Topic 4Water and aquatic food production systems and societies

4.3 Aquatic food production systems

Aquatic Food Production• Algae – human food source, agar gels

(around 30 million tonnes/yr harvested, largely in SE Asia)

• Fish – human consumption, animal/pet food, fish oil, food for aquaculture, gelatin, fertilisers (approx 20kg/capita/yr worldwide and increasing)

• Shellfish – mollusks (e.g. scallops), crustaceans (e.g. shrimp, lobsters)

• Others – reptiles (e.g. turtles, crocodiles, alligators), amphibians (e.g. frogs), mammals (e.g. whales, dolphins, seals)

Food Prices• World food prices have been

increasing recently• There is increasing meat and fish

consumption in MEDCs and LEDCs• More staple crops and fish are

being used as animal feed• Also more farmland is being used

to grow biofuels (especially in Brazil) - Land is becoming more expensive and more limited

• World oil prices are unstable and transportation costs are therefore increasing

World Food Price Index

Terrestrial and Aquatic Systems• In MEDCs we generally want a large variety of foods, and this also

gives a more healthy diet• This is leading to greater demand for meat and fish• Also driven by rising human population and changes in population

demographics • Terrestrial farming (e.g. arable and herbivore farming) harvests low

trophic levels• Aquatic farming (e.g. fish farming) generally harvests high trophic

levels• The Second Law of Thermodynamics shows that more energy must

be put into an aquatic system to harvest the same amount of biomass

Terrestrial and Aquatic Systems

Sea Fisheries and Sustainability• Mostly occurs near the coast. Bigger stocks since more nutrients available from river

discharge and upwelling (caused by strong winds and coastal currents)• Fisheries are only sustainable if the rate of removal < growth rate• However, most major fisheries are now over-exploited• The maximum sustainable yield occurs where population is increasing at its maximum

rate

MSY

Above MSY, yield is reduced by competition for resources

Below MSY, yield is decreased due to the small population

Fishing techniques

Sea Fisheries and Sustainability

• There are 2 major problems which prevent global sustainability:– The Tragedy of the Commons – Every country (and

individual fishermen) wants to catch fish in their own territorial waters before the stocks leave and head to those of another country.

– Short-term gain – It is easy (and tempting) to see the greatest gain over the short term rather than look towards long-term conservation of stocks

Sea Fisheries and Sustainability

• Possible conservation strategies include:• Reduce the size of fishing fleets• Reduce the size of individual fishing boats• Reduce net/mesh size (this helps to prevent

juvenile fish being caught which can then spawn)• Closed seasons• Exclusion zones/Marine Protective Areas (these

conserve habitats and allow fish to spawn)

The Downeaster Alexa

Case Study 1 - Newfoundland• Before 1950, the largest cod stocks in the world• From 1950s onwards introduction of technology to

exploit the stocks commercially• Fishing peaked in 1968 – 800 000 tonnes• The local and national government did not

intervene for fear of affecting jobs• The entire fishery collapsed• In 1992 it was closed completely, leading to the

loss of 42 000 jobs• It still hasn’t recovered

Newfoundland cod fishery collapse

Case Study - Newfoundland

Case 2 - Iceland• Most important industry in the country is cod fishing• Stocks began to decline in the early 1950s, but the

government decided to take action• They protected and expanded their territorial waters

aggressively. This lead to confrontations with the British Navy between 1952 and 1976 (The ‘Cod Wars’ *)

• Restrictions were introduced on fleet size, boat sizes, fishing gear and mesh size

• Introduction of closed seasons• Use of coast guard and inspectors to enforce restrictions

* Won by Iceland after it threatened to leave NATO The Cod Wars

Marine Hunting

• Includes hunting of seals, dolphins and whales• In the Western World this is largely seen as unethical– Marine mammals seen as intelligent and close relatives of

humans– Many hunting methods seen as causing unnecessary pain,

e.g. harpooning or clubbing– Some species have been driven close to extinction– Hunting of fur seals involves killing juvenile animals

• However hunting may play an important role in many indigenous communities, e.g. Inuit

Aquaculture• This is the farming of aquatic species (marine and

freshwater)• Not just as a food source. Also for commercial products,

pets, skins etc.• Fish, shellfish, reptiles and amphibians all farmed• Aquaculture is increasing as fisheries are declining (due to

over-exploitation)• Includes open systems and closed systems• Open systems are created by caging species in an existing

habitat (riverine or coastal)• Closed systems are created in tanks situated inland

Environmental Impacts of Aquaculture

• Loss of habitats, e.g. mangroves, to be replaced with closed systems (e.g. caged fish or shrimp)

• Generation of sediments (from faeces), smothering benthic habitats and creating anoxic conditions

• Generation of nutrients (from faeces) creating algal blooms and eutrophication of freshwater

• Contamination of with antibiotics and hormones• Pollution caused by antifouling paints which contain toxins

including heavy metals• Spread of disease in densely-packed populations• Escape of farmed animals (may outcompete or prey on indiginous

species)• Attraction of predators which may become trapped in cages