Maximum sustainable yield (MSY) is the highest annual catch of a fish population that can theoretically be harvested repeatedly without reducing the population over time. In IB ESS Subtopic 4.3, MSY should be used to help set fishing quotas.
How Does MSY Work?
A fish population increases through reproduction and decreases through natural mortality and harvesting. If the annual harvest equals or remains below the population's annual net increase, the stock can replace the harvested fish:
Population growth is usually slow when the stock is very small because few mature individuals can reproduce. Growth also slows near carrying capacity because competition for resources increases. MSY therefore aims to maintain the population where its net growth is high, allowing a relatively large catch while preserving the breeding stock.
| Situation | Likely consequence |
|---|---|
| Catch is below MSY | Fish stock is more likely to remain stable or increase |
| Catch equals MSY | Maximum theoretical long-term catch, assuming estimates are accurate |
| Catch exceeds MSY | Stock declines, potentially causing fishery collapse |