Topic 12: Environmental Impacts Of Fishing Flashcards
4 main types of environmental impacts of fishing
Population decline due to overfishing
Bycatch
Ghost fishing
Habitat damage
How can overfishing cause population decline?
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
What species of fish recover quicker from overfishing?
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
Give an example of a species that is vulnerable to overfishing
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
Impact of over-exploited local fisheries on countries like the UK
It will still be maintained by exploited fisheries just further away
What is bycatch ?
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
Give 3 reasons why bycatch might be unwanted
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
What impact does bycatch have, on the organisms in the bycatch?
They are usually dead or will be injured and not survive when they are thrown back into the sea
Compare the bycatch from different fishing methods
Purse seine nets/pelagic trawling have a lower bycatch usually than demersal trawling
Demersal trawling usually exploits mixed fisheries
Drift net bycatch
They are non selective and will catch any animals swimming near the surface including whales,dolphins,turtles and sharks
Pelagic long line fishing
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
Pelagic trawling bycatch
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
Demersal trawling bycatch
Seabed fish often live in mixed-species shoals so the chance of catching a mixture of species is high
Shrimp bycatch
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
What is ghost fishing?
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
5 ways habitats can be damaged by fishing
Seabed damage
Coral reef impact
Sea grass beds
Dynamite fishing
Food web impacts
What type of fishing causes the most damage to the seabed?
Demersal trawls
Trawl nets have chains or metal balls to disturb the seabed so that the organisms swim upwards and are caught
Impact of seabed damage
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
Coral reef impact
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
What are seagrass beds?
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
Impact on seagrass beds
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
Impact of dynamite fishing
The explosions kill coral and many other organism
When might dynamite fishing be used?
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
Food web impacts
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
