Aquatic Food Production Systems 4.3

Aquatic primary producers

• Phytoplankton - diatoms and microscopic marine algae

• Macrophytes - aquatic plants visible wo microscope

• Cyanobacteria - blue/green algae

Primary consumer

zooplankton

What does high biodiversity lead to

high stability and resilience

Benthic organisms

living in the bottom of water

Pelagic organisms

Swimming in the upper layers of water

Why did our consumption for fish increase?

• Shift in diet

• society is getting wealthier

• transport improved

• Increased supply from aquaculture

• fisheries are more effective

Why is fish industry important ?

• ½ billion make living from industry

• 3 billion ppl gain 20% of protein from fish

Result of increased consumption of fish

70% of fisheries are at limit

What is fishery

Fish harvested in some way

• capture of wild fish

• aquaculture

• fish farming

What does unsustainable wild fishing lead to?

Overexploitation and damage to the ecosystems directly

What is overexploitation

when the rate of resource extraction is faster than the ecosystem’s capacity to regenerate

What is the result of overexploitation ?

• declining stock

• habitat loss

• loss of biodiversity

• When population falls below recovery thresholds - fishery collapse

• disrupts food webs, economies and local communities

What are 3 unsustainable methods of wild fishing?

1. Bottom Trawling

2. Ghost Fishing

3. Poison and Explosives - cyanide and blast fishing

Bottom Trawling

• dragging heavy nets across seabed to catch benthic species

• habitat destruction - coral reefs, sponges

• bycatch

Ghost fishing

• capture and death of marine life due to lost/abandoned fishing gear

• affects over 100 000 mammals annually

Cyanide fishing and blast fishing

• stun live fish for aquariums

• damage to coral reefs

Why we can catch more fish now?

• Technology - satellite navigate systems

• larger fishing fleets with better freezing

• longer at sea

• indiscriminate fishing methods - bycatch

Tragedy of commons

• exploited resources seen as belonging to all

• lack of regulations

• leads to overexploitation in competition to catch the most

Maximum Sustainable Yield - MSY

• The highest possible annual catch that can be harvested from a natural population without reducing its capacity to replenish

• Fisheries aim to harvest the same number of fish as are naturally added - maintains fish population at a stable equilibrium

Whats MSY in comercial ventures?

• amount that can be taken without permanently depleting the stock

Whats Carrying Capacity (K)

• Maximum population of species that the resources in the ecosystem can sustain

• at ½ K population reproduces faster (balance between enough individuals to reproduce and sufficient amount of resources) - this is the point of MSY

What does carrying capacity depends on?

• reproductive strategy

• longevity

• the resources of the ecosystem

Why fishing at MSY still leads to population decline?

• population dynamics normally predicted on a model

• difficult to calculate precise population sizes

• difficult to model sex/age ration

• diseases/pollution not accounted for

How to make wild fishing more sustainable?

• Fishing permits on national/local scales

• fishing quotas limiting amount of fish that can be caught

• seasonal closures to allow fish to reproduce

• altering mesh size - juvenile can escape

What is Aquaculture

• farming of aquatic organisms under controlled conditions

Why is Aquaculture important?

• Provides a growing proportion of global seafood demands as wild fish stock decline

• contributed to food security, economic development and employment

Example of efficient aquaculture

• china produces 62% of all farmed fish

• grown in rice paddies and their waste acts as a direct fertiliser for rice

Example of Inefficient farming

• Shrimp and salmon fed of fishmeal from wildfish (leads to depletion of wild fisheries and predators who rely on those species)

• 2/3 mangrove swamps in Philippines replaced by fish farms = habitat loss, pollution, spread of disease

Positive impacts of Aquaculture

• Under correct management can support ecosystems by filtering water and sequestering carbon

• farming of filter-feeding bivalves can improve water quality by helping control excess nutrients

• Seaweed farming increases O2 in water, reduces acidity of the ocean

Negative impacts of aquaculture

• water pollution - chemicals and waste produces cause algal bloom

• fish escapes and invasions - wild fish can enter and transmit disease, compete or interbreed with local species

• Diseases, antibiotics and pesticides - antibiotic resistant bacteria, pesticides kill species in near waters

• barrier for migration

How to make fish farms more sustainable?

• livestock waste as food

• limit use of chemicals/antibiotics

• lower density in pens

• suing off-cuts to feed the fish

Ocean Acidification

• occurs when excess CO2 dissolves into seawater = carbonic acid

• Reduces availability of carbonate ions needed for shell and skeleton formation

• decline in mollusks and plankton

• marine food web destabilised

Effects of temperature increase on aquatic life

• warmer water holds less oxygen

• species fail to adapt quickly - local extinctions

• species migration

Effects of Coral bleaching on aquatic life

• corals live symbiotically with photosynthetic algae (zooxanthellae)

• Acidity = corals expel algae within their tissues - turn white

• bleached corals - reduced growth and reprodution

Strategies for sustainable management of freshwater and marine ecosystems

• policy and legislation

• international cooperation

• consumer awareness - eco labels to identify sustainably sourced food, education to chose locally sourced species

• MPA

What are MPA

• designed regions of the ocean where human activity is restricted or prohibited to conserve marine ecosystems and biodiversity

Functions of MPAs

• protect critical habitats

• provide nursery grounds

• conserve biodiversity

Types of MPAs

• No-take zones - activity is banned

• Multiple use zones

• seasonal zones

• community managed