2 In Natives

Ostrea Edulis – The European Flat Oyster

A Native Oyster

The European Flat Oyster (Ostrea edulis) is the indigenous oyster of Europe, and in these parts it is often called the Native or Flat oyster. In France, Ostrea edulis are known as huîtres plates (flat oysters) except for those that come from the Belon River estuary in Brittany, France, which are known as ‘Belons‘.

A full overview of the species can be found here, but in brief:

The native oyster Ostrea edulis has an oval or pear-shaped shell with a rough, scaly surface. The two halves (valves) of the shell are different shapes. The left valve is concave and fixed to the substratum, the right being flat and sitting inside the left. The shell is off-white, yellowish or cream in colour with light brown or bluish concentric bands on the right valve. Ostrea edulis grows up to 11 cm long, rarely larger. The inner surfaces are pearly, white or bluish-grey, often with darker blue areas.

Due to its unique taste, Ostrea edulis is commonly known as the oyster connoisseur’s oyster of choice, and I would have to agree. Not that there is anything wrong with a good Pacific / Rock, but for a pure taste of what an oyster is about, for me, it has to be a Native.

A History of Decline

The history of Ostrea edulis is fascinating and makes for depressing reading. As a species it has suffered a massive decline and we are lucky it is still with us; as one might expect the hand of man has played a huge part, if not the key part, in this decline.

Records show that Ostrea edulis has been gathered and consumed by humans since the Mesolithic, and they are commonly found in large quantities by archaeologists in shell middens. This document produced by Heriot Watt University for the DEEP oyster restoration project provides a fascinating discussion of Ostrea edulis in the Dornoch Firth on the east coast of the Highlands, and only a “stone’s throw” from our site.

However, over time the growth of the human population has resulted in over fishing, physical damage to benthic habitats, pollution and eutrophication. In particular, it would appear that a serious decline in species numbers coincided with arrival of the industrial revolution; the introduction of industrial trawling and railway systems, coupled with increased urban demand, seems to have be the key driver behind population decline across the European Atlantic coast.

One of the best, or should that be worst, examples is right here in Scotland. Scotland used to be home to a major flat oyster fishery which by the 18th century was of commercial scale, supplying a European wide market with an abundance of high quality oysters. The jewel in the crown of this operation were the Firth of Forth fisheries. It is hard to believe but the Newhaven fishery, in the Forth estuary, had annual landings of 59.9million, yes million, oysters from 1834 – 1836. However by 1874 – 1875 this had declined sharply to 815,850, decreased further to 55,140 by 1882 – 1883 and no landings were recorded in the following season. Shortly after this the fishery collapsed completely and in 1957 the European Flat Oyster was found to be extinct the Firth of Forth.

A perfect lesson in why unregulated commercial greed can leave such destruction in its wake. In addition, this has resulted in people in Scotland having little understanding of the rich history of oysters in our country. Living memory has ‘forgotten’ that at one time, oysters were the food of the common man and not the preserve of the rich as many perceive them to be today. They are not by the way, they are for everybody!

Disease

By the 20th Century the oyster industry in much of Europe was in serious decline and the majority of natural beds of Ostrea edulis have never recovered. The French industry did recover however, and thrived until the 1960s when large scale mortalities, – over 90%, were recorded in Ostrea edulis in Aber Wrach in Brittany. The parasite Marteilia refringens was diagnosed in dying oysters, and within three to four years most of the oyster growing regions within Brittany were infected with this parasite.

In addition, in 1979 Bonamia ostreae was detected in Ostrea edulis populations in France, Spain and Denmark. The parasite can cause over 90% mortality among oysters, when initially introduced into a naïve population. Bonamia has continued to spread throughout Europe and further damage the populations of Ostrea edulis, with knock on impacts for any associated fishing or farming activities.

As a result of over exploitation and disease the production of the European flat oyster constituted less than 0.2 percent of the total global production of all farmed oyster species in 2002. The bulk of production (97.7 percent) came from the rearing of the Pacific cupped oyster, Crassostrea gigas.

Restoration

Within Scotland Ostrea edulis is now listed as a Priority Marine Feature considered to be of conservation importance in Scotland’s seas. This has been replicated throughout Europe and there has been much recent debate about trying to restore Ostrea edulis beds across the continent. This has led to the foundation of the Native Oyster Restoration Alliance (NORA). The alliance is a European network aiming at reinforcement and restoration of the native European flat oyster (Ostrea edulis). Network members are representatives of governmental agencies, science, non-governmental organisations, as well as oyster growers and other private enterprises.

One of the key restoration projects is DEEP, mentioned above. The aim of this project is to restore Native European oysters to the Dornoch Firth. It has been pioneered by the Glenmorangie Whisky company in partnership with Heriot-Watt University and the Marine Conservation Society. Here is short clip detailing what they aim to achieve:

Our Role

And what of us? Well we are incredibly lucky to have a farm situated in such a pristine location, a rare occurrence in Europe today. As such, we have been able to experiment with growing Ostrea edulis on site and we have successfully managed to grow our trial stock to commercial size in our chosen equipment. Further to that, these oysters are clean and healthy and our site and stock are free of both of the diseases that have caused so much damage to the wild populations of Ostrea edulis.

This means we feel we are well placed to help supply stock for the many restoration projects that are starting and that is great for both us and the species itself. This year we shall have several thousand Ostrea edulis going to help in restoration, not many, but a small start and a step along the road.

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