Seasonal effects for catchability and selectivity

[k-doering-NOAA]

Imported from redmine, Issue #69406 Opened by @RickMethot on 2019-09-30 Status when imported: New

While working on the monthly shrimp models I see an obvious need to allow for a seasonal effect on catchability and I expect there have been situations in which seasonal selectivity would be useful.

It would be good to approach this generically across MGparms, catchability and selectivity

Currently the need for time-varying parameter is evaluated only in first season of the year, and it produces biology offsets for other seasons at that time. Perhaps this evaluation should be moved to the beginning of each season (note performance hit!)