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Chapter 12
Sustaining Aquatic
Biodiversity
Core Case Study: A Biological Roller
Coaster Ride in Lake Victoria
 Lake
Victoria has lost their endemic fish
species to large introduced predatory fish.
Figure 12-1
Reasons for Lake Victoria’s loss of
biodiversity:

Introduction of Nile perch for sport fishing
• Ate majority of other fish



Lake experienced algal blooms from nutrient
runoff.
Invasion of water hyacinth has blocked sunlight
and deprived oxygen.
Nile perch is in decline because it has eaten its
own food supply.
AQUATIC BIODIVERSITY
 We
know little about the biodiversity of the
world’s marine and freshwater systems.
 However, established 3 general patterns

The greatest marine biodiversity occurs in:
• coral reefs,
• estuaries
• deep ocean floor.


Biodiversity is higher near the coast than open
sea because of habitat and food source variety
Biodiversity is higher is higher on the ocean
bottom than surface
AQUATIC BIODIVERSITY
 Provides
important ecological and economic
services.

Twice that of cropland
 About
½ world’s population relies on ocean
for main food source.
 Chemical compounds: many medical uses

Antibiotic, anticancer, hypertension, bone
reconstruction
HUMAN IMPACTS ON AQUATIC
BIODIVERSITY
 Human
activities have destroyed, disrupted
or degraded a large proportion of the world’s
coastal, marine and freshwater ecosystems.
Habitat Destruction
 Coral


Approximately 20% of the world's coral reefs
have been destroyed.
58% severely damaged
 Sea


reef
grass & kelp beds
Provides habitat, food source, erosion protection
Disappearing at alarming rate
Habitat Destruction
 Ocean




Levels
During the past 100 years, sea levels have risen
10-25 centimeters.
Levels are predicted to continue to rise
Coastal cities at risk
Maldives
• Low lying chain of islands in Indian ocean
• Threat of being submerged
Habitat Destruction
 Mangrove


Forests
We have destroyed more than 1/3 of the world’s
mangrove forests
Critical for habitat, beach erosion protection,
storm surge protection, & flood control
Habitat Destruction
 Coastal



Wetlands
We have destroyed more than 1/2
Mainly beach development: houses, resorts
Critical for habitat, beach erosion protection,
storm surge protection, & flood control
Habitat Destruciton
 Ocean




bottom
Being destroyed by dredging and trawler fishing
boats
“Plowing” the sea bed
Takes decades to centuries to recover
Scientists call it the most destructive fishing
practice
Figure 12-2
HUMAN IMPACTS
 Area
of ocean before and after a trawler net,
acting like a giant plow, scraped it.
Figure 12-2
Invasive Species
 Invasive




species are an increasing threat
Arrive in ballast from ships, dumped aquariums,
or intentional released
Bioinvaders are blamed for about 2/3 of fish
extinctions in the U.S. between 1900-2000.
Asian Swamp Eel: rapid reproduction, burrows
into mud banks, wriggles across dry land
Purple Loosestrife: called purple plague,
spreads rapidly
Population Growth and Pollution
 Almost
1/2 of world’s people live on or near
a coastal zone
 80% of ocean water pollution comes from
land-based human activities.



Fertilizer runoff causes algae blooms & fish
die-offs
Industrial waste
Trash
Population Growth and Pollution
 Each
year plastic items dumped from ships
and left as litter on beaches threaten marine
life.
Overfishing

Fishing is an ancient human
tradition that is now a
worldwide resource
extraction industry.

Several decades of
overfishing in all of the
world’s oceans has pushed
commercially important
species, e.g. cod, into steep
declines from which
recovery is unlikely.

Fishing fleet
In 1992, Canada’s 500 year old
cod fishery collapsed,
destroying 40,000 jobs

Total ban on fishing

Stocks still have not recovered
Fish market, Norway
Sustainable Yields
 The
maximum sustainable yield (MSY) has
been exceeded by too many vessels catching
too many fish, especially fish of reproductive
age, often using wasteful and destructive
methods

Bycatch: unwanted species thrown back into sea
dead or dying
 Modern
industrial fishing can cause 80%
depletion of a species in 10-15 years
Sustainable Yields

Sustainable yields apply to all harvests that require some
organisms to be left after harvesting to replenish the
stock.

Yields above the sustainable limit will eventually cause
the depletion of the stock.
Fisheries especially need to use sustainable yields (SY).
SY =
Total biomass
Total biomass at time t
at time t + 1 Energy
Energy
= (annual growth and recruitment) - (annual death and emigration)
Yield
Population growth
Population at 1/2 K
(carrying capacity)
Population
replenished by time
of next harvest
Overfishing

The build up of large scale fishing fleets has contributed to
widespread overfishing and damage to the marine
environment.
Bottom trawls and dredges cause large scale physical damage
to the sea floor. Sea mounts are particularly vulnerable.
Lost fishing gear (particularly drift nets) threatens marine life,
including birds and mammals that are non-target species.
Purse seines can catch whole schools of fish and non-target
species (bycatch)
Drift net
Purse seine
Fish farming
in cage
Trawl flap
Trawler
fishing
Spotter airplane
Sonar
Purse-seine fishing
Trawl
lines
Trawl bag
Long line
fishing
Fish
school
Drift-net fishing
Float Buoy
Lines with
hooks
Deep sea
aquaculture cage
Fish caught
by gills
Fig. 12-A, p. 255
Overfishing and Extinction:
Gone Fishing, Fish Gone
 About
75% of the world’s commercially
valuable marine fish species are over fished
or fished near their sustainable limits.




Big fish are becoming scarce.
Smaller fish are next.
We throw away 30% of the fish we catch.
We needlessly kill sea mammals and birds.
Why is it Difficult to Protect Aquatic
Biodiversity?




Human ecological footprint is expanding.
Much of the damage to oceans is not visible to
most people.
Many people incorrectly view the oceans as an
inexhaustible resource.
Most of world’s ocean lies outside legal
jurisdiction
PROTECTING AND SUSTAINING
MARINE BIODIVERSITY
 Laws,
international treaties, and education
can help reduce the premature extinction of
marine species.




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1975 CITIES
1979 Global Treaty on Migratory Species
1972 Marine Mammal Protection Act
1973 Endangered Species Act
1976 US Whale Conservation & Protection Act
1995 International Convention on Biological
Diversity
IWC – International Whaling Commission
PROTECTING AND SUSTAINING
MARINE BIODIVERSITY
 Six
of the world’s seven major turtle species
are threatened or endangered because of
human activities.
 Since 1989 the U.S. government has
required offshore shrimp trawlers to use turtle
exclusion devices.


Sea turtle tourism brings in almost three times as
much money as the sale of turtle products.
Reconciliation ecology
Case Study: The Florida Manatee
and Water Hyacinths
 Manatee
can eat
unwanted Water
Hyacinths.
 Endangered due to:





Habitat loss.
Entanglement from fishing
lines and nets.
Hit by speed boats.
Stress from cold.
Low reproductive rate
Figure 12-B
Case Study: Commercial Whaling
of 11 species – hunted to commercial
extinction.
 Blue whale – to brink of biological extinction
 1970 – US stopped whaling & banned all
whale imports
 International Whaling Commission (IWC)
banned commercial whaling in 1986
8
Case Study:
Commercial Whaling
 Despite
ban, Japan,
Norway, and Iceland kill
about 1,300 whales of
certain species for scientific
purposes.

Although meat is still sold
commercially.
 Hope
to reverse
international ban
MARINE SANCTUARIES
 Fully
protected marine reserves make up less
than 0.3% of the world’s ocean area.

Studies show that fish populations double, size
grows by almost a third, reproduction triples and
species diversity increases by almost one fourth.
 Call
for 30% protected
 Some communities work together to develop
integrated plans for managing their coastal
areas.

1975 Australia’s Great Barrier Reef;1/3 protected
Revamping Ocean Policy
 Two
recent studies called for an overhaul of
U.S. ocean policy and management.






Develop unified national policy.
Double federal budget for ocean research.
Centralize the National Oceans Agency.
Set up network of marine reserves.
Reorient fisheries management towards
ecosystem function: Catch Limits
Increase public awareness.
MANAGING AND SUSTAINING
MARINE FISHERIES
 There
are a number of ways to manage
marine fisheries more sustainably and protect
marine biodiversity.
 Some fishing communities regulate fish
harvests on their own and others work with
the government to regulate them.

Modern fisheries have weakened the ability of
many coastal communities to regulate their own
fisheries.
Solutions
Managing Fisheries
Fishery Regulations
Bycatch
Set catch limits well below the
maximum sustainable yield
Use wide-meshed nets to allow
escape of smaller fish
Improve monitoring and enforcement
of regulations
Economic Approaches
Use net escape devices for sea
birds and sea turtles
Sharply reduce or eliminate fishing
subsidies
Ban throwing edible and
marketable fish back into the sea
Aquaculture
Charge fees for harvesting fish and shellfish
from publicly owned offshore waters
Restrict coastal locations for fish
farms
Certify sustainable fisheries
Protected Areas
Control pollution more strictly
Establish no-fishing areas
Depend more on herbivorous fish
species
Establish more marine protected areas
Nonnative Invasions
Rely more on integrated coastal
management
Kill organisms in ship ballast water
Consumer Information
Label sustainably harvested fish
Publicize overfished and threatened species
Filter organisms from ship ballast
water
Dump ballast water far at sea and
replace with deep-sea water
Fig. 12-7, p. 261
PROTECTING, SUSTAINING, AND
RESTORING WETLANDS
 US
has lost ½ of wetlands
 Federal permit is required to develop
wetlands – has cut wetland loss by 80%
 Attempts by developers to weakened this law
 Mitigation – allows destruction of existing
wetland as long as equal area of same type
is created or restored
Figure 12-8
Solutions
Protecting Wetlands
Legally protect existing wetlands
Steer development away from existing wetlands
Use mitigation banking only as a last resort
Require creation and evaluation of a new wetland before
destroying an existing wetland
Restore degraded wetlands
Try to prevent and control invasions by nonnative species
Fig. 12-9, p. 264
Case Study:
Restoring the Florida Everglades
 The
world’s largest ecological restoration
project involves trying to undo some of the
damage inflicted on the Everglades by
human activities.




90% of park’s wading birds have vanished.
Other vertebrate populations down 75-95%.
Large volumes of water that once flowed through
the park have been diverted for crops and cities.
Runoff has caused noxious algal blooms.
Restoring the
Florida
Everglades
 The
project has
been attempting
to restore the
Everglades and
Florida water
supplies.
Figure 12-10
PROTECTING, SUSTAINING, AND
RESTORING LAKES AND RIVERS
 Lakes
are difficult to manage and are
vulnerable to planned or unplanned
introductions of nonnative species.
 For decades, invasions by nonnative species
have caused major ecological and economic
damage to North America’s Great lakes.

Sea lamprey, zebra mussel, quagga mussel,
Asian carp.
PROTECTING, SUSTAINING, AND
RESTORING LAKES AND RIVERS
 Dams
can provide many human benefits but
can also disrupt some of the ecological
services that rivers provide.



119 dams on Columbia River have sharply
reduced (94% drop) populations of wild salmon.
U.S. government has spent $3 billion in
unsuccessful efforts to save the salmon.
Removing hydroelectric dams will restore native
spawning grounds.
PROTECTING, SUSTAINING, AND
RESTORING LAKES AND RIVERS
 We
can help sustain freshwater fisheries by
building and protecting populations of
desirable species, preventing over-fishing,
and decreasing populations of less desirable
species.
 A federal law helps protect a tiny fraction of
U.S. wild and scenic rivers from dams and
other forms of development.

National Wild and Scenic Rivers Act (1968).
Natural Capital
Ecological Services of Rivers
• Deliver nutrients to sea to help sustain
coastal fisheries
• Deposit silt that maintains deltas
• Purify water
• Renew and renourish wetlands
• Provide habitats for wildlife
Fig. 12-11, p. 267