Overfishing and the State of the Worlds Fisheries - PowerPoint PPT Presentation


PPT – Overfishing and the State of the Worlds Fisheries PowerPoint presentation | free to view - id: 3a8e6-MWFlN


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

Overfishing and the State of the Worlds Fisheries


Sharks (by catch in so many areas) ... Farmed fish are fed 5 pounds of fish meal (by-catch) for every pound of fish flesh produced... – PowerPoint PPT presentation

Number of Views:713
Avg rating:4.0/5.0
Slides: 26
Provided by: CCDS


Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Overfishing and the State of the Worlds Fisheries

Overfishing and the State of the Worlds Fisheries
  • Marine Biology
  • May 2006

The worlds commercial fleet…
  • According to UN FAO/World Bank
  • 50 trawlers caught 20 of the worlds fish
  • 1 of 3.5M fishing boats account for more than
    half of world wide catch
  • 10 of the worlds 15M fishers are employed on
    large scale commercial vessels that receive
    almost all of the 25-50B in world wide
    government subsidies
  • The large scale industrial fishing fleet has
    increased 22 since 1991 largely driven by
  • Since 1975, the size of the fleet has expanded 2X
    faster than rise in catches
  • 125B/yr is spent to catch 70B worth of fish.
    Most of the difference are these subsidies
  • Many say these subsidies promote overfishing…gee,
    ya think?

The Worlds Fisheries Fleet…
  • Dominated by huge industrial fishing fleets that
    using sophisticated sonar, huge nets, spotter
    planes, and ships that can process and freeze
    their catch at sea (55 of commercial catch comes
    from the ocean)
  • 99 of the above is caught from coastal waters….
  • Aquaculture33 of catch
  • Inland freshwater12 of catch
  • 1/3 of world harvest is used as animal feed, fish
    meal and oils

Spotter airplane
Trawler fishing
Fish farming in cage
Purse-seine fishing
trawl flap
trawl lines
trawl bag
Long line fishing
Fish caught by gills
Lines with hooks
Drift-net fishing
(No Transcript)
Drift Net Fishing
  • Drift net fishing on the high seas beyond the
    exclusive economic zone of any nation was banned
    in 1991 by the UN General Assembly because of its
    potential to harm all fish stocks and marine
  • This type of fishing involves the use of a net,
    up to twenty miles in extent, that is generally
    anchored to a boat and left to float with the
  • The net is set out at night and pulled in at
    sunrise, making it difficult for aircraft
    surveillance to catch them in the act.
  • On average, a drift net vessel can scoop up half
    a ton of fish per day.
  • Method often results in an over harvesting and
    waste of large populations of non-commercial
    marine species (by-catch) by its effect of
    sweeping the ocean clean. The by-catch also
    includes marine mammals and seabirds.

Depths of water fished in this manner typically
range from 15m to 140m with some fisheries going
as deep as 1800m Lengths of nets can vary from
between 50m to 200m and lengths of fleets from
between 300m and 3000m. The amount of netting
being fished, whether deployed in the water
column or set on the seabed, at any one time can
range from between 2km and 30km. Soak times, the
time that a fleet is left on the seabed to fish,
can range from a 6 hour tidal soak up to 72
Most selective type
A trammel net consists of three layers of net. A
slack, small mesh, inner panel of netting is
sandwiched between two outer layers of netting,
which are taught and have a larger mesh size.
Trammel nets are used to catch demersal, benthic
and pelagic species…HIGH LEVELS OF DISCARD…
The length of longlines can range from a few
hundred meters in coastal fisheries, to more than
100 km in large-scale mechanized fisheries, to
which thousands of hooks can be attached.
Purse Seining Methods
Trawler Fishing/Bottom Trawling
Stop here
Bottom/Benthic Trawling Equipment
Untrawled vs. Trawled
Bottom Trawling
  • Bottom trawling involves dragging huge, heavy
    nets along the sea floor. Large metal plates and
    rubber wheels attached to these nets move along
    the bottom and crush nearly everything in their
  • Bottom trawling and dredging reduce habitat
  • complexity.
  • Repeated trawling and dredging change seafloor
  • Bottom trawling reduces the productivity of
    seafloor habitats.
  • Marine species that live in stable environments,
    such as deep water corals and sponges, are
    generally more susceptible to damage.
  • All evidence indicates that deep water lifeforms
    are very slow to recover from such damage, taking
    decades to hundreds of years - if they recover at
  • Major threat to deep sea/marine biodiversity
  • If allowed to continue, the bottom trawlers of
    the high seas will destroy deep sea species,
    before we have even discovered much of what is
    out there. Like clear cutting old growth forests
  • Outright destroys increases turbidity and
    smothers deep sea corals etc

(No Transcript)
(No Transcript)
Examples of Overfished Species
  • Rockfish (aka Pacific Red Snapper)
  • Live to 100yrs and dont breed until they are 7
    to 20 years old Bottom trawling gear is used
  • Orange Roughy (NZ, Aus, NE Atlantic)
  • Lives to 100yrs, dont breed until at least 20
    years old bottom trawling used
  • Chilean Seabass (Chile, NZ, Aus, S. Atlantic)
  • Half of them in market are caught illegally
    lives 40 years and breeds late in life
  • Atlantic Cod (New England)
  • Some species are so overfished they are now
    threatened or endangered bottom trawling gear
  • Sharks (by catch in so many areas)
  • Most dont reproduce quickly enough to keep up
    with global demand for meat and fins 50 million
    sharks are killed each year for their fins alone!
    Mercury contamination a problem!

The sad state of affairs…the damage…
  • According to UN FAO and others
  • 90 of large fish populations have been
    exterminated in the last 50yrs
  • 70 of global fish stocks are fully exploited,
    overexploited, or depleted
  • For 200 major fish resources, 35 are overfished,
    25 are being fished to max. potential, and 40
    are in development phase.
  • Hence, 60 of worlds stocks require immediate
    and appropriate management measures
  • Fisheries rely on relatively few species
  • 22 species at over 100K ton/yr five groups make
    up 50 of global fisheries
  • Fisheries are increasingly targeting smaller
    lower value pelagic species (b/c large predatory
    fish are mostly gone) that eat lower on food
    chain and are more subject to fluctuations in
    annual productivity
  • 2.3 Billion pounds of by-catch in USA alone in
  • World wide 1/4 of total catch is throw overboard
    as by-catch
  • Shrimp trawlers discard 85 of their catch making
    it arguably the most environmentally harmful
    fish a person can consume
  • According to USFWS
  • 14 species (20 of worlds fish) are so
    overfished that if there was an immediate halt,
    it could take up to 20 years for recovery

Overfishing and Habitat Degradation and its
connection to declines in fish harvests
  • Potentially renewable
  • Sustainable Yield
  • Difficult to determine in mobile populations
  • Yearly variability due to several factors
  • Harvesting surplus of one species could have
    trophic impacts on others
  • Overfishing
  • Over time can lead to commercial extinction
  • Also increases by catch (27M metric tons/yr)

Major Threats to Fisheries
  • Too many boats!
  • Destruction of coastal habitats (important
    breeding and nursery grounds)
  • 80-90 of all fish caught within 200mi of coast
  • Pollution
  • Chemical, nutrient, sediment runoff
  • Global warming
  • Decline of coral reefs
  • Ozone depletion
  • Increasing population growth (esp. on coast!)

Trends in Fisheries Production over time…
  • Between 1950 and 1999, annual commercial fish
    catch (salt fw) increased almost X5
  • Per capita increase of seafood more than doubled
  • Since 1982, the annual commercial fish catch has
    increased very little and per capita fish catch
    has been falling since 1992
  • Due in large part to overfishing, pollution,
    habitat loss, and population growth especially in
    the coastal zone (50 of world lives here)

Fig 16-19
Is Aquaculture the Answer?
  • ()Often promoted in press as a good way to boost
    global production while taking pressure off
    overharvested marine fisheries
  • (-) Significant loss of sensitive coastal
    ecosystems, lots of issues with untreated waste
    fouling the water antibiotic contamination, use
    of fish meal depletes seas to feed aquaculture
    fish, parasites and disease from farmed species
    can spread to wild fish populations
  • 1.5 million hectares of mangroves converted to
    shrimp farms
  • 2lbs of wild fish to grow 1lb of shrimp
  • Currently supplies 1/3 of commercial harvest
  • 90 of oysters, 40 of salmon (75 in US), 65 of
    fw fish
  • China is the world leader (68 output)
  • Mostly grain fed or fish meal vs. phytoplankton
    in aquaculture systems in developing countries
  • Farms vs. Ranches (anadromous species)

Figure 16-22
Farmed fish are fed 5 pounds of fish meal
(by-catch) for every pound of fish flesh produced…
How do we move towards sustainability?
  • Improved Fishery Regulation Management
  • Reduce commercial fleet
  • Set, monitor, and enforce fishery quotas well
    below MSY
  • Reduce by-catch
  • Establish no fishing area and marine protected
    areas to facilitate recovery and genetic
  • Strengthen commitment to biodiversity by
    improving coastal management and land use that
    promote sustainable fishing and ecological
  • Economic Approaches
  • Sharply reduce or eliminate subsidies
  • Impose User-pay fees for public waters and use
    the to fund fishery management
  • Public Awareness and Consumer Info
  • Aquaculture
  • Restrict locations to avoid destruction of
    mangroves etc
  • Enact stricter pollution regulations
  • Increase production of herbivorous fish vs. fish
    meal fed fish

What can you do?
  • Be an educated consumer!
  • Ask where the fish comes from and how it is
  • Use seafood guides to avoid overfished species,
    to choose sustainably caught fish, and to avoid
    fish laden with mercury!
  • Seafood Guides here
  • Great info at Seafood Alliance
About PowerShow.com