Capture-based aquaculture of groupers
Mark Tupper
WorldFish Center
Penang, Malaysia
E-mail: Этот адрес электронной почты защищён от спам-ботов. У вас должен быть включен JavaScript для просмотра.
Natasja Sheriff
WorldFish Center
Penang, Malaysia
E-mail: Этот адрес электронной почты защищён от спам-ботов. У вас должен быть включен JavaScript для просмотра.
Tupper, M.; Sheriff, N. 2008. Capture-based aquaculture of groupers. In A. Lovatelli and P.F. Holthus (eds). Capture-based aquaculture. Global overview. FAO Fisheries Technical Paper. No. 508. Rome, FAO. pp. 217–253.
SUMMARY
The economies of China and Southeast Asia have developed rapidly over the past two decades, leading to the emergence of a wealthy class with substantial disposable income. This has led to an increasing demand for fish in the region (Birkeland, 1997). The “live fish trade” of the Indo-Pacific has expanded rapidly in recent years, and now targets many species (Johannes and Riepen, 1995; Sluka, 1997, Sadovy and Vincent, 2002). Groupers are greatly valued for the quality of their flesh, and most species command high market prices. Groupers are the most intensively exploited group in the live fish trade, and the high prices paid by exporters to local fishermen mean that target species may be heavily over-fished (Morris, Roberts and Hawkins, 2000).
In order to alleviate the pressure on wild grouper stocks, many nations have promoted aquaculture in the hopes of producing a more sustainable grouper yield. However, full-cycle culture of most grouper species is not yet possible, although several important advances have been made in recent years. For this reason, about two-thirds of all grouper culture involves the capture and grow-out of wild seed (Sadovy, 2000). This is known as capture-based aquaculture (CBA).
There are at least 16 species of groupers that are cultured in many Southeast Asian countries, including Indonesia, Malaysia, Philippines, Taiwan Province of China, Thailand, China Hong Kong Special Administrative Region (SAR), the southeast of the China and Viet Nam (Sadovy, 2000). Grouper culture is also undertaken in India, Sri Lanka, Saudi Arabia, Republic of Korea, Australia, the Caribbean and in the southeastern United States of America. Despite the huge popularity of live fish in China and Southeast Asia, only 15–20 percent of the amount consumed each year comes from aquaculture, as culture is principally constrained by limited and unreliable supplies of wild seed and the difficulties of spawning in captivity.
Grouper seed is collected using a variety of methods. Capture methods are generally artisanal and the fishermen employ a variety of artificial habitats. Some grouper seed collection methods are more damaging than others. Clearly destructive methods include those that result in high mortality, involve high levels of bycatch, and/or cause damage to the fish habitat. A further problem is that some methods result in monopolization of the local fishery by a few individuals. Destructive methods include scissor nets and fyke nets, which are already banned in some areas. The mortality rates that follow capture and transport are not well documented; estimates for over the first 2 months after harvest are quite variable (30–70 percent), depending on the quality of fry, the level of transport stress, and the presence of disease and cannibalism (Pudadera, Hamid and Yusof, 2002).
Because full-cycle culture of most grouper species is not yet possible, approximately 66–80 percent of all grouper culture involves the capture and grow-out of wild seed and the volume of seed caught each year exceeds hundreds of millions of individuals (Sadovy, 2000). When seed catches are compared to the numbers of marketable fish produced, the results strongly suggest crude and wasteful culture practices. Sadovy (2000) estimated that about 60 million seed fish are needed to produce the regional total of 23 000 tonnes of table-size live fish from culture annually.
Trash fish is commonly used for feeding in grouper cage culture, but its increasing cost, shortage of supply, variable quality and poor feed conversion ratios indicate that this form of feed may not be the best from either a nutritional or an economic point of view. A dependable supply of cost-effective, non-marine, sources of alternative protein must be provided if grouper farming is to remain profitable. Millemena (2002) demonstrated that up to 80 percent of fishmeal protein can be replaced by processed meat meal and blood meal derived from terrestrial animals with no adverse effects on growth, survival, and food conversion ratio (FCR). From an economic standpoint, replacement of fishmeal with cheaper animal by-product meals in practical diets can alleviate the problem of low fishmeal availability and high costs.
Recent research suggests that the ecological footprint of capture-based grouper aquaculture is large (Mous et al., 2006). Support for grouper CBA is often based on the assumption that the natural morality of early juvenile grouper is very high, so that the fishery is not adding substantially to this natural mortality and therefore not affecting adult population size to any great extent. This assumption remains untested for most grouper species. However, recent research suggests that the period of very high mortality occurs during and immediately after settlement, and that juvenile grouper surviving more than a few days have a much higher chance of survival (Tupper, 2007). In addition to problems of bycatch, wasteful mortality, and overfishing, cage and net culture can create other environmental problems, most notably point-source pollution which can have adverse effects on coastal waters, and particularly on coral reefs.
As a contributor to rural livelihoods, particularly those of coastal fishers, grouper aquaculture can generate potentially large financial benefits. The high value of grouper on the export market ensures that farmers are able to generate a profit even when stocks suffer heavy mortalities. Despite high initial investment costs, studies have shown that with appropriate support, even the poorest can benefit from grouper culture, with implications for both household well-being and community development. However, based on the information reviewed in this report, capture-based aquaculture may not be the best means to ensure a steady and sustainable supply of grouper for either the live or “non-live” fish trades. This is due to a number of problems including low availability of seed, destructive and wasteful seed collection techniques, removal of large numbers of early life history stages with subsequent impacts on adult populations and conflicts with capture fisheries, and pollution and disease resulting from culture operations.
The obvious solution to some of the problems of CBA for grouper is to develop closed-cycle hatchery rearing for all the grouper species sought by the market. Important advances in full-cycle culture have been made for several species, particularly in Taiwan Province of China, and full-cycle culture appears financially feasible given a large enough capital investment. However, given the financial means of most grouper culturists, and the difficulty in rearing most grouper species, it remains unlikely that many of these species will be hatchery-reared in the near future. In the meantime, steps must be taken to improve the management of both CBA and capture fisheries for grouper.
INTRODUCTION
The economies of China and Southeast Asia have developed rapidly over the past two decades, leading to the emergence of a wealthy class with substantial disposable income. This has led to an increasing demand for fish in the region (Birkeland, 1997). The “live fish trade” of the Indo-Pacific has expanded rapidly in recent years, and now targets many species (Johannes and Riepen, 1995; Sluka, 1997; Sadovy and Vincent, 2002). Groupers are greatly valued for the quality of their flesh, and most species command high market prices. Groupers are the most intensively exploited group in the live fish trade, and the high prices paid by exporters to local fishermen mean that target species may be heavily over-fished (Morris, Roberts and Hawkins, 2000). Trade often follows a pattern of sequential over-exploitation; the most highly sought species are fished out in country after country, before the less valuable species are targeted and fished intensively (Sluka, 1997; Johannes and Riepen, 1995). Wealthy customers pay very high prices for endangered species in Chinese and Southeast Asian markets. In 1997 the red grouper, Epinephelus akaara, fetched US$42/kg in China Hong Kong SAR markets. In 2004, restaurants were charging US$225 for only the lips of the humphead wrasse, Cheilinus undulatus. Thus, fishermen will go to great lengths in order to catch every fish, and this has already contributed to regional population crashes of species, including Epinephelus akaara and Epinephelus striatus (Morris, Roberts and Hawkins, 2000; Sadovy, 2001a).
The impact of intensive fishing is exacerbated by the K-selected life strategies of these genera, their tendency to form predictable spawning aggregations and their occurrence on relatively shallow, easily accessible coral reefs, which are severely over exploited in many parts of the world. For many of these species, spawning aggregations represent the total reproductive output for a given year, and many species consistently return to the same aggregation area, year after year. Fisheries often target spawning aggregations, since they are consistent in time and space and large numbers of fish can easily be caught in a short time (Rhodes and Tupper, 2007). When fishing pressure removes a high proportion of the fish forming these aggregations, these may quickly decline, and within a few years may cease to form altogether (Johannes et al., 1999; Sadovy and Eklund, 1999).
A large proportion of the world’s groupers are caught in artisanal fisheries, and even low-level artisanal fisheries can adversely affect stocks of these highly vulnerable species. Recreational fishing may also have significant impact on stocks; for example, the recreational fishery of groupers accounts for up to 35 percent of Florida’s (United States of America) total grouper catch (Morris, Roberts and Hawkins, 2000). The global catch of groupers showed a 68 percent increase from 100 724 tonnes in 1991 to 168 943 in 2000. In order to alleviate the pressure on wild grouper stocks, many nations have promoted aquaculture in the hopes of producing a more sustainable grouper yield. Because grouper are particularly difficult to culture in closed systems, full-cycle culture of most grouper species is not yet possible (although several important advances have been made in recent years). For this reason, about two-thirds of all grouper culture involves the capture and grow-out of wild seed (Sadovy, 2000). This is known as capture-based aquaculture (CBA).
There is a strong link between fishing activity and the capture-based seed used for farming, with declines in premium species from the overfishing of grouper adults. However, the reasons for this decline cannot be evaluated without careful, controlled studies, as falling catches may in fact be due to a combination of different causes: overfishing of the adults which produce the juveniles, habitat degradation and pollution, destructive fishing techniques, high export demand, etc. (Johannes, 1997; Sadovy, 2000). A more holistic management approach to establish the links between adults and juveniles is necessary.