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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 l.jpg

Over Fishing

Oceans 11

What is fishing l.jpg
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 l.jpg
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.

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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.

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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.

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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.

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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

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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

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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

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What Happen?

  • Mismanagement?

    • Fishing mortality exceeded sustainable level estimates

    • Stocks never achieved 50% of predicted total allowable catch

    • Canadian fleet over harvested cod

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  • 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

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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

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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.

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  • 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

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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

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  • Through regulation and laws control the total allowable catch

  • Effective regulation should be consistent with biology

  • International Compliance

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Responsible Recreation

  • Increasing evidence suggests impacts of recreational fishing

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  • 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 l.jpg
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