rfb rule

Why does the advice go down even if the index is going up?

Response

• The previous 2 over 3 rule calculated catch advice based on the trend from a bio-mass index. In addition to this, the rfb rule also considers

1. the exploitation of the stock based on catch-length data and
2. includes a biomass safeguard that reduces the catch advice if the biomass index falls below a trigger value. The catch advice calculated with the rfb rule is a result of all these considerations combined. Furthermore, the trend in the biomass index is calculated by using da-ta from the most recent five years, i.e. an increase in the index in a single year does not necessarily result in a positive biomass trend.

## What to do if new life-history parameters such as L∞ are found; is there a need to recalculate things back in time?

• There is no need to annually update life-history parameters. If new growth pa-rameters are available and these are substantially different from previous esti-mates, these should be used. To ensure consistency in the calculation, derived values such as the reference length LF=M should also be updated and the historical mean catch length compared to this new reference length. Growth parameters and derived metrics such as the reference length should be periodically reevalu-ated, e.g. every 3-5 years, following a similar schedule to benchmarks for Catego-ry 1 data-rich stocks, but kept constant in-between unless there is compelling new evidence for a change.