Notes, definitions and guidelines

The Annex to this document contains comments received after 15 April, which have not been translated into Spanish. The comments were provided by Mr Doug Butterworth.

 

 

Some general comments:

1. I think when terms are used we must be careful to distinguish whether we are referencing an absolute quantity, or a rate which can either refer to a per capita measure or a per time unit measure. For example, population size is an absolute quantity. But "recruitment" is not: it is certainly a per time unit (usually per year) measure, and is often also expressed in per capita terms. Similar problems arise with "fecundity" - I have previously seen this used only in a per capita (as well as per time unit) sense, so was a little surprised to see a different sense implied in suggestions concerning reproductive success and potential. There's no fundamental problem here, merely a need to take care to specify whether or not "rate" is intended when a term is used, and whether that rate is per capita or per time unit or both.

2. How parsimonious do we wish to be with the definitions? Certainly some explanatory text is desirable, but I'm concerned that in "talking around" some of the associated concepts in the definition text, we may be getting ourselves into unnecessary trouble and potential discussion. For example, in the final sentence suggested under recruitment, in most fisheries contexts one would expect the reverse of what is stated as expected for declining populations. Similarly the statement under reproductive potential that "removal of individuals that have not or have just reached reproductive age will result in a decline in the growth rate of the population" does not hold for populations subject to a high level of compensation in their dynamics. My own preference is for the "If in doubt, leave it out" dictum in such circumstances.

Finally to some more specific comments:

3. The word "offspring" has been introduced - is it or is it not intended to be synonymous with "recruitment" as used here?

4. Species: I concur with Kevern Cochrane's views circulated on this matter. A further complication concerns the statement "'population' .... also covers the stocks traditionally used in fisheries": is the definition of "Sub-populations" currently in Annex 5 being retained, as that looks more to me like the sense in which fisheries use the word "stocks".

5. Population size: I agree with Sue's idea of using "effective population size" rather than "mature individuals", though naturally the former then needs definition. Re the 5000 figure, I also concur with Sue that consideration needs to be given to modification there. In general, I support the concept in the other document that Sue circulated that extent of decline (a relative measure) is the more important concern here, but for populations that were small in their pristine state, absolutes do have relevance in the context of concerns about demographic stochasticity and loss of genetic diversity - I gather (though stand open to correction) that the absolute size at which such factors are thought likely to start playing a role is perhaps an order of magnitude less than 5000.

6. Over-exploitation: In the context of the criteria per se, Sue may well be correct that this term doesn't need definition. However, it has become somewhat central to the wider debate as to whether or not the implied need for "protection .... against over-exploitation" in the CITES Convention pre-amble implies that CITES Appendix II listing is an intended mechanism to facilitate this, or rather related only to possible extinction threats. This is a particularly sensitive point in discussion of the CITES criteria in fisheries circles, and while it is clearly not for the CWG to choose between the different interpretations different countries express on this matter, it could nevertheless be helpful to further debate to have a clear definition of what exactly is meant by "over-exploitation". Given that, I don't see that the MSY level concept can be avoided. For example, the difficulty with the alternative definition Sue offered, although it certainly beats mine in the parsimony stakes (!), ("over-exploitation occurs when harvest decreases population growth to below replacement  ....") is that this must occur, and is not necessarily undesirable, when a population is reduced from its pristine level to an optimal level (such as the MSY level) for harvesting.

7. I think the further document of definitions (especially that re decline) which Sue circulated is particularly helpful. My one possible concern (as Pamela Mace already knows) relates to the matter of whether a "decline is more worrisome for a low productivity species than it is for a high productivity species", Certainly this is true in the context of recovery - one will achieve recovery faster in the latter case. But the issue for CITES is threat of extinction (per se). I'm interested in whether in that context the greater worry for lower productivity species is merely folk-lore (superficially plausible lore though this indeed seems to me), or there is actually empirical evidence to support this contention.