Aquatic Resources

Environmental impacts of fishing:

Population decline:

• If mortality rates > birth rates, populations decline
• Therefore, K-selected species are more vulnerable to overfishing

Ending overfishing:

• Stocks have  in the last 60 years
• 2008, fishing limit on bluefin tuna introduced

By-catch:

• 90% of shrimp fishing is by-catch
• Exceeding quotas creates by-catch

Habitat damage*:

• Habitat fragmentation: Exposure to predators
• Dynamite fishing: Stuns fish using shockwaves; Destroys habitats
• All impacts influence the food webs

*Seabeds cannot be destroyed only damaged.

Reducing environments impacts:

Catch quotas:

• Limits on the total weight brought back to port and sold.
• The quota must be divided up by all boats in a fleet.
• Works best for fish found in single species shoals

Fishing equipment:

• Trawling nets with built-in escape panels; This allows non-target species to avoid becoming by-catch.
• Different net mesh sizes: This can allow juvenile fish to escape nets
• Acoustic deterrent devices: Produces sound waves that repel aquatic species which communicate using echolocation.
• Biodegradable fishing equipment: Prevents ghost fishing
• Different hook shapes/sizes: Specially designed to only catch target species
• Decoys: Deter birds from becoming susceptible to ghost fishing.

Restricting fishing methods:

• Limiting the time turtles are in nets to prevent them becoming bycatch
• Closed Seasons
• Minimum catchable size
• Maximum Catch Size
• Protected Individuals
• Captive rearing and release: Population seeding

Aquaculture:

Intensive aquaculture:

• High inputs in a small area
• Artificial control of abiotic and biotic factors to maximise productivity: High food inputs for carnivorous species; Fish farms; Monoculture; Growth hormones; Small nets; Pesticides.

Extensive aquaculture:

• low inputs over a large area
• Introducing a fish to a pond and allowing it to feed on wild food: Maintaining habitats; Protection from predators; Natural food; Pest control species; Decreases disease

Species selection:

• Location: Does the specie thrive in the local abiotic factors.
• Market demand; MEDC’s raise carnivorous species based on flavour/popularity, whilst LEDC’s  raise herbivorous or omnivorous species that feed off naturally occurring vegetation or waste.

Selective breeding:

• Size
• Colour
• Quality
• Quantity
• Disease resistance
• Number of offspring
• Maturity age
• Aesthetics
• Fat-muscle ratio
• Eggs and milt are collected from mature individuals (sometimes using hormone injections)

Sex control:

• Sex in fish can be controlled hormonally, regardless of genetics.
• In some species, it is desirable to have a specific sex: Growth rates; Breed stock; Caviar (Andalucía)

Controlling biotic factors:

• Increased stock density increases the spread of parasites and diseases.
• This is controlled using:Circulating water tanks (fish naturally swim against the flow); Pesticides; Biological control (lump suckers)
• In outdoor systems, competition and predators can become a problem.
• These are controlled by: Netting; Bird scarers; Culling of predators
• Herbivorous fish are more likely to find natural food.
• Carnivorous fish need artificial feeding.

Controlling abiotic factors:

• Temperature: Dependant on species, warmer temperatures increase growth rates, but decrease oxygen; Increases metabolic reaction rates
• Dissolved oxygen: Fish with high oxygen requirements need aerated tanks; Food waste and faecal matter need to be removed; Fish with low oxygen requirements can be kept at greater densities.
• Day length: Reproduction is affected by day length; Some species stop growing when they become sexually mature.
• Water flow: Fish often swim against the flow of water; This is used to get individuals to swim on the same direction, decreasing collisions and disease spread.

Intensive vs Extensive:

• Carnivorous species, like salmon, are fed of small oily (like herring) fish which are caught easily
• This is due to them being shoaling species

Polyculture:

• Total productivity can be increased by rearing non-competitive species together
• Integrated multi-trophic aquaculture

Aquaponics:

• A combination of hydroponics and aquaculture
• Hydroponic productivity increases because of the nutrients and organic matter supply: Fish faeces is full of nutrients that the plants use
• Aquaculture benefits due to the nutrients being removed
• The excess nutrients can cause eutrophication
• This can cause deoxygenation.

Replacing fishing:

• Advantages of aquaculture: High productivity; High food conversion rates (energy ratios); Herbivorous species feed off naturally growing plant species or crop waste
• Disadvantages of aquaculture: Carnivorous species have lower productivity; Carnivorous species are fed off fished species; Some species cannot be raised in captivity.
• For large scale aquaculture to replace fishing, it needs to become more sustainable
• Environmental impacts that need to be reduced include: Food supply impacts; Habitat loss; Pesticide pollution; Development of antibiotic resistant bacteria; Lice control impacts; Wild gene pool impacts; Introduction of non-indigenous species; Organic waste pollution

Practical skills:

Scientists want to investigate whether distance from a river mouth impacts the diversity of corals

• Location: In field
• Sampling type: Systematic sampling
• What is being measured: How many different species of corals in each given area
• Equipment: Transect (tape measure), Quadrat
• How do you collect the data: Diving down at even intervals, Simpson diversity index
• How much data: 30 samples for a statistical test
• How do you make the data accurate: Same weather conditions, same tide level

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