Nonnative Oysters in the Chesapeake Bay (2004) / Chapter Skim
Currently Skimming:
7. Oyster Aquaculture
7. Oyster Aquaculture
Pages 150-161
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 150... ...
For instance, the Romans built ponds to stockpile the harvest and collected spat on wooden branches (Clark, 1964; Heral and Deslous-Paoli, 1991~. However, the true development of oyster culture in Europe was initiated during the 18th century to sustain the harvest after increased fishing effort depleted the natural beds and fishing regulations failed to halt the precipitous decline in oyster landings.
|
From page 151... ...
Oyster culture in the Chesapeake Bay has been a technologically unsophisticated practice, relying mainly on natural spatfall in public beds and using extensive on-bottom culture. Aquaculture methods have not been employed to any appreciable extent in the Chesapeake Bay, not even methods to maximize spat recruitment using artificial spat collectors.
|
From page 152... ...
It should be noted that in several countries the development of integrated coastal zone management planning has facilitated the use of coastal resources through spatial allocation of reTABLE 7.1 Simplified Description of Various Methods for Oyster Culture Production Natural Spatfall Hatchery Products Natural strains | Selected strains Seed Supply Harvest (public beds) Spat collectors (oyster shell to plastic PVC tubes and dishes)
|
From page 153... ...
West Coast (Jones and Jones, 1982~. Hatchery-produced oyster larvae made oyster farmers independent of natural seed sources and paved the way for the development of broodstock management and genetic improvement programs.
|
From page 154... ...
.. ~ NONNATIVE OYSTERS IN THE CHESAPEAKE BAY Oysters raised predominantly for shucked meat production are set onto oyster shells from the processing plants after the shell has been aged for at least a year.
|
From page 155... ...
As a consequence, many farms opt to purchase seed from nursery facilities at sizes ranging from 2 to 20 mm. Growth to harvestable size is accomplished in a variety of systems such as rigid plastic mesh bags attached to ropes anchored on the bottom or secured to intertidal racks or suspended in trays or lantern nets suspended from floating longline or raft structures.
|
From page 156... ...
The subtidal culture practices include on bottom, submerged on-bottom cages, fixed tables and rafts, floating rafts, and longlines. Unless policies are developed to manage concurrent uses of bay waters, spatial conflicts are likely to arise from the use of raft and floating systems that impede navigation and will consequently limit the amount of area available for oyster culture.
|
From page 157... ...
West Coast produce about 37.5 billion Pacific oyster "eyed larvae" each year, of which about 12 billion are triploid (Nell, 2002~. The commercial value of triploid Pacific oysters comes from reduced sexual maturation, which results in retention of better meat quality through the spawning season and superior growth, at least in productive waters (Davis, 1988; Garnier-Gere et al., 2002~.
|
From page 158... ...
Such a high percentage of triploids appears to be optimistic based on the reported rates of triploid induction in Pacific oysters by commercial hatcheries (Guo et al., 1996~. Even at 99% triploidy, an introduction of this size could potentially introduce 10,000 reproductively competent, nonnative oysters to bay waters, as critics and an ad hoc review panel of the Chesapeake Bay Program argued.
|
From page 159... ...
The percentage of diploid cells is higher for chemically-induced triploids and varies among individuals, as a function of tissue type, and possibly among species. The risk that reversion presents to any proposed introduction of triploid nonnative oysters is that the germinal tissue of triploids may revert to the diploid state, making the oyster reproductively competent.
|
From page 160... ...
The relative reproductive potential of triploid females crossed with diploid males is 0.0045%, which suggests that inadvertent introductions of diploid males with triploid females might raise the reproductive potential of nonnative triploid introductions by an order of magnitude. Similar data on the reproductive potential of triploid Suminoe oysters have not yet been published.
|
From page 161... ...
Triploids may also revert to the diploid state as they age, but probably less than 1% of a mated triploid cohort might eventually produce normal gametes if they remain in the field more than 3 or 4 years. Triploids are not always completely sterile.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.