Introduction to stock assessment
Unit 3.3: Uncertainty
DFO Pacific Mollusc Program 2022 survey.
Photo credit: DFO
Given the use of statistical techniques, making assumptions, and the general incompleteness of knowledge about natural systems, all stock assessments inherently involve some level of uncertainty. Scientists make logical and defensible assumptions about stocks during stock assessments. It is critical for scientists to communicate uncertainty in order to provide managers with advice for decision making.
Uncertainty does not mean an error has been made. It means that there is a range of possible outcomes, some of which are more likely to happen than others. It may also mean there was not enough data to parse out plausible outcomes.
Potential sources of uncertainty include:
- natural variability in population dynamics (for example, different levels of recruitment between years)
- the population dynamics used in modelling (for example, predator-prey relationships, stock-recruitment relationships, environmental and climate factors) are not understood
- missing data (for example, unreported catch)
- measurement and sampling error
- the extent to which management policies will be successfully implemented is not known (for example, how well catch will match total allowable catch projections, changes to policy)
DFO incorporates uncertainty into the calculation of stock status and reference points.
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