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Winter floods encouraging fish spread?


Rice Crackers

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I took a walk this afternoon along the River Oughton in Hitchin. It's a trickle of a chalk stream that feeds a nature reserve and feeds into the river Hiz, then the Ivel, which holds a good head of fish.

 

I've lived in Hitchin for seven years and never once witnessed a fish in there. Anyway I saw a swirl in the water that could only have been a fish and when I moved near to the water to investigate, a Chub of about 1-2lb swam off upstream. As I walked upstream I saw 4-5 more.

 

My only theory on this is that the winter floods swelled the rivers to the point that fish felt comfortable moving upstream from the river Ivel, which can only be a good thing provided the poor little fellas don't get stranded as the level drops.

 

Has anyone else noticed similar patterns?

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I fished the upper reaches of one of my trout streams last week, and although I have fished this particular stretch at intervals for the last sixty years, I caught chub from it for the first time in my life. This stretch requires a walk of a mile and a half there and another mile and a half back, so receives very little angling pressure.

 

I only fished for an hour (scrambling along small streams is a bit demanding for an old fogey) and caught two small trout (returned), a sizeable trout (hot smoked for a late breakfast) and two chub of about half a pound each (returned to comply with the law but against my better judgement). I have caught chub from the same stream lower down (where it is joined by other streamlets and is slower and deeper) in the past, but these recent chub were about two miles further upstream.

 

The upper reaches of my streams tend to dry up in late hot summers, but the winter floods see trout running upstream to spawn - some may get trapped the next summer, but most obviously drop down again in good time, as do enough of the fry to keep the population going. They would become extinct if it were otherwise. I can't speak for whether those chub might get trapped or not, but I would think it unlikely that they would become established - the conditions (clear fast shallow water, no weed growth) favour trout and the chub would be at a competitive disadvantage. The available biomass in these small streams only supports relatively few fish.

 

I have noticed that chub and pike invasions of the lower parts of my trout streams seem to be sporadic - one year they are there, three or four years later they are gone. The boundaries between "trout only" and "trout and coarse" move up and down, and not necessarily in response to variations in yearly rainfall, because the flow in most Wealden streams is pretty constant in all but the upper reaches. That is because whilst the upper reaches rely on surface water, lower down the many small aquifers of porous sandstone provide a constant flow of groundwater.

Edited by Vagabond

 

 

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