Availability of “seed” for capture-based aquaculture - grouper

Generally, groupers spawn on offshore reefs where they form aggregations of tens of thousands of individuals, in a few specific locations. They produce pelagic larvae that may disperse over hundreds of kilometres in the course of 20-50 days and experience high density-independent mortality. Larvae, transported to near-shore nursery habitats settle as juveniles in sea-grass beds, mangroves, oyster reefs, and marshes (Coleman et al. 1999).

For this reason grouper “seed” is mainly caught in coastal areas, particularly around sea-grass, mangrove and shallow brackishwater areas near river mouths and estuaries, as well as in tidal pools and around reefs. The peak grouper “seed” season is often associated with the relatively wet months in the year (e.g. monsoon seasons); in several areas, grouper “seed” collectors have claimed that their best catches were associated with windy weather (Johannes and Ogburn 1999). This is consistent with a number of recent studies into recruitment pulses of settlement-stage reef fish – including groupers – that accompanied windy weather, which apparently caused the fish to be transported shoreward (e.g. Shenker et al. 1993; Dixon, Millich and Sugihara 1999).
The volume of “seed” caught each year exceeds hundreds of millions of individuals (Sadovy 2000). The greatest catches tend to be of the smallest size classes (1–3 cm); during peak seasons a catch can be of tens of thousands by a single unit of gear, in a single night, by one fisherman (e.g. using a fyke net). Even larger sizes of fish are being captured in massive numbers region-wide each year.

 

It is a sobering thought to realize that the equivalent of the typical annual amount of seed produced in the hatcheries in the whole of SE Asia (excluding Taiwan Province of China), i.e. 20 000–80 000 fry, can be caught by one fisherman in one night (Sadovy 2000).
When “seed” catches are compared to the numbers of marketable fish produced, the results are astonishing and strongly suggest crude and wasteful culture practices. To produce the regional estimate of 23 000 tonnes of table-size live fish from culture annually (roughly 10 000 tonnes of which is included in the regional live reef fish trade (LRFT) volume provided above), about 60 million seed fish are needed (Sadovy 2000). The trade in grouper “seed” throughout South East Asia is complex and extensive (Figure 60).
The major destinations of the trade routes for grouper “seed” are Hong Kong, China and Taiwan Province of China, while the major sources are the Philippines, Thailand, and, to a lesser extent, Indonesia, Malaysia and Taiwan Province of China. Two-thirds of the production from Taiwan Province of China is based on the grow-out of hatchery reared fry; this country also exports both hatchery produced seed, and imports and re-exports capture-based “seed”.
Some of the trade is probably illegal because of a concern in some countries about keeping adequate numbers for local use, or the importation of disease with the seed (e.g. between Malaysia and Hong Kong, Taiwan Province of China and Thailand; from Johore (Malaysia) through Singapore to Taiwan Province of China; between Myanmar and Thailand; and from Taiwan Province of China to the People’s Republic of China). Some trade from Viet Nam to the People’s Republic of China may also be illegal, but this can not be substantiated.
Other identified minor trade routes are from Indonesia and the Philippines to Brunei Darusallam, and from the People’s Republic of China to Hong Kong. Sri Lanka has supplied seed to Hong Kong. Seed also enters the People’s Republic of China from Thailand and Taiwan Province of China through Hong Kong. In this survey, the roles of Singapore, Sri Lanka, Japan and the Republic of Korea have not been included, although they play a minor part in various aspects of the live reef fish trade. The absence of detailed trade data makes it difficult to fully evaluate trade routes (Sadovy 2000).