Fishing - Productivity, Populations And Techniques Flashcards
Define Overfishing:
Catching too many fish at once, so breeding population becomes too depleted to recover.
What features of the Orange Roughy make it particularly vulnerable to overfishing?
- Live in deep waters
- Need Seamounts (destroyed by bottom trawling)
- Slow Growth
- Late sexual maturity
- Only produce few eggs
Define Pelagic fishing:
Fishing for species that live in open water above the seabed, often near the water surface.
Define Demersal fishing:
Demersal fishing includes fishing for species that live on the seabed.
What species are caught by bottom trawling?
- Whitefish like cod and haddock
- Prawn, shrimp and squid can also be caught though this method
Why do fisheries use bottom trawling?
- Efficient way to catch large quantities of fish and shellfish that live on the sea floor.
- Around a quarter of wild-caught seafood is caught by this method every year.
Is bottom trawling harmful?
- Bottom trawl gears come into contact with the seabed and this can cause damage to the habitats and marine organisms found there is fishing activities are not well managed.
- Corals are particularly vulnerable as they may not be able to recover.
- Associated with high levels of unwanted catch (bycatch) - as nets used can be unselective. Leads to accidental capture of non-target species or young or undersized fish.
Can the seabed impact of bottom trawling be reduced?
- Avoid bottom trawling in areas with more sensitive habitats through seabed mapping and habitat surveys.
- Areas containing more sensitive habitats can be closed to fishing all together (by the government,, regional fisheries management authorities or even voluntarily).
- In some cases, to obtain a fishing license, they must agree to only bottom trawl in certain areas.
- Modifying gear used and how it is operated - limiting the weight and size of gear and decreasing the number of contact points between gear and seabed.
How can bottom trawl fisheries reduce bycatch?
- Many fisheries modify their fishing gear to reduce bycatch.
- Understanding which non-target species are at risk of being caught, and how to avoid them is also important.
- Bycatch reduction devices are an effective way to allow unwanted species to escape trawl nets.
- Exclusion devices have also virtually eliminated turtle bycatch in the Australian Northern Prawn Fishery.
Demersal Trawling (Summary)
Dragging a net along the seabed to catch bottom dwelling fish.
Pros: High catch effectiveness.
Cons: Low catch selectivity, high energy inputs, damage to seabed (food, shelter and breeding).
Pelagic Trawling (Summary)
Pulling a net through the water above the seabed.
Pros: High catch efficiency, more selective than demersal trawling, no seabed damage.
Cons: Still low selectivity, high energy inputs, high opportunity for overfishing due to large nets.
Demersal Longlining (Summary)
Laying a line of weighted hooks on the seabed to catch bottom dwelling fish.
Pros: More selective than trawling, lower energy inputs than trawling.
Cons: Lower effectiveness than trawling, damage to seabed.
Pelagic Longlining (Summary)
Laying a line of floating hooks near the surface of the water to catch pelagic fish.
Pros: More selective than trawling, lower energy inputs than trawling, no seabed damage.
Cons: Lower catch effectiveness, high bycatch of seabirds and sharks.
Shellfish traps (Summary)
Specially designed cages baited to catch shellfish.
Pros: High specificity, low energy use and low environmental impacts.
Cons: Not very effective.
Purse Seining (Summary)
A large net that surrounds a school of fish, which are then caught by a smaller net.
Pros: Very high efficiency and higher selectivity than demersal methods.
Cons: Size of net leads to large amounts of bycatch, high overfishing potential and high energy inputs.
Drift Netting (Summary)
Floating nets draped across an area of ocean to catch passing fish.
Pros: more selective than trawling, lower energy usage and less environmental impacts than trawling.
Cons: Less effective than trawling.
