Promising spat collection trials in New Caledonia
Monday, 02 November 2009 14:32

There are times when one needs to listen to nature to seek the fantastic opportunities it can offer. Aquaculture that is based on spat collection is one of these. At certain times, millions of free-swimming pelagic shellfish larvae float within the water column, seeking a substrate to settle on. By submersing spat collectors at the right time and place, an unlimited supply of bivalve spat can be harvested and then grown to commercial size.

 Motivated by the New Caledonian development agency ADECAL and the willingness of local entrepreneurs, SPC’s Aquaculture Section, together with a team of divers, has been undertaking a spat collection campaign targeting tropical scallops in New Caledonia’s lagoon.

New Caledonia has diverse tropical scallop resources that could be harvested commercially given their various size ranges. Two species in particular — Mimachlamys gloriosa and Bractechlamys vexillum — can be collected in great quantities using spat collection techniques. M. gloriosa and B. vexillum are the most common scallop species found in New Caledonia’s lagoon. B. vexillum is a mobile species that lives exclusively on soft-bottoms while M. gloriosa lives fixed on algae, sponges or on hard substrates. Spawning of these species occurs year round with some seasonal peaks. 

For an initial spat collection trial it was decided that the spat collectors would be submerged during the winter, which corresponds to one of the spawning peaks for these species. Four sites were identified for spat collection: Nouville, Tontouta and La Foa in the Southern Province, and Pagop in the Northern Province. Previous trials carried out in Nouville are showing promising results already. The area around Pagop area was also sampled the year before and has also scored promising results, while Tontouta and La Foa were new sites that were never tested. 

Most of the spat collectors were made from locally available materials (e.g. onion bags filled with a 1-m² shade cloth). Some other types of collectors (including commercial Tahitian collectors and other prototypes) were also trialed. A small float was attached to each spat bag in order to keep it above the seafloor because the lines were fixed down in the water column, towards the substrate. Anchorage was made with either sand bags or other types of moorings that were placed using scuba. All spat collection lines carried 30 bags and were placed at three different sites in each area in order to define the potential of the different stations that were sampled. 

Collectors were left in the water for two months so that spat could settle and grow to a size at which they could be identified. In mid- to late August 2009, the team went back and harvested the collectors. All collectors were recovered and catches were identified by Dr Paul Southgate, bivalve specialist and head of the Aquaculture Division at Australia’s James Cook University. M. gloriosa and B. vexillium were the most represented species in the catch, although many other shells were also collected (but with no commercial importance) but which may have potential for sale as specimen shells. A key to the identification of scallop spat is currently being produced as a tool for farmers. 

Overall, the initial study results are promising, with spat numbers ranging from 0–400 scallops per bag, depending on the site and the type of collection device used. The size at which the scallops were collected ranged from 5–19 mm; smaller specimens were put back to the lagoon. The project will soon start a grow-out trial period for the collected spat using suspended culture techniques on longlines. 

For more information contact SPC’s Aquaculture Officer, Antoine Teitelbaum, at This e-mail address is being protected from spambots. You need JavaScript enabled to view it