Topic 12: Environmental Impacts Of Fishing

Question 1

4 main types of environmental impacts of fishing

Answer 1

Population decline due to overfishing
Bycatch
Ghost fishing
Habitat damage

Question 2

How can overfishing cause population decline?

Answer 2

Population of any species will decline if the mortality rate exceeds the birth rate
K-selected species are most vulnerable to overfishing-fewer young at older age
Some species reach a catchable size before they reach sexual maturity, so overfishing could remove the entire breeding population

Question 3

What species of fish recover quicker from overfishing?

Answer 3

R-selected species because they breed at a younger age and produce more young
The populations recover more rapidly after over-fishing
E.g. herring, yellow fin tuna

Question 4

Give an example of a species that is vulnerable to overfishing

Answer 4

Greenland shark
It was fished commercially for lubricating and lamp oil until the 1960s
Main threat now is deep-sea trawling bycatch
It can live over 400 years, doesnt start breeding until 100-150 years and it produces few young

Question 5

Impact of over-exploited local fisheries on countries like the UK

Answer 5

It will still be maintained by exploited fisheries just further away

Question 6

What is bycatch ?

Answer 6

The catch that is not wanted
Usually non-target species included in the catch of target species, or individuals too small to be legally sold

Question 7

Give 3 reasons why bycatch might be unwanted

Answer 7

Immature fish- too small to sell, will affect future catches
If the catch quota for a species has already been reached- must be discarder
Species with no commercial value

Question 8

What impact does bycatch have, on the organisms in the bycatch?

Answer 8

They are usually dead or will be injured and not survive when they are thrown back into the sea

Question 9

Compare the bycatch from different fishing methods

Answer 9

Purse seine nets/pelagic trawling have a lower bycatch usually than demersal trawling
Demersal trawling usually exploits mixed fisheries

Question 10

Drift net bycatch

Answer 10

They are non selective and will catch any animals swimming near the surface including whales,dolphins,turtles and sharks

Question 11

Pelagic long line fishing

Answer 11

Albatrosses are large seabirds that collect food near the water surface
They are usually caught by long line fishing and drown because of it
They have a low reproduction rate, and lay one egg every second year, but it takes 7-10 years before they start breeding
So populations can be seriously effected

Question 12

Pelagic trawling bycatch

Answer 12

Pelagic pair trawls for sea bass can kill porpoises
Because the porpoises are trying to catch the bass but get trapped in the nets and drown

Question 13

Demersal trawling bycatch

Answer 13

Seabed fish often live in mixed-species shoals so the chance of catching a mixture of species is high

Question 14

Shrimp bycatch

Answer 14

Shrimp use trawling nets with very small mesh size so few bycatch animals can escape
E.g. crabs,molluscs,sea urchins,starfish
Can make up to 99% of shrimp trawling

Question 15

What is ghost fishing?

Answer 15

When discarded or lost fishing gear can continue to trap and kill marine organisms
Dead organisms that are trapped often act as bright so more organisms get caught and die

Question 16

5 ways habitats can be damaged by fishing

Answer 16

Seabed damage
Coral reef impact
Sea grass beds
Dynamite fishing
Food web impacts

Question 17

What type of fishing causes the most damage to the seabed?

Answer 17

Demersal trawls
Trawl nets have chains or metal balls to disturb the seabed so that the organisms swim upwards and are caught

Question 18

Impact of seabed damage

Answer 18

Shallow aerobic surface layer of seabed is mixed with deeper anaerobic layers
Nets can destroy slow growing organisms, like sea fans and deep water corals

Question 19

Coral reef impact

Answer 19

Coral y polyps are sensitive to physical damage
Killed if they are pressed up against the sharp coralite cup they are attached to
Nets,traps,ropes,discarded gear can all cause physical damage

Question 20

What are seagrass beds?

Answer 20

Grass-like flowering plants that grow on shallow sandy areas of the relatively protected tropical sees
Important nursery grounds for many species of fish that live on coral reef or in deep water as adults

Question 21

Impact on seagrass beds

Answer 21

Disturbance by trawling kills the plants
The roots are no longer holding sand grains together
Currents and waves move sand around making it difficult for new plants to colonise and become established

Question 22

Impact of dynamite fishing

Answer 22

The explosions kill coral and many other organism

Question 23

When might dynamite fishing be used?

Answer 23

It is illegal in most countries- still carried out in remote areas
Especially where substinence fishermen find it difficult to catch fish with other methods

Question 24

Food web impacts

Answer 24

Reducing the number of any species will affect the other organisms in the same food web
E.g. competitiors can become more common, or prey, or predators rarer