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Over Fishing. Oceans 11. What is “fishing”?. Exploitation of marine organisms for sustenance, profit, or fun. Examples: Fish- cod, halibut, salmon, redfish, stripped bass… Shellfish Mollusks- clams, scallops, oysters, abalone… Crustaceans- crabs, shrimp, lobster… Reptiles- turtles

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oceans 11

Over Fishing

Oceans 11

what is fishing
What is “fishing”?
  • Exploitation of marine organisms for sustenance, profit, or fun.
  • Examples:
    • Fish- cod, halibut, salmon, redfish, stripped bass…
    • Shellfish
      • Mollusks- clams, scallops, oysters, abalone…
      • Crustaceans- crabs, shrimp, lobster…
    • Reptiles- turtles
    • Mammals- whales
why do we fish
Why do we fish?
  • Survival- many costal communities, particularly in developing countries, fish as a primary food source.
  • Recreation- fishing for fun.
  • Profit- commercial exploitation as a means of earning a livelihood.
what are some of the effects of fishing on humans
What are some of the effects of fishing on humans?
  • Sociology- in some places people need to fish to survive, in many others they simply want to fish as a mode of recreation.
  • Economics- individuals and regions can be dependent on fishing as a source of income.
  • Ecology- natural systems are easily disrupted by fishing.
what is over fishing
What is “over fishing”?
  • Removal of organisms from the marine environment by humans at a rate which cannot be sustained by the local ecosystem and therefore significantly alters natural ecosystem.


  • Fishing a population faster than it can replace itself; the population decreases in size as a result.
how big is the problem
How big is the problem?
  • The world marine catch is nearly 100 million tonnes per year.
  • 27 millon tonnes of by-catch (almost 1/3 of total catch) is thrown back dead into the ocean

Larger shrimps fetch a higher price, there is an incentive for discarding smaller fish as shown left.

what are some consequences of over fishing
What are some consequences of over fishing?
  • Much more complicated than reduction of one species
  • Trophic interactions
    • Examples: Salmon, killer whale, sea otter
  • Change in ecosystem structure
  • Loss of biodiversity
consequences by catch
Consequences…By - Catch!

By-catch is all non-target species caught with target species whether retained then sold or discarded

  • One example of by-catch is dolphins caught in tuna nets.
  • Often a problem with widespread use of unselective fishing gear
  • Bottom trawling disturbs everything on the ocean floor
collapse of the north atlantic cod fishery
Collapse of the North Atlantic Cod Fishery
  • Canadian cod stock severely depleted by local and distant water fleets
  • Canada declared Extended Fisheries Jurisdiction in 1979 to control and rebuild the fishery
  • Expected a rise in Total Allowable Catch (TAC) by 1985
  • Instead the fishery continued to decline and effectively closed in 1992
what happen
What Happen?
  • Mismanagement?
    • Fishing mortality exceeded sustainable level estimates
    • Stocks never achieved 50% of predicted total allowable catch
    • Canadian fleet over harvested cod
  • Upper limit was used to calculate harvest quota every year
  • When upper limit became insufficient to economically support fishery quota was increased
  • Short term economic gain won out over biology
the irony
The Irony
  • Biologists could see the catastrophe happening and were powerless to stop it
  • Long term economic loss (closure of fishery) far outweighs short term benefit
    • Economy loses more
now what
Now what?
  • How can we fish only to an extent which does not significantly alter it and the natural system in which it occurs?
  • Widely varying degrees of opinion.
  • Estimating populations
  • Estimating catch
  • Predicting population

change based on…

    • catch.
    • environmental statistics
    • limited knowledge of life history.
  • Tends to err on the side of over harvest
  • Doesn’t always consider ecology
some solutions
Some Solutions:
  • Marine Protected Areas
    • Effective if:
      • Large enough
      • Protect source populations
      • Effectively enforced
    • Currently well below 1% of marine systems are protected by MPA’s
  • Through regulation and laws control the total allowable catch
  • Effective regulation should be consistent with biology
  • International Compliance
responsible recreation
Responsible Recreation
  • Increasing evidence suggests impacts of recreational fishing
  • Conservation of marine fisheries impacts peoples livelihoods, survival, and recreation.
  • It influences the marine and terrestrial environments.
  • It is everyone\'s responsibility.
case study the impact of overfishing please put all answers on looseleaf
Case Study: The Impact of Overfishing***Please put all answers on looseleaf!
  • Vocab: list the definition of the following

fishstock, net growth rate,


  • Do case study but omit “l” and “m”
  • Do only question #2 from Questions for Application and Further Research