Alosa alosa might be disappearing from the river Garonne in France.
The Allis Shad was once relatively common in parts of the UK, but it has now all but disappeared. It is a close relative of the herring, but migrates into fresh water to spawn. The Allis Shad requires clean, cool water and is not able to negotiate rapids in the way that Salmon can. (Shad Ecology)
Traditional fishery disappearing
There is a long-standing tradition of fishing for Allis Shad (Alosa alosa) in the river Garonne in South-West France. Phillipe and Sebastien Gautier are professional fishermen, and they report very poor catches from the Garonne over the past few years (Ref: ‘Le Republicain’ – Jeudi 24 Mai 2007 – page 31). They blame increasing water temperatures at migration and spawning time.
Water Temperature
The ‘Alose’ (Allis Shad) prefers cool water for migrating and spawning. Recently the temperature of the river Garonne has probably been too high for them. This might be a consequence of more general ‘Global Warming’, or maybe more specifically related to the effect of using the water to cool nuclear power plants (as the Gautier brothers suggest). Whatever the reason, the water is becoming too warm!
Global warming and Nuclear Power
It would be ironic if both were contributing to the demise of the Allis Shad, since Nuclear Power generation is often put forward as a way of reducing carbon emissions and thereby reducing the ‘Greenhouse Effect’. If these fish are suffering from the general effects of global temperature increase which is (in their case) exacerbated by the nearby presence of a nuclear power plant they are indeed unfortunate!
Spawning Grounds
It is, of course, very difficult to decide where any particular fish was heading when it was caught, but this information is needed before conservation measures can be put in place. New research might make this easier. It has been found that the hard parts of fish can hold traces of the water chemistry of the place where the fish grew up. In particular the ‘otoliths’ (hard structures in the head of the fish) can be analysed, and the results can help decide which population the fish in question came from. For more technical details see: Otolith Chemistry
Helping Fish Travel Upstream
The French take their fisheries very seriously indeed and they have pioneered many engineering solutions to the problems that migrating fish encounter when they reach man-made barriers. The fish often have to find ways to pass dams etc.. (See ‘Fish Lifts and Fish Locks the French Experience’) If it turns out to be true that cooling water also poses a significant threat to migrating fish they will have a whole new set of problems to resolve.
Recipe
The Allis Shad is not only appreciated for its beauty! (See Alose a l’oseille).
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