What factors affect the supply and use of fish? - PowerPoint Presentation

Slide1

What factors affect the supply and use of fish?

Learning outcomes:To describe and explain the main physical factors that affect fish stocks.To understand how technological changes and government policies have led to overfishing.Slide2

Starter - finish the sentence

Fishing is …

Fishing is the collection of a wide range of species including fish and shellfish.

Fishing is the last large- scale human hunting activity.

Fishing provides an important source of protein. Especially in LEDCs.

Reading - World Fisheries

Factfile

and World Fish Production, 2004 Slide3

OUTCOME 1 - What physical factors affect the supply and use of fish?

The

two most important factors that affect marine productivity are light and nutrients.WHY?Discuss in pairs why each of the following factors might affect availability of light and nutrients.Depth of water

LatitudeTurbidity (cloudiness of the water)Proximity to the coastLook at the map showing the productivity of different ocean areas. Write down 3 facts about it.Slide4

Factors

Explanation

Depth of waterLight essential for photosynthesis cannot penetrate deep water. The depth that light can penetrate is called the photic zone. Kelp or algae that anchor to the sea bed are only found in shallow water.

LatitudeThe tilted axis of the earth produces seasonal variations in sunlight intensity and day length. In polar regions these variations are extreme resulting in algal blooms that support rich food webs

Turbidity

Where fine sediments are washed in by rivers or where stormy weather disturbs sediments turbidity is increased. This

affects light penetration and photosynthesis.

Proximity to the coastProductivity is maintained where fresh nutrients are continually arriving such as in a coastal area where rivers bring nutrients from the soil it’s catchment area. These rarely get carried out to open ocean so productivity out at sea is often low unless there is an upwelling.

OUTCOME 1 - What physical factors affect the supply and use of fish?Slide5

The Tragedy of the Commons

Marine fishing is a classic example of the tragedy of the commons.No one owns the fish in the sea until they are caught, but all those who fish affect one another.

As long as individuals and groups benefit from using a resource, exploitation will continue even when then resource begins to degrade.Key Principle = although selfish behaviour may not be in an individual’s long term interest, neither is it in an individual’s interest to be unselfish unless everyone is.

OUTCOME 2 -

To understand how technological changes and governments have led to

overfishing

This has resulted in overfishing which is when fish

are harvested faster than they can breed to replace themselves.Slide6

Hi-tech fishing vessels ‘the strip miners of the sea’

LORAN (Long range navigation) and GPSFishing techniques such as trawling, dredging, purse seine and surround nets

Technological Advances which have improved the efficiency of fishing

OUTCOME 2 -

To understand how technological changes and governments have led to

overfishingSlide7

Surrounding net

Seine

Bottom otter trawls

Dredge

Cone-shaped net kept open by otter boards which is dragged across the ocean floor

Used for pelagic species e.g. tuna surround fish from the sides and from underneath, thus preventing fish from escaping by diving downwards.

A very long net, with or without a bag in the centre. Operated with 2 long ropes fixed to its ends for hauling and herding

demersal

fish

Heavy, metal structures, sometimes with teeth to scrape along or cut through the bottom in order to catch mussels, scallops, oysters

etc

OUTCOME 2 -

To understand how technological changes and governments have led to

overfishingSlide8

Are Governments to blame?

OUTCOME 2 -

To understand how technological changes and governments have led to

overfishing