Chapter 14: Wildlife, Fisheries,
and Endangered Species
Wildlife, Fisheries, and
Endangered Species
• Common history of exploitation, management and
conservation
• When saving a species, what is it we really want
to save?
– 1. A wild creature in a wild habitat, as a symbol to us of
wilderness.
– 2. A wild creature in a managed habitat.
– 3. A population in a zoo.
– 4. Genetic material only.
Wildlife, Fisheries, and
Endangered Species
• Involves science and values
• Many reasons for wishing to save
endangered species.
• Policies and actions differ widely depending
on goal chosen.
Single-Species Wildlife
Management
• Conservation and management often
viewed each species as a single population
in isolation.
– 1. The population could be represented by a
single number, its total size.
– 2. Undisturbed by human activities, a
population would grow to a fixed size, called
the “carrying capacity”.
– 3. Environment, except for human-induced
changes, is constant.
Single-Species Wildlife
Management
• This perception illustrated by the S-shaped
logistic growth equation.
• Two goals resulted:
– 1. For a species we intend to harvest: maximum
sustainable yield
– 2. For a species we intend to conserve: remain
at its carrying capacity
Single-Species Wildlife
Management
• This approach failed.
– None of the assumptions were true.
– Population cannot be represented only by a
single number.
– Do not remain at a fixed carrying capacity.
– The environment is not constant.
Single-Species Wildlife
Management
• Necessary to include an ecosystem and
landscape context for conservation and
management.
• New goals:
– For a species to be harvested: sustain a
harvestable population in a sustainable
ecosystem
– For a species that is threatened or endangered:
minimum viable population
Logistic Growth Curve
• Include the following ideas:
– A population that is small in relation to its
resources grows at a nearly exponential rate.
– Competition among individuals in the
population slows the growth rate.
– The greater the # of ind, the greater the
competition and the slower the rate of growth.
– Eventually, a point is reached, called the
“logistic carrying capacity”.
Logistic Growth Curve
– At this level, the # of births in a unit time
equals the number of deaths, and the population
is constant.
– A population can be described simply by its
total #.
– Therefore, all individuals are equal.
– The environment is assumed to be constant.
Carrying Capacity
• Has three definitions.
– 1. Logistical carrying capacity- the # of ind is
just sufficient for the available resources.
– 2. An abundance at which a population can
sustain itself w/o any detrimental effects that
would decrease the ability of that species to
maintain that abundance.
– 3. Optimum sustainable population- the max
pop that can be sustained indefinitely.
Logistic Growth Curve
• Another key concept is that the population
size that provides the max sustainable yield
– Exactly one-half of the carrying capacity.
– Other estimating MSY will lead to
overharvesting.
The Grizzly Bear
• An endangered species
– US Fish and Wildlife Service must meet the
requirements of ESA
– Became endangered as a result of hunting and
habitat loss.
– Removed because dangerous to humans and
livestock
The Grizzly Bear
• Restore to what?
– Past abundance (this is unknown)
– Also lack good estimates of present abundance
• Estimates include 1,200 in contiguous states, 32,000
in Alaska and 25,000 in Canada
– Based on Lewis and Clarks records (and a
number of assumptions)
• The # of grizzly bears in 1805 in the US was 12,000
– Another approach is to ask what the min viable
pop is.
The American Bison
• Brought close to extinction for 2 reasons
– Hunted to make coats that were fashionable in
Europe.
– Killed as part of a warfare against the Plains
peoples.
The American Bison
• Bison have recovered
– Profitable for ranchers
– Currently 200,000- 300,000 Bison
• Estimates of original herds range for 10s of
millions to > 50 million
– After Civil War protest over the slaughter
• 15 years later only 1000+/- remained
Improved Approaches to Wildlife
Management
• Four principles of wildlife conservation
– A safety factor in terms of population size, to
allow for limitations of knowledge and the
imperfections of procedures.
– Concern w/ the entire community of organisms
and all the renewable resources.
– Maintenance of the ecosystem of which the
wildlife are a part.
– Continual monitoring, analysis, and assessment.
Improved Approaches to Wildlife
Management
• Principles broaden the scope from a narrow
focus on a single species to inclusion of the
ecological community and ecosystem.
Time Series and Historical Range
of Variation
• Time series– set of estimates over a # of years.
• Historical range variation– the known range of abundance of a population
of species over some past time interval
– E.g. American whooping crane
Age Structure as Useful
Information
• An additional key to successful wildlife
management.
• E.g. salmon from the Columbia River, WA
– Shift in catch towards younger ages, along with
an overall decline in catch, suggests that the
fish were being exploited to a point at which
they were not reaching older ages.
– Early sign of overexploitation
Harvests as an Estimate of
Numbers
• Another method of estimating animal
populations is to use the # harvested.
• Previous animal abundance can also be
estimated by
– Catch per unit effort
• Assumes same effort by all per unit time (same tech)
• So if you know the total time spent in hunting and
catch per unit effort, you can estimate total pop
– E.g. bowhead whale
Fisheries
• Fish are an important food source
– 16% of the world’s protein
• Continental shelves provide 90% of fish
harvest
– Areas of high algae production to support food
chain
– Upwelling
Fisheries
• The world’s fish harvest has increased
greatly since the middle of the 20th century
– Increase in # of boats
– Improvements in technology
– Increases in aquaculture production
The Decline of Fish Populations
• Evidence that fish populations were
declining came from the catch per unit
effort.
– Suggests fishing depletes fish quickly
– About 80% decline in 15 years
• Commercial fisheries are mining a resource
not sustaining it.
The Decline of Fish Populations
• Chesapeake Bay
– Famous for oysters and crabs
– Breeding and spawning ground for many
commercially valuable species
– Food webs very complex
– Also influenced by runoff, introductions,
development, alteration in salinity
The Decline of Fish Populations
• Crisis has arisen for one of the living
resources most subjected to science-based
management.
– Management based on logistic growth curve
– Fisheries subjected to the “tragedy of the
commons”
The Decline of Fish Populations
• Fishing gear can be destructive to habitat.
– Ground-trawling equipment destroys the ocean
floor
– Long-line fishing kills sea turtles and other
non-target surface animals
– Large tuna nets have killed dolphins.
Can Fishing Ever be Sustainable?
• Few wild biological resources can sustain a
harvest at a level that meets even low
requirements for a growing business.
• We can turn to farming fish (aquaculture)
– Important food source in China, growing
worldwide
– Can create environmental problems
• E.g. Atlantic salmon fisheries cause water pollution
and loss of genetic diversity
The Current Status of
Endangered Species
• The # of species listed as threatened or
endangered increasing
• IUCN maintains a list known as the Red
List
–
–
–
–
20% of all know mammals at risk
31% of amphibians
3% of fish
12.5% of plants recently extinct or endangered
The Current Status of
Endangered Species
• The term endangered species as defined by the
ESA
– “Any species which is in danger of extinction
throughout all or a significant portion of its range…”
– With the exception of insect pests
• The term threatened species
– “Means any species which is likely to become an
endangered species w/in the foreseeable future
throughout all or a significant portion of its range.”
How a Species Becomes
Endangered and Extinct
• Local extinction
– Occurs when a species disappears from a part
of its range but persist elsewhere.
• Global extinction
– Means a species can no longer be found
anywhere
How a Species Becomes
Endangered and Extinct
• Rate of extinctions has varied over geologic
time
– From 580 million years ago until industrial
revolution about one species per year
– Rate of evolution of new species =or > the rate
of extinction
– Average longevity of a species 10 million years
• Other periods of “punctuated extinctions”
How People Cause Extinctions
and Affect Biological Diversity
•
•
•
•
By hunting or harvesting.
By disrupting or eliminating habitats.
By introducing exotic species.
By creating pollution.
How People Cause Extinctions
and Affect Biological Diversity
• The IUCN estimates 75% of the extinction
of birds and mammals since 1600 have been
caused by humans.
– Current extinction rate estimated to be 1,000
times greater than extinction rate in Pleistocene
Good News
• Species whose status has improved
– Elephant seal
– Sea otter
– Many bird species effects by DDT, including
bald eagle, brown pelican, white pelican,
osprey and peregrine falcon.
– Blue whale
– Gray whale
Can a Species be too Abundant?
• Sea lions now number 50,000 and have
become a problem in S.F. and S.B. Harbors
• Mountain lions in California
– Both mountain lion and human population
growing
– People building in lion habitat
– Attacks more common
The Kirtland’s Warbler and
Environmental Change
• Many species are adapted to natural
environmental change.
– If change eliminated the species can become
endangered
• Kirkland’s warbler in Michigan
– From 1951-1971 found to be declining
– Nest in jack-pine woodlands that are between
6-12 years old
The Kirtland’s Warbler and
Environmental Change
• Jack pine adapted to fire
– Cones open only after they are heated
– Trees intolerant of shade
– Abundance of dead branches
• Kirkland’s warbler requires change at short
intervals
– Fire approximately every 20-30 years
The Kirtland’s Warbler and
Environmental Change
• Fire suppression became the practice in
1927 and area replaced with economically
useful species.
• Now the Recovery Plan calls for prescribed
burns
Ecological Islands and
Endangered Species
• An ecological island
– an area that is biologically isolated, so a species
living there cannot mix w/ any other population
of the same species.
• Mountain tops
• Ponds
• Real geographic islands
Ecological Islands and
Endangered Species
• Almost every park is a biological island.
• How large must an ecological island be to
ensure survival of a species?
– Depends on species requirements
Using Spatial Relationships to
Conserve Endangered Species
• Red-cockaded woodpecker
– An endangered species
– Nests in old dead or dying pines
– Feeds on pine bark beetle which hare a pest to the tree
• A new approach to conservation
– Overlay a map of one’s habitat requirements over a
map of the other’s
– Co-occurrence can be compared and allow maintenance
of all three specie