DP Biology: Fisheries and populations

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Fisheries and populations

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  • Fisheries and populations

In this activty students look at the advantages and the limitations of the three methods of estimating fish populations, echo-location, capture-mark-release-recapture and study research about the cod stocks of tha Baltic sea and two theories about algal blooms, one top down theory and another bottom up.

Lesson Description

Guiding Question

A 'bell activity' for the student or a question that will be answered during the lesson.

Activity 1 - Sustainable fisheries. Problems and Methods

Look at the slides which outline three methods of population estimation in fisheries and their limitations.

  

Questions to answer

  1.  Outline why is important to understand the whole food web, in order to understand the sustainability of fish populations?

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  2. Explain what the consequence to the smaller fish would be of taking away too many top predators through overfishing.

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  3. List two assumptions made when using Fishing catch size to estimate populations of fish.

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  4. Name an advantage and a limitration of the population estimation methods described in the slides.
    Method. . . . .   Advantage   . . . . . .. . . . . .    Limitation    . . . . .
    Echo-location of fish
     
    Capture-Mark-Release-Recapture
     
    Fishing catch records
     
  5. Outline three examples of international measures which can be taken to improve fisheries management
    (other than estimating populations).

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  6. Describe how overfishing of a top predator can reduce the top down control of algal blooms.

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  7. Outline the bottom up control of algae, and describe how it normally controls populations of aquatic algae.

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Make introductory notes using the worksheet below. Conserving fish stocks - problems and methods student worksheet

Activity 2 - Baltic fisheries managment

Carry out the analysis on the Fisheries management student worksheet.

This exercise helps students to consider the limitations of tagging and catch analysis.

Activity 3 - Reading about Algal blooms and overfishing

Read the following articles to find out more about how the top predators in an ocean ecosystem can have a top down effect on algal growth, and if they are removed what happens.

https://www.esa.org/esablog/research/reduced-predator-populations-lead-to-algal-blooms/

https://www.nature.com/news/2009/091201/full/news.2009.1116.html

Teacher's notes

The first activity is an introduction to some of the issues around fisheries management.  Obviously fish populations are key to this.

Students could look through the slides and make notes, or the teacher could lead a class discussion and then students complete the notes.

An alternative would be to give a slide to a pair of students and then ask them to research a little and explain this to the class.

There are model answers here Sustainable fisheries - model answers

In activity two, a case study of fisheries conservation, taken from the Baltic sea, is used to give students an opportunity to look at some real data and to consider the limitations of the capture-mark-release-recapture method.

There are model answers here: Fisheries management - model answers 

Activity three is really extension work for students who are interested to read a little more.