Management and preservation of the giant fish species of the Mekong. (by N.S. Mattson, K. Buakhamvongsa, N. Sukumasavin, N. Tuan and O. Vibol)

Niklas S. Mattson¹, Kongpheng Buakhamvongsa², Naruepon Sukumasavin³, Nguyen Tuan⁴ and Ouk Vibol^5
1Aquaculture of Indigenous Mekong Fish Species Component, MRC Fisheries Programme, P.O. Box 7035, Vientiane, Lao PDR
²Assessment of Mekong Fisheries Project, Living Aquatic Resources Research Center, P.O. Box 7980, Vientiane, Lao PDR
³Surin Inland Fisheries Station, Surin, 32000 Thailand
⁴Research Institute for Aquaculture No 2, 116 Nguyen Dinh Chieu, District 1st, HoChiMinh City, Vietnam
⁵Aquaculture of Indigenous Mekong Fish Species Component, #186, Norodom Blvd., P.O. Box 582, Phnom Penh, Cambodia,

ABSTRACT

Some 1 200 fish species are recorded from the Mekong and among them there are several that grow to a very large size. This paper focuses on large fishes in the Mekong, particularly the Mekong giant catfish (Pangasianodon gigas), the giant carp (Catlocarpio siamensis) and the Jullien's golden carp or seven-striped barb (Probarbus jullieni). They deserve special attention in the context of conservation. C. siamensis (giant barb) is not on the Red List, but is becoming increasingly rare in the Mekong. In general, large-bodied fish tend to be more susceptible to fishing, partly because of their relative mobility, which increases the likelihood of encountering fishing gears. The situation for the Probarbus spp is further aggravated in that fishers target them at the spawning grounds. A number of recommendations are put forward for the preservation of these species. These will have to be translated into agreements and management plans implemented by the riparian countries of the Mekong River. It is assumed that the agreed basin-wide management objective is to restore and maintain viable wild populations of the species considered here, as well as preserving the ecosystem as a whole

1. INTRODUCTION

The Mekong River is the largest river in Southeast Asia and one of the great rivers of the world. The main channel of the Mekong, from its origin to its mouth in the South China Sea, supports a variety of different fish assemblages, based on differences in physical characteristics as well as differences in historic configuration. Some 1 200 fish species are recorded from the Mekong (Rainboth, 1996), but recent work indicates that the total number of species is about 1 700 (Rainboth, pers. comm. 2001). This number will undoubtedly increase as additional taxonomic studies and fish surveys are completed. Among the 1 200 fish species, there are several that grow to a very large size.

This paper focuses on large fishes in the Mekong, particularly the Mekong giant catfish (Pangasianodon gigas), the giant carp (Catlocarpio siamensis) and the Jullien's golden carp or seven-striped barb (Probarbus jullieni), as they are potential "flagship species" in the context of conservation. As such they deserve special attention since they are potential focal points for awareness raising and education on issues relating to the preservation of Mekong biodiversity and fish production. However, the focus on individual species, which is a common feature of conservation projects, is unlikely in itself to ensure preservation of the ecosystem. Even though preservation of biodiversity in a wider sense is necessary for safeguarding ecosystem stability and functions, it is not sufficient, since many other factors also influence the ecosystem.

This paper discusses some issues relating to rarity and the development of policies for management.

2. THE STATUS OF MEKONG GIANT FISH

P. (Pangasius) gigas (giant catfish) and P. jullieni (Jullien's golden carp or seven-striped barb) are classified as 'endangered' on the 2000 IUCN Red List, while Probarbus labeamajor and Probarbus labeaminor are listed but classified as 'data deficient' (Table 1). It appears that the population sizes of the three species have decreased substantially over the last decades. C. siamensis (giant barb) is not on the Red List, but is becoming increasingly rare in the Mekong, and Rainboth (1996) maintains that it is overfished and suggests that the catch should be strictly regulated by size.

Table 1

Mekong finfish listed in the 2000 IUCN Red List of threatened species

*, CR: Critically Endangered, DD: Data Deficient, EN: Endangered, LR: Lower Risk, VU: Vulnerable, EW: Extinct in the wild (for a full description of the classification, see http://www.redlist.org/categories_criteria.html)

3. ON RARITY AND SIZE

It is relevant here to consider the meaning of the term 'rare' in the context of biodiversity. While it may be rightly assumed that many fish species are threatened due to human activities, such as overfishing or alterations to the environment (dams etc.), species may also be rare for other reasons. Some taxa are rare because they are evolving, and others may be relics of very old groups. On an evolutionary time scale, new taxa have always evolved and others disappeared. In fact, from this point of view most of the species that ever existed on Earth are extinct. The implication is that even in natural environments (with no perceptible influence from human activities) rare species will be found. Therefore, attempting to preserve all species that are rare or appear to be threatened is perhaps misplaced effort. However, as distinct from this natural process, the rate at which species are now disappearing has accelerated greatly due to man's activities. It is accepted that evolution cannot produce new species at the same rate. Hence global attention is now being given to maintenance of biodiversity, most notably through the Convention on Biological Diversity (http://www.biodiv.org/).

Based on the limited information available, it appears that the population sizes of the three species have decreased substantially over the last decades. They have in common that they grow to large, even colossal, sizes. Froese and Torres (1999) conclude, from data in FishBase, that the proportion of threatened fishes increases substantially for maximum sizes exceeding 100 cm, and that most fish species that grow to this size are threatened. In addition, the available evidence indicate that non-guarding species (applies to all three taxa) appear to be more at risk of being threatened than live bearers and nest/egg guarders (classification by Balon, 1990).

On the assumption that large species in general have lower population densities than small-bodied species, and also that there is a minimum population size that is required to avoid genetic problems (see below), it may be argued that larger species require larger areas. This is another possible cause for the decline of the large species, in that increasing disruption of migration corridors, from construction of dams and weirs, means fragmentation of existing habitats and isolation of sub-populations.

Typically, fisheries tend to first deplete the largest species, and subsequently gradually change the exploitation pattern towards smaller sized fish (Pauly et al., 1998). In general, large bodied fish tend to be more susceptible to fishing, partly because of their relative mobility, which increases the likelihood of encountering fishing gears. Add to this the preference of most fishers for large, valuable fish, and the fishery itself appears as a plausible cause of their decline. The situation for the Probarbus spp is further aggravated in that fishers target them at the spawning grounds.

4. PROPOSED MANAGEMENT TECHNIQUES

Any management action aimed at improving the situation of threatened species or reintroduction of extinct species must start by identification of the possible reasons for rarity. Failing this, efforts aimed at improving or re-establishing populations are likely to fall short. Notably, this implies that stocking aimed at supplementation or re-introduction of a threatened or extinct species should only be considered after the factors that cause rarity or extinction have been alleviated.

It is unlikely that it will be possible to address the factors that cause rarity of the Giant Mekong species in isolation from the rest of the ecosystem. Management policies for their preservation will have to be developed together with the other sectors and users that influence the system. It is suggested that the approach most likely to attain the objective is adaptive (or experimental) management, which implies integration of experiences and scientific information from multiple disciplines into models that attempt to make predictions about alternative policies (see e.g. Walters, 1997). Successful experimental management and application of its results will require a high degree of coordination between those involved, and this may best be achieved through the Mekong River Commission^[3]'s Basin Development Plan (BDP) initiative.

The following recommendations are written in terms of outcomes to be achieved. These will have to be translated into agreements and management plans implemented by the riparian countries of the Mekong River. It is assumed that the agreed basin-wide management objective is to restore and maintain viable wild populations of the species considered here, as well as preserving the ecosystem as a whole (the recommendations would be somewhat different for other objectives).

• Studies and workshops have identified the main reason(s) for rarity and actions have been taken to alleviate these:

  - based on available data and knowledge, one or more models have been created (these may range from simple, verbal models to complex, computerized models);

  - hypotheses have been formulated and screened to eliminate those that are unlikely to have given rise to the observed data;

  - experiments have been designed and implemented to test the hypotheses (the experiments may range from small to large, ecosystem scale; the time factor is an issue: large-scale ecosystem experiments may give more reliable results but take a long time, whereas small-scale experiments usually give quicker results);

  - the results of the experiment(s) have been analyzed and the main reason(s) for rarity identified;

  - the results of the experiments have been used to further refine the management system(s) towards alleviation of the factors that cause rarity;

  - at all stages in the process, gaps in data and knowledge will be identified and prioritized, and sufficient resources assigned to fill the high priority gaps.

• The major sub-populations and their breeding grounds are known, both in terms of ecology and population genetics.

• A basin wide monitoring programme is in place, covering ecology, genetics, life history requirements.

• Relevant data and meta data are stored and made available to scientists and the public.

• A breeding and stocking programme is in place

  - broodstock is maintained in sufficient numbers and with appropriate genetic profile(s) (the life cycle is closed on station);

  - genetically and otherwise appropriate seed fish are stocked if/when considered relevant.

• Aquaculture (which has different objectives) is developed in parallel, recognizing that captive populations can contribute to understanding the biology of wild organisms, either through simple observation or specifically designed experiments.

• Participatory management of the breeding grounds is in place, possibly involving compensation for lost income to fishers.

5. CONCLUSIONS

It seems likely that the giant Mekong fish considered here are threatened due to human activities, and a set of recommended outcomes, including experimental management, are detailed which may help to identify the factors that need to be managed in order to secure the future of these species. Management aimed at preserving self-sustaining natural populations of the giant Mekong fish species populations will most likely be a subset of management of the aquatic resources of the basin. It is unlikely that efforts to save the wild populations of the giant species will be successful unless an ecosystem approach is used. To accomplish this on a basin-wide scale will require collaboration with other sectors, and this may best be carried out through the MRC's Basin Development Plan. It is in this context that the special characteristics of the giant species become apparent; they are very obvious and suitable for catching the imagination and interest of non-specialists among the public as well as policy makers.

Failing the ecosystem approach, preservationists will have to resort to keeping the threatened organisms in captivity, for possible future re-introduction to the wild. However, unless simultaneous efforts are made to also preserve the stability and function of the ecosystem, this amounts to little more than a cosmetic approach that addresses symptoms and not causes.

References

Balon, E.K., 1990. Epigenesis of an epigeneticist: the development of some alternative concepts on early ontogeny and evolution of fishes. Guelph Ichthyol. Rev. 1: 1-48.

Froese, R. and A. Torres, 1999. Fishes under threat: An analysis of the fishes in the 1996 IUCN Red List. In: Towards policies for conservation and sustainable use of aquatic genetic resources (R.S.V. Pullin, D.M. Bartley and J. Koiman, eds.). ICLARM Conf. Proc. 59. 277 p.

Pauly, D., V. Christensen, J. Dalsgaard, R. Froese and F. Torres Jnr, 1998. Fishing down marine food webs. Science 279: 860-863.

Rainboth, W. J., 1996. FAO Species Identification Field Guide for Fishery Purposes. Fishes of the Cambodian Mekong. FAO, Rome. 265p + 27 plates.

Walters, C., 1997. Challenges in adaptive management of riparian and coastal ecosystems. Conservation Ecology [online]1(2):1. Available from the Internet. URL: http://consecol.org/vol1/iss2/art1