Fish Farming - Environmental Problems Flashcards
What is the need for fishmeal?
Salmon predatory, carnivorous fish needing a high protein diet
Salmon pellets contain 40-60% fishmeal
Estimated that >2kg of fishmeal is needed to produce each kg of farmed ocean fish or shrimp
What alternate sources are under development to provide protein for fish?
Soyabean
Chinese working on a yeast that grows on old corn stalks to replace more than half fish meal in fish feed
Polychaete worms
What are the 2 major wastes associated with fish farming?
Food Waste
Fish Faeces - 25-30% dry weight of food voided as faeces
What are the main feeding methods within a fish farm?
Hand feeding
Operator controlled cannon feeding
Computer controlled feeding systems
Demand feeding
What are the 3 major waste categories in fish farming?
Soluble fraction - material excreted as urine or across gills, or leached from soil sinks
Solids - uneaten feed pellets, faeces, scales, mucus, detritus
Chemicals - food additives, immersion treatments, equipment treatments
How does this waste impact on the water column?
Hypernutrification and eutrophication are aided by the high levels of nutrient waste (nitrogen, phosphorus, vitamins)
How do cage structures impact on the environment?
Dampen currents Cage current 35-81% of external velocity 95% recovered 20 diameters downstream of structure Impacts sediment and benthos Effects up to 50m radius Enriched C, P, N and reduced O2 Anoxic sediments generate H2S, ammonium and methane Sediment degassing is visible at surface H2S highly toxic to fish
What management strategies are in place to reduce effluent impact?
Collecting funnels
Single point mooring - spreads impact over wider area
Fallowing (leave area untouched) - recovery can take 2-10 years though
Repeated trawling of the area to assist oxygenation and mineralisation of wastes
Why are chemicals used in farmed fish with regards to colouration?
Wild food is high in astaxanthin providing salmon etc with their pink colour
Synthetic analogue fed to farmed fish (carophyll pink)
Stats on antibiotics and steroids effects on the environment
Only 20-30% administered orally is taken up, rest to environment; problems with emerging resistance
Steroids - Inducing maturation, sex reversal, low doses, no percieved human hazard
How does fish farming impact on birds?
Physical damage by protective netting
Deliberate killing
Disturbance by aquaculture activities and scaring devices
Disruption of natural habitat
Why are heron detrimental to fish farms?
Can cause up to 30-40% loss of fry and juvenile fish at pond farms
Can consume 100kg fish/yr
Scotland has 38% of British and Irish population
3,800 breeding pairs plus 11,400 birds over winter
West coast important refuge in severe weather
Normally eat fish <20cm (butterfish, cod, flatfish, gobies)
How do fish farms impact on wild fish populations?
Interbreeding
Competition from introduced species
Contamination (introduction of pathogens)
Predation
How have farmed salmon been modified to improve yield?
Normal salmon only make growth hormone in some tissues and stop making it in winter, GM salmon are injected with growth gene and promoter sequence from ocean pout resulting in them being able to produce growth hormone in all tissues in all seasons
Can grow 5-50% as big and stop growing when they reach sexual maturity
Also antifreeze gene from winter flounder has been added
How is fertility controlled using hormones?
Introduced gene prevents the expression of the hormone gonadotropin releasing hormone (GnRH)
Without GnRH fish are sterile
Can be made fertile by dosing with purified GnRH
How is fertility controlled using chromosomes?
Fertilisation is external so chromosome manipulation is easy
Newly fertilised salmon eggs have 3 sets of chromosomes, usually expels one set
Pressure or temperature shock just after fertilisation prevents this
Extra set of chromosomes interferes with gonad development, theoretically sterile
e.g. triploid rainbow trout are used
What acts are in place to control fish farm pollution?
Control of Pollution Act (1974)
Water Act (1989) - fish farms deemed trade premises with trade effluents
- enabled water boards to impose conditions on cage farms
How are fish farms monitored?
Logistically impossible to monitor all farms
- <250t exempt, unless water quality problems
- 250-500t hyrdrographic survey plus annual sediment and benthos survey
- > 500t same as above + twice yearly water quality survey
Additional Reading - Nutrients
Ackefers + Enell, 1994
- nutrient levels given off by aquaculture comparatively small when compared to industry, agriculture and forestry
- land based systems offer much better control over nutrient deposition
Additional Reading - Chemicals
Tovar et al., 2000
- Intensive aquaculture significantly increases ammonia and suspended solids in a waterway
Additional Reading - Environment Jellyfish
Lo et al., 2008
- removal of oyster farms significantly reduced jellyfish (Aurelia aurita) population
- thought that cages provided shade and substrate to allow polyps to grow, causing a population surge
Additional Reading - habitat modification
Primavera (1997 + 1998)
Hundreds of thousands of hectares of magroves and coastal wetlands transformed to milkfish and shrimp ponds
- loss of ecosystem services provided by mangroves; nurseries for juvenile finfish, coastal protection, flood control and sediment trapping
Additional Reading - Impact of mangrove destruction on other habitats
Ogden 1988
mangrove destruction can impact negatively on sea grass beds and coral reefs
Additional Reading - Fishmeal catch
Naylor et al., 2000
North sea exploitation of fish for fish food has saw a decrease in cod, seal and seabird populations
Pauly 1987
Exploitation of anchoveta in Peruvian upwelling system has saw to a decline in seabird and mammal populations
Additional Reading - non-indigenous animals
Hansen et al., 1993
Atlantic salmon (Salmo salar) frequently escape from net pens
- As much as 40% of Atlantic salmon caught by fishermen in the North Atlantic ocean are of farmed origin
