The New Management Procedure (NMP) adopted by the International Whaling Commission (IWC) in 1976 failed for three reasons. First, although it specified how catch limits were to be calculated given certain information about the size and productivity of a whale stock, it failed to detail how this information would be determined or what data needed to be collected to facilitate this. Secondly, the catch limits which the NMP produced fluctuated too widely over time for the orderly development of the whaling industry. Finally, there was no specific mechanism for adjusting catch limits to reflect the greater or lesser scientific uncertainties that applied to different stocks.

To cater for the last of these concerns, the RMP adopts a different philosophy to the NMP. The NMP catch limits were based on scientists' "best" assessments of the state of a resource (about which scientists could seldom agree!). In contrast, the formulae of the RMP have been developed so that under a wide range of possibilities for the true (but unknown) status of a stock and its dynamics, the catch limits provided will neither put the stock at risk, nor waste the resource (through unnecessarily small catches), in the long term.

The approach underlying the RMP formulae is one which mathematicians call "Bayesian." Essentially, this approach says that one takes one's initial ideas about the status of the stock, and successively improves these ideas as further data are forthcoming. For the RMP, these data consist of a time-series of abundance estimates for the stock obtained by means of sighting surveys. A simplified description will be given of the way the formulae of the RMP turn the information from a sighting survey (together with the historic series of catches from the stock) into a catch limit for the resource. The dependence of the result upon the precision with which the survey determines the abundance of the stock will be illustrated.

Some choices made in specifying the formulae for the RMP seem rather arbitrary. In fact, these selections were made in the context of the three objectives set down by the Commission for the RMP. These were stability of catch limits, that exploitation not seriously increase the risk of extinction, and making possible the highest possible continuing yields from a stock. Performance cannot be simultaneously optimized for all three objectives -- for example greater catches must involve higher risk -- so that tradeoff selections had to be made by the Commission between alternative possible "tunings" of the RMP. These choices were based on the anticipated performance (in terms of catch, risk, and catch stability) of different tunings, where this performance was evaluated by means of computer simulations of the application of the RMP to a whale stock. Some comments will be made about the robustness (insensitivity to uncertainties) achieved by the RMP, and the pertinence of the "protection level."

When the first sightings survey of a stock is carried out, and the RMP is applied to determine the initial catch limit, the result depends on four factors: the abundance estimate from the survey the c.v. (coefficient of variation) which measures the precision of the survey, the cumulative historic catch, and how that catch was distributed over time. Some examples will be given of how these factors inter-relate. Other features of the RMP to be discussed are a catch phase-out rule (how catch limits are adjusted downwards if a regular series of surveys fails to continue), and rules intended to ensure that, over the longer term, the proportion of females in the catches does not exceed 50%. (Note that the RMP as at present is for baleen whales only, and thus could not, for example, be applied to sperm whale stocks for which a percentage differing from 50% might be appropriate.) Although the RMP sets catch limits for five successive years, it does not (as yet) include any "block quota" option whereby adjustments can be made for shortfalls or overruns in catches in one year during the remainder of this five year period.

Descriptions thus far have related to the application of the RMP to an isolated stock of whales. One of the major difficulties that arose when applying the NMP, was how to deal with uncertainty about the appropriate placement of the boundaries between different stocks. Inappropriate decisions on the placement of a stock boundary could lead to severe (albeit unintended) depletion of a stock. Certain "multi-stock rules" have been added to the RMP do deal with this problem.

Essentially, the RMP's solution to the multi-stock problem is to set catch limits on a much smaller scale than the traditional Management Areas used under the NMP. Thus, for example, Antarctic minke whale catch limits were set previously for 60E longitude sectors; under the RMP, catch limits would be set for each 10E sector, to prevent the problems which could result from inappropriate concentration of catches in certain areas under the previous management regime. Further rules that apply to evaluating these limits, known as "capping" and "cascading," will be described, together with the basis for deciding whether either of these two mechanism needs to be invoked in a particular case.

Examples of likely catch limits for the Antarctic minke whale under the RMP, both immediately and over the next twenty years, will be presented and discussed. The dependence of the twenty year projections upon the range and intensity of future surveys will also be illustrated.

The Commission has decided that before the RMP may be implemented for any set of whale stocks, five further aspects need to be addressed to turn the RMP into a "Revised Management Scheme" (RMS). The two of these five aspects which are of a scientific nature will be discussed: minimum standards for data, and guidelines for conducting surveys and analyzing the results.

The RMP makes use of two types of data: A series of historical catches by sex and a series of absolute abundance estimates together with information on their statistical properties. No information on values of biological parameters is used.

The procedure consists of two components: A core procedure which is used to calculate catch limits for particular areas and so-called multistock rules which can modify the catch limits calculated by the core procedure in cases where there is uncertainty about stock boundaries in the region being managed.

For given values of stock productivity and depletion (fraction of present population size to initial size), a catch limit control law sets a nominal catch limit. This nominal catch limit is zero if the stock is depleted to less that 54% of its initial level. This is the nominal protection level. Otherwise, the catch limit as a fraction of the present stock size increases linearly with depletion.

Nominal catch limits are calculated for a range of values of productivity and depletion. Then, given the catch history and the series of sightings survey estimates, the probability of each nominal catch limit is calculated. Then a catch limit with a high probability becomes the actual catch limit. (The precise definition is rather technical and the values depend on how the procedure is tuned. With the tuning chosen by the commission in Reykjavik in 1992, the actual catch limit - call it C -is chosen such that there is roughly a 42% probability that the catch limit should be C or less).

A region to be managed is split up into a number of small areas. A number of small areas can be combined to form a medium area. The multistock rule options are of three kinds:

1. Small area rule. The core procedure is applied to each small area and a catch limit set for each independent of the others.

2. Catch capping rule. The core procedure is also applied to a combination of small areas (a medium area) and a catch limit set for this larger area. If the sum of the catch limits for the small areas exceeds the catch limit for the medium area they are reduced proportionally.

3. Catch cascading rule. The core procedure is only applied to a medium area and a catch limit is set for that area. This catch limit is then distributed onto the individual small areas in proportion to the relative abundance in each area.

In general 3 will give the highest catch limit and 2 the lowest.

1. The use of incoming data is downweighted relative to prior assumptions about depletion and productivity. This results in limited utilization of the data and thus the procedure "learns" very slowly.

2. The tuning of the procedure decided by the Commission at its meeting in Reykjavik (72% of initial stock size for a stock with 1% MSYR) is very conservative. This tuning is chosen so as to ensure that a stock with low productivity ends at a high stock level, well above what is though to be the most productive level. It follows that for this tuning, stocks with more realistic values of productivity will be greatly underexploited. This tuning is thus doubly conservative, first it assumes extremely low productivity for the stock and secondly it demands that such a stock finishes at very high level.