Class 39 -- The Oceans

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Class 39 -- The Oceans

• FOOD RESOURCES OF THE OCEANS
• World Fish Catch
• Dynamics of fish populations and fishing
• Over-exploited fisheries
• Management to get maximal harvest of fish

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FOOD RESOURCES World fish catch increased 4-fold
from l950 to 1995 in 1953 23 Million Metric
Tons in 1970 50 Million Metric Tons in
1995 85 Million Metric Tons
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FOOD RESOURCES World fish catch plateau??? in
1995 85 Million Metric Tons in 2003 85 Million
Metric Tons
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Open Ocean Areas- Small Harvest Fisheries near
upwelling zones High trophic level fish, e.g.,
Tuna
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Coastal Areas Large Harvest Often good nutrient
supply Shorter, more efficient food chain
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Upwelling Areas -- e.g., West coasts Very high
primary productivity. Harvest small,
fast-growing, phytoplankton-eating species
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• What is the "maximum sustainable yield?
• Not well known for most commercial fish stocks.
• Estimates 1/3 to 2/3 of total production

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OVER-EXPLOITATION
If the harvest is too large, the population
shrinks and reproduction slows - then next years
harvest will be smaller and everyone suffers The
goal Harvest as much as possible while still
allowing sufficient reproduction for the future A
sustainable harvest
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EXAMPLES OF OVER-EXPLOITATION

• 1. Peruvian anchovies.
• Over-fished at peak harvest (l970 12 million
  metric tons)
• Devastating 1972 El Nino
• Decrease to 2 million metric tons per year
• Recent recovery

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Anchovy harvest declined drastically in 1972,
and stayed at low levels for more than ten years.
Harvest increased after the El Niño 1982-83, and
reached a maximum level of 9.7 million tons in
1994, a level which was the highest since the
collapse of the fishery in 1971 - 1972. Harvest
fell after the El Niño of 1997-98, but this
decline was followed by a rapid recovery in 1999
and 2000. The species has been declared as fully
exploited. The main fisheries management
measures are Total Allowable Catch, minimum
harvesting size and reproductive closed seasons.
SOME SHARED FISH STOCKS OF SOUTH EASTERN PACIFIC
(by Jorge Zuzunaga, GOVT OF PERU, 2002)
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Note 1997 El Niño
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• 2. Pacific Salmon -- Overfishing and
  environmental degradation.
• Degradation of spawning streams
• dams
• altered stream banks (reduced shade)
• water quality

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3. Grand Banks Cod Fishery-- Overfishing and
environmental degradation
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2008 UN Report The world economy could be 50
billion richer if fisheries were managed
better Half the world fishing fleet could be
scrapped, and the remaining half would catch as
much fish.
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Fisheries management The individual right to
fish versus long-term health of the fish
population Other environmental damage Logging,
dams, etc.
...Mortgage......Tuition Bills..
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Ecosystem-based fisheries management
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Effectiveness of the world's fisheries management
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One way to harvest more from the oceans Harvest
lower on the food chain Antarctic
krill? Harvest phytoplankton directly?
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Fish to avoid
Slow reproduction/ Overharvesting Chilean sea
bass (toothfish) Shark- Mercury hazard
also Monkfish (like Anglerfish) Orange
Roughy Bluefin tuna (sushi)
http//www.montereybayaquarium.org/cr/seafoodwatch
.aspx
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• Whales
• Some species hunted to near-extinction
  e.g., Gray
• Whaling banned Numbers have rebounded
• Others still perhaps 100x less than pre-whaling
  numbers