SUSTAINABLE YIELD PRACTICE PROBLEMS
ANSWER KEY
1. Sustainable yield can be defined as
I. annual growth and recruitment – annual death and emigration
II. (total biomass t time t + 1) – (total biomass at time t)
III. The highest rate at which natural capital can be exploited without reducing its original stock.
a.
b.
c.
d.
I and II only
I and III only
II and III only
I, II and III
2. In a deer population of 1000, each year an average of 100 die from natural causes and 250 are born.
Assuming no immigration or emigration, the sustainable yield is _____.
a. 100
b. 150
c. 350
d. 1150
3. For a particular year, for the fishing grounds of an island nation, assume:
R = the biomass of young fish reaching harvestable size
G = the growth in biomass of fish already of harvestable size
M = the loss of fish through death and emigration
B = the biomass of the total fish population at the start of the year
The sustainable yield of the fishing grounds could be calculated using which of the following?
a. R + G – M
b. M – M
c. B + R + G – M
d. R + G
4. What is the maximum sustainable yield for a resource?
a. The difference between natural capital and natural income
b. The rate of decrease in natural capital
c. The sustainable rate of harvest of a resource
d. The point at which the original stock is depleted
5. What is the maximum sustainable yield of a crop equal to?
a. Natural income
b. Natural capital
c. Carrying capacity
d. Total biomass
6. If the harvesting of a fish population were to exceed the sustainable yield in one year, this would mean
a.
b.
c.
d.
The natural capital had been reduced but the natural income had increased.
The natural capital remained the same but the natural income had been reduced.
The natural capital had been reduced and the natural income would be reduced in the following year.
The natural capital remained the same but the natural income would be reduced in the following year.
7. Resources that have a sustainable yield equal to their natural productivity are
a. Natural income
b. Renewable natural capital
c. Replenishable natural capital
d. Non-renewable natural capital
8. A forest has a volume of 800 000 million m3 of timber. In one year, 150 000 m3 of timber are harvested and
100 000 m3 of timber are added by normal tree growth. Which of the following statements is correct with
regard to this year?
a. The maximum sustainable yield was 800 000 million m3 of timber
b. Harvesting exceeded the natural income by 100 000 m3 of timber
c. The natural capital remaining was 750 000 m3 of timber
d. The natural income was 100 000 m3 of timber
9. Which of the following statements about natural capital is correct?
a. Coal and timber are examples of non-renewable natural capital.
b. Replenishable natural capital cannot be naturally replaced at a rate comparative to its consumption.
c. Metals are renewable natural capital because they are not destroyed and can be recycled.
d. Carbon dioxide and oxygen are examples of replenishable natural capital.
10. Sustainable yield can be defined as
I. (annual growth and recruitment) – (annual death and emigration)
II. The gain in biomass (or energy) per unit time remaining after subtracting metabolic and other
natural losses
III. The highest rate at which natural capital can be exploited without reducing its original stock
b.
c.
d.
e.
III only
I and II only
II and III only
I, II, and III
11. The diagram below shows the energy flow in a river ecosystem in temperate latitudes. All energy values are
kJ m-2 yr-1. Calculate the sustainable yield of older fish.
SY = inputs – outputs
SY = ( 95 + 17 + 615 + 4 + 60 + 45 + 2780 ) – 3500
SY = 3616 - 3500 = 116 kJ m-2 yr-1
12. The graph below shows the commercial catch of salmon (a species of fish) in a river system in North America
between 1866 and 1966.
a. Identify the lowest catch between 1870 and 1966 and state the year in which it was recorded.
Catch 2.0X103 tonnes (accept 1.7 to 2.3X103 tonnes)
Year 1959 (accept 1959-63)
b. Describe and explain the shape of the graph. (4pts max)
Descriptions: (3 pts max)
 Graph starts at close to zero in 1866
 Large increase in catch/yield until 1879
 Long-term decline after 1879
 Substantial fluctuations from year to year
 e.g. approximately 8X103 to 16X103 tonnes
between 1885 and 1920s
 yet range remained approximately
constant for 35-40 years
(ANY OTHER REASONABLE POINT.
CANNOT SIMPLY REPEAT MINIMUM
VALUE ALREADY GIVEN CREDIT IN
PART A.)
Explanation:
 Specific and relevant example of pollution affecting salmon e.g. acid
rain
 Initially high because resources previously not exploited
 Fluctuations might be due to weather/climate
 Fluctuations might be due to prices/economic factors
 Fluctuations might be due to predator-prey relationships
 Long-term decline may be due to overexploitation/exploitation above
sustainable yield
 Linked to improvements in fishing technologies
 A reduction in catch suggests a reduction in population size
(ANY OTHER REASONABLE POINTS. AT LEAST ONE
“EXPLANATION” POINT IS NEEDED TO ACHIEVE FULL MARKS. )
c. State what is meant by the term sustainable yield.
The rate of increase in natural capital/natural income
The rate at which a resource can be used without the original stock being depleted
The cropping of a resource at such a rate that its long-term productivity is not degraded (OWTTE)
d. State and explain how the graph might help in the estimation of the sustainable yield from the fishery.
Sustainable yield may be estimated by long-term monitoring of catch
Catch/yield of 19X103 tonnes around 1880 may have been above sustainable level
As this high catch was followed by major fall
Yield of 8X103 to 16X103 tonnes between 1885 and 1920s may have been unsustainable
As catch recovered after each fall
As population declines, so sustainable yield declines
So long-term decline from 1930s onwards (7X103 to 2X103 tonnes)
May be due to catch being above sustainable yield
(ANY OTHER REASONABLE POINTS)