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The Revised Management Procedure is the rigorously tested process developed by the IWC’s Scientific Committee to provide advice to the Commission on safe, risk-averse catch limits for commercial whaling of baleen whales.  Elements of the RMP, particularly the computer modelling components, are now used in a variety of non-whaling contexts both within and outside the IWC.  To date it has not been used in the regulation of whaling, and the moratorium on commercial whaling remains in place. 


The moratorium on commercial whaling was introduced by the IWC in 1982, and came into full effect in 1986.  This decision was taken for a number of reasons.  These included differing attitudes to the acceptability of whaling, and difficulty agreeing on catch limits due to scientific uncertainties in the information needed to apply the management procedure that was then in place (called the ‘New Management Procedure’).

Following the moratorium decision, the Commission asked the Scientific Committee to develop a new approach to providing advice on the setting of catch limits that was both safe and practical. 

At the outset, the Scientific Committee recognised the need to learn from previous difficulties and in particular to recognise the limitations of both the data it had, and the data it was likely to be able to obtain.  To give a simplified example, there was no point developing a management procedure that required an estimate of the natural mortality rate if this piece of information could never be obtained.

This was a complex piece of work and it took the Scientific Committee eight years to complete.  The new process was called the Revised Management Procedure (RMP).  It was adopted by the Commission in 1994 and set a new standard in scientific management advice for marine and other living resources.  This was in part because the RMP was the first such process to take into account the large levels of uncertainty inevitable in disciplines like cetacean science. 

On adopting the RMP, the Commission stated that it would not be used to set catch limits until agreement was also reached on the Revised Management Scheme (RMS) which covers different aspects of whaling regulation such as observer schemes and other measures to ensure catch limits were not exceeded.  Negotiations on the RMS continued until 2006 when the Commission recognised it had reached an impasse.  More information on the RMS can be found here.

Conservation and Management Objectives

The Commission set three commercial whaling objectives for the Scientific Committee to consider when developing the RMP.  It decided that the greatest priority should be given to the second objective which relates to conservation.  The objectives are summarised below:

  1. Catch limits should be as stable as possible
  2. Catches should not be allowed on stocks below 54% of the estimated maximum number of whales that the environment can support.  This maximum number is known as ‘carrying capacity.’
  3. The highest possible continuing catch should be obtained from the stock.

The role of computer modelling 

The RMP has two elements: the now-completed Catch Limit Algorithm which is generic and can be used to calculate catch limits for any single baleen whale population; and the ongoing Implementation work on how the CLA is then applied for particular species and areas.   The CLA and Implementation process are described below.  

Computer modelling is essential to both elements.  In long-lived species such as whales, it would take decades to determine whether a proposed management approach worked, and the consequences if it did not could be severe.  Modelling  allows scientists to test the effect of alternative management strategies on simulated whale populations, taking into account scientific uncertainty about whales, their habitat and future changes.  This enables them to examine the potential effects of thousands of different scenarios, forecasting best and worst case consequences far into the future in order to determine whether a strategy provides robust advice.  This use of computer simulation and testing in light of scientific uncertainty was groundbreaking in its field, and is becoming widely used in fisheries and other wildlife management. 

Click here to see just some of the huge range of types of uncertainty that were tested when developing the CLA, and are now tested as part of the Implementation process.

The huge breadth of different scenarios tested reflects the inevitable scientific uncertainty regarding whales and their environment. These included:
  • Several ways of modelling how a population behaves (and associated assumptions).
  • Starting from different population sizes.  These ranged from 5-99% of the unexploited (initial, pre-whaling) number.
  • Different assumptions on the rates of maximum productivity of the population (the excess of births over deaths which causes a population to rise), including changes in these rates over time.
  • Various levels of uncertainty and bias in the estimated population size.
  • Various frequencies of abundance surveys (whether they occur annually, every five or ten years).
  • Changes in the carrying capacity (the maximum population size that the environment can support) over time.  This simulates potential problems caused by factors like climate change or habitat degradation.
  • Errors in historic records of catches or abundance.
  • Occurrence of catastrophes simulating unpredictable events such as major disease.
  • For the Implementation process only, matters related to uncertainty about stock structure (described below, in the section on Implementation).

The Catch Limit Algorithm (CLA)

After several years of intense work and rigorous computer simulation testing, the Scientific Committee developed a procedure for determining safe catch limits, applicable to any population of baleen whales.  Computer modelling tested the performance of several potential approaches against many assumptions and problems before one, now known as the Catch Limit Algorithm, was finally chosen as best meeting the Commission's objectives.  This took into account uncertainty and reduced data requirements as much as possible by requiring just two essential pieces of information which can be collected relatively reliably:

  1. estimates of the number of whales (‘abundance estimates’) taken at regular 6-year intervals, and the statistical uncertainty associated with the estimates;
  2. estimates of numbers of past catches (allowing for the uncertainty in historic records) and numbers of present catches (assumed to be known reliably).

The CLA is a key component of the RMP.  As a design feature, the CLA does not allow catches from a stock estimated to be below 54% of its estimated pre-catching population.  The level of maximum productivity for whales is thought to be around 60%.  Catches are set so that the population will stabilise at around 72% of its pre-catching level, in accordance with the Commission's choice of 'tuning' level. 

Click here to read more about the balance of objectives and 'tuning.'

When presenting the CLA to the Commission, the Scientific Committee provided three options or 'tunings' - 0.60, 0.65 and 0.72 - that it believed were acceptable, but it recognised that choosing amongst them was a political rather than a scientific matter.  All three options were in line with a precautionary approach.  In this context, 'tuning' refers to the balance between the conservation objectives and the catch objectives established by the Commission.


The highest (0.72) tuning gives greater weighting to conservation objectives - the whale population stabilises at around 72% of carrying capacity and provides lower catches.  For the lowest (0.60) tuning, the population stabilises at around 60% of carrying capacity and provides higher catches.  The Commission chose the highest tuning (0.72).

Regular abundance estimates are essential to the 'feedback' way in which the CLA works.  If no recent abundance estimate is available catches are set to zero.  The Committee has developed guidelines and rules to ensure abundance estimates are of sufficient quality to be used (i.e. they must be within the levels of uncertainty tested by the computer simulations used to develop the CLA).  The guidelines specify how the information should be obtained, and how the resulting data should be analysed.  The most recent version of these requirements and guidelines can be found here (13Supp507_518_ReqGuidSurv.pdf).

Click here to read more about how the CLA works as a 'feedback' procedure.

  • uses a wide range of possible values for the level of depletion of the stock (the extent to which historic commercial whaling has reduced the original, pre-exploitation population);
  • uses a wide range of possible values for the whales’ productivity (the excess of births over deaths); and   
  • assumes greatest uncertainty in the first estimate of abundance;
  • estimates a wide range of potential catch limits.

At each subsequent review of new abundance and catch information, the CLA learns more about the likely true situation of the stock and narrows the range of potential catch limits. The chosen catch limit from the range is such that around 58% of the possible limits are greater than the recommended limit.

Implementation/Implementation Review

Before the generic CLA could be used in the 'real world,' a mechanism had to be developed to allow it to  be applied to specific baleen whale species in specific regions.  It would be relatively straightforward to apply the CLA to a static, isolated whale population that does not mix with others, but this is not the case for most whale populations.  

An Implementation is the exercise undertaken by the Scientific Committee before it provides advice on safe catch limits for a particular species in a particular area.  This exercise takes into account all that is known about populations of the species in what is termed a Large Area (usually an ocean basin), and addresses specific uncertainties.  Implementations are reviewed at regular intervals (normally 6 years) to take into account new information; each of these is called an Implementation Review.

Formal requirements, guidelines and a timetable for the Implementation process have been developed and can be found here (13Supp495_506_ReqGuidRMP.pdf). The process is summarised in the diagram below.

RMP Implementation Process Final