concept

Maximum sustainable yield

The largest amount that can be taken from a population each year while the population holds its level. Under logistic growth that point sits at exactly half of environmental carrying capacity, where surplus reproduction peaks. It sounds tidy, and it has failed repeatedly in real oceans. Three reasons: carrying capacity and growth rate measured at sea carry very wide error bars, so a quota can exceed genuine replacement without anyone knowing; at low density populations breed worse than predicted rather than better; and catch per unit effort can look stable while a stock collapses, because vessels get better at finding the last aggregations. The 1992 Grand Banks cod collapse is the classic lesson.