Aquatic Food Production Systems Flashcards
What are the three major zones of the ocean?
Benthic zone = ocean floor (seabed) e.g. plaice
Demersal zone = layer of water just above the seabed e.g. orange roughy
Pleagic zone = the water column e.g blue fin tuna
What two photic zones are there?
Photic = uppermost layer of a body of water, where there is enough light for photosynthesis
Aphotic = lower layers of a body of water, where not enough light penetrates for photosynthesis
What are the three latitudes of the ocean?
High latitude waters = areas of ocean close to the poles (polar waters)
Mid latitude waters = areas of the ocean around halfway between a pole and the equator (temperate waters)
Low latitude waters = areas of ocean close to the equator (tropical waters)
What are sub-tropical gyres?
- Massive areas of ocean which circulate clockwise in the northern hemisphere, anticlockwise in the southern hemisphere
- Cool current move towards the equator and warm current moving polewards
- Important role in redistributing heat away from the equator and so regulating the planet’s temperature
What are the two types of plankton?
Phytoplankton = plant plankton, oceans primary producers
Zooplankton = animal plankton, higher tropic levels of ocean ecosystems
What are Nekton?
Swimming organisms - live in the pelagic zone
What are Benthos?
Organisms which live in and on seabed
What is nutrients?
Substance that provides nourishment essential for the maintenance of life and for growth
- a chemical needed to support photosynthesis and primary production, e.g. nitrogen, phosphorus, and silicon
What is productivity?
Rate of generation of biomass in an ecosystem, expressed in units of mass per volume per unit time
Ocean productivity largely refers to the production of organic matter by phytoplankton
What is primary productivity?
The creation of new organic matter form inorganic compounds, generally occur through photosynthesis.
What is gross primary productivity?
The total amount of organic material created by the producers
What is net primary productivity?
The amount of organic material left to support consumers at higher trophic levels (once losses to respiration by the producers themselves are removed) NPP = GPP — R
What is the Thermocline?
An abrupt temperature gradient in a body of water, marked by a layer above and below which the water is at markedly different temperatures
What is water stratification?
The division of the water column into layers
What is pelagic trawling?
- When a net is dragged through open water behind a boat.
- Used for shoal species e.g. anchovies and mackerel.
What are the advantages of pelagic trawling?
- High species selectivity = single shoal species = few non-target species are caught.
- High catch effectiveness = large shoals of fish can be caught in one go.
- Medium energy inputs = low resistance as it is through open water.
What are the disadvantages of pelagic trawling?
- Medium environmental impacts = due to shrimp trawling can result in bycatch, or bycatch of predator species , as well as its very easy to overfish.
- Medium energy inputs = actively dragging net, boat requires fuel.
What is demersal trawling?
- When a net is dragged along the seabed behind a boat.
- E.g. scampi, organic roughy, plaice and shrimps.
What are the disadvantages of demersal trawling?
- Low species selectivity = seabed fish tend to live in mixed species shoals = high bycatch.
- Low catch effectiveness = individuals belonging to demersal species tend to be spread over a wide area.
- Higher energy inputs = net is actively dragged along seabed with lots of resistance requiring more fuel.
- High environmental impacts = high levels of bycatch and habitat damage.
What is purse seining?
- When a curtain like net is laid around a shoal of fish and the weighted bottom edge is pulled tight underneath creating a bowl shape.
- E.g. herring and anchovies.
What are the advantages of purse seining?
- High species selectivity = shoals of single pelagic spices = less bycatch
- High catch effectiveness = large shoals can be caught and the tightness of the net beneath them means few escape.
- Medium energy inputs = resistance form open water is low.
- Medium environmental impacts = limited bycatch.
What are the disadvantages of purse seining?
- Medium energy inputs = net is actively moved through the water and smaller limiting nets need to bring the catch onto the boat.
- Medium environmental impacts = very easy to overfish.
What is drift netting?
- Long curtain like net (gillnets) are trailed along behind a boat. Then are anchored to seabed. Fish are caught by the gills as they try to swim through them.
- E.g. tuna and herring.
What are the advantages of drift netting?
- Low energy inputs = passive/static method, as the net is spread out and then left to catch the fish.
- Medium environmental impacts = mesh size can be specific to the size of fish being caught allowing other species and young fish to escape = allows population regeneration.
What are the disadvantages of drift netting?
- Low species selectivity = will often catch whales, dolphins, turtles and sharks.
- Medium catch effectiveness = do not target shoals with high conditions.
What is longlining?
- When a long line with baited hook attached is trailed along behind a boat.
- E.g. cod and haddock = demersal longlining
- E.g. tuna and squid = pelagic
What are the advantages of longlining?
- High species slectivity, target species bait and bird scaring lines used.
- High catch effectiveness, low density populations.
- Low energy inputs, passive static technique
- Low environmental impacts, easy to avoid by catch
What are the disadvantages of longlining?
- Albatrosses get caught on the hooks when diving for their own fish.
- Sharks and turtles also affected.
What is shellfish trapping?
When baited cages are left on the seabed with a buoy attached.
E.g. crabs and lobsters.
What are the advantages of shellfish trapping?
- High species selectivity, any bycatch and be released.
- low energy inputs, passive static technique.
- Low environmental impacts, inefficient so hard to overfish and bycatch can be released.
What are the disadvantages shellfish trapping?
- Low catch effectiveness, easy to escape.
What are the environmental impacts of fishing?
- Population decline caused by overfishing
- Changed age structure
- Bycatch
- Ghost fishing
- Habitat damage
- Food web impacts
What is the maximum sustainable yield?
- The greatest biomass that can be removed each year without the population suffering long-term decline. = carrying capacity.
What are the problems with MSY?
- Often interpreted as a fixed catch size, when due to changing environmental factors it may need to be reassessed more often.
- Difficult to accurately estimate
What are the methods of reducing environmental impacts of fishing?
- Catch quotas = legal limits on the total weight of fish that can be landed = avoids population decline.
- Restricted fishing effort = limits on the size of boats/number of days a year spent fishing = “
- No-take zones = in spawning and nursery grounds = “ important for species with low fecundity.
- Closed seasons = in breeding area = “ unpopular as breeding season is where fish gather together.
- Captive rearing and release = “ boost wild populations.
- Minimum catchable size = “
- Maximum catchable size = reduces change to age structure.
- Protected individuals = reduced change to age structures.
- Changes to net design = acoustic deterrents, TEDSs, mesh size and mesh design = reduces bycatch.
- Changes to line design = sinkers, curved hooks, targeted bait = reduced bycatch.
- Biodegradable equipment = reduces ghost fishing.
- Radio-tracked equipment =reduces ghost fishing.
- Ban-drift nets = in vulnerable habitats, avoids habitat damage.
What is aquaculture?
The farming of fish and other aquatic food species.
Commercially in freshwater environments, saltwater environments and brackish.
What is extensive aquaculture?
- Traditional from and mainly makes use of natural ecosystem functions.
- Low stock densities
- Low inputs
- Low control of biotic and abiotic factors
- Relatively cheap
- Lower yields
- More energy efficient
- Less environmental impacts
What is intensive farming?
- Modern form and involves largely artificial set-ups.
- High stock densities
- High inputs
- High control of biotic and abiotic factors
- Expensive
- Higher yields
- High environmental impacts
What is trophic level efficiency?
The percentage of energy from a trophic level that is used by the organisms of the next tropic level for growth and reproduction.
How are species selected for aquaculture?
- local conditions and species adaptions = what species are best adapted to the local conditions e.g. salmon and trout are importantly in cooler temperature regions while tilapia thrive in warmer tropical regions
- market demand = in MEDCs the main species raised by aquaculture are carnivores such as salmon and trout for their flavour and popularity, in LEDCs often herbivores such as carp and tilapia as the require low food inputs.
How are adults selected for breeding?
Adults with desirable qualities:
- disease resistance
- rapid growth rate
- good appearance
Eggs and milt are collected from mature individuals
How is the gender of aquaculture species controlled?
If a young fish are given female hormones they will develop into a female adult
Which gender is favourable depends on the species:
- rainbow trout = female meat tastes better
- tilapia = male tilapia are more energy efficient and grow larger
- Tripoli’s fish = infertile as they have three sets of chromosomes, so if they escape they cannot reproduce
How are pests and diseases controlled in aquaculture?
- where water flows between tanks of different age groups if it flows from young to old = decreases risk of spreading disease
- lower stocking densities reduces risk of contact, collisions and spread of disease resistance
- pesticides or biological control e.g. wrasse eat sea lice
- tanks with circulating water currents encourage all the fish to swim in the same direction so there is less contact
How is competition and predation controlled in aquaculture?
Fencing, netting, bird scarers
- culling of pest species
How is nutrition controlled in aquaculture?
- herbivores more likely to find natural food in their lagoons
- carnivore fish need artificial food control
How are abiotic factors controlled in aquaculture?
Temperature = warmer temperatures increase metabolic rates and growth but can reduce levels of dissolved oxygen which may be unsuitable for some species
Dissolved oxygen = aerated tanks, food and faecal matter must be removed as they can cause deoxygenation
Day length = having long day lengths delays maturation and increases the size so they reach
Water flow = fish swim against the flow of the water, this can be used to get all the fish to swim in the same direction, reducing collision damage between fish which improves the appearance of the saleable fish
What is shrimp aquaculture?
Most shrimp farms are in tropical areas, 10% of the world mangroves have been destroyed rot create costal shrimp farms
- ovary development and egg production are increased by eyestalk ablation where one or both eyestalks are broke off, this simulates the low light levels that stimulates breeding.
- in extensive systems the shrimps feed on plankton naturally produced in lagoons
- in intensive systems nutrients are added to increase growth of algae
What is salmon aquaculture breeding?
- fish are chosen with desirable qualities such as fast growth, shape and colour
- adult fish in breeding condition are stripped of their eggs and milt
- fertilised eggs are raised in aerated tanks
- after hatching the young fish are moved through a series of tanks as they get bigger
- 12-18 months in they become ready to move to seawater tanks
How are limiting factors controlled in salmon aquaculture?
- dissolved oxygen kept high
- temp kept not too high
- flow rate fairly high to produce more muscular fish
- constant flow = avoids collision
- pests, parasites and diseases controlled
- light levels controlled to induce smoltification of young fish
How are polycultures used in aquaculture?
- bottom feeding can disturb sediments and re-suspend nutrients which increase the growth of plants and phytoplankton
- total productivity van be increased by rearing other species together
What is IMTA?
Integrated Multi-Trophic Aquaculture
- a polyculture system where species in different trophic levels benefit from each other
- fed aquaculture = species are given food e.g. shrimps or salmon
- inorganic extractive aquaculture = species that absorb inorganic nutrients for growth e.g. seaweed/algae
- organic extractive aquaculture = species that catch food items such as plankton e.g. filter feeding fish
- macro algae help absorb ammonia and other phosphates
What are aquaponics?
- combines hydroponic crop production with aquaculture
- the drainage water from the hydroponic system is returned to the aquaculture system
Supplying the hydroponic system with inorganic and organic nutrients - suitable hydroponic species = leafy salad vegetables
- suitable aquaculture species = tilapia, carp, catfish
What are rice fish systems?
Rice is grown in flooded paid fields = fish Cana Lao be kept in the fields increasing overall food production
