Native Oyster

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.

 

The harvesting of native oysters (Ostrea.edulis) and Pacific oysters in the the Fal Estuary for commercial purposes is an activity with more than two centuries history.  And it is the last remaining commercially viable native oyster fishery in the UK.

Despite the decline in the native oyster fisheries seen in the past for which Bonamia, 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). 

Since 2014 the fishery has been managed by Cornwall Inshore Fisheries and Conservation Authority (CIFCA), they carry out annual surveys of the fishery.

Landings of native oysters declined in the winter of 2018 /2019 due to decreased demand for oysters from traditional French markets. large numbers of oysters (11,000 tonnes ) were placed on lays to grow on that season. There was an increase in landings of queen scallops which allowed the fishery to remain profitable. 

According to the detailed annual surveys carried out by Cornwall IFCA the stocks of oysters within the limited area of the Fal fishery fluctuate but remain within safe limits. A detailed stock assessment is not carried out but overal picture is of increased distribution and density of oysters on the beds and in recent years there has been a well documented increase in numbers of the scallop Mimachalmys varia (marketed as Queen scallops).

 

Stock is assesed via route 2 - there is no concern for fishing pressure but there is concern for stocks due to signs that this fishery is declining in its productivity.  Stock rating is now 0.5. Landings are low partly due to poor markets. No detailed stock assessment is carried out but detailed annual surveys by CIFCA show that the stock  density on the oyster beds fluctuate. The unique nature of this sail and oar fishery means it is unlikely to collapse however it may not be operating at its best potential while stocks are low. Management restricts efficiency of fishery but sets no catch limits. and thus has no clear solution to potential over-fishing in future. Impact of gear on seabed within SAC results in capture method score 0.5. Dredges are lightweight but there are no published studies proving a reduced impact.

The Truro River oyster fishery (producing Fal Oysters) is unique in its management, in that oysters can only be harvested using sail and oar power and dredges can only be hauled by hand. This is the only fishery of its kind and the overall effect has been to limit the fishery by making it more inefficient. In the recent article by Long et al (see references) this is argued to be the cause of the long-term success of this fishery in comparison to other less sustainable fisheries. The fishery has recently become the responsibility of Cornwall Inshore Fisheries and Conservation Authority. The 2016 Regulatory order for Fal Fishery modernised the regulation from the old fishery bye-laws and reduced the area which can be fished taking away the southern area of the fishery where the fishery overlapped with protected mearl beds and seagrass beds. Additionally an exclusion zone was also introduced around an area of seagrass found off Penarrow point. The minimum size of oysters which can be removed from the fishery are those which can hang on a ring of  67mm diameter can be harvested and oysters which pass through the ring must be put over the side of the boat back onto the fishery, or put onto oyster lays - areas on the very low shore set aside for oysters to be stored. There is a closed season for oyster fishing between 1st April and 30th September inclusive.  All dredges used must be licensed (Licence fee is currently £165 per year). Dredging can only be carried out between the hours of 9am and 3pm on weekdays and 9am and 1pm on a Saturday - there is no dredging allowed on a Sunday. The dredges themselves are limited to a maximum width of 1.2m, and the dredge must not have teeth, tines or other digging projections. The dredge must not exceed a weight of 20kg. These restrictions combined with the fact that only manual handling of dredges is allowed restricts the impact of the dredges on the seabed and makes this method of dredging far more sustainable than scallop dredging or oyster dredging under power. Cornwall IFCA fal fisheries Managment Plan 

 

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”