Fishing and Aquaculture

Question 1

What is an area of upwelling?

Answer 1

Colder, nutrient rich waters come to the surface.

Question 2

Why is there low productivity in open ocean?

Answer 2

Nutrient-rich water remains at depth. Not lots of nutrients in light zone.

Question 3

How do you estimate the biomass of the fish stock at any point in time?

Answer 3

Biomass now = biomass one year ago + growth + birth - mortality - catch

Question 4

What is the Maximum Sustainable Yield in Fishing?

Answer 4

The largest amount of a resource that can be regularly harvested without causing a decline in the basic stock of that resource.

Question 5

What’s needed for the Maximum Sustainable Yield?

Answer 5

• Current biomass/individuals.
• Annual growth.
• Breeding rate.
• Survival rate.

Question 6

What are some limitations of Maximum Sustainable Yield?

Answer 6

• Fish pop. are mobile, migrate long distances.
• Uneven distribution of fish pop.
• Difficult to collect large portion of pop. to be representative.

Question 7

What are the 2 ways the biomass of a stock increases?

Answer 7

1) Growth.
2) Recruitment - young fish are recruited to adult pop. to replace losses. Any not recruited will not survive.

Question 8

What are drift nets?

Answer 8

Net that fish can’t see - fish gills get trapped.
Can be demersal or pelagic.
Catches tuna, herring, salmon etc.
Lots of bycatch.

Question 9

What are purse seine nets?

Answer 9

Net laid around a shoal of fish - trapping them.
Catches tuna, sardines, herring etc.

Question 10

What is bottom trawling (demersal trawling)?

Answer 10

Dragging a net along the seabed by boat for food.
Damages benthic communities and corals.

Question 11

What is demersal longlinging?

Answer 11

Line of baited hooks.
Catches tuna, squid etc.
Lots of bycatch.

Question 12

What is crab/lobster pots/shellfish traps?

Answer 12

Traps that have bait inside.
Catches crabs, crayfish, lobsters etc.
Damages demersal ecosystem.

Question 13

What is ghost fishing?

Answer 13

Discarded/broken fishing equipment fish get caught in.
Dwindles fish pop., damages habitats.

Question 14

What is bycatch?

Answer 14

Non-target species are caught instead of desired species.
Trawling for shrimp quite wasteful - many others get trapped and cannot escape.

Question 15

What is the food web?

Answer 15

One species removed = more abundant competitors. Animals feeding on that species become rarer.
E.G. Leatherback Turtles major predators of jellyfish. Turtles become bycatch = reduce pop. = jellyfish pop. blooms.

Question 16

What is habitat damage and seabed disturbance?

Answer 16

Trawling and dredging disturbs seabed and kills species, destroys habitats, causes bycatch.
Coral reefs vulnerable.
Seagrass meadows vulnerable (bind sand together).

Question 17

What is overfishing?

Answer 17

Fish overfished, decreases a pop. size.
E.g. Tuna don’t breed until big enough.
Greenland Shark don’t reach sexual maturity for decades.

Question 18

What is factory fishing?

Answer 18

Factory ships store vast amounts of fish, ‘mother ship’ follows it so fish can be processed onboard. Can stay in the sea for months.
Uses larges amounts of fuel.

Question 19

How do quotas and limits on individuals caught help prevent overfishing?

Answer 19

It stops people from taking more fish than they should. Also can ban taking fish above or below a specific size.
e.g. in some areas, people must release female lobsters who have reached sexual maturity (eggs visible).

Question 20

How does fishing equipment design and use help prevent overfishing?

Answer 20

• Certain mesh size so smaller fish can escape.
• Acoustic deterrent devices, e.g. high frequency sounds to deter dolphins (dolphin pingers).
• Biodegradable/radio tracked equipment reduces ghost fishing.
• Curved hooks less likely to catch birds/turtles.

Question 21

How do fishing restrictions help prevent overfishing?

Answer 21

• Using smaller boats.
• Fishing at night when birds are not hunting.
• Minimum/maximum catchable size.
• Closed seasons (bans during breeding).
• Ban drift nets/demersal trawling.
• Set up no take zones.
• Protect indivduals.

Question 22

How does captive rearing and release help prevent overfishing?

Answer 22

• Increases the wild species pop., reducing overfishing/extinction.
• Increases survival chances as many fish do not make it after they hatch.

Question 23

Salmon - How different factors are controlled.

Answer 23

• Water temp. not too high.
• Dissolved oxygen levels kept high with water sprays.
• High water rate to produce muscular fish.
• Constant water flow direction so less injuries.
• Removal of diseased fish and use of antibiotics and pesticides.
• Controlled light levels to induce smoltification (freshwater –> saltwater) of young fish.
• Controlled food chain to increase efficiency. Fed pellets of herring etc with added plant food.

Question 24

How are single-sex cultures achieved?

Answer 24

1) Small number of females (XX) given male hormone, testosterone.
2) Able to produce sperm, all of which have an X chromosome, so can only produce female offspring.

Question 25

What is the purpose of high stocking densities?

Answer 25

Have more fish without spending as much money running multiple tanks.

Question 26

What is the purpose of restriction of fish movement?

Answer 26

Will use more energy growing, less energy moving = more money made.

Question 27

What is the purpose of the water current speed being controlled?

Answer 27

Fish won’t injure themselves. Can also control muscle quantity.

Question 28

Why is a build up of organic waste a problem in aquacultures?

Answer 28

• Deoxygenates water as it decomposes.
• Can monitor food, effluent treatments for freshwater.

Question 29

Why is a food supply for farmed fish a problem?

Answer 29

• Wild fish overfished for them.
• Use more plant products/farm herbivorous fish.

Question 30

Why is growth of parasites a problem in aqaucultures?

Answer 30

• Can kill them/cause disease.
• Can spread to wild pop. (e.g. lice on salmon).
• Can be solved with biological control (wrasse eat lice) or pesticides.

Question 31

What are polycultures? How are they sustainable?

Answer 31

• Rearing different species together.
  E.g. silver carp eat phytoplankton, Bighead Carp eat zooplankton, Grass Carp eat vegetation - can be kept together.

Question 32

What is integrated multi-trophic aquaculture? How is it sustainable?

Answer 32

• Species in different trophic levels benefit from one another.
  3 levels:
• Fed aquaculture = species given food. (shrimp)
• Inorganic extractive aquaculture = species that absorb inorganic nutrients (algae).
• Organic extractive aquaculture = species that catch food items (plankton for filter feeding fish).

Question 33

What are aquaponics? How is it sustainable?

Answer 33

• Combines hydroponic crop production with aquaculture.
• Water from AC used in HP system, drainage water from HP returned back to AC.
• Increases productivity of HP system due to supply of inorganic nutrients and organic matter.
  Suitable species = Tilapia, Carp, Catfish (AC) —- Lettuce, Spinach, Watercress (HP)