On difficulties in interpreting probability-based measures of risk in trade-offs situations

In a number of recent instances, the Pelagic Working Group has been finding itself in difficulty when selections need to be made between management options where the trade-off involves a measure of risk, typically expressed as the probability of abundance dropping below some chosen low level. The essential problem is that even if one makes a management measure considerably more onerous, this achieves only a small change in this probability. Understandable argument from the industry then is why such a heavy penalty if it achieves so little – is this marginal reduction of the risk measure meaningful?