Announcements

1
Announcements

• No lecture on Wednesday, November 24th
• Problem set is due that day
• Midterm Exam will be handed out on Wednesday in
  lecture
• Kevin will have office hours in Girvetz 2307 today

2
Summary from Friday

• Biodiversity
• ecosystem services
• control of ecosystem services
• redundancy
• keystone species
• island biogeography
• patterns of biodiversity on islands
• why islands can have high biodiversity
• biodiversity hotspots

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Two-minute quiz

• Based on what you know about patterns of
  biodiversity on islands, which of the channel
  islands would you expect to have the lowest
  biodiversity?
• What factors do you need to consider?

4
Factors to consider

• distance from mainland other islands
• age of the island
• size of the island
• land use history on the island
• history of invasions
• climate differences between islands
• current
• physical structure (elevation, etc.)

5
Fisheries

• A fishery can be defined as
• human harvest of wild marine resources for food
  and industry
• Its not just fish also crustaceans, mollusks,
  marine mammals, turtles, etc.

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People keep catching more
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Why do we care about fisheries?

• Humans must be fed
• cheap source of protein
• 16 of global human animal consumption
• Catch continues to rise
• hypothesis 1 fish are abundant, we can continue
  to harvest more and more
• hypothesis 2 we are approaching a maximum
  harvest and catch will stabilize
• hypothesis 3 we are already over-fishing and
  collapse is eminent

8
Where does fishing occur?

• Major fishing areas are closely associated with
  net primary production in the ocean
• estuarine areas
• continental shelf
• upwelling zones
• Many fishing zones are in international waters

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Where does fishing occur?
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How do people fish?

• Small-scale operations
• traditional methods
• small boats
• hand-pulled nets
• small area, near shore
• ? less developed countries

• Large-scale operations
• fully mechanized
• large vessels
• lots of technology
• larger area, offshore
• ? more developed countries

11
What do people fish?

• best are chosen first (optimal foraging theory)
• prey switching occurs when the best choice is not
  available

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What do people fish?

• higher trophic level fish are preferred
• larger
• more tasty
• eating lower on the food chain
• more environmentally sound
• not by choice- but because large fish are gone

boom and crash of anchovy fishery
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What do people fish?

• Fish occupy a variety of different niches
• Some are opportunists, some are competitors
• Competitors take longer to recover when
  over-fished
• Currently, even opportunist species are having
  difficulty recovering
• Cod has a huge reproductive capacity
• Despite complete closure of Georges Bank fishery,
  it has had difficulty coming back

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Is fishing efficient?

• ecological efficiency energy captured vs. energy
  used by the fisher
• large-scale fishery has higher bycatch

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Drift net fishing

• Notoriously high bycatch
• Wall of death

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Announcements

• Midterm will be handed out at end of class
• No class on Wednesday, Nov. 24th
• Ask questions about the problem set now!

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Summary from Monday

• Fisheries arent just fish
• Why do we care about fisheries?
• reduction in catch over time
• Where do people fish?
• What do people fish?
• How do people fish?
• the efficiency of fishing
• preventing and reducing bycatch

20
Two minute quiz

• True or False
• Purse seine nets are also known as walls of
  death due to the overwhelming bycatch of
  dolphins caught in them while fishing for tuna.
• The cod population on Georges Bank is having a
  difficult time recovering because they reproduce
  slowly.
• Aquaculture makes up about 50 of the total fish
  harvest of the world.

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Reducing Bycatch

• charismatic species get attention
• dolphins swim above schools of tuna
• 400,000 killed each year in 1970s and 1980s
• legislation passed for dolphin-safe measures
• drop one side of net to allow dolphins to swim
  out
• turtles swim near shrimp
• trawl nets have large turtle bycatch
• turtle excluder devices (TED)
• turtles naturally swim towards surface

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• Dolphins can be released from purse seine nets by
  dropping one edge of the net
• Longline fishing has a low risk of dolphin bycatch

23
Reducing Bycatch

• charismatic species get attention
• dolphins swim above schools of tuna
• 400,000 killed each year in 1970s and 1980s
• legislation passed for dolphin-safe measures
• drop one side of net to allow dolphins to swim
  out
• turtles swim near shrimp
• trawl nets have large turtle bycatch
• turtle excluder devices (TED)
• turtles naturally swim towards surface

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Is fishing efficient?

• agricultural efficiency energy produced vs.
  energy spent on production
• large-scale fishery spends much more energy

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ratio of 1 energy inputs energy outputs
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Is fishing efficient?

• economic efficiency benefits derived vs. costs
  incurred
• in a large-scale fishing operation, people make
  more money
• why? smaller operations just cover costs

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Is fishing efficient?

• economic efficiency benefits derived vs. costs
  incurred
• in a large-scale fishing operation, people make
  more money
• why? smaller operations just cover costs
• ? economics override ecological or agricultural
  measures of efficiency

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Tragedy of the Commons

• no one owns the sea, but everybody uses it
• first-come, first-served
• catch as much as you can as fast as possible
• who will police sustainable use?
• environmentalists?
• countries that depend on fishing?
• subsidies
• provide jobs
• encourage over-fishing

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Why are fisheries difficult to manage?

• Interface of biology and economics
• Biology is often oversimplified
• models can be difficult to build, because it is
  hard to know how many fish are out there
• what is the maximum of fish that can be removed
  without causing the population to decline?

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Building a simple model

• Assume logistic growth
• Density-dependent factors govern growth
• Sustainability is possible if
• rate of catch lt rate of growth

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• Maximum Sustainable Yield (MSY)
• The maximum harvest that is possible without
  reducing future harvest.
• Rate of catch is rate of growth

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Harvesting at MSY is dangerous

• Harvesting right at maximum sustainable yield
  should NOT be the goal because
• assumes the following are known exactly
• Population size
• Population growth rate
• Relationship between size growth
• Harvest level

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Now add economics

• Assumptions
• Prices for fish are constant
• additional cost of catching an extra fish is
  constant
• amount of fish caught per unit effort is
  proportional to population size
• Thus, rate of harvest rate of benefit or income

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Consider Effort

• Harvest benefit income gross profit
• Assumption
• harvest at rate of growth
• Effort (expressed as a percentage)
• Assumptions
• cost increases linearly with effort
• effort is low when population is high
• effort is high when population is low
• Fishers need to fish at a rate where benefit is
  at least equal to cost

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Announcements

• No class on Wednesday, Nov. 24th
• Ask questions about the problem set now!

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Summary from Wednesday

• Reducing bycatch
• turtle excluder devices
• Fishing efficiency
• agricultural efficiency
• economic efficiency
• Why fisheries are difficult to manage
• Tragedy of the commons
• Building a simple model

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Fisheries Models
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harvesting in the red zone
(greater than maximum
sustainable yield) is not sustainable
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harvest (benefit or income)
benefit matches cost at this point
cost
Rate of harvest (benefit or income) Cost
minimum population where fishing is economically
viable
K
0
Population Size
Effort
0
100
40
Expensive fishery
only profitable when population sizes are large,
likely to be sustainable
cost
benefit matches cost at this point
Rate of harvest (benefit or income) Cost
minimum population where fishing is economically
viable
K
0
Population Size
Effort
0
100
41
Cheap fishery
profitable at small population size, likely to be
unsustainable
benefit matches cost at this point
Rate of harvest (benefit or income) Cost
cost
minimum population where fishing is economically
viable
K
0
Population Size
Effort
0
100
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When a fish becomes rare, the price increases
population is further reduced by fishing pressure
benefit matches cost at this point
Rate of harvest (benefit or income) Cost
cost
minimum population where fishing is economically
viable
K
0
Population Size
Effort
0
100
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Government subsidies
maintain jobs, provide protein, but lead to over-
fishing
Unsubsidized cost
Rate of harvest (benefit or income) Subsidized or
Unsubsidized cost
Subsidized cost
minimum population where fishing is economically
viable
K
0
Population Size
Effort
0
100
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What causes over-fishing?

• Overly-simplistic models
• little attention to how age and size structure
  affect population growth
• little attention to density-independent factors
  that influence recruitment
• currents
• climate
• Bad management
• large government subsidies
• emphasis on short-term benefit rather than
  sustainability

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Can an over-fished fishery recover?

• Sometimes
• if enough breeding pairs still exist
• if the habitat has not been degraded by fishing
• if another species has not taken over the
  habitat, shifting food web dynamics

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Solutions to over-fishing

• Reduce bycatch
• Cut back on fishing in general
• loss of jobs
• loss of food
• loss of culture
• Aquaculture

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Aquaculture

• farming fish and shellfish for commercial use
• in 1977, 14 (by ) of fish sold were farmed
• in ponds, lakes, estuaries or coastal regions
• create a fenced off area for fish
• fertilization to increase primary productivity
• problems
• high density of fish ? disease
• pollution in water ? pollution in fish
• pathogens in shellfish
• fish kills in eutrophic waters

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Biological Magnification

• toxins accumulate in organisms
• often stored in fatty tissue
• magnification as you move up the food chain

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Salmon farm - Pacific Northwest
Fish cages Burma/Myanmar
Fish cages - France
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Aquaculture

• artificial ponds ? more controlled
• benefits
• flowing water flushes waste material away
• controlled diet and disease monitoring
• harvest when growth slows ? maximize profit
• artificial spawning
• problems
• high cost ? certain fish favored
• farmed fish escape into the wild (Tilapia in
  Everglades)
• destruction of natural habitat to make ponds

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Case Study Salmon Farming

• People like salmon
• Wild populations are threatened
• Farming used as a solution for providing people
  with the fish they want to eat

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Case Study Salmon Farming

• problems with salmon farming
• escapes
• interbreeding with wild population
• genetic engineering
• competing with wild populations
• farmed salmon are fed wild-caught fish
• 3 pounds of wild fish for 1 pound of farmed
  salmon
• pollution from waste and left-over food
• disease spread
• high density of fish in cages
• aesthetics

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Mangroves ? Shrimp ponds

• Destruction of
• nursery for wild fish
• flood control