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Looking in the rear-view mirror: bias and retrospective patterns in integrated, age-structured stock assessment models
- Source :
- ICES Journal of Marine Science. 72:99-110
- Publication Year :
- 2014
- Publisher :
- Oxford University Press (OUP), 2014.
-
Abstract
- Retrospective patterns are systematic changes in estimates of population size, or other assessment model-derived quantities, that occur as additional years of data are added to, or removed from, a stock assessment. These patterns are an insidious problem, and can lead to severe errors when providing management advice. Here, we use a simulation framework to show that temporal changes in selectivity, natural mortality, and growth can induce retrospective patterns in integrated, age-structured models. We explore the potential effects on retrospective patterns of catch history patterns, as well as model misspecification due to not accounting for time-varying biological parameters and selectivity. We show that non-zero values for Mohn’s ρ (a common measure for retrospective patterns) can be generated even where there is no model misspecification, but the magnitude of Mohn’s ρ tends to be lower when the model is not misspecified. The magnitude and sign of Mohn’s ρ differed among life histories, with different life histories reacting differently from each type of temporal change. The value of Mohn’s ρ is not related to either the sign or magnitude of bias in the estimate of terminal year biomass. We propose a rule of thumb for values of Mohn’s ρ which can be used to determine whether a stock assessment shows a retrospective pattern.
Details
- ISSN :
- 10959289 and 10543139
- Volume :
- 72
- Database :
- OpenAIRE
- Journal :
- ICES Journal of Marine Science
- Accession number :
- edsair.doi...........c8c5d2289ea2c284bd7865f3ea14aafa