This program improvement involves review of two overarching section: (1) Principle 1 Clarifications and (2) Metapopulations.

Principle 1 Clarifications

This section explores the three main topics below:

  • Scoring stock status: To measure ‘fluctuations around’ target reference points (TRPs), we proposed that the exploitation level or fishing mortality rate, F, should be scored as part of the stock status. Clarifications were also proposed on the different ways that Maximum Sustainable Yield (MSY) may be estimated (both ‘common’ and ‘best practice’, and the implications of these for scoring).
  • Scoring harvest control rules (HCRs): We proposed that dynamic HCRs need not be formally ‘in place’ to achieve a 60 score, at least in cases where the stock is currently above BMSY and existing mechanisms are available that give a reasonable expectation that fishing mortality will be effectively controlled when needed, or has been controlled up to this point with no adverse impacts on the stock.
  • Principle 1 Structure: A restructure of the Performance Indicators (PIs) was proposed, with stock status measured against specific levels that (1) avoid recruitment impairment, and (2) target MSY (rather than the actual reference points used in the fishery). Further, scoring issues from PIs 1.1.2 and 1.1.3 moved to the HCRs PI 1.2.2 to avoid redundancies in scoring.

To find out more about the history of development for the Principle 1 Clarifications, please click here.


A metapopulation can be defined as a group of subpopulations in which local dynamics are driven in part by the movement of larvae, juveniles and adults to and from other subpopulations in the group. In these situations, a biological unit stock may consist of several interconnected sub-populations, such that targeting of one of the sub-components affects the others to some degree. Connectivity is usually provided by larval dispersion, but can also be created through adult migration.  These exchanges generate “source” populations with net export of individuals and “sink” populations with net import of individuals.

Ignorance of such spatial structures in fisheries assessment and management may result in biases when estimating population parameters and stock status; setting of inappropriate management targets and harvest levels; and may lead to higher risks of fisheries depletion.

To find out more about the history of development for the Metapopulation fisheries, please click here.