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.