Environmental and biodiversity impacts of capture-based aquaculture

Yvonne Sadovy de Mitcheson
The University of Hong Kong
China, Hong Kong Special Administrative Region
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Min Liu
The University of Hong Kong
China, Hong Kong Special Administrative Region
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Sadovy de Mitcheson, Y; Liu, M. 2008. Environmental and biodiversity impacts of capture-based aquaculture. In A. Lovatelli and P.F. Holthus (eds). Capture-based aquaculture. Global overview. FAO Fisheries Technical Paper. No. 508. Rome, FAO. pp. 5–39.

SUMMARY

The project “Towards sustainable aquaculture: selected issues and guidelines”, implemented by the Food and Agriculture Organization of the United Nations (FAO), seeks to address selected key issues of sustainability in relation to current global aquaculture practices and developments. 

The specific thematic area, use of wild fish and fishery resources for aquaculture production, is identified, an important component of which is aquaculture production systems based on capture-based aquaculture (CBA). Around this thematic area, two review papers, one covering social and economic aspects, the other environmental and biodiversity issues of wild resource use, and ten background papers on selected marine and freshwater species used for CBA, have been compiled.

The thematic review on environmental and biodiversity issues, reported on herein, covers a wide range of representative marine and freshwater, vertebrate and invertebrate species used for CBA, selected from the four major taxonomic groups of cultured organisms, molluscs, crustaceans, echinoderms and finfishes with the following objectives:
• to summarize the life history stage(s) and habitat(s) of seeds collected from the wild, the regions and countries where CBA is taking place, why and how they are being used, capture method(s) and volumes with associated bycatch and discards;
• to diagnose and discuss the current and/or potential impacts of CBA practice on the environment and wild stocks;
• to review current agreements and legislation for ensuring sustainability of wild seed fisheries and trade for CBA, methods to reduce bycatch and their implementation, and to discuss potential management measures at national and international levels;
• to discuss the fundamental relationships between life history stages being exploited and impacts on wild stocks; and
• to provide recommendations for sustainable wild seed and capture fisheries and CBA practices.

The review concludes that major representative species from the four different taxonomic groups share characteristics of high market demand, and high predictability in time or location leading to ease of capture and accessibility. Most CBA species are high value, luxury, species, rather than regular food fish or invertebrate species used for cheap daily consumption.
Although issues of disease, environment and biodiversity are also relevant to hatchery-based aquaculture (HBA), there are certain considerations specifically or indirectly pertinent to CBA practices and matters relevant to both CBA and HBA. With the extensive practice and development of CBA-related fisheries (seed fisheries), international transport and growing trade of wild seed both regionally and globally, problems of disease and genetic pollution associated with transfers and escapes of wild seeds may be a matter for concern. Moreover, the non-selective use of many gears associated with CBA, wasteful bycatch associated with the capture of certain species, high post-capture mortality of target species, and extensive use of fish feed (sourced from wild fish and hence a further pressure on wild populations) for grow-out, could mean that certain seed fisheries are not sustainable and have a negative impact on other fishery sectors of the same, or different, species.
Current and recent management measures, as well as those being developed that are applicable to various aspects of wild seed fisheries associated with CBA, are summarized and discussed. Management measures need to respond to problems noted in various fisheries, including declining catches, control of fishing gears, bycatch and damage to substrate. Wild seed fisheries for CBA are typically not managed or controlled effectively and most management measures are relatively recent, developed or adopted after the seed fishery has declined substantially.
CBA is an economic activity that is anticipated to expand in the short term, and is very likely to continue into the long term for many species. CBA is practised because it has become necessary or desirable as a livelihood, as an alternative means of controlling access to fishery resources, to meet market demand and, if practised properly, to enhance yield. It does not necessarily, as is often assumed, or even desirably, lead to HBA, does not demonstrably take pressure off wild stocks, and is typically practised with high value species, often for export or luxury markets, rather than inexpensive food alternatives for local use. Recommendations are provided that include the need to apply the precautionary principle, refer to the FAO Code of Conduct for Responsible Fisheries (CCRF), seek measures to reduce mortality of captured animals and to minimize bycatch of non-target species. For CBA activities, it is important to develop management approaches, especially where different life history phases of a stock are exploited by different fishing sectors, develop clear objectives and definitions in each case and consider culture practices that reduce dependence on carnivorous species and seek cheaper alternatives to provide affordable food for local use.

INTRODUCTION

Given growing shortages in many fishery resources, aquaculture is widely considered to be important for food provision and for reducing pressure on fisheries in both developing and industrialized countries. Aquaculture production has developed since the 1970s at an average annual increase rate of 8.8 percent with growth accelerating in recent years (FAO, 2007). Among the 200 or so species of mollusc, crustacean and finfish cultured, many are based on “grow-out” or “fattening” of wild-caught “seeds” (see “Definitions” below), the seeds ranging from very early in life to adults. In all cases these “seeds” are held for varying time in captivity and/or fed and/or protected from predators until they reach marketable size (FAO, 1997a, 2006; Ottolenghi et al., 2004). This practice, the “growing-out” or “fattening” of wild-caught “seeds”, is referred to as “capture-based aquaculture” (CBA), and involves a range of marine and freshwater, vertebrate and invertebrate species. The fish production from such growing-out or fattening practices is estimated to be at least 20 percent of the total annual fish aquaculture production with a value of US$1.7 billion (FAO, 2004; Ottolenghi et al., 2004). Although CBA has been practised for decades, it was not until 2004 that the descriptive term, CBA, was introduced to clearly define this practice and to distinguish it from hatchery-based aquaculture (HBA) on the one hand, and capture fisheries on the other hand (Ottolenghi et al., 2004). In reality, CBA is a hybrid of these two practices but differs in important ways from both as a means of food production and in relation to fishing pressure on wild populations.
CBA has several widely assumed advantages resulting from its history and its apparent practical simplicity. For example, it is widely considered that the economic cost of seed taken directly from the wild is lower compared to seed reared in hatcheries for many species. It is also commonly believed that CBA is conducted on animals caught locally to culture operations and, therefore, that the risks of exotic disease transfer and genetic pollution to the environment and wild stocks are low to non-existent (Munro and Bell, 1997). These perspectives largely stem from the early practice of what has come to be known as CBA in some species of keeping alive in captivity animals taken in the local fishery to maintain them fresh for short periods of time until the market price improved or they were needed. Over time these practices expanded considerably to include trading of species both regionally (defined as within the geographical range of the species) and globally (defined as out of the geographical range of the species) or for extended maintenance in captivity for grow-out (Islam et al., 1996; Mohan Joseph, 1998; Bagarinao, 1999; Jeffs et al., 1999; Sadovy, 2000; Ottolenghi et al., 2004).
One other factor that makes CBA appealing is the belief that taking fishes or invertebrates when they are small and young and placing them into captivity for feeding and protection from predators reduces their natural mortality. In this way, the practice is widely assumed to increase productivity by enhancing survivorship relative to natural levels at a given size or age. This may or may not be true and depends on many factors, most importantly on the life history stage(s) at which animals are removed from the wild and the volumes involved. While this subject is covered in more detail below, for those species in which natural mortality levels become very low within a few weeks or months of settlement, their capture before sexual maturation but after this early high natural mortality period could substantially affect the sustainability of natural populations. Moreover, the degree of bycatch and discards and the mortalities of wild seeds during and after capture (i.e. from capture and during culture) can be extremely high, factors rarely considered when examining the culture of such species. Combined, these factors mean that the costs, both economic and environmental/biodiversity, of CBA are substantially higher for some species than previously thought and the impacts of CBA on natural stocks generally not considered (Naylor et al., 2000; Sadovy, 2000; Sadovy and Vincent, 2002; Ottolenghi et al., 2004). Nonetheless, as demand for seafood grows and over-fishing and competition for fishery resources increase, CBA is inevitable and must be addressed directly to ensure sustainable practices especially when it is not considered, or has proven unlikely, to be a stepping stone to HBA.
As a combination of aquaculture and capture fisheries, CBA exhibits characteristics of both practices. For example, captive grow-out for CBA uses the same systems (e.g. extensive and intensive; ponds, cages and tanks), consumes the same natural resources (e.g. land, water and labour), and utilizes the same feeds (e.g. formulated/
pellet feed or fresh feed that contain mainly small fishes and shellfish) as HBA. CBA also encounters some of the same problems, such as production of wastes and resultant contamination of the environment, diseases and their treatment and transfer. On the other hand, wild seed collection of many species for CBA has many similarities to typical capture fisheries, in terms of capture methods (including some that are destructive) and seasons, catch sizes, catch per unit effort (CPUE), bycatch and discards, stock assessment and fishery management. In more extreme cases, CBA is little more than a capture fishery of juveniles, almost always unmanaged, and hence a clear and additional threat to the long term sustainability of targeted species.
CBA poses unique challenges to resource managers at a time when aquaculture is increasingly viewed as essential for future food production and for reducing over fishing. The extent to which CBA contributes to both is, based on current practices for many species, far from clear. On the positive side, CBA is often a step towards HBA, a transition phase which allows much to be learned about rearing species before the challenges of hatchery production can be met. Conversely, some species used for CBA are also taken as part of traditional capture fisheries in fishing sectors that focus on adult fish, rather than seeds, and the removal of different life history stages by separate fishing sectors can lead to conflicts and problems of equity. Removing too many larvae and juveniles (i.e. immature individuals) for CBA, for example, could compromise stock persistence in the adult capture fishery sector because insufficient juveniles persist to maintain reproductive output, or vice versa. In addition, the option of CBA in over-fished stocks has resulted in the transfer of fishing effort from dwindling adults to juveniles possibly compromising stocks (Naylor et al., 2000; Sadovy, 2000; Sadovy et al., 2003; FAO, 2004; Ottolenghi et al., 2004). In such cases, the apparent increased food production from CBA can come at the cost of reduced fishery captures leading to questions of equity and efficiency of use of limited fishery resources.
Notwithstanding concerns over CBA, it continues to be extensively practised despite limitations noted in the supply of wild seed in some cases and where there are no moves towards HBA. There are growing concerns, therefore, that the practice itself may be one more cause of reductions in seed availability and the adult fisheries that these support. Given these concerns and the ever-growing interest and focus on aquaculture in general, there has emerged a need for both developing and industrialized countries to create and implement a comprehensive framework of regulations and market mechanisms to ensure that the practice of CBA is conducted in a sustainable manner, and to understand more about CBA practices in general.
To achieve sustainable CBA there is a need for gathering data on the biology, practices and seed collection (seed fisheries) of CBA species. A wide range of representative marine and freshwater, vertebrate and invertebrate species used in CBA practices selected from four major groups, molluscs, crustaceans, echinoderms and finfishes are examined in this review. There are five objectives in relation to the selected species: (1) to summarize the life history stage(s) and habitat(s) of seeds collected from the wild, and the regions and countries where CBA is taking place and to indicate why and how they are being used; (2) to gather data on capture method(s), volumes, and associated bycatch and discards (when information is available); (3) to diagnose and discuss the current and/or potential impacts of CBA practices on the environment and wild stocks, based on the findings of (1) and (2); (4) to discuss current/recent and/or potential impacts in relation to transfer of wild caught seeds in relation to diseases, genetic pollution, etc., providing examples, as appropriate; and (5) to review current agreements and legislation for ensuring sustainability of wild seed fisheries and trade for CBA, methods to reduce bycatch and their implementation, and to discuss potential management measures at national and international levels. The theoretical relationship between life history stages of certain species, their exploitation and its impacts on wild stocks, especially in relation to management decisions, are discussed. Finally, recommendations are given, based on information gathered in the present review for sustainable wild seed and capture fisheries and CBA practices.
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