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How British Waterways are destroying the annual natural spectacle of Bream spawning in the Old River Lea


Each Spring, around the beginning of May, hundreds and hundreds of mature Bream make their way up the Old River Lea until they arrive at the upper limit of the twice daily tides below the sluices at Lea Bridge in Hackney. They can be seen in large shoals, all along the stretch from below the sluices past the Friends Bridge to around the outfall from the storm relief channel, awaiting the best conditions for them to spawn.

They are waiting until the tide from the Thames is at its lowest and the river water flowing from beneath the controlled sluices by Lea Bridge allows the slowest clearest flow to reveal the bottom living Tapegrass emerging above the surface. As these conditions are approaching they can be clearly seen, each of them, vigorously defending their chosen patches of Tapegrass.

As more patches of this grass emerge above the surface the fish become increasingly excited until more and more females are breaking above the surface and propelling themselves at speed across the clumps of grass on their sides ejecting their sticky eggs as they go. Nearby males then release their white sperm-laden fluid or 'milt' in a sudden flush to flow over the eggs which have adhered to the Tapegrass.

These first outbreaks of spawning trigger a crescendo from hundreds of fish which agitates large stretches of the surface and turns the shallow river white with milt.

I was first told last year about this amazing natural spectacle by Dave Rackstraw a local allotmenteer and keen river watcher. He has been watching it occur for about a dozen years. It is knowledge that is shared by other local river watchers and anglers. Unfortunately it does not seem to have reached the ears of the officials who work for the various agencies which have the responsibility of safeguarding and improving conditions in this part of the river.

We know this because they seem content to allow two critical events to happen. One of which is at present preventing these fish from spawning and the other will soon destroy permanently the low tidal conditions which the Bream actively seek in which to spawn.

Firstly we have observed, on many occasions last year and again currently this year, as the water level drops and the fish are becoming increasingly agitated, that suddenly the upstream sluices are opened some more, greatly increasing the water flow rate and increasing its depth over the spawning site. This causes the fish to immediately lose interest and shows how discerning they are about their best chances of spawning successfully.

I have recently written about this to British Waterways who are responsible for conditions in the Lea Navigation Canal which is full of water from the River Lea. It is from the canal that the Lea Bridge sluices allow water to flow into this stretch of the Old River Lea. Their reply clearly demonstrates that they have no interest in allowing the best conditions of flow and level for the Bream to spawn.

They say “A steady flow is ... needed in the Old River Lea to assist with maintaining water levels on a low tide, otherwise this river could potentially run dry on a low tide. This constant moving water helps to keep the water fresh and avoid stagnation. So the primary function of these sluices is water conveyance and the sluices have to be opened to enable this function, depending on the upstream water levels.”

I suspect that they have not hitherto been aware of this mass spawning behaviour and how critical a low flow period is to its success. They seem to be concerned about the water and indifferent to the fish.

Secondly British Waterways are about to impound the Old River Lea and prevent the tidal flows into the river via Prescott Channel in Bow. They are in the later stages of constructing a lock and a barrage at Prescott Channel. Their contractors will, some time in June, fit the second of two 'fish belly gates' next to the lock and then raise them both hydraulically to achieve 'tidal lock out'.

This will mean in the future that the water in this whole stretch of the Old River Lea will be maintained around the current high water level. This will remove completely the low water conditions which the Bream are actively seeking for spawning.

A description from the scientific literature about lake Bream shows how critical this clean shallow water is for these fish to spawn. “Within a natural bream spawning habitat, eggs were distributed in the most shallow water accessible to spawning females,..... No eggs were found below a depth of 40cm [16ins]. We assume that shore spawning fish such as bream actively search shallow water habitats with clean spawning substrate to enhance egg attachment and subsequent survival.” *

Even with a fish pass fitted to the Prescott Channel water control structure it is difficult to know how Bream will in future find the right conditions in the impounded river Lea to spawn. It would seem that this year we are seeing this wonderful natural spectacle near Friends bridge for the last time.

The fish remain around these spawning grounds until about the middle of June. If you want to see this great assembly of them you should go to Friends bridge around low water on a fine warm sunny day when you may be lucky enough to catch sight of them.

* From: 'Is bream spawning mediated by water level fluctuations? Probst, Peters and Eckmann, Topic 10, page 17 at University of Konstanz workshop 2005


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