Chapter 21

Suggested answers to questions from the textbook

1. Name the four methods that could be used to increase the harvest ofthe sea. Which method do you think has the greatest potential?

Ans. Four methods are:

a. Improve fishing technology

b. Fertilizing the water

c. Eating organism from bottom of food chain

d. Aquaculture. Aquaculture seem to have the greatest potential.

2. What are upwelling currents and how do these affect the productivityof the sea?

Ans. Current that moves from the ocean floor to the surface due to convention.These currents bring nutrients that have settled on the bottom to the surfacewhere they are needed for plant growth.

3. Why should we eat phytoplankton instead of fish? What problems haveto be overcome to make the harvest of phytoplankton viable?

Ans. It takes 100kg of plant plankton to produce 10kg of fish. The problemshowever exist to effectively harvest the plankton, and process and presentthe food to make it a usuable food and source.

4. How much of our annual catch comes from aquaculture?

Ans. 10% of annual catch is produced by aquaculture.

5. What is aquaculture?

Ans. Aquaculture is a method of selectively breeding, rearing and harvestingsea organisms.

6. The great upsurge in interest in aquaculture in recent years givesthe impression that it is a new industry. When was it first developed?

Ans. Aquaculture was first developed 2000 B.C

7. What was the first species of fish developed in aquaculture?

Ans. The first fish farmed was carp in China.

8. Give two reasons why many people believe farming the sea is the answerto the future food shortages.

Ans.

a. Many world fisheries are poorly managed with little thought for conservingdiminishing fish stocks.

b. A fishing vessel cannot go out all the time to catch fish. It maysit at the wharf for weeks at a time when the weather is rough. Every daythe fishing vessel stays home represents a day's lost income. In contrast,a pond containing prawns or fish can be harvested at any time so the farmercan plan and manage the business more predictably.

9. What percentage of our food comes from the oceans?

Ans. 4% of the worlds food comes from the sea.

10. Who proclaimed the first closed fishing season in India?

Ans. In 600 BC, fish were being reared in ponds in India. There wereeven laws protecting the fish. Edict V of King Asoka's Pillar (246 BC) protectedcertain fish during the middle of their spawning season (that is, a closedseason).

11. How are oysters grown on a farm?

Ans. Most oyster farms operate by collecting spats and putting them ontomanufactured racks to grow (Figure 214.2). These are the 'rack and stick'farms which are found along our coastline (Figure 214.3).

12. What is a suspension culture and how is it helpful to oysters?

Ans. The oyster's natural predators are starfish and other benthic animals.To protect them, the Japanese developed suspension cultures. This methodallows the spat to develop on strings suspended from rafts away from bottom-dwellingpredators and the possibility of being covered by silt.

13. Why are oyster racks painted with tar?

Ans. The racks are painted with tar to prevent woodworms eating themaway.

14. How are mussels grown?

Ans. Some mussels are grown on ropes hung from pontoons. The larvae settleon the ropes where they mature.

15. How does a pearl form?

Ans. Oysters produce pearls when grains of sand or other foreign materialget inside the shell and irritate the oyster. The oyster responds by producingsubstances made from calcium carbonate to surround the object. Pearl formationis also triggered by tiny parasitic worms which may burrow into the shell.

Oysters can be manipulated to produce a greater number and more perfectlyshaped pearls than occur naturally. These are called cultured pearls.

16. Name one difficulty in raising mudcrabs.

Ans. Mud crabs are very territorial and will fight when crowded together.They are also cannibals and many of the young are destroyed by the adults.Another difficulty with farming mud crabs is that they burrow under themud during the day and come out to feed at night. This causes problems withthe structure of the ponds (they burrow into the dam wall) and makes thecrabs difficult to harvest.

17. What does the term 'moulting' refer to?

Ans. Moulting occurs when the outside shell is shed off which is thenreplaced by the soft shell underneath. Each soft shell can increase in sizewhich allows the redclaw to grow.

18. What is the fastest growing plant in the world?

Ans. The fastest growing plants is the species macrocystis.

19. Why is it difficult to harvest seaweed and oysters from the wild?How has this been overcome by seaweed and oyster farmers?

Ans. One problem is that farmers have to ensure that the natural oceanicconsumers of seaweed do not harvest the crop before they do.

20. Define the terms:

a. fecundity

b. invertebrates

c. hermaphrodites

d. polyculture

Ans.

a. Fecundity - the number of eggs produced by a female each breedingseason

b. Invertebrate - animals which do not have a backbone.

c. Hermaphrodites - animal which can produce male and female sex

d. polyculture - multiple cropping

21. Why are the young of oysters called spats?

Ans. Many years ago people believed the adult oyster simply spat theyoung out.

22. What is a intensive farming system? How has this lead to a pollutionproblem?

Ans. Intensive underwater farms have large numbers of animals in smallamounts of water. These required large amounts of food which can decay onbottom and need to be flushed regularly. Therefore organic rich water isintroduced into waterways.

23. How long are imported aquarium fish kept in quarantine? Why mightthis be a problem?

Ans. Aquarium fish are put into quarantine for 2 weeks this may causea problem if disease is slow to show its effect.

Diving deeper - some suggested answers

1. Arrange an excursion to a local aquaculture farm. Find out how thefarmed species behaves in the wild and how the farmer has used this behaviouron the farm.

Suggestions.

A list of farms can be found from the Department of Primary Industries.

2. Research aquaculture methods to raise any one of the following marineorganisms:

· barramundi

· oysters

· mussels

· scallops

· seaweed

· salmon

· tuna

· pearls

· crayfish

· prawns

Detail farming methods to raise the young and to maturity.

Discuss any negative environmental effects of the aquaculture methodsand how farmers have planned to counteract these effects.

Suggestions.

Subscribe to the Austasia Journal .... Aquaculture

Address: Turtle Press PO Box 279 SANDY BAY 7005

Check of the Web Pages.

3. See your vocational education school co-ordinator to arrange a structuredwork placement or work experience on a aquaculture farm.

Suggestions:

See your school voc ed co-ordinator

4. Complete a chart on the life cycle of a aquacultured animal or plant.

Suggestions:

Use your school library. Find a parent in the aquaculture industry. Writeto TASSAL Ltd for an information pack.

Address: TASSAL

GPO Box 1645, Hobart Tasmania, 7001.

5. Research the export of live fish to Asian markets. Find out how valuableindividual marine organisms are and what methods are used to ensure thatthe highest quality of product reaches the market.

Address:

Try local fisheries officers or fisheries Government departments