Transcript Aquatic Ecology Notes

Aquatic Ecology
Notes
Chapter Overview Questions
What are the basic types of aquatic life
zones and what factors influence the
kinds of life they contain?
 What are the major types of freshwater
life zones, and how do human activities
affect them?

Chapter Overview Questions
What do we know about aquatic
biodiversity, and what is its economic
and ecological importance?
 How are human activities affecting
aquatic biodiversity?
 How can we manage and sustain the
world’s marine fisheries?

Chapter Overview Questions
(cont’d)
How can we protect, sustain, and
restore wetlands?
 How can we protect, sustain, and
restore lakes, rivers, and freshwater
fisheries?

Chapter Overview Questions
Why is water so important, how much
freshwater is available to us, and how much of
it are we using?
 What causes freshwater shortages, and what
can be done about this problem?
 What are the advantages and disadvantages
of withdrawing groundwater?
 What are the advantages and disadvantages
of using dams and reservoirs to supply more

Chapter Overview Questions
(cont’d)
What are the advantages and disadvantages of
transferring large amounts of water from one
place to another?
 Can removing salt from seawater solve our
water supply problems?
 How can we waste less water?
 How can we use the earth’s water more
sustainably?
 What causes flooding, and what can we do
about it?

WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
Water keeps us alive, moderates
climate, sculpts the land, removes and
dilutes wastes and pollutants, and
moves continually through the
hydrologic cycle.
 Only about 0.02% of the earth’s water
supply is available to us as liquid
freshwater.

WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL

Comparison of
population sizes
and shares of the
world’s freshwater
among the
continents.
Figure 14-2
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
Some precipitation infiltrates the ground
and is stored in soil and rock
(groundwater).
 Water that does not sink into the ground or
evaporate into the air runs off (surface
runoff) into bodies of water.


The land from which the surface water drains
into a body of water is called its watershed or
drainage basin.
Unconfined Aquifer Recharge Area
Evaporation and transpiration Evaporation
Precipitation
Confined
Recharge
Area
Runoff
Flowing
artesian
well
Recharge
Unconfined
Aquifer
Infiltration Water
table
Stream Well
requiring a
pump
Lake
Infiltration
Fig. 14-3, p. 308
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
We currently use more than half of the
world’s reliable runoff of surface water
and could be using 70-90% by 2025.
 About 70% of the water we withdraw
from rivers, lakes, and aquifers is not
returned to these sources.
 Irrigation is the biggest user of water
(70%), followed by industries (20%)
and cities and residences (10%).

Salinity
 The
saltiness.
Niches
What Kinds of Organisms Live in
Aquatic Life Zones?

Aquatic systems contain floating, drifting,
swimming, bottom-dwelling, and decomposer
organisms.

Plankton: important group of weakly swimming,
free-floating biota.

Phytoplankton (plant), Zooplankton (animal),
Ultraplankton (photosynthetic bacteria)
Necton: fish, turtles, whales.
 Benthos: bottom dwellers (barnacles, oysters).
 Decomposers: breakdown organic compounds
(mostly bacteria).

Phytoplankton
 Description
– small drifting plants
 Niche – they are producers that support
most aquatic food chains
 Example – cyanobacteria & many types of
algae
Zooplankton



Description – herbivores that feed on
phytoplankton or other zooplankton
Niche – food stock for larger consumers
Example – krill; small crustaceans
Nekton
 Description
– larger, strongswimming consumers
 Niche – top consumers in the
aquatic ecosystem
 Example – fish, turtles, and whales
Benthos
 Description
– bottom-dwelling
creatures
 Niche – primary consumers,
decomposers
 Example – barnacles, oysters, and
lobsters
Freshwater
Ecosystems
FRESHWATER LIFE ZONES

Freshwater life
zones include:

Standing (lentic)
water such as
lakes, ponds, and
inland wetlands.

Flowing (lotic)
systems such as
streams and rivers.
Figure 6-14
Flowing Water
Ecosystems
Because of different
environmental conditions in
each zone, a river is a system
of different ecosystems.
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
Freshwater Streams and Rivers:
From the Mountains to the Oceans

Water flowing from mountains to the sea
creates different aquatic conditions and
habitats.
Figure 6-17
Headwater Stream
Characteristics
A
narrow zone of cold, clear water that
rushes over waterfalls and rapids. Large
amounts of oxygen are present. Fish
are also present. Ex. trout.
Downstream Characteristics
 Slower-moving
water, less oxygen,
warmer temperatures, and lots of
algae and cyanobacteria.
Energy Source
 Gravity
Standing Water
Ecosystems
Lakes, ponds, etc.
Life in Layers
Life in most aquatic systems is found in
surface, middle, and bottom layers.
 Temperature, access to sunlight for
photosynthesis, dissolved oxygen
content, nutrient availability changes
with depth.


Euphotic zone (upper layer in deep water
habitats): sunlight can penetrate.
Lakes: Water-Filled
Depressions

Lakes are large natural bodies of standing
freshwater formed from precipitation, runoff,
and groundwater seepage consisting of:

Littoral zone (near shore, shallow, with rooted
plants).
Limnetic zone (open, offshore area, sunlit).
 Profundal zone (deep, open water, too dark for

photosynthesis).
 Benthic zone (bottom of lake, nourished by dead
matter).
Littoral Zone
A
shallow area near the shore, to the
depth at which rooted plants stop
growing. Ex. frogs, snails, insects,
fish, cattails, and water lilies.
Limnetic Zone
 Open,
sunlit water that extends to the
depth penetrated by sunlight.
Profundal Zone
 Deep,
open water where it is
too dark for photosynthesis.
Thermal
Stratification
Lakes: Water-Filled
Depressions
Figure 6-15
Definition
 The
temperature difference in deep
lakes where there are warm
summers and cold winters.
Lakes: Water-Filled
Depressions

During summer and winter in deep
temperate zone lakes the become
stratified into temperature layers and
will overturn.
This equalizes the temperature at all
depths.
 Oxygen is brought from the surface to the
lake bottom and nutrients from the bottom
are brought to the top.

Causes
 During
the summer,
lakes become stratified
into different
temperature layers that
resist mixing because
summer sunlight warms
surface waters, making
them less dense.
Thermocline
 The
middle layer
that acts as a barrier
to the transfer of
nutrients and
dissolved oxygen.
Fall Turnover
 As
the temperatures begin to drop,
the surface layer becomes more
dense, and it sinks to the bottom.
This mixing brings nutrients from
the bottom up to the surface and
sends oxygen to the bottom.
Spring Turnover
 As
top water warms and ice melts,
it sinks through and below the
cooler, less dense water, sending
oxygen down and nutrients up.
Freshwater
Wetlands
Freshwater Inland Wetlands:
Vital Sponges

Inland wetlands
act like natural
sponges that
absorb and store
excess water
from storms and
provide a variety
of wildlife
habitats.
Figure 6-18
Freshwater Inland Wetlands:
Vital Sponges
Filter and degrade pollutants.
 Reduce flooding and erosion by absorbing
slowly releasing overflows.
 Help replenish stream flows during dry
periods.
 Help recharge ground aquifers.
 Provide economic resources and recreation.

Marshes
 An
area of temporarily flooded, often
silty land beside a river or lake.
Swamps
A
lowland region permanently covered
with water.
Hardwood Bottomland Forest
 An
area down by a river or stream
where lots of hardwoods, like oaks,
grow.
Prairie Potholes
 These
are depressions that hold water out
on the prairie, especially up north in
Canada. It is a very good duck habitat.
Peat Moss Bog
A
wet area that over time fills in (the last
stage of succession is peat moss). It can
be very deep. In Ireland, they burn this
for wood.
Importance of freshwater
wetlands
 They
filter & purify water.
 Habitat for many animals and
plants.
Historical Aspects

Developers and farmers want Congress to
revise the definition of wetlands. This
would make 60-75% of all wetlands
unavailable for protection. The Audubon
Society estimates that wetlands provide
water quality protection worth $1.6 billion
per year, and they say if that wetlands are
destroyed, the U.S. would spend $7.7
billion to $31 billion per year in additional
flood-control costs.
Estuaries
Definition
A
partially enclosed area of coastal
water where sea water mixes with
freshwater.
Salt Marshes

The ground here is saturated with water and
there is little oxygen, so decay takes place
slowly. It has a surface inlet and outlet, and
contains many invertebrates. It is also the
breeding ground for many ocean animals. Ex.
crabs and shellfish.
Mangrove Forests

These are along warm,
tropical coasts where there is
too much silt for coral reefs to
grow. It is dominated by salttolerant trees called
mangroves (55 different
species exist). It also helps to
protect the coastline from
erosion and provides a
breeding nursery for some
2000 species of fish,
invertebrates, and plants.
Importance of Estuaries
Just one acre of estuary provides $75,000
worth of free waste treatment, and has a
value of about $83,000 when recreation and
fish for food are included.
 Prime Kansas farmland has a top value of
$1,200 and an annual production value of
$600.

The Everglades
Southern Florida to the
Keys
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.

Problems

As Miami develops, it encroaches on
everglades. Plus, it prompts people vs. wildlife.
It is freshwater and local areas are draining it.
Restoring the
Florida
Everglades

The project has
been
attempting to
restore the
Everglades and
Florida water
supplies.
Figure 12-10
Restoration
 Build
huge aqueduct, or find other
sources of fresh water an protect it
federally under endangered species
act, etc.
The Water
Resource
Importance
 Leonardo
da Vinci said
that “Water is the driver
of nature.” Without
water, the other nutrient
cycles would not exist in
their present forms, and
current forms of life on
earth could not exist.
Hydrogen Bonds
Attraction Between Molecules
 The
strong forces of attraction
between molecules of water.
Heat Capacity
 Water
changes temp very slowly because it
can store heat. This protects living
organisms from the shock of abrupt
temperature changes.
Heat of Vaporization
 The
temperature at which water
turns to vapor.
Universal Solvent
 Water
can dissolve a
wide variety of
compounds. This
means it can easily
become polluted by
water-soluble
wastes.
Expansion When Frozen
 Ice
has a lower density than
liquid water. Thus, ice floats on
water.
Hydrologic Cycle
Surface Water
 Examples
– streams, rivers, and lakes
 Source – precipitation
 Watershed – Ex. small streams  larger
streams  rivers  sea
Groundwater
Aquifers–porous rock w/ water flowing through
 Water Table – the level of earth’s land crust to
which the aquifer is filled
 Renewability – the circulation rate of
groundwater is slow (300 to 4,600 years).

Water Usage
 Irrigation
– watering crops
 Industry – coolant (power plant)
 Domestic and Municipal – drinking,
sewage, bathwater, dishwater & laundry
Problems
Too Much Water
 Problems
include flooding, pollution
of water supply, and sewage
seeping into the ground.
TOO MUCH WATER
Heavy rainfall, rapid snowmelt, removal of
vegetation, and destruction of wetlands
cause flooding.
 Floodplains, which usually include highly
productive wetlands, help provide natural
flood and erosion control, maintain high
water quality, and recharge groundwater.
 To minimize floods, rivers have been
narrowed with levees and walls, and
dammed to store water.

TOO MUCH WATER

Comparison of St. Louis, Missouri under
normal conditions (1988) and after
severe flooding (1993).
Figure 14-22
TOO MUCH WATER

Human activities have contributed to
flood deaths and damages.
Figure 14-23
Forested Hillside
Oxygen
released by
vegetation
Diverse
ecological
habitat
Evapotranspiration
Trees reduce soil
erosion from heavy
rain and wind
Steady
river flow
Agricultural
land
Leaf litter
improves soil
fertility
Tree roots stabilize
soil and aid water
flow
Vegetation releases
water slowly and
reduces flooding
Fig. 14-23a, p. 330
After Deforestation
Tree plantation
Roads
destabilize
hillsides
Gullies and
landslides
Evapotranspiration decreases
Ranching accelerates
soil erosion by water
and wind
Winds remove fragile
topsoil
Agricultural land is
flooded and silted up
Heavy rain leaches
nutrients from soil and
erodes topsoil
Rapid runoff
causes flooding
Silt from erosion blocks rivers and reservoirs
and causes flooding downstream
Fig. 14-23b, p. 330
Too Little Water
Examples
 Examples
include drought and
expanding deserts.
Overdrawing Surface Water
 Lake
levels drop, recreation use drops,
fisheries drop, and salinization occurs. Ex.
Soviet Union (Aral Sea); the inland sea
drained the river that fed into it. Now it’s
a huge disaster (read pg. 322 in text).
1964
1997
Case Study: The Aral Sea Disaster

Diverting water from the Aral Sea and its
two feeder rivers mostly for irrigation has
created a major ecological, economic, and
health disaster.
About 85% of the wetlands have been
eliminated and roughly 50% of the local bird
and mammal species have disappeared.
 Since 1961, the sea’s salinity has tripled and the
water has dropped by 22 meters most likely
causing 20 of the 24 native fish species to go
extinct.

Aquifer Depletion
 This
harms endangered species,
and salt water can seep in.
Salinization of Irrigated Soil
 Water
is poured onto soil and
evaporates. Over time, as this is
repeated, nothing will grow there
anymore.
U.S. Water Problems
Surface Water Problems
The polluted Mississippi River (non-source point
pollution) has too much phosphorus.
 In the Eerie Canal, which connects the ocean
to the Great Lakes, lampreys came in and
depleted the fish. The zebra mollusk is also a
problem in the Great Lakes.

Effects of Plant Nutrients on
Lakes:
Too Much of a Good Thing

Plant nutrients from a lake’s
environment affect the types and
numbers of organisms it can support.
Figure 6-16
Effects of Plant Nutrients on
Lakes:
Too Much of a Good Thing

Plant nutrients from a lake’s
environment affect the types and
numbers of organisms it can support.

Oligotrophic (poorly nourished) lake:
Usually newly formed lake with small
supply of plant nutrient input.
 Eutrophic (well nourished) lake: Over
time, sediment, organic material, and
inorganic nutrients wash into lakes causing
excessive plant growth.
Effects of Plant Nutrients on
Lakes:
Too Much of a Good Thing

Cultural eutrophication:

Human inputs of nutrients from the
atmosphere and urban and agricultural
areas can accelerate the eutrophication
process.
Mono Lake
 (like
the Dead Sea) This has a huge
salt concentration due to man’s
draining.
Colorado River Basin
 These
are dams &
reservoirs that feed
from the Colorado
River all the way to
San Diego, LA, Palm
Springs, Phoenix &
Mexico. So far has
worked because they
haven’t withdrawn
their full allocations.
See pg306.
The Colorado River Basin

The area
drained by
this basin is
equal to more
than onetwelfth of the
land area of
the lower 48
states.
Figure 14-14
IDAHO
WYOMING
Dam
Aqueduct or
canal
Salt Lake City
Upper Basin
Denver
Grand Junction
UPPER
BASIN
Lower Basin
UTAH
NEVADA
Lake
Powell
Grand
Canyon
Las Vegas
COLORADO
Glen
Canyon Dam
NEW MEXICO
Boulder City
CALIFORNIA
Los
Angeles
ARIZONA
Palm
Springs
San
Diego
All-American
Canal
Albuquerque
LOWER
BASIN
Phoenix
Yuma
Mexicali
Gulf of
California
Tucson
0
100 mi.
0
150 km
MEXICO
Fig. 14-14, p. 318
Case Study: The Colorado Basin –
an Overtapped Resource

The Colorado River has so many dams
and withdrawals that it often does not
reach the ocean.
14 major dams and reservoirs, and
canals.
 Water is mostly used in desert area of the
U.S.
 Provides electricity from hydroelectric
plants for 30 million people (1/10th of the
U.S. population).

Case Study: The Colorado Basin –
an Overtapped Resource
Lake Powell, is
the second
largest
reservoir in the
U.S.
 It hosts one of
the
hydroelectric
plants located
on the
Colorado River.
Figure 14-15

Groundwater Problems
 These
include pollution, salt,
and draining too much.
Other Effects of Groundwater
Overpumping

Sinkholes form
when the roof of
an underground
cavern collapses
after being
drained of
groundwater.
Figure 14-10
Groundwater Depletion:
A Growing Problem


Areas of
greatest aquifer
depletion from
groundwater
overdraft in the
continental U.S.
The Ogallala, the world’s largest aquifer, is
most of the red area in the center (Midwest).
Figure 14-8
Ogallala Aquifer

This is the world’s largest known aquifer, and
fuels agricultural regions in the U.S. It extends
from South Dakota to Texas. It’s essentially a
non-renewable aquifer from the last ice age
with an extremely slow recharge rate. In some
cases, water is pumped out 8 to 10 times faster
than it is renewed. Northern states will still
have ample supplies, but for the south it’s
getting thinner. It is estimated that ¼ of the
aquifer will be depleted by 2020.
Global Water Problems
Impacts of Human Activities on
Freshwater Systems

Dams, cities, farmlands, and filled-in wetlands
alter and degrade freshwater habitats.
 Dams, diversions and canals have fragmented
about 40% of the world’s 237 large rivers.
 Flood control levees and dikes alter and
destroy aquatic habitats.
 Cities and farmlands add pollutants and excess
plant nutrients to streams and rivers.
 Many inland wetlands have been drained or
filled for agriculture or (sub)urban
development.
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
Core Case Study: A Biological Roller
Coaster Ride in Lake Victoria

Reasons for Lake Victoria’s loss of
biodiversity:
Introduction of Nile perch.
 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.

Stable Runoff

As water runs off from rain, it’s supposed to get
into rivers, and finally off to the sea. But when
we dam rivers, less goes to the ocean, meaning
the brackish water (where the river hits the
ocean) becomes more salty. This is the
breeding ground for many fish and
invertebrates. This harms the ecology of the
area.
Drinking Water
Problems
Coliform Bacteria

The W.H.O. recommends there be
zero colonies of bacteria per
100ml of drinking water and 200
colonies per 100ml of swimming
water. The average human
excretes 2 billion organisms per
day (see how easily untreated
sewage can contaminate water?).
Oxygen Demanding Wastes
 These
are organic wastes that can be
decomposed by aerobic bacteria
(causes lack of oxygen). Fish die as a
result of a lack of oxygen.
Water-Soluble Inorganic
Chemicals
 These
include acids, salts, mercury,
and lead. They make water unfit to
drink.
Organic Material
 These
include oil, gas, plastics,
pesticides, and detergents.
Population Growth
 Problems
include over-drawing
fresh water, pollution, and overbuilding so that water can’t
seep into the ground.
Sharing Water Resources

There are water wars out west.
California bought the water from the
Colorado River, but Arizona wants it.
Who owns it? The same thing is
happening in Texas. More water rights
are sold than the actual amount of
water. How do you share water? This
is a problem all over the world.
Water Management
Dams and Reservoirs
•Description: A dammed stream that can
capture & store water from rain & melted snow.
•Benefits: Hydroelectric power; provides water
to towns; recreation; controls floods downstream
• Problems: Reduces downstream flow;
prevents water from reaching the sea (Colorado
River) devastates fish life; reduces biodiversity.
USING DAMS AND RESERVOIRS
TO SUPPLY MORE WATER

Large dams and reservoirs can produce
cheap electricity, reduce downstream
flooding, and provide year-round water
for irrigating cropland, but they also
displace people and disrupt aquatic
systems.
Provides water
for year-round
irrigation of
cropland
Provides
water for
drinking
Reservoir is
useful for
recreation
and fishing
Can produce
cheap
electricity
(hydropower)
Downstream
flooding is
reduced
Flooded land
destroys forests
or cropland and
displaces people
Large losses of
water through
evaporation
Downstream
cropland and
estuaries are
deprived of
nutrient-rich silt
Risk of
failure and
devastating
downstream
flooding
Migration and
spawning of
some fish are
disrupted
Fig. 14-13a, p. 317
Powerlines
Reservoir
Dam
Intake
Powerhouse
Turbine
Fig. 14-13b, p. 317
Case Study:
China’s Three Gorges Dam

There is a debate over whether the advantages
of the world’s largest dam and reservoir will
outweigh its disadvantages.
The dam will be 2 kilometers long.
 The electric output will be that of 18 large coalburning or nuclear power plants.
 It will facilitate ship travel reducing transportation
costs.
 Dam will displace 1.2 million people.
 Dam is built over seismatic fault and already has
small cracks.

Dam Removal

Some dams are being removed for ecological
reasons and because they have outlived their
usefulness.
In 1998 the U.S. Army Corps of Engineers
announced that it would no longer build large dams
and diversion projects in the U.S.
 The Federal Energy Regulatory Commission has
approved the removal of nearly 500 dams.
 Removing dams can reestablish ecosystems, but
can also re-release toxicants into the environment.

Water Diversion
•Description: Damming a river to
control where the water flows
•Benefits: Keeps water where we
want it- cities!
•Problems: Drains wetlands, destroys
land
Desalinization
•Description: Removing salt from salt
water
•Benefits: Freshwater
•Problems: Uses lots of energy; costs
3-5X’s more money; what do we do
with the salt?
DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES

Removing salt from seawater by current
methods is expensive and produces large
amounts of salty wastewater that must be
disposed of safely.

Distillation: heating saltwater until it
evaporates, leaves behind water in solid form.
 Reverse osmosis: uses high pressure to force
saltwater through a membrane filter.
DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES

Seeding clouds with tiny particles of
chemicals to increase rainfall towing
icebergs or huge bags filled with
freshwater to dry coastal areas have all
been proposed but are unlikely to
provide significant amounts of
freshwater.
Harvesting Icebergs
•Description: Towing massive icebergs to arid
coastal areas (S. California; Saudi Arabia)
•Benefits: freshwater
•Problems: Technology not available; costs
too high; raise temperatures around the earth.
INCREASING WATER SUPPLIES BY
WASTING LESS WATER
Sixty percent of the world’s irrigation
water is currently wasted, but improved
irrigation techniques could cut this
waste to 5-20%.
 Center-pivot, low pressure sprinklers
sprays water directly onto crop.

It allows 80% of water to reach crop.
 Has reduced depletion of Ogallala aquifer
in Texas High Plains by 30%.

Drip irrigation
(efficiency 90–95%)
Gravity flow
(efficiency 60% and
80% with surge
valves)
Center pivot
(efficiency 80%–95%)
Water usually comes from
an aqueduct system or a
nearby river.
Above- or belowground pipes or tubes
deliver water to
individual plant roots.
Water usually pumped
from underground and
sprayed from mobile
boom with sprinklers.
Fig. 14-18, p. 325
Conservation
•Description: Saving the water we have
•Methods: recycling; conserving at home;
xeriscaping; fix leaks
•Benefits: Saves money; Saves Wildlife
•Problems: bothersome to people; lack of
caring; laziness
Fishing Problems & Techniques
The major decline in the worldwide
catch of fish since 1990 is because of
over-fishing.
 By-catch- fish or animals that were not
meant to be caught.

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.

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
Purse Seines
Purse Seines
A large purse-like net is put into the
ocean and is then closed like a
drawstring purse to trap the fish.
 Tuna is a fish typically caught in purse
seines
 Dolphins are a by-catch of purse seines

Long-line fishing
Lines are put out that can be up to 80
miles long w/ thousands of baited
hooks on them. These are left out freefloating for days and then the boat
comes back and picks them up.
 Pilot whales, dolphins, sea turtles, and
birds are by-catch of this technique.

Drift-net fishing
Each net hangs as much as 50 feet below the
surface and up to 34 miles long.
 Anything that comes into contact w/ these
nearly invisible nets are entangled.
 This leads to overfishing
 Many unwanted fish and marine mammals,
turtles and seabirds are caught.

HUMAN IMPACTS ON AQUATIC
BIODIVERSITY

Area of ocean before and after a trawler
net, acting like a giant plow, scraped it.
Figure 12-2
Population Growth and Pollution

Each year plastic
items dumped
from ships and
left as litter on
beaches threaten
marine life.
Figure 12-3