Introduction to stock assessment
Unit 1.3: Stock status and reference points
The Precautionary Approach Policy defines 3 stock status zones to categorize stock health:
- healthy
- cautious
- critical
These zones are created by defining reference points that act as boundaries between zones. Stock status can be used to:
- inform total allowable catch
- drive harvest decision rules
- evaluate how well harvest strategies are working
Reference points are used as targets to achieve or as limits to avoid. There are many different methods for estimating reference points that reflect:
- data availability
- biological knowledge of the species
- model availability
Reference points can be updated as:
- new data become available
- new models are developed
- stocks experience changes in productivity
Reference point definitions
Limit reference point
Limit reference point (LRP) is the stock status below which serious harm is occurring to the stock. There may also be impacts to the ecosystem, other species, and long-term loss of fishing opportunities.
Upper stock reference point
Upper stock reference point (USR) is a threshold below which fishing must be reduced to avoid reaching the LRP. The USR must be set at an appropriate distance above the LRP to provide sufficient opportunity for managers to recognize a declining stock status and sufficient time for management actions to take effect.
Target reference point
Target reference point (TRP) is the overall stock level target. It is determined by setting productivity, broader ecological, and socio-economic objectives for the fishery. It is typically set at or above the USR.
Removal reference
Removal reference is the maximum removal rate of a fish stock. It is less than or equal to the stock's maximum sustainable yield. It can be expressed in terms of:
Stock status and reference points
Video transcript
[background music begins]
[Visual: The words, “Stock Status and Reference Points” appear.]
[Visual: The words, "Fisheries and Oceans Canada uses 3 stock status zones to categorize fish stock status (critical, cautious, or healthy)" appear.]
Narrator: Fisheries and Oceans Canada uses 3 stock status zones to categorize fish stock status (critical, cautious, or healthy).
Narrator: This figure shows how the amount of fish that can be removed from a stock might change for each stock status zone.
Narrator: Removal Rate is shown on the y axis, and Stock Status is shown on the x axis.
[Visual: The graph appears with Removal Rate on the y axis, and Stock Status on the x axis. Below the graph, a legend displays “1 Limit Reference Point; 2 Upper Stock Reference Point; 3 Removal Reference; 4 Target Reference Point.”]
[Visual: At the top, the graph is divided into 3 sections and colours; a horizontal red bar on the far left is labelled “Critical zone”, a horizontal yellow bar in the middle is labelled “Cautious Zone”, and a horizontal green bar on the far right is labelled “Healthy Zone.”]
Narrator: When a stock is in the healthy zone, the removal rate can remain constant (as you can see in 3);
[Visual: A horizontal solid line labelled 3 is displayed in the Healthy Zone section on the far right.]
The vertical dotted line, 4, shows the target reference point, where managers would generally like the stock to be.
[Visual: The horizontal line labelled 3 is intersected by a perpendicular vertical dotted line labelled 4, also in the Healthy Zone section of the graph.]
Narrator: However, when the stock enters the cautious zone, or drops below the Upper Stock Reference Point or USR, fishing must be progressively reduced to avoid reaching the Limit Reference Point or LRP. You can see the dotted line descending lower and lower until it hits the LRP, showing how fishing rates might be reduced in the cautious zone.
[Visual: The number 1 appears on the graph at the intersection of the far left “critical zone” and middle “cautious zone” denoting the location of the Limit Reference Point. A descending diagonal dotted line labelled 2 is displayed across the middle “cautious zone” section of the graph, connecting the horizontal line in the far right “healthy zone” section to the x axis at the intersection between the middle “cautious zone” and far left “critical zone” sections.]
Narrator: Below the LRP, fishing is kept at the lowest possible level to promote stock growth and avoid serious harm to the stock.
[Visual: A horizontal dotted line connects the right side of the far left Critical Zone section of the graph with the y axis.]
[Music ends]
[Visual: Graph fades out to black.]
[Visual: The Fisheries and Oceans Canada logo appears.]
[Visual: The Government of Canada logo appears.]
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