Scallop aquaculture
Globally the scallop aquaculture industry is now well established, with a reported annual production totalling over 1,200,000 metric tonnes [3] from about 12 species.
Collection of wild spat has historically been the most common way obtaining young scallops to seed aquaculture operations.
Most methods involve a series of mesh spat bags suspended in the water column on a line which is anchored to the seafloor.
While initial attempts to culture scallops in hatcheries were fraught with extremely low spawning and high larval mortality rates,[5] a number of successful techniques have now been developed.
[2] Following settlement, the larvae undergo metamorphosis where they rearrange their body form to begin their life as a seafloor dwelling juvenile scallop.
Mortality rates are often highest during metamorphosis as larvae go through a series of behavioral and anatomical changes such as loss of the velum (the larval feeding structure) and development of new filter-feeding mechanisms and gills.
Such a system would have large advantages over other forms of culture as tight control of feed and water parameters could be maintained.
Longlines have proved effective for most farms to date and have the added advantage of being able to be completely submerged (with the exception of marker buoys) so to reduce visual pollution.
Pearl nets are typically hung ten to a line and have the advantage of being light and collapsible for easy handling.
Flow rate of water and algae is adequate and scallops will usually congregate around the edges of the circular net to maximise their food intake.
This method results in a similar growth and mortality rates as ear hanging but has the advantage of being able to set scallops from a small size.
This method is quick and cost effective and has been used to a great extent in the European Queen Scallop (Aequipecten opercularis) industry.
[8] Growing scallops in suspended plastic trays such as oyster cages can serve as an alternative to equipment like lantern nets.
The main advantage of using methods of bottom culture is in the lower cost of reduced buoyancy needs as equipment is supported by the seabed.
[8] Wild ranching is by far the cheapest of all forms of scallop farming and can be very effective when large areas of seabed can be utilized.
[8] Scallops are filter feeders that are capable of ingesting living and inert particles suspended in the water column.
[11] Recently, with the increase of enclosed farming techniques, a large amount of work has been directed at development of an artificial microalgal substitute that is more cost effective than traditional feeds.
[12] Microalgae cultures may also be manipulated in order to produce algae with a more desirable protein, lipid and carbohydrate profile and much work is being conducted in this area.
[13] Similar positive results for growth and survival have been observed in larvae fed with high protein diets.
[2] ASP is a neurotoxin produced by some marine diatoms and has also been reported in scallops from the Northwest Atlantic (Bird & Wright, 1989).
[19] Once scallops have been grown, harvested and processed the principal end product is the meat, which usually consists of just the adductor muscle (fresh or frozen).
This is a result of filter-feeding bivalves removing suspended solids, unwanted nutrients, silt, bacteria and viruses from the water column so to increase water clarity which, in turn, improves pelagic and benthic ecosystems, particularly by promoting growth of vegetation such as seagrasses.
This has been well observed in Russia where culture of scallops in partially closed bays has resulted in eutrophication and so changes in species composition and structural and functional parameters of pelagic and benthic communities.
This is in line with a large body of data showing bivalve aquaculture activities result in various environmental changes including changes in hydrological regime, ecological communities (including planktonic communities), biochemical composition of waters, biodeposits and invertebrate settlement success.
[2] Furthermore, aquaculture farms are a source of visual pollution and so often attract public opposition in highly populated coastal areas.
