CITES is the Convention which governs international trade in endangered species. For example, no international trade is permitted in species listed in CITES' Appendix I. With what are such species "endangered"? The criteria governing CITES listings make clear that "endangered" refers to "threatened with extinction". Furthermore, lest there be any doubt about the meaning of "extinction" in this context, this is clarified by the Red List Categories for threatened species developed by IUCN, the International Union for Conservation of Nature and Natural Resources, which defines a taxon as "extinct" when there is no reasonable doubt "that the last individual has died" (IUCN, 1994).

Currently, all species of baleen whales are listed on CITES' Appendix I. Proposals were made to the Harare CITES meeting to downlist some populations of whales, including the Western North Pacific stock of Bryde's whales. In IUCN's formal recommendations on proposals to that CITES meeting (TRAFFIC, 1997), they stated that the International Whaling Commission's (or IWC's) Scientific Committee estimated the mature female component of this Bryde's whale population to be 51% of its pre-exploitation level. They went on to comment that this indicated the population to be "borderline with respect to meeting the biological criteria for inclusion in CITES Appendix I."

There are two important elements of the rationale underlying IUCN's comments in this case which merit attention. Both are arguably quite consistent with CITES' present listing criteria. First, the 51% figure quoted was the most conservative of a number of alternative estimates evaluated by the IWC Scientific Committee at that time (IWC, 1997). (This is an aspect whose linkage to the Precautionary Principle will be discussed further below.) And secondly, the criterion applied for recommending an Appendix I listing for the population, was a reduction to below 50% of its pre-exploitation level.

At that same CITES meeting, a proposal for the establishment of a Working Group for Marine Fish Species was made. This eventually failed to gain acceptance, but it is not that proposal itself that is of pertinence to the topic of this paper. Rather, it is one of the arguments offered by its proponents: that some marine fish species, subject to large scale commercial harvesting, currently qualified for inclusion in CITES Appendices.

It was in linking these two matters – the motivation given for the Marine Fish Species Working Group and the criterion argued to apply to the Bryde's whale proposal – that my concerns arose. Because, under such arguments, there would be few marine fish species currently under commercial harvest which would NOT be placed on CITES Appendix I. The consequent suspension of all international trade in such species would have enormous deleterious socio-economic consequences.

Nor could I see genuine biological justification for such listings. Typically in fisheries, reduction of a population to somewhere in the range of some 30-60% of its pre-exploitation level is considered appropriate for optimal utilization to secure a maximum sustainable yield. Certainly many fish populations have been reduced below such levels. But that doesn't mean that they cannot continue to produce sustainable, although not optimal yields, nor that all harvesting has to cease while management secures their recovery to higher levels capable of producing larger sustainable yields, nor (most certainly) does it mean that they are necessarily in any imminent danger of extinction.

Extinction occurs when a population is reduced below what is termed its "critical depensation" level – the level below which it cannot sustain itself even in the absence of a harvest. Empirical studies to estimate what that level might be for marine species harvested commercially, are perhaps not as advanced as they could be (see Butterworth, 1999, for further discussion of this matter). But even so, typically such levels hardly seem likely to exceed some 10%, at most, of pre-exploitation abundance, rather than 50% which relates more to a desired target for optimal utilization.