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.