Maryland Department of Natural Resources

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Glossary

  • box oyster - Pairs of empty shells joined together by their hinge ligaments. These remain articulated for months after the death of an oyster, providing a durable estimator of recent oyster mortality (see gaper).
  • bushel - Unit of volume used to measure oyster catches. The official Maryland bushel is equal to 2,800.9 cu. in., or 1.0194 times the U.S. standard bushel (heaped) and 1.3025 times the U.S. standard bushel (level).
  • cultch - Hard substrate, such as oyster shells, spread on oyster grounds for the attachment of spat.
  • dermo disease - The oyster disease caused by the protozoan pathogen, Perkinsus marinus.
  • dredged shell - Oyster shell dredged from buried ancient (3000+ years old) shell deposits. Since 1960 this shell has been the backbone of the Maryland shell planting effort to produce seed oysters and restore oyster bars.
  • fresh shell - Oyster shells from shucked oysters. It is used to supplement the dredged shell plantings.
  • gaper - Dead or moribund oyster with gaping valves and tissue still present (see box oyster).
  • Haplosporidium nelsoni - The protozoan oyster parasite that causes MSX disease.
  • infection intensity, individual - Perkinsus sp. parasite burdens of individual oysters, estimated by RFTM assays and categorized on an eight-point scale. Uninfected oysters are ranked 0, heaviest infections are ranked 7, and intermediate-intensity infections are ranked 1-6. Oysters with infection intensities of 5 or greater are predicted to die imminently.
  • infection intensity, mean sample - Averaged categorical infection intensity for all oysters in a sample: sum of all categorical infection intensities (0-7) ÷ number of sample oysters. Oysters populations whose samples show mean infection intensities of 3.0 or greater are predicted to experience significant near-term mortalities.
  • infection intensity, mean annual - Averaged categorical infection intensities for all annual survey oysters: sum of all sample mean intensities ÷ number of annual samples
  • intensity index, sample - Categorical infection intensities averaged only for infected oysters: sum of individual infection intensities (1-7) ÷ number of infected oysters
  • intensity index, annual - Categorical infection intensities averaged for all infected survey oysters: sum of all sample intensity indices ÷ number of annual samples
  • market oyster - An oyster measuring 3 inches or more from hinge to mouth (bill) (ventral margin).
  • mortality (observed), sample - Percent proportion of annual, non-fishing oyster population mortality estimated by dividing the number of dead oysters (boxes and gapers) by the sum of live and dead oysters in a sample: 100 x [number of boxes and gapers ÷ (number of boxes and gapers + number of live)]
  • mortality (observed), annual - Percent proportion of annual, bay-wide, non-fishing oyster mortality estimated by averaging population mortality estimates from all samples collected during an annual survey: sum of sample mortality estimates ÷ number of survey samples
  • MSX disease - The oyster disease caused by the protozoan pathogen Haplosporidium nelsoni.
  • MSX frequency, annual - Percent proportion of sampled populations infected by H.nelsoni(MSX): 100 x (number of sample with MSX infections ÷ total sample number)
  • Perkinsus marinus - The protozoan oyster parasite that causes dermo disease.
  • prevalence, sample - Percent proportion of infected oysters in a sample: 100 x (number infected ÷ number examined)
  • prevalence, mean annual - Percent proportion of infected oysters in an annual survey: sum of sample percent prevalences ÷ the number of samples
  • RFTM assay - Ray's fluid thioglycollate medium assay. Method for enlargement, detection, and enumeration of Perkinsus marinus cells in oyster tissue samples. This diagnostic assay for dermo disease has been widely used and refined for over fifty years to date.
  • seed oysters - Young oysters produced by planting shell as substrate for oyster larvae to settle on in historically productive areas. If the spatfall is adequate, the seed oysters are subsequently transplanted to growout (seed planting) areas, generally during the following spring.
  • small oyster - An oyster older than one year old but less than 3 inches (see market oyster, spat).
  • spat - Oysters younger than one year old.
  • spatfall, spatset, set - The process by which swimming oyster larvae attach to a hard substrate such as oyster shell. During this process the larvae undergo metamorphosis, adopting the adult form and habit.
  • spatfall intensity - The number of spat per bushel of cultch. This is a relative measure of density used to calculate the spat index.
  • spatfall intensity index - The arithmetic mean of spatfall intensities from 53 fixed reference sites or Key Bars: sum of Key Bar spatfall intensities ÷ number of Key Bars
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