Harvesting Shellfish
Bivalve shellfish
Bivalve shellfish use a filter feeding mechanism that filters water from their
environment. If the water contains bacteria, viruses or other contaminates,
these filter feeding organisms can accumulate toxins and concentrate bacteria
within their bodies. The diseases found in the shellfish may be passed on to
humans if the shellfish are consumed. Diseases found in shellfish range from
mild gastroenteritis (stomach ache) to typhoid fever and infectious hepatitis.
The shellfish harvest in Boundary Bay has been closed since 1962 due to the
presence of potentially harmful bacteria and viruses found in the water. There
are many possible sources of contamination and testing for each type of bacteria
and virus is costly and ineffective due to their low concentrations. In order to
determine the safety of shellfish harvesting, regulatory agencies test for the
presence of indicator species rather than the actual pathogens.
Eelgrass Oysters
Fecal Coliforms
Fecal coliforms belong to a group of bacteria that are currently being used as
an indicator species by Canadian agencies to determine the sanitary quality of
water and shellfish in the water and the possible presence of disease causing
organisms. Coliforms are used as an indication of sewage pollution because
coliform bacteria such as Escherichia coli (E. coli) are directly associated
with the intestinal tracts of humans and warm-blooded animals such as livestock.
Fecal coliforms are not normally present in sea water, so their presence in
areas such as Boundary Bay indicates sewage contamination and possible risk of
disease.
E. coli
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The water quality standards for shellfish harvest have been set at: the median
or geometric mean fecal coliform Most Probable Number (MPN) does not exceed
14/100 ml and not more than 10% of the samples exceed 43/100 ml in the multiple
tube fermentation (MTF) test. Fecal coliforms are usually present in sewage at
levels around 6 million/100 ml. The standard for drinking water is 0 fecal
coliforms/100 ml, and the swimming standard is 100 fecal coliforms/100 ml. |
Shellfish harvesting closures due to contamination can be seen on Environment
Canada’s website:
http://www.pac.dfo-mpo.gc.ca/ops/fm/_private/Biotoxins/closures/sanitary_e.htm |
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