While reading though fly fishing entomology books to put together all the species writeups, I've noticed that several authors write about many mayfly species migrating toward shore in preparation for emergence. They describe this phenomenon both for hatches that emerge on the surface and for those that crawl out on land. The suggested manner of imitation is often to fish a nymph on the swing from the center of the river up into the shallows.
Here's a typical example, from Fred Arbona's excellent book Mayflies, the Angler, and the Trout
The naturals of Isonychia and Siphlonurus nymphs are perpetually on a mini-exodus toward the bank during the summer months, and anglers aware of this biology stand to do well with opportunistic trout capitalizing on nymphal migration.
And, so as not to single out one author, here's a piece from the Stenonema ithaca
page of Hatches II:
Prior to emergence, fish nymph patterns deep with occasional twitches to simulate the migratory crawling habits of the naturals.
skeptical of these ideas.
For one thing, I've never seen a mayfly species emerge preferentially near the bank. Many prefer specific substrates or depths
, but these things are rarely concentrated right next to shore. The tails of pools, eddies, shallow flats, and other habitats provide the same sort of easy swimming.
Also, "migrate" is a strange word for it. Nymphs may not be as fast as trout, but they can move at a respectable clip, and I can't see it taking them weeks or even days to go from the middle of a stream to the side. I think an Isonychia
nymph could do it in under a minute in most rivers. It's like "migrating" from your bedroom to your kitchen when you wake up. Nymphs might take more time and stop at every rock along the way to rest, but such a punctuated migration is hardly what the books bring to mind.
Even if nymphs migrate exactly as suggested, I very much doubt that it happens in such concentrated numberas as dun emergences or spinner falls. It is surely a more gradual event, and there are surely individual nymphs in all different stages of the "migration" and not just along the shore. I doubt there is enough of an increase in nymphs along the shore to warrant a trout takin the extra risks involved in shallow water.
I think it would take some serious observation (like LaFontaine did with his scuba gear) to verify that trout "follow" a mass migration of nymphs toward shore to feed on them. I've not heard of any such observations for this phenomenon. Has anyone else?
My guess would be that somebody thought up this idea and other writers have just echoed it for years. They probably fished nymphs in the manner suggested, caught fish, and considered the hypothesis proven. My guess is that the nymphs do
get more active and these people caught fish because of that, and not because of the exact manner of imitation. People may also catch trout feeding along the banks for various other reasons.
Anyone else have a hard time swallowing this conventional wisdom?