Q

APES 5.8 Impacts of Overfishing

Enduring Understanding:

  • When humans use natural resources, they alter natural systems.

Learning Objective:

  • Describe causes of and problems related to overfishing.

Essential Knowledge:

  • Overfishing has led to extreme scarcity of some fish species, which can lessen biodiversity in aquatic systems and harm people who depend on fishing for food and commerce.
  • Unregulated commercial fishing can lead to the extinction of certain fish species incredibly quickly
  • Note that commercial fishing also involves the capture and sale of crustaceans, sharks, cephalopods, etc.
  • Overfishing is the textbook example of tragedy of the commons

Techniques

Long-Line

  • Long lines with hooks along it is held up by buoys are dragged behind a ship
  • Fish are attracted to the baited hooks and are caught
  • These lines can be up to 28 miles long
  • These can be set at any depth as well, depending on what one is intending to catch
  • Very efficient
    • Lots of fish are caught in one pass
  • Unregulated fishing can reach overfishing very fast
  • There are many nontarget species that are also going to go for the bait and get caught

Drift Net/Gill Net

  • Long nets are dragged through the open ocean behind a ship
  • Can be set at different depths
  • The fish swimming nearby are caught by their gills on the nets and then eventually brought up
  • Has many of the same pros and cons of long line

Purse Seine

  • Large cylindrical net with drawstrings, let down under a boat
  • Fish filter in or schools are targeted
    • The bottom is closed, then the top
    • The net is then drawn up, bringing up a “purse” of fish
  • Can be up to 650ft across and deep
  • Can be tailored for a certain size/species
  • Same pros and cons

Trawling

  • A cone net is dragged through either open ocean or across the bottom of the ocean
  • When dragging across the bottom, everything is destroyed and the material is kicked up
    • Any ecosystem down there is obliterated

Sonar

  • How the fish are found
  • Very effective to find high concentrations of fish for best collection spots
  • Saves time and fuel
  • Can help catch fish too well
  • Can interfere with the sonar systems of other marine animals like whales

Impacts

Bycatch

  • Caught species that were not intended to be collected
  • Bycatch is almost never picked out and gently returned to the ocean
  • They are either processed with everything else or tossed back into the water, living or not
  • Luckily, there have been technological improvements where bycatch is not as common
    • But the majority of fishing boats do not have this and continue to harm nontarget species

Solutions

  • Setting catch limits based on maximum sustainable yield (MSY)
    • Study a fish species undisturbed to understand its population changed throughout the year
    • Make an informed decision on how many and be fished with minimal damage to the population
    • Ensure that the population can restore itself year after year
  • Limit age/size of fish that can be caught
    • For example, not catching fish that are in the prime of their breeding period
  • Modify techniques to reduce bycatch
    • A TED, turtle exclusion device, can be put on trawling nets to help turtles get out while keeping smaller fish in
  • Implement laws/treaties that protect critically endangered species
    • For example, the great white shark is protected by the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES)
    • Remember that there needs to be enforcement for these laws or parameters
    • Like subsidies for those who follow it, fines for those who don’t, debt forgiveness from one country to another, etc.