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4.3. AQUATIC FOOD PRODUCTION SYSTEMS (Unsustainable wild fishing industry,…
4.3. AQUATIC FOOD PRODUCTION SYSTEMS
Knowledge and Understanding
aquatic systems provide a source of food production
unsustainable use of aquatic ecosystems can lead to environmental degradation and collapse of wild fisheries
aquaculture provides potential for increased food production
highest rates of productivity are found near the coast or in shallow seas where upwellings and nutrient enrichment of surface water occurs
harvesting certain species can be controversial e.g. seals or whales - ethical issues arise over biorights, rights of indigenous cultures and international conservation legislation
Marine ecosystems and foodwebs
marine ecosystems (oceans, mangroves, estuaries, lagoons, coral reefs, deep ocean floor) are usually very biodiverse therefore have high stability and resilience
some are more productive than others - one half of marine productivity is in coastal regions above the continental shelf
continental shelf is the extension of continents under the seas and oceans - it creates shallow water - important because 50% of oceanic productivity but only 15% of its area, upwellings bring nutrient rich water up the continental shelf, light reaches shallow seas so producers can photosynthesise and countries can claim it as theirs to exploit and harvest
UN convention on the Laws of the Sea (UNCLOS) in 1982 said continental shelves belong to countries from which they extend - 200 nautical miles out is the exclusive economic zone
deep oceans where light does not reach have low productivity as the only food sources are chemotrophs and dead organic matter that descends from above
Phytoplankton can photosynthesise- make up 99% of primary productivity in the sea, zoo plankton eat phytoplankton and their waste
marine organisms can be classified as - benthic (living on or in the sea bed) or pelagic (living surrounded by water from above the sea bed to the surface)
Fisheries - industrial farming and hunting
about 90% of fishery activity is in the oceans and 10% in freshwater
fisheries include
Shellfish - oysters, mussels and molluscs (including squid)
some vertebrates - e.g. eels, tuna etc,
according to FAO (food and agriculture organisation) - more than 70% of world's fisheries are fully exploited, in decline, seriously depleted or too low to allow full recovery
global fish catch is no longer increasing even though technology is improving - demand is rising but fishermen can't find or catch enough fish
Aquaculture - the farming of aquatic organisms in both coastal and inland areas involving interventions in the rearing process
farmed fish production was more than beef production in 2011
ways in which fish farming is becoming more sustainable
fishmeal uses more trimmings and scraps which would have been wasted in the past
livestock and poultry processing waste is substituted for fishmeal
US department of agriculture found that eight species of carnivorous fish can get enough nutrients from alternative sources without eating other fish
China - produces 62% of all farmed fish in the world - mostly carp or catfish grown in rice paddies - waste is used as fertiliser for rice
other aquaculture systems are less efficient than China - mangrove swamps in philippines have decreased by 2/3 in 40 years
impacts of fish farms
loss of habitats
pollution (antifouling agents, antibiotics added to fish pens etc.)
spread of diseases
escaped species including genetically modified organisms which may survive to interbreed with wild fish
escaped species may also outcompete native species and cause the population to crash
Unsustainable wild fishing industry
once larger fish specimens are overfished we catch smaller and smaller ones so they are not able to mature and reproduce
commercial fishing is informed by satellite technology, gps and fish finding scanning technology - increasing the amount we can exploit
fishing fleets have become larger and with modern refrigeration techniques, including blast freezing, they can stay at sea for weeks or even an entire season
there are factory ships that process the catch at sea
trawlers drag huge nets over the seabed virtually clear cutting it
about a quarter of the global fish catch goes into fish meal and fish oil products to feed animals to feed us
about 20 million tonnes are by-catch - thrown back into the ocean
Maximum sustainable yield
sustainable yield - increase in natural capital i.e. natural income that can be exploited each year without depleting the original stock or its potential replenishment
carrying capacity is dependent on - reproductive strategy, longevity and indigenous resources of the habitat or ecosystem
SY = total biomass at time t + 1 / energy - total biomass at time t / energy
each breeding season / year new individuals enter the population (either new offspring or immigrants) - if the number recruited is larger than the number leaving (dying or emmigrating) then there is a net rincrease - if the difference in population between initial size to new population size is harvested then the pop will remain the same - maximum sustainable yield
OR SY = annual growth and recruitment - annual death and emmigration
harvesting the maximum sustainable yield normally leads to population decline because populations are normally predicted (modeled) rather than counted, also disease may strike the population