Part 4e. Methods of increasing food production and improving sustainability

4e. Overfishing, sustainable fish stocks

Issues with fish farms

Doc Brown's Biology exam study revision notes

There are various sections to work through,

after 1 they can be read and studied in any order.

Sub-index of notes on increasing food production

Index of notes on ALL aspects of food production

re-edit 11/05/2023


4(e) To avoid overfishing and keep fish stocks at sustainable levels

(Fish farms - advantages and disadvantages)

We must only take out numbers of fish that still allow breeding at a rate to keep a constant sustainable population.

A sort of 'rate of breeding = rate of fishing' = 'sustainable situation'!

You can do this in several ways:

(i) Placing limits on the numbers of fish extracted from the lake or fishing ground.

(ii) Fishing nets can have various mesh sizes depending on the species being fished.

This controls the size of fish caught and helps reduce the number of accidently 'unwanted' and resulting 'discarded' fish.

A bigger mesh will allow smaller fish to 'escape' and grow into breeding adults, hence helping to maintain fish stocks.

(iii) Fish can be 'factory farmed' in cages where they cannot escape (fish farms or aquafarms).

In fish farms, the cages are placed in more sheltered estuaries or bays to minimise the effect of rough water and their natural food is often supplemented with other fish-based protein products. There is a quite a lot of criticism of ALL factory farming methods (see section (f) below) and the following comments ....

Nearly half of all fish consumed worldwide each year are raised in aquafarms. Farmed fish spend their entire lives in cramped, sometimes dirty enclosures, and many suffer from parasitic infections, diseases, and debilitating injuries - which means chemicals and antibiotics are used to help the fish survive.

Food is added to the enclosed nets to feed the fish, who then produce large amounts of waste. The waste can leak out causing eutrophication and death of wild species - the waste contains pathogens. Fish farms are breeding grounds for parasites, again these can escape and threaten wild species.

Predators like seals and sea lions are attracted this food resource, but can get trapped in the nets and die.

The farmed fish can escape and compete with indigenous species of fish.

Fish tank farms only contain one species and are therefore low on biodiversity - they are kept free of any plants or predators, the parasites and microorganisms are usually killed.

For more see section on reduction of biodiversity

The Food and Agriculture Organization of the United Nations reports that the aquaculture industry is growing three times faster than land-based animal agriculture, and aquafarms will surely become even more prevalent as our natural fisheries become exhausted, is this good sustainability?


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