4.3F Conservation and Management of Global Fisheries (HL) Notes

Accurate Fish Stock Assessment

1. Accurate assessment of fish stocks and monitoring of harvest rates are crucial for ensuring that fishing remains sustainable.
2. Without these measures, overfishing can deplete fish populations faster than they can reproduce, leading to ecological imbalance and economic loss.

Methods of Measuring Fish Stocks

1. Catch Data Analysis

1. Data collected from commercial and recreational catches provide insight into the number and types of fish being caught.
2. Information includes species, size, and weight of the catch, helping to estimate the population’s distribution and abundance.
3. This data can reveal whether the population is stable, growing, or declining.

2. Tag and Recapture Studies

1. Individual fish are captured, tagged, released, and later recaptured to estimate population size, growth rate, and movement.
2. This method provides direct, field-based data on population dynamics.

3. Scientific Research Surveys

1. Conducted using research vessels that employ sonar, trawl nets, or underwater cameras to estimate population abundance.
2. Surveys can detect fish distribution patterns and age structures.

4. Logbook Monitoring

1. Fishers maintain logbooks recording catch quantities, fishing locations, and gear types.
2. In countries like the UK, vessels must submit data within 48 hours of docking.
3. These records help monitor compliance with quotas and detect changes in harvest rates.

Monitoring Harvest Rates

1. Harvest rates represent how much of a stock is removed by fishing.
2. Monitoring ensures catches remain below levels that threaten population sustainability.
   1. Electronic Monitoring Systems (EMS): Cameras and sensors on vessels record fishing activity.
   2. Catch-per-unit-effort (CPUE): Compares catch volume to fishing effort (e.g., hours or number of nets). A decreasing CPUE suggests declining stock abundance.
   3. Satellite Tracking: Monitors vessel locations to prevent illegal fishing and ensure compliance.

Risks of Harvesting at Maximum Sustainable Yield (MSY)

1. The Maximum Sustainable Yield (MSY) is the largest catch that can be taken from a fish population without causing long-term decline.
2. However, this concept has limitations.

1. Inaccuracy in Data

1. MSY calculations rely on estimates of carrying capacity, population growth rate, and reproductive rate.
2. These parameters fluctuate with temperature, salinity, and predation levels.

2. Positive Feedback Risk

1. Overharvesting reduces reproductive potential.
2. Fewer fish breed → smaller future generations → further decline.
3. Can cause rapid collapse of fish stocks.

3. Economic and Enforcement Challenges

1. Fishing crews may exceed quotas due to economic pressure or lack of monitoring.