Scallops

The consideration of water quality in scallop farming is important. As with other bivalves, scallops filter phytoplankton; they can also filter bacteria or viruses some of which can be a risk to human health and often derived from land-based activities such as water treatment, storm drainage and diffuse agricultural run-off. Bio-toxins may also be contained in seasonally occurring marine algae (Harmful Algal Blooms or HABs)^{1, 2} which the scallops can ingest.

Rigorous controls need to be in place in regards to harvesting shellfish such as mussels in order to protect consumers; ensuring that those sold into the supply chain meet strict food safety (health and hygiene) standards³. The UN Food and Agriculture Organisation (FAO) has developed the Codex Alimentarius or “Food Code” which is a set of voluntary standards, codes of practice and guidelines covering food and its production, including those for bivalve molluscs^{4, 5}, and specifically scallops⁶ . The aim of the Codex is to protect public health and to support balanced trade relationships in food, and all World Trade Organisation (WTO) signatories are obliged to observe them. In practice, most countries have laws that are very broadly equivalent to Codex guidelines but differ from them in the detail.

European Hygiene Regulations⁷ state that shellfish business operators are responsible in ensuring that bivalve molluscs meet strict standards. The UK Food Standards Agency, in compliance with European regulations, has classified shellfish harvesting areas and beds on the basis of the level of the bacterium E.coli in mollusc flesh. Depending on shellfish production area classification (A, B or C) certain procedures must be followed to enable harvested mussels to enter the market. Molluscs harvested from Class A areas can go straight to market, but they are often purified (depurated) to provide additional assurance of quality; those harvested from Class B areas must be purified before being sold to consumers. All molluscs sold on the UK market must contain less than 230 cfu (colony forming units) of E.coli per 100 g of flesh^{8, 9}.

Depuration is a technique whereby live shellfish and bivalves such as mussels and oysters are placed in systems with continually circulated and sterilised seawater in order to remove undesirable substances, pollutants, parasites or organisms of possible harm to human beings (e.g. pathogenic bacteria)¹⁰. Depuration however is not a method widely used for scallops; shucking is. Shucking involves the removal of all the viscera from the scallop to leave only the edible parts, and this removes the vast majority of bacteria and viruses, as well as algal bio-toxins the scallop may have ingested¹¹. As scallops are not eaten raw (unlike other shellfish such as oysters), appropriate cooking also eliminates these risks, as well as those potentially posed by norovirus¹². End product testing of live shellfish is also undertaken in countries such as the UK, to ensure shellfish products that enter the market are safe to eat^{13, 14}.

For many reasons, there is an on-going societal need to reduce coastal water pollution, and this is of particular importance to protect and enable the growth of bivalve aquaculture. Legislation exists to control water pollution, for instance that in the UK¹⁵, but pollution incidents do occur, and efforts continue to improve water quality^{16, 17}.

Active management (i.e. continuous, real time decision making, taking account of all the available information enabling shellfish producers to decide what action to take in regards to when and where to harvest), is an important tool to reduce the risks from poor water quality and HAB episodes¹⁸, especially in inshore waters.