Introduction to stock assessment
Unit 1.2: What is stock assessment?
Video transcript
[background music begins]
Narrator: Stock assessments aim to answer 3 main questions:
[Visual: The words, “Stock assessments aim to answer 3 main questions” appear.]
[Visual: A large number “1” appears in the top left of the screen.]
[Visual: The words, “What has happened to the stock? Reconstruct the stock's history and its response to past harvest and environmental conditions” appear.]
Narrator: 1. What has happened to the stock? Scientists use past data to reconstruct the stock's history and its response to past harvest and environmental conditions.
[Visual: A large number “2” appears in the top left of the screen.]
[Visual: The words, “What is the current state of the stock? Evaluate the stock's status under current harvest and environmental conditions” appear.]
Narrator: 2. What is the current state of the stock? Next, scientists evaluate the stock's status under current harvest and environmental conditions.
[Visual: A large number “3” appears in the top left of the screen.]
[Visual: The words, “What might happen to the stock? Project the stock's response to different management actions” appear.]
Narrator: 3. What might happen to the stock? Finally, scientists project the stock's response to different management actions.
[Music ends]
[Visual: Text fades out to black.]
[Visual: The Fisheries and Oceans Canada logo appears.]
[Visual: The Government of Canada logo appears.]
DFO is responsible for ensuring the sustainable use of fish in Canada as a renewable resource. The goal of stock assessment is to provide science advice to managers about the risks and uncertainty associated with taking different management actions.
Stock assessments use statistical and mathematical calculations to determine a stock's status and, where possible, project how it will react to different management actions in the future. The results of DFO's stock assessments are presented and validated during scientific peer review meetings. From this, science advice is generated to inform decision making.
Click through these boxes to familiarize yourself with more key terms:
Abundance
Abundance (N) is the total number of fish in a stock.
Biomass
Biomass (B) is the total weight of all fish in a stock.
Productivity
Productivity is the rate at which biomass is generated in a stock.
Spawning stock biomass
Spawning stock biomass (SSB) is the total weight of all fish in a stock that have reached reproductive maturity.
Recruitment
Recruitment occurs when new fish are added to a population. It is commonly measured when small or young fish grow large or old enough to be caught in a fishery (which may be affected by catch limits or gear type) or scientific survey.
Cohort
A cohort or year-class is all fish in a stock born in the same spawning year. The amount of recruitment determines the strength (in other words, relative abundance) of a cohort.
Fishing mortality
Fishing mortality (F) is the measure of deaths in a stock due to all fishing activities, including:
- targeted fishing
- bycatch and discards
- other incidental mortality in other fisheries
Natural mortality
Natural mortality (M) is a measure of deaths in a stock due to everything other than fishing, such as:
- predation
- disease
- prey availability
- competition for resources
Fishing effort
Fishing effort is a measure of fishing activity using metrics such as:
- the number of nets or lines used
- the number of fishing vessels deployed
- the number of hours spent fishing
Catchability
Catchability is a concept that reflects the efficiency of a fishery. It is the combination of availability (the likelihood that a fish will enter fishing gear) and selectivity (the likelihood of retention once a fish enters fishing gear). Gear selectivity is affected by gear design, such as mesh type and size, escape panels, and hook size.
Blue American Lobster in Nova Scotia.
Photo credit: Ben Zisserson, DFO
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