Fishing and Aquaculture Flashcards
What is an area of upwelling?
Colder, nutrient rich waters come to the surface.
Why is there low productivity in open ocean?
Nutrient-rich water remains at depth. Not lots of nutrients in light zone.
How do you estimate the biomass of the fish stock at any point in time?
Biomass now = biomass one year ago + growth + birth - mortality - catch
What is the Maximum Sustainable Yield in Fishing?
The largest amount of a resource that can be regularly harvested without causing a decline in the basic stock of that resource.
What’s needed for the Maximum Sustainable Yield?
- Current biomass/individuals.
- Annual growth.
- Breeding rate.
- Survival rate.
What are some limitations of Maximum Sustainable Yield?
- Fish pop. are mobile, migrate long distances.
- Uneven distribution of fish pop.
- Difficult to collect large portion of pop. to be representative.
What are the 2 ways the biomass of a stock increases?
1) Growth.
2) Recruitment - young fish are recruited to adult pop. to replace losses. Any not recruited will not survive.
What are drift nets?
Net that fish can’t see - fish gills get trapped.
Can be demersal or pelagic.
Catches tuna, herring, salmon etc.
Lots of bycatch.
What are purse seine nets?
Net laid around a shoal of fish - trapping them.
Catches tuna, sardines, herring etc.
What is bottom trawling (demersal trawling)?
Dragging a net along the seabed by boat for food.
Damages benthic communities and corals.
What is demersal longlinging?
Line of baited hooks.
Catches tuna, squid etc.
Lots of bycatch.
What is crab/lobster pots/shellfish traps?
Traps that have bait inside.
Catches crabs, crayfish, lobsters etc.
Damages demersal ecosystem.
What is ghost fishing?
Discarded/broken fishing equipment fish get caught in.
Dwindles fish pop., damages habitats.
What is bycatch?
Non-target species are caught instead of desired species.
Trawling for shrimp quite wasteful - many others get trapped and cannot escape.
What is the food web?
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.
What is habitat damage and seabed disturbance?
Trawling and dredging disturbs seabed and kills species, destroys habitats, causes bycatch.
Coral reefs vulnerable.
Seagrass meadows vulnerable (bind sand together).
What is overfishing?
Fish overfished, decreases a pop. size.
E.g. Tuna don’t breed until big enough.
Greenland Shark don’t reach sexual maturity for decades.
What is factory fishing?
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.
How do quotas and limits on individuals caught help prevent overfishing?
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).
How does fishing equipment design and use help prevent overfishing?
- 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.
How do fishing restrictions help prevent overfishing?
- 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.
How does captive rearing and release help prevent overfishing?
- Increases the wild species pop., reducing overfishing/extinction.
- Increases survival chances as many fish do not make it after they hatch.
Salmon - How different factors are controlled.
- 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.
How are single-sex cultures achieved?
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.
What is the purpose of high stocking densities?
Have more fish without spending as much money running multiple tanks.
What is the purpose of restriction of fish movement?
Will use more energy growing, less energy moving = more money made.
What is the purpose of the water current speed being controlled?
Fish won’t injure themselves. Can also control muscle quantity.
Why is a build up of organic waste a problem in aquacultures?
- Deoxygenates water as it decomposes.
- Can monitor food, effluent treatments for freshwater.
Why is a food supply for farmed fish a problem?
- Wild fish overfished for them.
- Use more plant products/farm herbivorous fish.
Why is growth of parasites a problem in aqaucultures?
- 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.
What are polycultures? How are they sustainable?
- Rearing different species together.
E.g. silver carp eat phytoplankton, Bighead Carp eat zooplankton, Grass Carp eat vegetation - can be kept together.
What is integrated multi-trophic aquaculture? How is it sustainable?
- 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).
What are aquaponics? How is it sustainable?
- 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)
