3. Underlying Issues

3.2 - Assumptions

The justifications of all three proposals rely heavily on the acceptance of four basic assumptions:

(i). That all three species have conservative, "K-selected" life history strategies, that in turn demand precautionary, risk-adverse management to avoid extinction;

(ii) That population declines, even in local areas, reflect increased risks of biological extinction at the global level;

(iii) That inferences about declining populations and increased risks of commercial extinction constitute reasonable evidence for the Parties to act upon;

(iv) That there are conservation advantages in allocating to a global population, the status (known or inferred to be the case), of a local population.

Resolution Conf. 9.24 makes provision for such evidence to be used in support of specific listing proposals (see below), but the robustness of these assumptions needs to be considered carefully.

(i) Life history theory

Sharks are generally considered highly K-selected species, and have traits like slow growth rates, late maturation, long gestation, low fecundity and long lives. They have low intrinsic rates of population growth (r), which means that their ability to recover rapidly from stock depletion is compromised relative to other species (Compagno 1990, Bonfil 1994; AC 1996). For example, most teleost fish are r-selected: they reproduce at an early age, produce huge numbers of offspring with low survival rates, but generally have the ability to recover rapidly after depletion. One group thus appears more vulnerable to population declines and biological extinction than the other.

This view of "competing life history strategies" is overly simplistic (Begon 1996). Whilst r-selected species have a higher potential rate of increase, their populations are also prone to large-scale fluctuations driven by environmental factors. Thus populations reduced by excessive harvest, may not be equally vulnerable to extinction. K–selection involves the notion of strong density dependence (K = carrying capacity) and compensatory responses. When individuals are removed from a population, resources become more abundant, juvenile survival rates increase, and unoccupied territories become re-filled. Compensatory mechanisms cause intrinsic r to increase, sometimes greatly, when population size is decreased. By extending reproduction over many years, producing well-formed young, and having a range of different age classes in the population at any one time, there is significant buffering against extinction by K-selected species such as sharks (Walker 1998) relative to r-selected species.

It may be appropriate to assume some species are more vulnerable to population reduction in harvest operations because of their general life history strategies, but this is quite different to judging them as being more vulnerable to biological extinction. Information on responses to harvest, and some species-specific information on life history parameters are needed (see below).

(ii). Population reduction versus risk of extinction

A listing on CITES implies a species is threatened with extinction (Appendix I) or will become so unless trade is regulated (Appendix II). However, in the case of fisheries, differences between resource depletion and biological extinction are simply vast.

As clearly enunciated in Annex 5 of Resolution Conf. 9.24 (definition of decline), standard fisheries and wildlife harvest practice involves deliberately reducing populations in order to extract a sustained yield. Depending on the species, it’s abundance, and the costs of harvesting, species may become "commercially extinct" at levels which have little or nothing to do with biological extinction. That is, when densities decline to a level where it is no longer economically viable to harvest them (SSG 1996) and thus support a commercial fishery. The species itself may still be represented by millions of individuals and be in no danger of biological extinction.

There is clearly a further distinction that needs to be made between reducing abundance at local and global levels, and changing risk of extinction at local and global levels. With geographically restricted species, the loss of a small number of populations may lead to an increased risk of extinction for the entire global population of a species. However, in the case of globally distributed marine species, such as R. typus, C. carcharias and C. maximus, local depletion may be somewhat insignificant in terms of changing the risk of extinction of the global population.

The central issue with fisheries is not one of protecting marine species from biological extinction, but rather of managing stocks to ensure the long-term sustainability of harvests and of the benefits they provide to people (Butterworth 1999). Past experience has shown that shark stocks can be harvested sustainably to provide stable fisheries, but that careful management is required to avoid declines likely to constrain fisheries returns (Stevens et al. 1997). In the absence of careful management, population declines may occur, reducing abundance and fisheries incomes – but this does not necessarily enhance the risk of biological extinction.(iii).

 Inference

The Parties clearly agreed (Resolution Conf. 9.24) to allow "inference" to be an acceptable tool for assessing the status of species for listing on Appendix I and II. But in this case, the three proposals rely heavily on inference and anecdotal evidence. Local trends, supported by sketchy and non-significant data, are extrapolated, and then purport to give reliable estimates of projected, global population declines. The link with extinction is not well made. Life history characteristics are inferred to represent a direct measure of vulnerability to extinction, when at best it may signal vulnerability to population decline. Shark fishery management is hampered by a lack of biological and fishery data, but a lack of data should not be used to justify inferences that may be highly spurious. If so, inference will contribute to lack of management rather than to improved management, and may well prevent the critical data being collected. The available evidence at best indicates some population declines in local areas, and does not indicate any threat of extinction is looming locally or globally.

(iv). Applying the status of the worst local population to a global population

Globally distributed species represent a complex situation for any organisation attempting to define a single set of rules to apply throughout a species’ range. The status of most globally distributed species ranges from good to bad, with various "in-between" positions. It makes no conservation sense to attempt to manage an abundant species at a local level as though it was rare, nor to manage a rare population as though it were abundant. Nor does it make sense to reward effective conservation efforts within a country by applying the status of the worst local population to the global population. Annex 3 of Resolution Conf. 9.24 indicates that split listing should be avoided where possible, but when implemented, should be on the basis of national or continental populations. For globally distributed species, such split listings would seem the only way in which appropriate management can be linked to appropriate status if some local populations are indeed threatened by international trade.