BIOL 3500Ecology

1
Lecture 17

• BIOL 3500Ecology
• Chapter 18

2
Learning Objectives

• Contrast
• Clear- vs. selective cutting
• Define
• Maximum sustainable yield
• Sustainability
• Discuss
• The need for fisheries management
• Problems facing fisheries managers
• How your seafood choices can affect the biosphere
• Environmental costs of forestry

3
The Need for Management

• We rely heavily upon wild, native populations of
  plants and animals
• Seafood
• 71 from wild oceanic populations
• 10 from wild freshwater populations
• Only 19 farm-raised
• Forest products
• 90 from native forests
• Only 10 is farmed

4
First Recognized Fishery Impacted

• Late 1800s North Sea catches decline, cause is
  debated
• C.D.J. Peterson (Danish fisheries biologist)
  develops Peterson or Lincoln Index
• Mark-recapture of fish
• Early 20th Century WWI causes stop in fishing in
  North Sea
• After war, catches temporarily huge
• In time, catches decline again

5
Sustained Yield

• Yield amount harvested in a given time
• Sustainability the level of an activity that
  wont cause permanent environmental damage
• Maximum sustainable yield (MSY) highest
  possible level of harvest, without permanent
  damage to population

6
MSY and K
7
Math Notes on Yield

• dN/dT rN(K-N)/K qEN
• Similar to logistic growth, but has new term
• q is efficiency of predator
• E is the effort (ie size of fishing fleet,
  length of season)
• N is the number of prey
• 3 basic parts
• Exponential (rN)
• Logistic (K-N)/K
• Yield qEN

8
7th Inning Stretch
9
Fisheries Management

• Ideally, MSY is the goal
• Gives most food over long-term
• Sustainable
• Production of new individuals offsets the harvest

10
Problems for Fisheries Managers

• Data are difficult to obtain
• Population size
• Survivorship
• Reproduction
• Sex ratio
• Carrying capacity will change!
• Political concerns short-term economic gains
  easier to justify than long-term

11
Decline of the Pacific Sardine

• 1940s and 50s population over-exploited
• Healthy populations reproduce over 5 age classes
• Overharvest shifted reproduction to just 2
  youngest age classes
• 2 bad years for reproduction decimated population

12
Decline of the Great Lakes Fishery

• Before 1812, fishery largely untapped
• 1820, fishing industry established
• WW1, gill nets introduced
• 1950s nylon gill nets even deadlier
• Big fish now rare, perch and smelt increasing

13
Audubon Society and Seafood

• Audubon Society Wallet Card website
• Note this changes occasionally
• Questions
• Why are farmed Tilapia and farmed catfish
  environmentally sound?
• How does Audubon feel about wild Alaskan vs.
  farm-raised salmon? Why the difference?
• AnnieAppleseedProject
• Why are some species of tuna in both green and
  yellow?

14
Forestry Practices

• Clear-cutting
• Causes erosion
• Destroys biodiversity
• Selective-cutting
• Removes only mature trees, or small groups in
  patches

15
Rotation Time

• The time between tree harvests
• Shorter time (15-40 years) for pulp, fence posts
• Longer time needed for regular pine lumber
• Longest time (80 to 120 years) needed for
  hardwood furniture

16
Environmental Costs of Forestry

• Nutrient loss in plant biomass
• Soil erosion
• Impact on fisheries
• Both soil erosion and fertilizer bad for fish
• Biodiversity (only 1 species is replanted)