Native Oyster

Ostrea edulis

Native Oyster

Image | Sarah McCartney, Cornwall Wildlife Trust

Description

Native oysters are highly prized but across their range they are becoming more and more rare. The stocks of native oyster in Falmouth and the Helford estuary are healthy and in Falmouth the Truro River Oyster fishery (whch produces Fal Oysters) is uniquely managed through a bylaw that has effectively frozen the fishery in time by banning the use of motors so that oyster are still collected using traditional sailing and rowing vessels. This makes Fal Oysters highly sustainable as well as a world famous delicacy.


Sustainability Overview

This low impact artisanal fishery is a great example of a the preservation of shellfish stocks through a simple ruling that has also preserved a traditional way of life and created a niche fishery product that has high marketing value.

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When is best to eat?

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Sail and Oar

Truro rIver and Fal Estuary

Sustainably harvested using lightweight dredges that are towed by traditional sail boats and rowing boats. The unique management of this fishery has resulted in a sustainable harvesting regime that has kept stocks healthy for 150 years.

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How we rate fish

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Cornwall Good Seafood Guide rates fish on sustainability using a scale of 1 to 5.

1, 2 and 3 are recommended, Fish to avoid are rated 5.

We use the system devised by the Marine Conservation Society (MCS) so our scores are comparable with the scores produced by MCS for the UK and fisheries from all around the world. For more information on scoring click here.

Sustainability Overview

This low impact artisanal fishery is a great example of a the preservation of shellfish stocks through a simple ruling that has also preserved a traditional way of life and created a niche fishery product that has high marketing value.

Native Oyster

Biology

The native or flat oyster is a filter feeding, bivalve mollusc. They live on the seabed in relatively shallow coastal waters and estuaries (from the lower shore to 80m). They prefer habitats sheltered from strong wave action which tend to be muddy, but require something hard for larval settlement - usually shells or stones. All native oysters start out as males, and throughout their lives change back and forth from male to female. In Britain, breeding normally takes place in the summer. It reaches maturity at about 3 years old. The average reproductive size for the oyster is about 5cm. Oysters can reach a shell length of up to 11cm, and occur in variable shapes. Native oysters have a rough shell that is yellow, pale green or brown in colour, sometimes with bluish, pink or purple markings. The two halves of a native oysters shell are different shapes. The left shell is deeply concave and fixed to the substratum, the right being flat with rougher edges and sitting inside the left, acting as a lid. Inner surfaces of both valves or shells are smooth and usually pearly, white or bluish-grey, often with darker blue areas.The shell shape is a good way to distinguish native oysters from Pacific oysters, which were introduced to the UK in 1926, and which compete with the native oyster for space and food. Native oysters have rounder shells with smoother edges, while their Pacific relatives have a more elongated shell with deeply grooved edges. A single female oyster can produce 2 million eggs. Although usually up to about 11cm long, native oysters can grow to more than 20cm and can live as long as 20 years.
 

Stock Info

From CEFAS lower Fal and Percuil – The harvesting of native oysters (O.edulis) and pacific oysters in the the Fal Estuary for commercial purposes is an activity with more than two centuries history. The Truro Oyster Fishery is the second largest fishery for the native oyster in the United Kingdom (walker and Laing , 2006).
Despite the decline in the native oyster fisheries seen in the past for which Bonamiois, pests, competition from slipper limpets chemical contaminants and TBT had contributed, the small fishery using sailing dredgers and hand dredging has been recovering in Carrick Roads (Walmsley and Pawson, 2007). 
In March 2009, members of the Carrick Maritime Division of Carrick District Council and the Shellfish Resource Team of CEFAS undertook a stock assessment for native oysters. The assessment included sampling across the inner and outer harbour, in three main sections. Results indicated high abundance of large oysters exceeding minimum landing size of 65mm length across the three sections surveyed. The highest density (approximately 40 oysters per dredge haul) was found in the harbour section. Medium sized oysters (50—64mm), those that are likely to grow sufficiently to enter the fishery in the following 2 seasons, were found widely distributed throughout the survey area and were locally abundant at Turnaware point, around themed point of the Easter Bank and lower half of the Western Bank.
 

Management

The Truro River oyster fishery (producing Fal Oysters) is unique inits management in that oysters can only be harvested using sail and oar power and dredges can only be hauled by hand. The fishery has recently become the responsibility of Cornwall Inshore Fisheries and Conservation Authority. In the Helford the shell fish beds are managed through a several order effectively making the stocks and beds private. The minimum size of oyster which is harvested is determined by the fishery byelaws (in 2007, only oysters which hang on a ring of 2 5/8th inch (equivalent to 66.3mm) diameter
can be harvested and oysters which pass through the ring must be put over the side of the boat back onto the fishery).
 

Capture Info

Native oysters from the truro river (Fal) oyster fishery are caught using low impact and heavily restricted methods. Lightweight dredges (without teeth) are pulled over the oyster beds and are hauled by hand. They are also farmed on oyster beds or 'lays'. 

References

Classification of bivalve mollusc Production areas in England and Wales, Sanitary Survey Report) Fal estuary(lower) and Percuil river 2012 CEFAS Kershaw and Campos
COUNCIL REGULATION (EC) No 510/2006 on protected geographical indications and protected designations of origin “Fal Oyster”  
 

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