Syllabus Edition
First teaching 2024
First exams 2026
Fish Stock Assessment & Sustainable Harvesting (HL) (DP IB Environmental Systems & Societies (ESS))
Revision Note
Fish Stock Assessment & Sustainable Harvesting
Importance of assessing fish stocks and monitoring harvest rates
Fish stock assessment is the process of estimating the size and health of fish populations in a given area
Accurate assessment is essential to understanding the number of fish available for sustainable harvesting
It helps ensure that the population can reproduce and thrive over time
Monitoring harvest rates involves tracking how many fish are caught by fisheries over a specific period
Sustainable fisheries aim to ensure that the rate of fish caught does not exceed the population’s ability to reproduce
This helps to prevent overfishing
Why assessment and monitoring matter:
Without accurate assessments, there is a risk of overestimating fish stocks
This can lead to overfishing and population collapse
Monitoring ensures that fisheries
Follow regulations
Maintain harvest rates that do not threaten the long-term survival of fish populations
Methods of assessing fish stocks and monitoring harvest rates
Trawl surveys:
Dragging nets through the water to sample fish populations
Provides data on species, size, and abundance for stock estimates
Acoustic surveys:
Uses sonar to detect fish schools by bouncing sound waves off them
Ideal for pelagic species like herring and mackerel
Allows for quick, large-area population assessments
Landing records (catch data):
Collects data from official port records
Tracks the amount of fish brought ashore by fisheries
Helps compare actual catches with estimated sustainable levels
Ensures harvest rates do not exceed stock regeneration
Portside sampling:
Collects data on fish size, age, and species at ports
Provides insights into the health and reproductive potential of stocks
On-board observations:
Trained observers on fishing vessels record catch details and monitor compliance
Observers provide independent verification of the data, ensuring accurate reporting of catches
Reduces underreporting and bycatch misreporting
Research surveys:
Independent scientific expeditions assess fish stocks using trawl or acoustic methods
Provides unbiased, reliable data on population trends
Tag and recapture surveys:
Fish are tagged, released, and later recaptured to estimate population size and movement
Often used for highly migratory species like bluefin tuna
Helps track fish growth rates and migration patterns
Risks of fishing at maximum sustainable yield (MSY)
MSY is the largest number of fish that can be caught each year without reducing the fish population in the long term
MSY is only an estimate because:
The MSY value is calculated using models
These models are based on assumptions about fish population growth, mortality rates, and environmental conditions
Because fish stocks and ecosystems are complex, MSY estimates are always uncertain and can be inaccurate
If fisheries aim to harvest at the exact MSY, they risk overestimating and depleting the population
Risks of exceeding MSY:
Overfishing occurs when the harvest rate exceeds the population’s ability to reproduce
A reduction in fish numbers can lead to positive feedback
The reduced population becomes even more vulnerable to overfishing because there are fewer mature individuals to reproduce (lower reproductive potential)
This leads to a rapid decline in fish stocks
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