Early life stage modelling of Browns Bank haddock: 1983-85 the FEP years

D. Brickman and K. T. Frank

The representation of mortality is one of the weak points in an early life stage (ELS) model. An ELS model is described with constant mortality for egg and larval stages. The model is used to simulate the stage 4 egg, and larval data from the 3 FEP years 1983-85. The model is initialized using published abundance and mortality estimates, and its output is compared to FEP field data. We find that the model, in general, does a poor job of reproducing both the spatial/temporal and area-integrated versions of the data. To understand the discrepancy, we derive an integrated version of the model (the ELSIM) and analyze its properties.

We show that the assumption of constant mortality has implications with respect to what we would expect to find in field data, and use this information to show that a constant mortality ELS model is not consistent with the FEP data, but rather a year-day dependent mortality is likely more appropriate. We thus derive a method for evaluating whether sequential stage field data is consistent with a constant mortality model.

We show that the ELSIM run with a simple year-day dependent egg and/or larval mortality function can fit the FEP abundance data. Transferring this function to the ELS model improves model performance, but details of the spatial distribution of larvae still need more work.