EVSC20004 Lecture Notes - Lecture 25: Australian Fisheries Management Authority, Great Australian Bight, Common Fisheries Policy
21 Jun 2018
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Harvesting of the sea, trophic cascades and phase shifts
1. Total world catch and Australia’s fisheries
2. Types of fishing and their effects
3. Fishing down marine food webs
4. Trophic cascades and ecological phase shifts
World fisheries catch:
There has been an increase in world catch driven by industrialisation of fisheries
(necessity) and increased population (Fish a major source of protein)
oFishery landings levelled at 90 million tons per year
oWild fisheries have plateaued, but marine and inland fisheries have increased
to compensate
There has been continuous shift to new species and new areas to maintain catch
levels
Our oceans are considered ‘fully fished’
oFew unutilised resources remain
oAbout 75% of commercially important fish are fully or over-exploited
(Snappers, tuna etc.)
Can’t take any more from that population of its over-exploited/ we
are already taking too much
Australia’s fishery catch:
Our fisheries are based on a quota system- the total allowable catch set each year by
scientists and managers and then allocated amongst license holders
Approximately 200 marine species are caught for food, 100 of which are caught in
Commonwealth waters (Government-controlled water)
oCommonwealth fisheries are worth $340 million dollars (2012-13)- not
including abalone and lobster fisheries
Managed by Australian Fisheries Management Authority
oFishery Status Reports are an annual publication from the Federal
government documenting status and management of fisheries
The amount of fish we catch in Australia is miniscule compared to other countries-
due to our low productivity oceans (low upwelling along our coastline- low bottom
up control)
Majority of fishing occurs in southeast Australia because this is the area where there
are the most people (Sydney, Melbourne etc.)
oWestern Australia- low productivity because warm, nutrient-poor water
passes there and down the Great Australian bight
oSouth-westerly winds cause mixing so south-east waters are more nutrient-
rich than on the west
30% of the public believe our wild fisheries are sustainable- think it is poorly
managed. However, this is not supported by the data
oIn 2013, 3 out of 93 stocks were subject to over-fishing
oFisheries are doing well
E.g. Tiger flathead:
find more resources at oneclass.com
find more resources at oneclass.com
Second biggest fishery in Australia, caught in Commonwealth
waters.
General rule is that fisheries are allowed to keep existing if it is
kept at 40% population (Reached 20%, but it built back up to
40% and have maintained, so fisheries have controlled this
well)
oFisheries gone wrong in Australia:
Southern Bluefin tuna:
Overfished but fishery still open
4% of virgin biomass remains
Orange roughy:
Fishery closed in 2005-06, overfished.
26% of virgin biomass remains
Types of fishing and their impacts:
Trawling: When a net is dragged behind a boat
oCan be pelagic (mid-water nets) or demersal (lower nets- benthic organisms)
oVery effective but indiscriminate (Don’t choose what you catch)
oHigh by-catch of small fish, invertebrates and large vertebrates e.g. turtles
Turtle exclusion devices have been employed to selectively allow fish
only to be caught, and not turtles- net is small enough for fish and not
big enough for turtles
In Australia, there is no market for by-catch (therefore, no value)
Prawn trawling catches 2% of the world’s total fisheries catch, but is
responsible for 33% of the world’s total by-catch
oTrawling can also cause habitat damage- because they’re so big, the area of
seafloor is modified and has become greater than the global terrestrial area
of deforestation
Turning complex benthic communities into simple communities
(Cleared)- lose complexity, lose space for these organisms to live in
Nets: Waiting for organisms to swim into the net (gillnet) or purse seine (drag it
through fish schools)
o‘Ghost nets’- abandoned nets that are lost due to storms or strong currents
that continue to catch organisms
oOccurs pelagic or demersal
oGill nets are non-selective, leads to high by-catch of non-target species
Line: e.g. Bluefin tuna
oPelagic or demersal long lines (Going to the bottom of the sea floor)
oBy-catch of birds, sharks, turtles
Trap: e.g. crayfish, crabs, octopus
oQuite selective fishing technique
oLimited by-catch
oGhost fishing is a problem when these traps aren’t collected at the end
Direct collection: Hand collection- wading, free-driving, SCUBA
oE.g. fish, shellfish, crustaceans, sea cucumbers
oPotential for over-exploitation
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Harvesting of the sea, trophic cascades and phase shifts: total world catch and australia"s fisheries, types of fishing and their effects, fishing down marine food webs, trophic cascades and ecological phase shifts. There has been continuous shift to new species and new areas to maintain catch levels. Our oceans are considered fully fished": few unutilised resources remain, about 75% of commercially important fish are fully or over-exploited (snappers, tuna etc. ) Can"t take any more from that population of its over-exploited/ we are already taking too much. Our fisheries are based on a quota system- the total allowable catch set each year by scientists and managers and then allocated amongst license holders. Approximately 200 marine species are caught for food, 100 of which are caught in. Commonwealth waters (government-controlled water: commonwealth fisheries are worth million dollars (2012-13)- not including abalone and lobster fisheries.
