MAFF and NCC disagreed about the legality and wisdom of farming the Manila Clam in Poole Harbour (UK).
The Grooved Carpet Shell (Ruditapes decussatus) is fished commercially in France, Portugal, Spain, and to a much lesser extent in the south of Britain. In an attempt to make the British fishery more productive the Manila Clam (R. philippinarum) has been introduced into British coastal waters, but this deliberate introduction of a non-native species into the wild was controversial.
MAFF and Economic Interests
Around 1980 the British government's Ministry for Agriculture, Fisheries and Food (MAFF) decided to explore the idea of a commercial fishery using the Manila Cam, and scientists began to study the animal in detail.
The sub-tropical origins of the Manila Clam seemed to suggest that it would be unable to breed successfully in British waters, so young 'seed animals' were deliberately released into mesh cages in the sea at Poole a decade later.
NCC and Environmental Interests
In 1981 the British government passed a law which banned the release of non-native animals into the wild.
The Nature Conservancy Council (NCC) considered that MAFF was breaking this law, and a dispute arose between these two government bodies – MAFF argued that containment in cages did not constitute 'release into the wild'.
MAFF also pointed out that the Manila Clam could not breed in British waters, but NCC was still concerned about the possible influence this species would have on natural ecosystems if it did somehow survive in the wild.
Manilla Clam Escapes
MAFF were wrong – the caged clams began to breed successfully, and fishermen exploiting the nearby cockle-beds began to find young Manilla Clams among the cockles in the 1990s. Either the clam was more adaptable than government scientists believed, or global warming had altered the marine environment sufficiently to allow breeding.
Exactly how widespread the Manila Clam has become is difficult to assess. John Humphreys (in The Biologist) points out that British identification keys do not contain the Manila Clam, and that surveys might well confuse it with the native Grooved Carpet Shell.
Where detailed distribution studies have been carried out around Poole Harbour the initial findings suggest that the Manila Clam has become widespread, but that it is not harming the native clam. It is even thought that its introduction might be having beneficial effects – by increasing the food supply for some of the wading birds for example.
This case study ('The introduction of the Manila clam to British coastal waters') illustrates a couple of important points:
- scientists can 'get it wrong', either by underestimating the adaptability of a species, or by failing to allow for future environmental change
- government departments can end up opposing one-another over the interpretation of their own laws.
References:
'The introduction of the Manila clam to British coastal waters' - John Humphreys, The Biologist (The Journal of the Society of Biology), October 2010.
Ruditapes decussatus, and Ruditapes philippinarum - United Nations (Fisheries and Aquaculture Department Factsheets).
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