4.3 Aquatic food production systems Flashcards
What part of the ocean holds 50% marine productivity?
The continental shelf holds 50% of marine productivity
- upwelling increases nutrients in water
- shallow so light can penetrate
- near coast so countries usually claim the rights
! Deep ocean = low productivity, does not belong to a specific country !
What part of the ocean has the lowest productivity rates?
Deep ocean!
(No/ very little light –> limited photosynthesis)
How does energy get into aquatic food webs?
- Phytoplankton - 99% of primary productivity in the oceans
- Zooplankton - eat phytoplankton and their waste
What are “fisheries”?
“Places where fish are caught/ harvested”
- 90% of fishery activity occurs in oceans
- Fish are important food sources for humans
- 70% of world’s fisheries are fully exploited, in decline, seriously depleted or too low to allow recovery
- Global fish catch is no longer increasing even though technology has improved
–> Therefore aquaculture is increasing greatly - farmed fish is becoming as common as wild caught fish
Why is the demand for aquatic foods increasing?
- population growth
- health reasons
- purchasing power availability
What is “purse seine”? (fishing with nets)
Usually involves a boat which locates a school of fish and uses a crane to take one end of a net around the school of fish.
These bags are then pulled aboard with the fish inside.
–> bycatch is extremely low as it is used once a school of fish has been identified
What is “trawling”? (fishing with nets)
Trawling is dragging a net through the water behind a boat.
–> can be done at the bottom and middle of the ocean
A bottom trawl may severely damage the habitat (eg. coral reefs..)
–> Therefore only carried out in places which have a replaceable habitat
What is “gillnet”? (fishing with nets)
Nets which are simply stuck to a wall with holes in it. Fish unknowingly swim into it and get stuck.
+ Doesn’t require a boat or heavy machinery
+ Often used in less developed areas of the world
- collects a lot of bycatch usually
What are “longlines”? (fishing with lines)
Longlines are very long fishing lines that have a hook every few feet. They can be many miles long.
Collects quite a bit of bycatch (around 1/5th)
–> higher developed countries usually use special hooks and weights that reduce bycatch
What is a “dredge”? (fishing with lines)
Dredging is similar to bottom trawling, but instead of a net, a metal rake of sorts is dragged across the bottom to collect shellfish and bivalves buried in the substrate.
–> bycatch is low
What is an ethical issue with fishing?
Harvesting some species such as whales and seals can be controversial.
Ethical issues arise over biorights, rights of indigenous cultures and international conservation legislation.
What are the problems with aquatic food production?
- 90% large predatory fish disappeared in last 50 years (eg. tuna)
- Demand is high and rising but global fish catch is in decline even though technology has improved.
–> Reason = overfishing
What are the characteristics of modern fishing trawlers?
- Larger, more powerful and can travel further
- Detect shoals of fish with precision (specialized radar and sonar)
- Use satellites for weather data
- Use satnav to navigate around oceans
- Improved fishing gear – larger but more indiscriminate nets
- Factory ships – fish sorted, gutted, filleted and frozen – therefore no need to return to home to land fish
What are some issues with modern fishing?
- Trawler nets are incredibly efficient at sweeping the sea. They capture pretty much all life in their path.
- Huge amount of bycatch.
- Damage sea floor and wipe out entire habitats/ecosystems
How can we make fishing more sustainable?
- Control number and size of fishing vessels
- Quotas
- Closed seasons
- Restricted areas – protect critical areas from fishing
- Limits on net size and type
! But strategies have limited success because !
- Not tightly regulated and enforced
- Illegal activity continues
- Catch more than quotas
- Fish in restricted areas or trespass into other fishing grounds
