Environmental impacts of fishing Flashcards
What will lead to population decline of a species?
When mortality exceeds birth rate
What type of species are more vulnerable to overfishing?
K-selected species
Why are K-selected species more vulnerable to overfishing?
because they produce fewer young and start breeding at an older age
What are some examples of K-selected species?
Orange roughy
Blue fin tuna
shark species
How could overfishing completely remove the breeding population of K-selected species?
They may reach a catchable size before they are sexually mature so survival of species relies on immature fish that might be caught before breeding
Why are r-selected species less vulnerable to overfishing?
breed at a young age and produce more young so population recover quickly
What are some example of r-selected species?
Herring
Atlantic Mackerel
Yellow fin tuna
What is an example of the exploitation of a k-selected species by fishing?
The Greenland shark
Bluefin tuna for the sushi industry
Orange roughy
Why was the Greenland shark hunted?
fished commercially for lamp and lubricating oil until the 1960’s
Why do populations of the Greenland shark struggle to recover?
they live for 400 years but only start breeding when they are 100-150 yrs old
What will happen will the Uk’s local fisheries become are over-exploited?
seafood supplies will be maintained by exploiting fisheries at increasing distances from the UK
What is by-catch?
the catch that is not wanted
What reasons may by-catch be unwanted?
Immature or too small
Quota has already been met
No commercial value
How are by-catch treated?
Usually thrown back into the ocean dead
What is the problem with immature fish by-catch?
may reduce future catches by killing the fish that would have grown to reach a saleable size
What is the problem of meeting a quota and by-catch?
even if a fish can be legally sold but the catch quota has already been met the fish must be discarded
What is the limitation of catch quotas?
If species are still being killed after quota is reached when fishing other species then the quota will fail to protect them
Only what’s bought back to land not what’s caught at sea
What are some examples of species selective fishing methods with reduced by-catch?
purse-seine nets or pelagic trawling
What is by-catch like from drift nets?
non-selective will catch any animal swimming near the surface
What are some examples of by-catch from drift nets?
whales
dolphins
turtles
sharks
What species are by-catch of pelagic long lines?
The albatross
What species do albatross hunt?
squid
krill
fish near surface
How do albatross become by-catch?
When diving for food they are caught on long line hooks where they drown
What is the problem with albatross being by-catch?
long living birds (50yrs)
Don’t start breeding till 7-10 yrs old
Low production rate 1 egg every second year
Population decline
Besides albatross what other species are by-catch of pelagic long line fishing?
Sharks
Turtles
What species is the by-catch of pelagic trawling?
Porpoises
How do porpoises become by-catch?
trying to catch the bass but become trapped in nets and drown
What is the by-catch like from demersal trawling?
seabed fish often live in mixed species shoals so chance of by-catch very high
What is the by-catch like from shrimp fishing?
shrimp trawling nets have a very small mesh size so by-catch struggle to escape
Very high
What species tend to be by-bycatch of shrimp fishing?
crabs
sea urchins
Molluscs
starfish
How much of the total catch can be by-catch from shrimp fishing?
99%
What is ghost fishing?
When fishing gear that has been discarded or lost and continues to trap and kill marine organisms
How does ghost fishing create a cycle?
the dead organisms caught act as bait and attract more individuals that also become trapped and die
What does demersal trawling need to do to be effective?
Need to disturb organisms so they swim upwards and are caught in the net
What do trawl nets often have to disturb the seabed?
chains
metal balls
What is destroyed when demersal trawling occurs?
destroy slow growing organisms such as sea fans and deep water corals
What is the impact of demersal trawling on coral reefs?
coral polyps sensitive to physical damage and can be killed if pressed against the coralite cup they live on
What can cause damage to coral reefs? (fishing equipment)
Nets
Traps
Ropes
Why are seagrass beds important?
nursery ground for young fish that live on corals or in deep water as adults
What is the problem with trawling on seagrass beds?
disturbance kills plants so their roots no longer hold the sand together which increases the water turbidity making it harder for the grasmtl grow back
What problem occurs when seagrass is killed exposing sand underneath?
currents and waves move sand increasing water turbidity making it hard for the reestablishment or the sea grass
How does dynamite fishing work?
pressure waves released by underwater explosions can stun or kill fish making them easer to catch
Id dynamite fishing legal?
No but still done in remote areas where subsistence fishermen struggle using other methods
Where is dynamite fishing commonly used?
In coral reefs where nets can’t catch fish
How does dynamite fishing affect corals?
explosions destroy coral and kill many other organisms
What are some examples of food web impacts of fishing?
competitors may become more common
their prey may become more common
their predators may become rarer
