Priors to include stock depletion before the start of the time series

[KaAdor]

Hello,
I am trying to apply spict to a stock for which input data includes ~40yr time series of commercial catches and a survey derived biomass index. I have cropped the time series of catches to match the time series of the survey. However, seeing as the survey started about 10 years after the development of the fishery, it does not cover the initial high catches. When scaling the biomass index to exploitable biomass, I am left with an index that shows low biomass with little to no fluctuations for the first 20 years of the survey. As a result, SPiCT greatly overestimates biomass in the second half of the time series where catches were low.

I was wondering if there was any way to include the initial boom and bust of the fishery in terms of priors, apart from bkfrac?

Thanks in advance!