Transcript emptying the ocean

Emptying the Oceans:
• The state of ocean fisheries
• Marine protected areas and
reserves
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Emptying the oceans
• Overharvesting is the worst marine problem
• We are putting unprecedented pressure on marine
resources
- Half the world’s marine fish populations are fully
exploited and can’t be fished more intensively
- 28% of fish population are overexploited and
heading to extinction
• Total fisheries catch leveled off after 1988
- Despite increased fishing effort
• The maximum wild fisheries potential has been
reached
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The global fisheries catch has increased
It is predicted that populations of all ocean species we
fish for today will collapse by 2048
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We have long overfished
• People began depleting sea life centuries ago
• Species have been hunted to extinction: Caribbean monk
seal, Steller’s sea cow, Atlantic gray whale
• Overharvesting Chesapeake Bay oyster beds led to its
collapse, eutrophication, and hypoxia
• Decreased sea turtle populations cause overgrowth of sea
grass and can cause sea grass wasting disease
• Overharvesting nearly exterminated many whale species
• People never thought groundfish could be depleted
- New approaches or technologies increased catch rates
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Fishing has industrialized
• Factory fishing = huge vessels
use powerful technologies to
capture fish in huge volumes
- Even processing and
freezing their catches at sea
• Driftnets for schools of
herring, sardines, mackerel,
sharks, shrimp
• Longline fishing for tuna and
swordfish
• Trawling for pelagic fish and
groundfish
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Fishing practices kill nontarget animals
• Bycatch = the accidental capture of animals
• Drift netting drowns dolphins, turtles, and seals
- Fish die on deck
- Banned in international waters
- But it is still used in national waters
• Longline fishing kills turtles, sharks, and over 300,000
seabirds/year
- Methods (e.g., flags) are being developed to limit
bycatch
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Dolphins and tuna
• Dolphins are trapped in purse seine nets used to catch
tuna
- Hundreds of thousands of dolphins were killed
• The 1972 Marine Mammal Protection Act forced fleets to
try to free dolphins
- Bycatch dropped dramatically
• Other nations fished for tuna, and bycatch increased
• The U.S. government required that nations exporting tuna
to the U.S. minimize dolphin bycatch
- Dolphin-safe tuna uses methods to avoid bycatch
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Dolphin deaths have declined, but …
• Rules and technology
have decreased dolphin
deaths
• Other animals (e.g.,
sharks) are still caught
• Dolphins have not
recovered
- Too few fish to eat
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Bottom-trawling destroys ecosystems
• Heavy nets crush organisms and damage sea bottoms
- It is especially destructive to complex areas (e.g., reefs)
• It equals clear-cutting and strip mining
- Georges Bank has been trawled three times
- Destroying young cod as bycatch
- The reason the cod stock is not recovering
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Modern fleets deplete marine life rapidly
• Grand Banks cod have been fished for centuries
- Catches more than doubled with industrial trawlers
- Record-high catches lasted only 10 years
• George Bank cod fishery also collapsed
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Industrialized fishing is destroying fisheries
Oceans today contain only one-tenth of the large-bodied
animals they once did
• Worldwide, industrialized fishing is depleting marine
populations with astonishing speed
- 90% of large-bodied fish and sharks are eliminated
within 10 years after fishing begins
- Populations stabilize at 10% of their former levels
• Communities were very different before modern fishing
- Removing animals at higher trophic levels allows
prey to proliferate and change communities
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Several factors mask declines
• Industrialized fishing has depleted stocks
- But global catch has remained stable for the past 20
years
• How can stability mask population declines?
- Fishing fleets travel farther to reach less-fished areas
- Fleets fish in deeper waters (now at 250 m)
- Fleets spend more time fishing and set more nets
- Improved technologies: faster ships, sonar mapping,
satellite navigation, thermal sensing, aerial spotting
• Fleets expend more effort to catch the same number of
fish
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We are “fishing down the food chain”
• Figures on total global catch do tell the whole story
• As fishing increases, the size and age of fish caught
decline
- 10-year-old cod, once common, are now rare
• As species become too rare to fish, fleets target more
abundant species
- Shifting from large, desirable species to smaller, less
desirable ones
- This entails catching species at lower trophic levels
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Purchasing choices influence fishing
practices
• Buy ecolabeled seafood
- Dolphin-safe tuna
• Consumers don’t know how
their seafood was caught
- Nonprofit organizations
have devised guides for
consumers
- Avoid: Atlantic cod, wildcaught caviar, sharks,
farmed salmon
Best choices: farmed
catfish, mussels,
oysters, tilapia
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Diversity loss erodes ecosystem services
• Factors that deplete biodiversity threaten ecosystem
services of the oceans
• Systems with reduced species or genetic diversity show
less primary and secondary production
- They are less able to withstand disturbance
• Biodiversity loss reduces habitat for nurseries for fish and
shellfish
• Less diversity leads to reduced filtering and
detoxification
- Resulting in algal blooms, dead zones, fish kills, beach
closures
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Fisheries management
• Based on maximum sustained yield to maximize harvest
- While keeping fish available for the future
- Managers may limit the harvest or restrict gear used
• Despite management, stocks have plummeted
- It is time to rethink fisheries management
• Ecosystem-based management shifts away from species
and toward the larger ecosystem
- Considers the impacts of fishing on habitat quality,
species interactions, and long-term effects
- Sets aside areas of oceans free from human
interference
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IV Emptying the Oceans
1. Describe the trends in global fish capture over
the past 55 years and over the past 20 years ,
and
2. Describe an example of how overfishing can
lead to ecological damage and fishery collapse
3. Name three industrial fishing practices, and
explain how they create by catch and harm
marine life.
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