Fish stocks and fishing intensity by group

Fish stocks are measured by biomass: the number of individuals multiplied by their mass. Fishing intensity by the fraction of the fish population that is caught in a given
year.

Both are given as a ratio of their levels at the maximum sustainable yield – the level at which we can catch the maximum amount of fish without a decline in fish
populations. A value of one maximises fish catch without decreasing fish populations. This is the target level.