negatively
affect the environment.
 In intensive aquaculture, a considerable amount of
organic wastes are produced in the form of
particulate (mainly the uneaten food, faeces) and
soluble substances (excreta) which increase
biochemical oxygen demand, nitrates and
phosphates in receiving waters.
Mass balance –
Phosphorous and Nitrogen
Oxygen Depletion
Oxygen is utilized in the vicinity of fish cages by
 the consumption of oxygen by the fish
 the consumption of oxygen by the release of
organic compounds that decompose in the water
column by chemical processes that use oxygen
(Biological Oxygen Demand, BOD).
 The consumption of oxygen by the primary
production (algae) and secondary production
(zooplankton) that are utilizing the additional
nutrients released by aquaculture.
Oxygen Depletion
 The absolute oxygen concentration at which the fish
can effectively extract oxygen from the water is
what matters most. Fish cannot extract oxygen
efficiently below 40% saturation. Generally oxygen
depletion is a localized phenomenon that affects
mainly the farm itself, and seldom extends very far
away from the farm site.
 However the algae that is utilizing the released
nutrients can bloom providing oxygen during the
day but utilsing oxygen during the night competing
with the fish. If it is a strong bloom, it can extract all
the oxygen leading to an algal bloom collapse and
fish kill.
Oxygen level in a fish pen – Bolinao, Philippines
Oxygen levels inside a fish pen
6
5
mg O2
4
3
2
1
0
8:00
10:00
12:00
14:00
16:00
18:00
20:00
Tim e
22:00
0:00
2:00
4:00
6:00
8:00
Faecal Matter
Fish faeces constitute a major and unavoidable form
of nutrient enrichment affecting the environment.
Modern fish feeds are produced in such a way as to
minimize the loss of nutrients (extruded pellets) and
by providing them in forms that can be easily
assimilated by the fish (largely protein and good
digestibility).
The nutrients that are not assimilated are excreted
mainly as soluble wastes such as urea and
ammonia, so the fecal matter consists mostly of
carbon and inert material.
Particulate material
 Fish farming in net cages affects the environment
by releasing large amounts of organic waste from
uneaten food and faeces.
 The amount of organic waste from cage farms can
be roughly estimated as 1,000 kg per tonne of fish
produced.
 Inputs at this level can have a marked impact on
benthic communities resulting in successional
changes in response to increasing inputs.
 There may be some consumption of particulate
matter by wild fishes attracted by aquaculture
facilities.
Particulate organic wastes
 Severe effects are generally confined to the local
area (a few hundred meters at most) and the total
area of seabed used for this purpose is insignificant
in terms of the total coastal resource.
 The extent and severity of effects depend on:
– The size and the production capacity of the farm
– The depth of the farming site
– The type of sediment beneath the cages
 On cessation of farming, recovery may take several
years.
 The main method of regulating and controlling the
size of fish farms such that the local environment is
not overwhelmed.
Effects on the Benthos
 Aquaculture impacts the structure of the benthic
communities.
 The number of macrobenthic species below fish
cages decreases and the community becomes
dominated by a few opportunistic species.
 In extreme situations the seabed becomes azoic.
 However this reduction in benthic diversity
normally does not exceed 25m from the cage
perimeter, followed by an increase in species
richness and diversity in the transitory zone.
 In case of coarse sediments the effect on sediment
communities is considerably lower.
Effects – distance from farm
Benthic Loading
 Benthic impacts are easy to identify and can be
clearly associated with fish farms, especially when
unconsumed feed or fecal pellets are present.
 The first stage is the initial deposition of fish farm
wastes on the bottom.
 The second stage, is much more complicated and
uncertain as to the fate of carbon and other
nutrients after the initial deposition on the bottom,
and are influenced by physical transport and
biological degradation and assimilation by other
organisms and removal.
Benthic Loading
 The initial effect of nutrient enrichment is almost always
an increase in benthic productivity, since there is more
food to feed the benthic community.
 This situation can persist for a long time if the degree of
enrichment is low, but the amount of deposition under
fish farms is usually so high that benthic scavengers
cannot process all of it, and some begins to decompose
through bacterial processes.
 This leads to reduced oxygen levels and increases in
sulfide concentrations, which are too stressful for many
bottom dwellers and therefore many species are driven
out and the species diversity falls.
Benthic Loading
 At extreme levels, only a few species can persist,
notably polychætes of the genus Capitella known as
indicator species.
 If the carbon loading is excessive then the capitellids
die out and eventually we find just bacterial mats; the
seabed becomes azooic and soon after totally anoxic.
Effects on Sediments
 The sediments under the cages is characterised by
 low values of redox potential,
 high content of organic material
 accumulation of nitrogenous and phosphorous
compounds.
 Occasionally this sediment layer is covered by
Beggiatoa-type mats, i.e. white-coloured
aggregations of bacteria living at the oxic-anoxic
interfaces that may release gas bubbles of H2S or
CH4.
Effects on Sediments
 Sediment profiles taken at various distances from
the edge of the cages have shown that the
thickness of the farm sediment varies considerably
with season and shows more obvious thichness
fluctuations than the surface concentrations of
chemical variables.
 The effects on sediment geochemistry are much
more severe in silty or muddy bottoms than on
coarse sediments.
Biological
 Sediments and nutrients may not necessarily be a
problem as natural breakdown processes or dilution in
the receiving waters can assimilate this, provided that
natural waters are not overloaded.
 The increased fertility of oligotrophic waters may even
bring positive effects on the local ecosystem, enriching
food availability for wild species.
 The risk of negative impacts of aquaculture wastes are
greatest in enclosed waters with poor water exchange
rates, where excessive production from aquaculture can
lead to eutrophication and other ecosystem changes
(e.g. algal blooms and low dissolved oxygen levels).
Soluble Effluents
 Soluble compounds, such as ammonia and urea
are a large part of the wastes released by fish
farms. However, unlike fecal matter which
accumulates in the immediate vicinity of the cages,
they can be flushed by movement of the water and
thus tend to approach an equilibrium level where
the rate of release into the water column is
balanced by flushing.
 Dissolved nutrients are not inevitably bad for the
environment, and, like moderate benthic carbon
loading, can even be beneficial.
Soluble Effluents
 Phytoplankton require nutrients to grow, and by
increasing primary production the release of
nutrients can stimulate the total productivity of the
system, including desirable commercially important
species such as oysters and mussels.
 Use of extractive species to extract nutrients from
the water column
– Mussels
– Oysters
– Seaweed
Dissolved nutrients
In general the total amounts of N and P loading are
linked with aquaculture intensity and with feed
conversion factors.
In Norwegian and Scottish coastal waters, around 55
percent and 17 percent, respectively, of all coastal
phosphorus discharge was attributable to
mariculture.
These discharges also contribute to the overall load
from inland and coastal environments in some
locations, together with discharges from agriculture,
forestry, industry and domestic waste.
Flushing rates
 Bad flushing
 Good flushing
Waste Feed
A significant amount of feed does not get consumed by
farmed fish and goes into the environment, which can
have significant impacts. Some of the feed
– is in the form of dust that is too small to be ingested by the fish
– gets lost through over feeding of the fish
– feed pellets are the wrong size for the fish.
 Excess pellets fall through the pen and can be found on
the bottom. These may be consumed by wild fish,
consumed by benthic organisms or breakdown into
nutrients by benthic assimilation.
Waste Feed
 Fine particles from the break-up of feed pellets settle
very slowly and are transported by currents in much the
same way as soluble nutrients, and can, among other
effects, contribute to Biological Oxygen Demand (BOD).
 Larger particles that fall to the bottom enrich the
sediments with carbon and other nutrients that can lead
to substantial changes in the benthic community.
Waste Feed
 The amount of wasted feed is decreasing, due to
strong economic pressure to reduce wastage as
much as possible since feed is usually the greatest
expense in fish farming.
 There has been a shift from trash fish to moist feed
and from moist feed, which tends to break up in the
water with consequent high loss rates, to the more
efficient dry feeds.
 Attention should be paid to paid to optimal feeding
schedules, both in terms of
– the amount of feed provided and when it is given
– careful choice of the type and size of feed pellets used
for fish at different stages of growth.
Turbidity
 One impact is to make water more turbid because
of the release of particulate matter. This is probably
not a serious concern in coastal environments,
where natural ambient turbidity is usually much
higher than any increment from fish farms, but in
clear water environments like lakes, and in isolated
coastal bays, the effect may be significant.
 The effect of increased turbidity is lower light
penetration, which can reduce primary production
by phytoplankton and by benthic macrophytes, and
possibly could reduce the feeding efficiency of
visual predators.
Disease Transmission – farmed to wild
 There are impacts from the transmission of disease
to wild stocks.
 The high density of fish in cages provides breeding
grounds for disease, and higher susceptibility to
disease
 Wild populations can receive a high level of
exposure to diseases since they can swim very
close to farm sites and often feed close by, but their
susceptibility is much lower.
 Little is known about the transmission of disease
from farmed stocks to wild stocks, but the
transmission of sealice from farmed salmon to wild
salmon has been documented.
Disease Transmission – farm to farm
 There are impacts from the transmission of disease
to from one farm to another.
 If one farm has a disease, this can be spread to
another farm by transfer of the disease organism
– Bacteria by currents
– Sealice by swimming
 Insurance companies will not insure farms that are
too close to each other as the risk of disease
transfer is high
Pharmaceuticals
 There are impacts from the release of medication
and pharmaceuticals that are used to treat disease
 The effects of antibiotics and other pharmaceuticals
on the environment is difficult to quantify.
 Little is known about how the various chemicals
used in fish farming affect wild populations that it is
almost impossible to estimate the secondary
effects, i.e., how they actually affect the
environment.
Pharmaceuticals
 Antibiotics
 Vaccines
 Treatments for fish disease
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– Baths
– Oral
Copper sulphate for control of algae and fungus
Methylene blue bath for treating fungus
Formalin bath for treating parasites
Potassium permanganate bath for treating bacteria
Disinfectants for eggs
Chemicals
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Detergents for cleaning
Disinfectants (floors, tanks)
Chlorine and Sodium thiosuphite for water sterilisation
Colouring in feeds (prawns and salmon)
Lime for treatment of ponds
Fertilisers for ponds
Tea seed cake for killing wild fish in a pond
Operational waste
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Feed bags
Daily mortality of fish
Plastic sacs from growing algae
Kitchen paper from cleaning hatchery tank skimmers
Post harvest
 Blood water from cutting gills
 Fish rinse water
 Waste fish from processing (Guts, head, skin, scales.
Etc)
Genetic Mixing
 Most farmed species, especially those of
finfish, are genetically different from the
native species, and there is concern about
genetic contamination of the wild species
 The viability of wild populations may be
threatened by interbreeding with
domesticated strains.
 Genetic mixing can occur from
– escape of farmed species into the wild (storm
damage, holes in nets).
– Use of wild caught fry from a different area
– Use of broodstocks collected from a different area
– Release of sperm or eggs from mature fish in cages
– Purchase of fry from other countries
Biodiversity
Aquaculture can affect local biodiversity in many ways.
Wild caught fry is still common for some particular marine
species. Repeated fishing for the juveniles of certain
species can drastically alter species composition by
preventing some of them from reproducing.
 the escape of alien species such as salmon and tilapia
can have deleterious effects on biodiversity. Tilapia are
highly invasive and exist under feral conditions in
every region in which they have been cultured or
introduced.
 If alien species allowed to escape, they can establish
spawning populations in the country of introduction
and dislodge native species from established food
niches or worse become a pest.
 A precautionary approach needs to be adopted with
regard to the use of alien species for aquaculture
purposes, particularly regarding biodiversity
conservation.