CAPTURE METHODS, VOLUMES AND IMPACTS ASSOCIATED WITH WILD SEED COLLECTION FOR CBA

The capture methods and associated bycatch and discards with wild seed collection for CBA, and their impacts on the environment and wild stocks are summarized for selected representative species from four major taxonomic groups, molluscs, crustaceans, echinoderms and finfishes; mortality from capture and during culture is indicated (when information is available) (Tables 3 and 4).

Estimated catch volumes of wild seeds for CBA are given, when data are available (Table 5). The actual and potential problems of bycatch and sustainability in relation to catch volumes and associated mortalities are highlighted using illustrative examples. Such information is essential for identifying management issues and needs for planning future developmental directions for aquaculture. Examples are provided from each of the four groups of species.
• CBA in molluscs typically involves the collection of spats. Spats settle on specially designed “collectors” or on natural substrates, often during well-known settlement seasons and in specific collection areas. Although this approach is thought to be associated with a low level of bycatch due to the methods used, there are possible but unknown potential impact(s) from over-collection of the wild spats.

Moreover, when settlement areas are modified or habitat dredged to install artificial settlement collectors, potential impact(s) on wild stocks of target or other species is (are) possible. Little is known of the early mortality rates in molluscs that would allow for management of this activity for CBA and there have been declines noted in both adults and spat supplies in areas where a wild seed collection exists for CBA for a number of species (Tables 3 and 5). Although the cause(s) for the declines is (are) unknown, given that spat catch volumes can involve tens to hundreds of tonnes (e.g. the Greenshell® Mussel Perna canaliculus), or tens of thousands to millions of spats, it is feasible that adult stocks are ultimately affected, especially if much of the annual settlement is concentrated in specific areas, or during specific seasons. It is quite possible that highly targeted collection of large numbers of spats could significantly affect population regeneration if a high proportion of settlers are removed for CBA each year.

• Crustacean wild seeds are collected by various methods for CBA and, as for molluscs, seed collection tends to be concentrated in specific locations and seasons when large numbers become temporarily available (Tables 3 and 5). For shrimps, the process of wild seed collection involves nets of various types, from push nets to towed/dragged nets in shallow coastal waters or creeks. Bycatch using such gears can be high from Asian and South American countries (e.g. Bangladesh, India, Malaysia, Philippines and Ecuador) and involve a variety of larvae and juveniles of commercial fishes and crustaceans as well as discards depending on the area fished (Petersson, 2002; SAPB, 2002; M.L. Cobo personal communication, 2007). Many millions of shrimp post-larvae are collected in the season within small areas (Table 5); mortality levels from capture to transfer to ponds appear to be low for at least one species (Penaeus monodon) (Petersson, 2002). For lobsters, wild seed are collected using artificial substrates on which the pueruli settle, as well as by nets of various kinds and while diving (with collection by hand or using cyanide) in some cases. Declines in seed availability have been noted in Asian countries.
• The relationship between the collection of very early stage seeds and the status of adult stocks has been shown in a few species identifying the need for a holistic look at such fisheries. For example, a relationship between settlement stage pueruli and numbers of resulting lobster adults was identified in Australia (Phillips et al., 2003; Gardner et al., 2006). This finding is extremely important for highlighting the link between settlement numbers and subsequent adult stock size and for setting a fishery quota for both pueruli and adults in this case. For mud crabs, nets, pots, shovels and hooks are all used to collect megalopa with catch rates estimated in one place at 60 000?70 000 per fisherman per night in the peak seasons, which may have negative impacts on wild stocks (Angell, 1992).
• Small holothurians are taken for CBA using specially designed seed collectors and by hand. Adult stocks of a number of species have shown marked declines and populations of some species have suffered over-exploitation for decades in some Asian countries (Lovatelli et al., 2004). Hatchery-based holothurian aquaculture (e.g. Japanese sea cucumber Apostichopus japonicus) has been well-developed in China in recent years (Chen, 2004); whether HBA of holothurias can reduce the impact on wild stocks and help stock recovery needs further investigation.
• In finfishes, seeds of a wide range of sizes are taken, and in large numbers, from settlement stage larvae through to adults. Adult and seed stocks have shown marked declines in almost all representative species, the result of some combination of over-exploitation of wild stocks of adults and seeds, habitat loss, etc. The heavy take of seed for some species is also prompted by the limited supply of hatchery-reared seeds (Table 4). Associated with seed collection, bycatch and mortalities can be high, leading to much wastage of target and non-target species in some areas or during certain activities. Examples include milkfish in Indonesia and the Philippines, shark catfishes in Cambodia and Viet Nam, mullets in Egypt, sea basses, snappers and porgies in Southeast Asia and Egypt (Table 4). In these species, capture methods range from nets, traps, hook-and-lines and trawlers, to chemicals and artificial shelters; many methods are not species-specific and can cause significant habitat disturbance and damage. Although bycatch species containing some commercially important finfishes and shrimps can also be used for CBA, most tend to be discarded, while a few might be consumed by humans, depending on size.