What does overfishing mean for the ocean? (Secondary) - Lesson Five

• Social Studies
• History
• +3
• 9th,10th Grade

Introduction

Lesson 5 – How do fishing methods impact the ecosystem? This lesson covers the different types of fishing methods used and how they impact the environment. Learning activities:  Research the different types of nets and what industry they are used by. Looking at how they contribute to by-catch and the potential damage to the ecosystem.

Instructions

Time: 45 minutes

Contact: [e-mail]
© Sea Shepherd 2022

Lesson 5 - How do fishing methods impact the ecosystem?

This lesson is provided by Sea Shepherd.  Sea Shepherd was founded in 1977 and is a marine conservation organisation working to protect the oceans and marine wildlife.  Sea Shepherd works globally on a range of issues impacting the oceans, running numerous direct action campaigns each year. 

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Introduction to IUU fishing and the impact of overfishing.

Types of nets - purse seine fishing

As discussed in previous lessons the types of nets used have a huge impact, such as purse seine fishing.  This lesson we will take a look at some of the other fishing methods used by the commercial fishing industries.

Introduction to IUU fishing and the impact of overfishing.

Types of nets - driftnets

There are numerous types of fishing styles and gear that are used to catch different species.

Driftnet refers to the setting of nets along the top of the ocean.  A driftnet is not anchored to the ocean floor, instead it hangs vertically in the water attached to ropes along the ocean surface with buoys and weights along the bottom. These nets are used to target pelagic fish, which simply means fish that are not in coastal waters, reefs or on the sea-bed. They live in open ocean and can be several kilometres under the surface.

Illegal poachers are often caught using illegal driftnets. In December 1991 the United Nations General Assembly approved a resolution banning the use of driftnets longer than 2.5kms in international waters, starting from 1993.  Yet over 25 years after the resolution poachers are still using driftnets. These types of nets are very destructive as they trap everything in their path.

Introduction to IUU fishing and the impact of overfishing.

Types of nets - gillnets

Gillnets are walls of netting set in a straight line that are very effective at trapping fish. Using floats on the surface the length of the lines can be adjusted to set the nets at varying depths. They are usually set several kilometres below the surface and can be many kilometres long.  They are used for deep living fish like toothfish.  Laws on gillnets vary between countries.

The use of gillnets goes back several centuries.  The traditional versions were made of organic materials, such as hemp, current nets are made from plastics and can float in the oceans for many years to come, trapping unsuspecting marine wildlife.  These earlier nets also had a much larger mesh that would allow younger fish to escape, allowing them time to grow and breed. Earlier cultures, which relied on fish, knew that to protect future fish numbers they had to take the more mature fish and only what they needed to survive.

Introduction to IUU fishing and the impact of overfishing.

Types of nets - longlines

Longlines are fishing lines that can run for up to 100 km with thousands of baited barbed hooks. They will catch everything that tries to go for the bait or any fish caught on the hooks, this includes sharks, seals or turtles.
 
These lines are also dangerous to sea birds, who will try to dive and take the bait from the hooks or the fish caught on them. There are two types of long lines, both consist of a main fishing line from which shorter lines containing hooks:
    Pelagic long line uses normal fishing line for the main line.
    Cable long line uses a heavy wire line for the main line.

Introduction to IUU fishing and the impact of overfishing.

Types of nets - trawling

There are two main types of trawling, the main one being bottom trawling.

Bottom trawling - This means the fishermen are dragging the nets along the seafloor scraping up everything in their path.  This method brings up with them all life and the habitat, including corals and sponges along with the fish, jellyfish, starfish. Any fish of reasonable size is sold separately, the rest is called ‘trash fish’ and is sent to be turned into fishmeal which can be used for food in fish farms, like prawn farms.  Bottom trawling is very destructive, wiping out habitat and ecosystem all in one go.

Introduction to IUU fishing and the impact of overfishing.

Types of nets - FAD's

These devices are designed to lure fish into an area to make it easier to find and catch fish.  The device can attract multiple species of pelagic fish.  

Small fish use the floating debris to hide from larger fish in the open ocean. Larger fish are also attracted and visit the debris in search of an easy meal.

There is no regulatory system in place to monitor the deployment and tracking of these devices.  These are used widely in the tuna fishing industry. They usually consist of a buoy or floats attached to the device, which is tethered to the ocean floor to keep it in one location.

Show this video (2.22 mins) from Sea Shepherd’s Operation SISO, which shows the retrieval of FADS.   https://www.youtube.com/watch?v=lrZ_g3ny0wM

www.seashepherdglobal.org

LEARNING ACTIVITIES

Refer Teachers Guide for Learning Activities.