# Explain how the capture-recapture method can be used to monitor changes in a population of water voles living along a riverbank over several years, and why accurate population estimates are important for conservation.

> OCR GCSE Biology A: Gateway Science (J247) — B6.1 Monitoring and maintaining the environment · Explain · 4 marks

> Water voles are a protected species in the UK whose populations have declined sharply due to habitat loss and predation by invasive American mink. Conservation organisations regularly monitor water vole populations along riverbanks to inform management decisions.

## Mark scheme (4 marks)

1. Animals are captured, marked in a way that does not harm them, and released back into the habitat
2. Time is allowed for marked individuals to redistribute/mix with the rest of the population before a second sample is captured
3. The proportion of marked individuals in the second sample is used to estimate the total population size
4. Accurate population estimates allow conservationists to identify whether the population is declining, so that appropriate conservation management can be put in place to protect the species/habitat

## Key terms

- [capture-recapture](https://www.gradenine.co.uk/glossary/capture-recapture)
- [population](https://www.gradenine.co.uk/glossary/population)
- [conservation](https://www.gradenine.co.uk/glossary/conservation)

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-capture-recapture-method-can-cafbf7c5) · Published by Druglandscape Ltd.