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oyster culture in Quiberon Bay. RISCO is a “Pôle Mer Bretagne” project with a collaboration between CRC Comité Régional de la Conchyliculture de Bretagne
Sud, Ifremer La Trinite sur Mer and different partners including UBS Laboratory Géoscience Marine et Géomorphologie du Littoral G.M.G.L Université de
Bretagne Sud, Vannes, Université de Nantes – Laboratoire LEMNA: Laboratoire d’Économie et Management de Nantes, Cochet Environnement and CER du
Morbihan Réseau nautile, Vannes
1.2 Objectives
The objectives of this study are to analyse RISCO data on oyster mortality, to determine effect of predators on oyster culture, to map the distribution of
different types of predators and to calculate the economic analysis of oyster mortality.
2 Literature Riview
2.1 Oyster Culture
Oyster farming is an aquaculture mariculture practice in which oysters are raised for human consumption. Generally, there are three methods in oyster
farming Marteil et al., 1979:
1.
On-bottom culture: shellfish or oyster are deposited on the ground or on bottom in the intertidal zone, or beyond the low tide of the seas in
deep water.
2.
Off-bottom culture: it is only practice on off- bottom at low tide. The oysters are placed in racks through pockets for example. All the
oysters rest on racks or tables that keep it up of a few decimeters.
3.
Suspended culture: the oysters are constantly immersed in the culture as in deep water, but it does not rest on the ground and are gathered
into bins or pockets, bonded in the bars or ropes, etc. Suspended between the water surface and depths varying from floating or fixed
facilities which is dominant in the sea. In figure 1, we can see methods of oyster culture.
Figure 1.Oyster culture
Commonly, in Asia there are two methods which have been done in oyster culture, there are Webster, 2007:
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1. The Floating raft, in example: China. They use bamboo to support the oysters while they are growing.
2. Stick culture, Sticks are placed vertically in soft mud bottom, catching spat from the water column.
In Indonesia, several methods of oyster culture have been experimented. The raft or floating method was tested in Banten Bay, Java, in the early 1970s as
well as the rack method in the estuarine waters of Pamanukan, Java. The stake and rock methods are also used. Oyster culture in Indonesia is largely experimental at
present Lovatelli, 1988. In Malaysia, three culture methods are practiced. The raft or floating
method is employed for oysters grown in riverine conditions where siltation is relatively heavy and tidal range is considerable. The pole and rack methods are
intertidal fixed-culture methods used for both spat collection and grow-out. The bottom oyster culture method as it is practiced in the Muar River requires no
special grow-out grounds Lovatelli, 1988. In China, several methods are being practiced: 1 Bottom method. The
oyster C. rivularis is cultured mainly on the bottom of estuaries of low salinity, 2 Stake method with bamboo, 3 Stone-bridge method. This method is
preferred for sandy muddy bottoms, 4 Raft method, and 5 Bottom method. Choi 2008 found that in Korea, the culture techniques are bottom culture
and long lines and rafts were introduced and the culture area subsequently expanded from the intertidal area to deeper waters offshore. There are 14 species
of oysters that have been identified in Korean waters, although only Crassostrea gigas is extensively used in oyster industry.
In Europe, there are several techniques in oyster culture: on-bottom culture, off-bottom culture, and suspended culture. On-bottom culture consists of
sowing oysters directly into the intertidal seabed about 25 of the total production or in deep water, 5–15 m depth 10. Off-bottom culture is done by
using plastic mesh bags set on trestles in the intertidal zone. This is now the principal technique used, accounting for 60 of the total production. Suspended
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culture 5 is done by the hanging oyster’s fixed on ropes or in baskets from special frames in the Mediterranean lagoons or on lines in the open sea. The
Brittany coastline is highly varied with numerous favorable bays and estuaries, and it has a longstanding tradition of flat oyster culture. Oysters are cultivated in
mesh bags 70 or in deep waters Buestel, et al. 2009. In the Bay of Quiberon, deep water culture has increased, with 100 farms producing about 10,000 t per
year from more than 2600 ha of concessions Buestel, 2007. In The United States, oysters can be grown either on or off the bottom of
the ground. Additionally, off-bottom techniques are being developed in Maryland on the Chesapeake Bay involving floatation devices made from PVC frames on
which these racks or bags can be placed Webster, 2007.
2.2 Factors affecting the oyster mortality
