A fishing cooperative catches one species of fish from a large lake. Scientists carried out repeated trials using two net mesh sizes in the same area for the same length of time.
Each test net was surrounded by a fine-mesh cover. Fish that escaped through the test mesh were trapped in the cover. No adult fish were found in the cover. The young fish in the cover were counted and then released alive.
The total number of fish entering the net system was the number retained in the test net plus the number trapped in the cover.
The table shows the mean results per trial.
| Mesh size in mm | Total number of fish entering the net system | Number of young fish that escaped through the test mesh |
|---|---|---|
| 40 | 1250 | 110 |
| 60 | 1180 | 300 |
Calculate the number of fish retained in each test net.
The cooperative must choose one of the mesh sizes. It has set two targets:
Evaluate which mesh size the cooperative should use.
87 exam-style questions on AQA GCSE Biology 7.5 Food production, covering 7.5.1 Factors affecting food security, 7.5.2 Farming techniques, 7.5.3 Sustainable fisheries, and 7.5.4 Role of biotechnology. Each one has a worked solution and a mark scheme showing where the marks go.