There

1

• Theres enough on this planet for everyones
  needs, but not enough for everyones greed
• Gandhi

2
Overexploitation

• Exploitation involves living off the land or sea,
  using plant and animal products for food,
  medicine, shelter, fiber, and other products
• It is the second most important threat to the
  survival of birds, plants, and mammals
• It is also the 3rd most important threat to
  freshwater fish extinctions

3
History of Overexploitation

• Humans have always been extractive by nature
  and primitive societies still largely follow
  this MO
• While much of this appears sustainable,
  archaeological and paleontological evidence
  suggests premodern people have been driving
  species to extinction for 1,000s of years

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History of Overexploitation

• Human colonization onto uninhabited islands or
  continents has typically been followed by mass
  extinction events of large-bodied vertebrates
  (e.g. Europe, parts of Asia, N and S Am,
  Madagascar and many Pacific islands
• We have awesome potential to kill (e.g. Passenger
  Pigeon, bison, and the Pau-Brasil tree)

5
History of Overexploitation

• Exploitation of plants and animals is a large
  interest not just in developing countries, but
  everywhere
• In the US, it is estimated hunting generates 700K
  jobs and has an economic impact of 61B (1)

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History of Overexploitation

• Impacts of Exploitation
• Most activities are directed at a single target
  species

7
Exploitation of Target Species

• Tropical Terrestrial Ecosystems
• Timber extraction is a major threat
• Approximately 5.8M ha of tropical forests logged
  each year (25 world)
• Single species approaches (e.g. mahogany) are
  difficult to compare to other methods, but it is
  better than clear cutting

8
Exploitation of Target Species

• A discrepancy between high inflation and slow
  growth rate of tree value creates the situation
  where cutting all trees irrespective of age is
  the best economic plan

9
Exploitation of Target Species

• Subsistence Hunting has been around for more than
  100K yrs, but consumption has greatly increased
• Impact varies tremendously across the tropics
• E.g. Sarawak (25K ton), Amazon (74-181K ton), C
  Af (1-3.7M ton)
• Much of this is too high (e.g. C Af is 6x higher
  than sustainable rates)

10
Exploitation of Target Species

• Hunting rates are unsustainably high across the
  Congo (solid) and Amazon (open).

Extraction rate
Sustainable Rate (20)
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Exploitation of Target Species

• Subsistence game hunting affects the structure of
  tropical forest mammal assemblages, as well as
  other groups through potential cascading effects

12
Exploitation of Target Species

• Nontimber forest products (NTFP)
• E.g. fruits, nuts, oil seeds, latexes, resins,
  gums, medicinal plants, spices, dyes, fibers, and
  may others
• The ethnobotanical studies have catalogued the
  wide variety of plants used by different groups
  (e.g. India, 6Kof 16K angiosperms used for
  traditional medicines, 79 of trees in 1ha of
  Amazon utilized)

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Exploitation of Target Species

• The traditional view of NTFP is usually assumed
  to be sustainable and is viewed as a promising
  alternative to exploitive practices and/or
  landclearing
• Extractive reserves are one of the of the fastest
  growing categories of protected areas in tropical
  forests
• The sustainability of these areas is not fully
  understood at this time

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Exploitation of Target Species

• However, in tropical rural areas, the combined
  value of consumption and sale of forest goods may
  not make them sustainable over longer time
  periods
• A boom in homeopathic remedies has resulted in
  gt150 sp of European plants becoming endangered
  and extirpation of many local populations

15
Exploitation of Target Species

• Another potential problem is the impact of
  harvesting on demographic processes and structure
• Overharvested populations will succumb to
  demographic collapse

16
Exploitation of Target Species

• Forestry
• Only 22 of the worlds original forest remain in
  large, relatively natural ecosystems
• Most are either boreal (48) or tropical (44),
  with only a fraction of temperate forests
  remaining (3)
• Many are currently threatened from increased
  pressure from logging

17
Exploitation of Target Species

• When commercial forestry expands into previously
  remote, roadless areas, it typically results in
  high levels of fragmentation of remaining stands
• A study of postlogging silviculture on wildlife
  suggests loss of structure (i.e. snags, woody
  debris) is particularly important to many species

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Exploitation of Target Species

• In Fennoscandia, 50 of the red-listed species
  are threatened because of forestry
• In WA, actively managed forests could support
  100 of biodiversity whereas timber management on
  a 50-yr rotation at the landscape level could
  support a maximum of 87
• Why? Largely structural simplification

19
Exploitation of Target Species

• Hunting of large mammals, small game, and
  waterfowl are also major target species in
  temperate regions
• Actively managing to increase game animals has
  proved wildly successful for many species (e.g.
  deer 500K to 30M)
• In TX populations are gt3M with 0.5M harvested
  annually

20
Exploitation of Target Species

• Waterfowl provide another resource to manage at
  high levels
• In 2001, approximately 19.4M birds taken
  involving 1.6M hunters
• While this may provide a skewed view of
  resources, their habitats frequently aid other
  species of concern (true of waterfowl, probably
  not for deer)
• Alternative source () for landowners

21
Exploitation of Target Species

• Aquatic systems, especially marine fisheries,
  have been well monitored
• Since the 1990s global catches have leveled off
  for the first time in history, despite better
  technology being constantly developed and utilized

22
Exploitation of Target Species

• Trends have leveled off (and fallen) with
  aquaculture increasing in importance

23
Exploitation of Target Species

• Wild stocks continue to decline due to poor
  management
• E.g. A recent survey of 232 stocks showed 83
  over the past 25yrs are on the decline
• E.g. Canadian cod 99.9 since 1960s
• By the way, are fish farms a good alternative to
  wild caught? Are they more productive?

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Exploitation of Target Species

• There are many species that are targets in the
  oceans
• There are several traits that many vulnerable
  species in common (easy to capture and
  biologically least productive)
• E.g. occupy shallow waters, form dense shoals in
  predictable locations, commercially valuable

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Exploitation of Target Species

• Chinese bahaba is a fish that meets this criteria
  (frequent byproduct of fishing)
• Its bladder is popular for medicinal properties
  (7x gold)
• Relatively late maturity

26
Exploitation of Target Species

• Some of these same traits apply to other groups
  that make species vulnerable
• E.g. abalone occur in shallow waters and species
  have been harvested from most valuable to
  leastdensities have changed from 1-5K/acre to
  lt1/acre

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Exploitation of Target Species

• Many freshwater taxa are subject to exploitation
  for food and other reasons
• In 2000, estimated 8.8M tons of inland fish
  caught (22.4M ton aquaculture)
• Economics in US, estimated 35M spent 38B spent
  fishing/yr
• Europe, estimate 21.3M anglers

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Exploitation of Target Species

• Populations of 4/7 sp of salmon (Onchorhyncus)
  listed as endangered
• Problem?
• Problem this may be the most visible fish
  species in the world
• While wild populations are supplemented with
  hatchery fish, they quickly show divergence
  (genetically, phenotypically) from wild
  populations

Overfishing and dams
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Exploitation of Target Species

• Other species are also exploited
• During 19th century, Ms of freshwater mussels
  were collected
• However, despite brief respite, currently Ms of
  kg are exported to Asia
• Currently, pollution, dams, dredging, siltation
  and invasives
• In US, currently 72 (of 297) considered
  endangered with 27 extinct

30
Impacts of Exploitation on Non-Target Species

• There are direct effects of exploitation, but
  there are also indirect effects
• In addition, there may be damage to the
  environment, causing changes in biological
  relationships or in landscapes or ecosystem
  functions

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Impacts of Exploitation on Non-Target Species

• Even logging directed at a single species can
  puncture a hole in the forest
• Even highly selective logging operations with
  modest levels of incidental damage to nontarget
  trees can generate enough structural disturbance
  by increasing desiccation and dry fuel loads
• Furthermore, mechanized logging itself triggers
  surface fires

32
Impacts of Exploitation on Non-Target Species

• Can you envision a scenario when loss of
  large-bodied frugivores may impact forest
  dynamics?
• Seedling recruitment is not clear under different
  levels of hunting pressure however, in some
  heavily hunted forest dispersal can decrease by
  60

90 in some forests
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Impacts of Exploitation on Non-Target Species

• In temperate regions, loss of large mammals can
  have deleterious effects
• Beavers are ecosystem engineers can dramatically
  alter the landscape
• Recently, they are making a comeback
• Loss of Grizzly bears had cascading
  effectsincreasing elk pop(s) and moose,
  decreasing riparian habitat, reducing songbird
  populations

34
Impacts of Exploitation on Non-Target Species

• When predators are excluded, some herbivore
  populations can get extremely abundant, altering
  plant communities (loss of 95 of a rare orchid
  in WV due to excessive deer browsing)

35
Impacts of Exploitation on Non-Target Species

• Marine fisheries are estimated to have a global
  by-catch of roughly 27M tons/yr
• How? Trawl fisheries, drift nets and gill nets
• Shrimp trawlers (with relatively small mesh size)
  are estimate to discard 5kg of by-catch for 1kg
  of shrimp

36
Impacts of Exploitation on Non-Target Species

• Is this just impacting fish?
• 19/21 Albatrosses (attempting to eat baited fish)
• Can they really be that impactful?
• Each boat may set 1,000s of hooks/day with a
  total of gt250M hooks/yr
• It is estimated that 20K sea turtles are caught
  in the Mediterranean/yr on hooks
• Up to 120K sea snakes taken in Aust/yr

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Impacts of Exploitation on Non-Target Species

• We were talking about the impact of exploitation
  on non-target species (e.g. by-catch, albatrosses)

38
Impacts of Exploitation on Non-Target Species

• Unfortunately there are many freshwater examples
  of problems
• No individuals caught since 2001
• May reach 300 kg
• Only spawn in specific rapids

39
Impacts of Exploitation on Non-Target Species

• Indirect freshwater effects
• Salmon bring a huge nutrient load into freshwater
  systems as they return to spawn and die (8x inc
  in macroinverts)
• Early evidence for a correlation between size of
  salmon runs from 1924 to 1994 and tree-ring
  growth rates

40
Biological Theory to Sustainable Exploitation

• Density dependent factors impacting the natural
  rate of increase

41
Biological Theory to Sustainable Exploitation

• Why should we think populations to be able to
  withstand the elevated mortality that occurs with
  most forms of exploitation?
• There may be compensatory birth and growth rates
  to somewhat offset elevated death rates

42
Biological Theory to Sustainable Exploitation

• If a large number of individuals are going to die
  from one time to the next, is thinning the
  equivalent?
• An easy way to approach the question of elevated
  mortality is to start with the logistic model,
  which gives the number of individuals at time t
  as

Nt Nmax / 1 ((Nmax/N0 ) 1)e-rt
43
Biological Theory to Sustainable Exploitation

• Where Nmax is the carrying capacity (which is not
  stable)
• Sometimes biomass is substituted for population
  size (B for N). Why?

Nt Nmax / 1 ((Nmax/N0 ) 1)e-rt
44
Biological Theory to Sustainable Exploitation

• Why should we think populations to be able to
  withstand the elevated mortality that occurs with
  most forms of exploitation?
• There may be compensatory birth and growth rates
  to somewhat offset elevated death rates

45
Biological Theory to Sustainable Exploitation

• Why should we think populations to be able to
  withstand the elevated mortality that occurs with
  most forms of exploitation?
• There may be compensatory birth and growth rates
  to somewhat offset elevated death rates

46
Biological Theory to Sustainable Exploitation

• Classic logistic population growth to a maximum
  pop(n) size

47
Biological Theory to Sustainable Exploitation

• The growth of this classic population is
• What is the relationship N Nmax ?
• Consider if the pop(n) is being exploited at a
  steady rate, then its rate of change per unit
  time (dN/dt) will be the difference between its
  surplus production and the yield (Y)

g(N) rN (1 N/Nmax)
dN/dt rN (1 N/Nmax) - Y
48
Biological Theory to Sustainable Exploitation

• Sustainable yield occurs at 50 of maximum pop(n)
  sizewhy?

49
Biological Theory to Sustainable Exploitation

• Stabilities of exploitation
• In theory, we have discovered where the MSY
  occurs
• Problem?

50
Impacts of Exploitation on Non-Target Species

• In terms of simple population dynamics, it is the
  surplus that can be removed in any given year
• Depending upon population size, that will vary
  greatly

51
Biological Theory to Sustainable Exploitation

• MSY occurs at intermediate pop(n) size

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Biological Theory to Sustainable Exploitation

• Stability of Exploitation
• There is a theoretical number of individuals
  takenany problems?
• Lots
• People rarely do as they are told
• Conditions do not always favor optimal growth

53
Biological Theory to Sustainable Exploitation

• Constant Quotas
• Constant quotas are determined when the number of
  individuals removed is independent of the
  population size (another way to thinksubtract Y
  from the surplus yield, rather than making Y
  proportion to N)
• This has been used to set many fishery quotas
  (e.g. Peruvian anchovies)
• Is this a good approach?

54
Biological Theory to Sustainable Exploitation

• Consider 3 levels of constant quota harvest (no
  relationship to N)

High Quota will always crash MSY Quota even
when above NMSY, pop(n) will decline Finally,
even Low Quota will decline if initial pop(n) is
low
55
Biological Theory to Sustainable Exploitation

• Proportional exploitation (constant effort)
• This approach ties takes to pop(n) size
• As long as the exploitation rate is below the
  intrinsic rate of natural increase, r, then all
  equilibria are stable
• Has been shown to be important in tracking actual
  take rates and the importance of monitoring
  pop(n) sizes

56
Biological Theory to Sustainable Exploitation

• Consider the size of the yield (Y), the
  exploitation rate (E) and the population size.

g(N) rN (1 N/Nmax)
Y EN (proportional exploitation) Substituting
rN (1 N/Nmax) EN And as long as Eltr then N
Nmax (1- E/r)
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Biological Theory to Sustainable Exploitation

• As long as E lt r, all equilibria are stable

58
Biological Theory to Sustainable Exploitation

• How do the two approaches compare?
• Examine data from Marten harvests
• Both approaches do relatively well at low rates

59
Biological Theory to Sustainable Exploitation

• Threshold Exploitation involves the use of pop(n)
  size thresholds to determine not only the rate of
  exploitation but also whether exploitation should
  take place at all
• Since all pop(s) fluctuate, it is this excess
  that will be harvested
• If a surplus does not exist, no take will be made
  (i.e. very safe approach)

60
Comparison of Approaches to Sustainable Yields

• There are many approaches to determining what
  approach should be established for sustainable
  yields
• Various strengths and weaknesses (think of a
  demographic model with all the parameters)

61
Comparison of Approaches to Sustainable Yields

• Surplus Production models are also called surplus
  yield models or production models
• Frequently used in fisheries
• If you know how yields have responded to
  different levels of exploitation effort over
  time, then you could estimate the dome-shaped
  yield curve (thus not requiring new data)

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Comparison of Approaches to Sustainable Yields
63
Comparison of Approaches to Sustainable Yields

• There are many pitfalls with this approach
  including it treats all years as replicates
• Consider Cod
• The largest fisheries collapse ever (Peruvian
  anchovy) in the early 1970s when it adopted a
  surplus production model that suggested levels
  were safe

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Comparison of Approaches to Sustainable Yields

• Yield-per-recruit models were developed
  originally as part of the dynamic pool concept
  in the landmark fisheries book written by
  Beverton and Hold (1957)
• The dynamic pool attempts to keep track of
  separate processes that add to a population (e.g.
  recruitment and growth) or subtract from it (e.g.
  natural and catch mortality)

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Comparison of Approaches to Sustainable Yields

• Imagine a species that becomes more valuable as
  it ages
• If exploitation is weak, most of the fish or
  trees will be large when taken
• If you wait too long, natural death occurs
• This model searches for the level of mortality
  that maximizes the yield under this tradeoff
  between numbers and value

66
Comparison of Approaches to Sustainable Yields

• Once the level of mortality has been found that
  maximizes the yield per recruit, we can calculate
  the total yield that will be obtained from a
  given level of mortality, if we know how many
  recruits are coming each year
• This approach is used in many countries
• Does require info about how the value (often
  size) of individuals increases with age, as well
  as an estimate of natural mortality rates

67
Comparison of Approaches to Sustainable Yields

• For some species ( or conservation) there is
  enough data for full-blown population models
• These models combine data on all demographic
  parameters (survival, age at maturity,
  age-specific mortality)

68
Comparison of Approaches to Sustainable Yields

• Assessment of population growth rates is a common
  practice to deduce whether populations are
  declining as a result of direct exploitation or
  exploitation of their habitats
• Another use is to diagnose the reasons for
  population declines and to suggest the likelihood
  of success of various management strategies (e.g.
  loggerhead turtles, eggs vs. older adults)

69
Comparison of Approaches to Sustainable Yields

• Projected annual strandings for Kemps ridley
  seas turtles under levels of compliance by
  shrimpers (current to full compliance)

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Comparison of Approaches to Sustainable Yields

• Adjustments based on recent results
• If we can monitor either the population itself or
  the numbers of individuals taken, we can adjust
  the quotas each yr based upon new information
• This is currently the approach for waterfowl and
  mammal hunting in the US (read Box 8.1 on martens)

71
Comparison of Approaches to Sustainable Yields

• Demographic rule of thumb
• Parameter-dependent models are useless for the
  vast majority of the worlds exploited
  specieswhy?
• One of the best-known rules of thumb models to
  determine if exploitation of tropical mammals can
  be sustainable
• It assumes maximum potential production (Pmax)
  occurs at about 60 of K

Pmax (0.6D x ?max) 0.6D
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Comparison of Approaches to Sustainable Yields

• Of course there are many potential problems with
  this simplistic model
• There are problems with cull rates compared to
  mortality rateswhy?
• Are density estimates accurate? Why?
• Estimating ?max is not easy and variable

73
Comparison of Approaches to Sustainable Yields

• There are spatial and temporal problems of
  establishing accurate production numbers

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Comparison of Approaches to Sustainable Yields
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Overexploitation