Topic 4A

Question 1

Maximum Sustainable Yield (MSY)

Answer 1

Largest yield/catch that can be taken from a species’ stock over an indefinite period

Question 2

Overfishing

Answer 2

Rate of harvest is higher than the rate of natural reproduction; Rate of fish catch per capita per year ↑ but rate of ↑ in fish is ↓ing

Question 3

Growth overfishing

Answer 3

Fish are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit (2 fishes at 5cm instead of 1 fish at 10cm –> doubles no. being caught)

Question 4

Recruitment overfishing

Answer 4

Mature adult population depleted to a level where it no longer has the reproductive capacity to replenish itself –> not enough adults to produce offspring

Question 5

Ecosystem overfishing

Answer 5

Balance of ecosystem & interaction among organisms are altered

Question 6

Tragedy of commons

Answer 6

Individuals exploit shared resource until dd overwhelms supply & resource becomes unavailable to all

Question 7

Causes of tragedy of commons

Answer 7

1. Weak management
2. Over-estimation of MSY
3. Climate change
4. ↑ in seawater temp
5. Ocean acidification

Question 8

Benefits of aquaculture

Answer 8

1. Meet worldwide dd for fish –> provide food security in Low-Income Food-Deficit Countries (LIFDCs)
2. Reduce post-harvest losses –> ↑ % of fish used for direct human consumption
3. Source of income –> ↑ed production = ↑ profit
4. Gender equality –> e.g. Bangladesh –> women farm near home –> stable fish prod. & have food –> gain respect –> develop understanding, process towards equality

Question 9

Disadvantages of aquaculture (By-catch)

Answer 9

1. Trash fish used in fish feed production (by-catch) : fish oil needed for essential FAs in fish diet –> retain by-catches for fish feed prod.; overall protein loss from ecosystems & global food supply bc FI:FO ratio not proportionate + trash fish can be fed to poor countries

Question 10

Disadvantages of aquaculture (habitat)

Answer 10

Habitat modification

1. Shrimp farming: deforestation of mangroves, accumulation of toxic wastes, loss of soil nutrients
2. Loss of direct ecosystem services: nutrient recycling, sediment trapping, coastal defence, shelter for juvenile fishes
3. Associated ecological effects: reduced mollusc productivity in mangroves & losses to seagrass beds & coral reefs

Question 11

Disadvantages of aquaculture (effluent)

Answer 11

Effluent discharge

1. Uneaten feed & fish faeces: nutrient pollution (excessive nitrate/eutrophication)
2. Sunken fish feed/faecal pellets around sea pens change biochemistry of benthic communities
3. Worsen water quality
4. Promote outbreaks of pathogens (water quality + stocking density)

Question 12

Disadvantages of aquaculture (intro of species)

Answer 12

Intro of exotic species

1. Competition for food, shelter, mates with native species
2. Hybridization (alters gene pool of wild population)
3. Endangers wild population

Question 13

Disadvantages of aquaculture (↑ed risk of infectious diseases)

Answer 13

1. International movement of farmed & wild aquatic animals thru trade
2. Gametes, fertilised eggs, fry, fingerlings & broodstock constantly moved to support aquaculture development
3. Potential carriers of pathogens
   E.g. White spot virus in shrimp

Question 14

Disadvantages of aquaculture (Wild harvest of broodstock)

Answer 14

1. Use wild broodstock to ↑ genetic diversity
2. Raise wild fish in captivity = lower high mortality rates characteristic of wild populations
3. ↑ by-catch rates

Question 15

Disadvantages of aquaculture (list all)

Answer 15

1. Trash fish used in fish feed production
2. Habitat modification (env. impact)
3. Effluent discharge (env. impact)
4. Intro of exotic species (ecological)
5. ↑ed risk of infectious diseases (ecological)
6. Wild harvest of broodstock (ecological)