Oyster Harvesting: Health and Safety
Harvesting bivalve shellfish in Mannion Bay is both unsafe and against the law. Sewage contamination and biotoxin closures are shown on the map based on the BC Centre for Disease Control‘s Shellfish Harvesting Status Map.
The area in yellow is closed year round to all shellfish harvesting due to natural contamination from toxins present in various species of plankton that oysters and other shellfish feed on. For information about toxic biotoxins see Plankton.
The area in pink is closed due to septic contamination. Sewage can originate from pleasure boats that lack holding tanks and moor overnight in Kwilákm; from Snug Cove’s live-aboard boats; and from poorly maintained private septic systems located on lands around the Bay. The Snug Cove Sewer System, which serves about 100 connections, and does not include Deep Bay or Snug Point residences, pipes partially treated sewage to release just off Dorman Point. From there, tide and current can sweep the sewage around Snug Point to settle in Kwilákm.
Diseases associated with sewage contamination include ear infections, diarrhea, and hepatitis. Monitoring water quality is critical for public health. During the swimming season, Vancouver Coastal Health tests water off Bowen’s beaches for the presence and quantity of fecal coliform bacteria.
Fecal coliform is an indicator the water that has been contaminated by sewage. When beaches are officially closed to swimming, you’d best stay out of the water.
What can we do? When private septic systems bordering Terminal Creek or Kwilákm are poorly maintained, they can leak raw or partially treated sewage and excess nitrogen into the sea. If you have your own septic system, set up a service contract for your system and commit to a regular schedule of maintenance with an inspection and pump out as needed.
Paralytic Shellfish Poisoning
How do oysters fit into this story? Because oysters feed by filtering microscopic organisms from the water, impurities and bacteria present in the water will stay behind in the oyster’s tissue and build up over time. As a result, bacteria can be 100 times more concentrated within the oyster’s tissue than in the surrounding water.
Red tide is a common name for harmful algal blooms which result from large concentrations of aquatic organisms. Harmful algal blooms happen when algae grows so much in an area of the ocean that it discolours the water with a reddish or reddish-brown colour. Water draining from the land and containing sewage and fertilizer can transport nutrients to the sea and stimulate bloom events. Red tides commonly bloom in late summer and early fall when the water is warm.
Bivalve shellfish (clams, oysters, and mussels) concentrate the poisons in their body. Paralytic shellfish poisoning (PSP) occurs when humans or other mammals (including your pet) eat bivalve shellfish contaminated with large concentrations of poisonous aquatic organisms. According to the BC Centre for Disease Control, PSP symptoms can include: tingling and numbness spreading from lips and mouth, dizziness, nausea, vomiting, and paralysis. Time between ingestion and onset is between 30 minutes and three hours. Respiratory failure and death can occur within 12 hours.