Aquatic Ecology Notes

1
Aquatic Ecology Notes
2
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?

3
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 worlds marine
  fisheries?

4
Chapter Overview Questions (contd)

• How can we protect, sustain, and restore
  wetlands?
• How can we protect, sustain, and restore lakes,
  rivers, and freshwater fisheries?

5
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 water?

6
Chapter Overview Questions (contd)

• 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 earths water more
  sustainably?
• What causes flooding, and what can we do about it?

7
The Water Resource
8
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.

9
Hydrogen Bonds
10
Attraction Between Molecules

• The strong forces of attraction between molecules
  of water.

11
Heat Capacity

• Water changes temp very slowly because it can
  store heat. This protects living organisms from
  the shock of abrupt temperature changes.

12
Heat of Vaporization

• The temperature at which water turns to vapor.

13
Universal Solvent

• Water can dissolve a wide variety of compounds.
  This means it can easily become polluted by
  water-soluble wastes.

14
Expansion When Frozen

• Ice has a lower density than liquid water. Thus,
  ice floats on water.

15
Surface Water

• Examples streams, rivers, and lakes
• Source precipitation
• Watershed Ex. small streams ? larger streams ?
  rivers ? sea

16
Groundwater

• Aquifersporous rock w/ water flowing through
• Water Table the level of earths land crust to
  which the aquifer is filled
• Renewability the circulation rate of
  groundwater is slow (300 to 4,600 years).

17
WATERS 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 earths water supply is
  available to us as liquid freshwater.

18
WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• Comparison of population sizes and shares of the
  worlds freshwater among the continents.

Figure 14-2
19
WATERS 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.

20
Hydrologic Cycle
21

Unconfined Aquifer Recharge Area
Evaporation and transpiration
Evaporation
Precipitation
Confined Recharge Area
Runoff
Flowing artesian well
Recharge Unconfined Aquifer
Stream Well requiring a pump
Water table
Infiltration
Lake
Infiltration
Unconfined aquifer
Less permeable material such as clay
Confined aquifer
Confining impermeable rock layer
Fig. 14-3, p. 308
22
Water Usage

• Irrigation watering crops
• Industry coolant (power plant)
• Domestic and Municipal drinking, sewage,
  bathwater, dishwater laundry

23
WATERS IMPORTANCE, AVAILABILITY, AND RENEWAL

• We currently use more than half of the worlds
  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).

24
Salinity

• The saltiness.

25
Niches
26
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).

27
Phytoplankton

• Description small drifting plants
• Niche they are producers that support most
  aquatic food chains
• Example cyanobacteria many types of algae

28
Zooplankton

• Description herbivores that feed on
  phytoplankton or other zooplankton
• Niche food stock for larger consumers
• Example krill small crustaceans

29
Nekton

• Description larger, strong-swimming consumers
• Niche top consumers in the aquatic ecosystem
• Example fish, turtles, and whales

30
Benthos

• Description bottom-dwelling creatures
• Niche primary consumers, decomposers
• Example barnacles, oysters, and lobsters

31
Freshwater Ecosystems
32
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
33
Flowing Water Ecosystems

• Because of different environmental conditions in
  each zone, a river is a system of different
  ecosystems.

34
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
35
Freshwater Streams and RiversFrom the Mountains
to the Oceans

• Water flowing from mountains to the sea creates
  different aquatic conditions and habitats.

Figure 6-17
36
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.

37
Downstream Characteristics

• Slower-moving water, less oxygen, warmer
  temperatures, and lots of algae and
  cyanobacteria.

38
Energy Source

• Gravity

39
Standing Water Ecosystems

• Lakes, ponds, etc.

40
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.

41
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).

42
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.

43
Limnetic Zone

• Open, sunlit water that extends to the depth
  penetrated by sunlight.

44
Profundal Zone

• Deep, open water where it is too dark for
  photosynthesis.

45
Thermal Stratification
46
Lakes Water-Filled Depressions
Figure 6-15
47
Definition

• The temperature difference in deep lakes where
  there are warm summers and cold winters.

48
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.

49
Causes

• During the summer, lakes become stratified into
  different temperature layers that resist mixing
  because summer sunlight warms surface waters,
  making them less dense.

50
Thermocline

• The middle layer that acts as a barrier to the
  transfer of nutrients and dissolved oxygen.

51
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.

52
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.

53
Freshwater Wetlands
54
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
55
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.

56
Marshes

• An area of temporarily flooded, often silty land
  beside a river or lake.

57
Swamps

• A lowland region permanently covered with water.

58
Hardwood Bottomland Forest

• An area down by a river or stream where lots of
  hardwoods, like oaks, grow.

59
Prairie Potholes

• These are depressions that hold water out on the
  prairie, especially up north in Canada. It is a
  very good duck habitat.

60
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.

61
Importance of freshwater wetlands

• They filter purify water.
• Habitat for many animals and plants.

62
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.

63
Estuaries
64
Definition

• A partially enclosed area of coastal water where
  sea water mixes with freshwater.

65
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.

66
Mangrove Forests

• These are along warm, tropical coasts where there
  is too much silt for coral reefs to grow. It is
  dominated by salt-tolerant 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.

67
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.

68
The Everglades

• Southern Florida to the Keys

69
Case Study Restoring the Florida Everglades

• The worlds largest ecological restoration
  project involves trying to undo some of the
  damage inflicted on the Everglades by human
  activities.
• 90 of parks 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.

70
Problems

• As Miami develops, it encroaches on everglades.
  Plus, it prompts people vs. wildlife. It is
  freshwater and local areas are draining it.

71
Restoring the Florida Everglades

• The project has been attempting to restore the
  Everglades and Florida water supplies.

Figure 12-10
72
Restoration

• Build huge aqueduct, or find other sources of
  fresh water an protect it federally under
  endangered species act, etc.

73
Problems
74
Too Much Water

• Problems include flooding, pollution of water
  supply, and sewage seeping into the ground.

75
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.

76
TOO MUCH WATER

• Comparison of St. Louis, Missouri under normal
  conditions (1988) and after severe flooding
  (1993).

Figure 14-22
77
TOO MUCH WATER

• Human activities have contributed to flood deaths
  and damages.

Figure 14-23
78

Forested Hillside
Oxygen released by vegetation
Diverse ecological habitat
Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Agricultural land
Steady river flow
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
79

After Deforestation
Tree plantation
Evapotranspiration decreases
Roads destabilize hillsides
Ranching accelerates soil erosion by water and
wind
Winds remove fragile topsoil
Gullies and landslides
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
80
Too Little Water
81
Examples

• Examples include drought and expanding deserts.

82
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 its a huge disaster (read pg.
  322 in text).

1997
1964
83
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 seas salinity has tripled and
  the water has dropped by 22 meters most likely
  causing 20 of the 24 native fish species to go
  extinct.

84
Aquifer Depletion

• This harms endangered species, and salt water can
  seep in.

85
Salinization of Irrigated Soil

• Water is poured onto soil and evaporates. Over
  time, as this is repeated, nothing will grow
  there anymore.

86
U.S. Water Problems
87
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.

88
Effects of Plant Nutrients on LakesToo Much of
a Good Thing

• Plant nutrients from a lakes environment affect
  the types and numbers of organisms it can support.

Figure 6-16
89
Effects of Plant Nutrients on LakesToo Much of
a Good Thing

• Plant nutrients from a lakes 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.

90
Effects of Plant Nutrients on LakesToo Much of
a Good Thing

• Cultural eutrophication
• Human inputs of nutrients from the atmosphere and
  urban and agricultural areas can accelerate the
  eutrophication process.

91
Mono Lake

• (like the Dead Sea) This has a huge salt
  concentration due to mans draining.

92
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 havent withdrawn their full
  allocations. See pg306.

93
The Colorado River Basin

• The area drained by this basin is equal to more
  than one-twelfth of the land area of the lower 48
  states.

Figure 14-14
94

IDAHO
WYOMING
Dam
Aqueduct or canal
Salt Lake City
Upper Basin
Denver
Grand Junction
Lower Basin
UPPER BASIN
UTAH
Colorado River
NEVADA
Lake Powell
COLORADO
Grand Canyon
Glen Canyon Dam
Las Vegas
NEW MEXICO
Boulder City
CALIFORNIA
Los Angeles
ARIZONA
Albuquerque
LOWER BASIN
Palm Springs
0
100 mi.
Phoenix
San Diego
Yuma
0
150 km
Tucson
Mexicali
All-American Canal
MEXICO
Gulf of California
Fig. 14-14, p. 318
95
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).

96
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
97
Groundwater Problems

• These include pollution, salt, and draining too
  much.

98
Other Effects of Groundwater Overpumping

• Sinkholes form when the roof of an underground
  cavern collapses after being drained of
  groundwater.

Figure 14-10
99
Groundwater Depletion A Growing Problem

• Areas of greatest aquifer depletion from
  groundwater overdraft in the continental U.S.

• The Ogallala, the worlds largest aquifer, is
  most of the red area in the center (Midwest).

Figure 14-8
100
Ogallala Aquifer

• This is the worlds largest known aquifer, and
  fuels agricultural regions in the U.S. It
  extends from South Dakota to Texas. Its
  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 its
  getting thinner. It is estimated that ¼ of the
  aquifer will be depleted by 2020.

101
Global Water Problems
102
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 worlds 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.

103
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
104
Core Case Study A Biological Roller Coaster Ride
in Lake Victoria

• Reasons for Lake Victorias 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.

105
Stable Runoff

• As water runs off from rain, its 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.

106
Drinking Water Problems
107
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?).

108
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.

109
Water-Soluble Inorganic Chemicals

• These include acids, salts, mercury, and lead.
  They make water unfit to drink.

110
Organic Material

• These include oil, gas, plastics, pesticides, and
  detergents.

111
Population Growth

• Problems include over-drawing fresh water,
  pollution, and over-building so that water cant
  seep into the ground.

112
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.

113
Water Management
114
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.

115
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.

116

Provides water for year-round irrigation of
cropland
Flooded land destroys forests or cropland and
displaces people
Large losses of water through evaporation
Provides water for drinking
Downstream cropland and estuaries are deprived of
nutrient-rich silt
Reservoir is useful for recreation and fishing
Risk of failure and devastating downstream
flooding
Can produce cheap electricity (hydropower)
Downstream flooding is reduced
Migration and spawning of some fish are disrupted
Fig. 14-13a, p. 317
117

Powerlines
Reservoir
Dam
Powerhouse
Intake
Turbine
Fig. 14-13b, p. 317
118
Case Study Chinas Three Gorges Dam

• There is a debate over whether the advantages of
  the worlds largest dam and reservoir will
  outweigh its disadvantages.
• The dam will be 2 kilometers long.
• The electric output will be that of 18 large
  coal-burning 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.

119
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.

120
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

121
Desalinization

• Description Removing salt from salt water
• Benefits Freshwater
• Problems Uses lots of energy costs 3-5Xs more
  money what do we do with the salt?

122
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.

123
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.

124
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.

125
INCREASING WATER SUPPLIES BY WASTING LESS WATER

• Sixty percent of the worlds 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.

126

Drip irrigation
(efficiency 9095)
Gravity flow
(efficiency 60 and 80 with surge valves)
Center pivot
(efficiency 8095)
Water usually pumped from underground and sprayed
from mobile boom with sprinklers.
Above- or below-ground pipes or tubes deliver
water to individual plant roots.
Water usually comes from an aqueduct system or a
nearby river.
Fig. 14-18, p. 325
127
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

128
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.

129
Overfishing and Extinction Gone Fishing, Fish
Gone

• About 75 of the worlds 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.

130
Trawler fishing
Fish farming in cage
Spotter airplane
Sonar
Purse-seine fishing
Trawl flap
Trawl lines
Fish school
Trawl bag
Drift-net fishing
Long line fishing
Buoy
Float
Lines with hooks
Deep sea aquaculture cage
Fish caught by gills
Fig. 12-A, p. 255
131
Purse Seines
132
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

133
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 free-floating 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.

134
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.

135
HUMAN IMPACTS ON AQUATIC BIODIVERSITY

• Area of ocean before and after a trawler net,
  acting like a giant plow, scraped it.

Figure 12-2
136
Population Growth and Pollution

• Each year plastic items dumped from ships and
  left as litter on beaches threaten marine life.

Figure 12-3