DR PAUL GARNER ON FISH MIGRATION

RULE OF THIRDS

GENERALLY speaking, a third of fish in a stretch tend not to move very far. A third will wander a few kilometres, while the remainder can wander off all over the place!

This is probably a survival strategy – in good times the ‘stay-at-homes’ will do best, because they are not wasting energy and increasing risk, while if something catastrophic happens in one area the ‘wanderers’ may well survive.

A DAILY ROUTINE OR BIG JOURNEY?

You tend to get different levels of movement/migration:

● Daily - Feeding, most of the fish in the population move anything up to a few kilometres.

● Seasonal (spawning, or a move to winter quarters) - Could be tens of kilometres.

● Lifetime - Some fish just head off and never come back! If they aren’t blocked they could travel many hundreds of kilometres in a lifetime.

In a study in the 1970s on the Witham, a tagged bream moved out of thi river (through the Wash, presumably) and up another river!

FLOODWATER GETS FISH ON THE MOVE

Fish will often move in floods, especially upstream. This is probably because they are able to get over natural obstructions more easily. A lot depends on the timing/water temperature – fish tend to move when water temperatures are favourable, not so much when it’s really cold.

THERE & BACK

We don’t really understand the mechanism, but fish are very good at finding their way back to the exact spot that they left some time before.

Years ago, for example, a friend and I monitored some dace in a shallow mill stream over several days. Those fish moved several hundred metres upstream to feed every night, but they would be in exactly the same position again the next morning.