The Observant Angler

Any time you are out fly fishing you should always be on the lookout for signs of actively emerging bugs and be prepared to adapt to unexpected situations. This past weekend my expectations for the usual Green Drake and PMD hatches did not materialize. Rising fish were sporadic at best and my Green Drake and PMD patterns were completely ignored. As the morning wore on I noticed an increasing number of Ameletus exuvia on the stream-side rocks and a few duns fluttering about.

Fresh Ameletus exuvia along the edge of a small freestone river.

These mayflies crawl out to emerge so there are no nymphs rising to the surface, no emerger stage, and the duns are generally not available to feeding trout. Despite this, the hatch can still provide for some good action on the nymph. 

Ameletus nymphs tend to inhabit the slower margins of streams but still like to be in proximity to faster flows. Their habit of darting out into deeper and faster water during emergence migrations can get them into trouble with trout lurking along the seams and waiting to pounce.

I switched to a mottled Hare's Ear type pattern in size 14 and targeted the softer water along the edges. The presentation included the usual segment of dead drifting but at the end of the drift I would swing the fly towards shore to imitate the nymphs swimming back to safety. Takes were both on the dead drift and on the swing.

I connected with a reasonable number of fish through the afternoon but the catch rate could have been higher if I had not been so focused on what worked in the past or was supposed to work. It is the observant and adaptable angler that sees the most success.

Drunella vs. Pteronarcys

As I mentioned in last week’s blog post, competition for resources can lead to more bugs in the drift as cohorts of individual species reach maturity – this is what we call intraspecific competition (intra = within, and specific = species). But competition between different species (interspecific competition) is also quite common.

In this week’s Short Shots video, a Green Drake nymph (Drunella grandis) is feeding on a dead Baetis nymph it has found. Along comes a much larger and brawnier Pteronarcys nymph who, after a short altercation, claims the prize for itself. In this case, instead of the loser being cast into the drift, it just sits nearby and sulks.

Taking Advantage of Pre-hatch Migrations

We often think of the opportunity to fish nymphs during pre-hatch or hatch migrations as being limited to insect groups that crawl out to emerge. But for insect groups that emerge at the surface in open water, like many mayflies and caddisflies, there are also migratory activities in the days leading up to a hatch that increases their exposure to feeding trout and imprint search images in the trout’s brain.

As each generation of each insect species approaches maturity, and the bugs become bigger, requiring more resources to support final development, competition for prime feeding spots heats up. This competition can result in more bugs in the drift through two mechanisms; direct conflict and intentional migration.

In direct conflict, two individuals battle it out over the most productive feeding spots. The loser if often cast into the drift, where it may tumble with the current for a few meters before regaining a foothold on the bottom. I once witnessed two Brachycentrus caddisfly larvae doing exactly this. It was a hard-fought battle, but in the end, one was ejected into the current and went tumbling downstream.

Brachycentrus caddisfly larvae lined up in prime feeding stations. As the water level changes,
the best spots on the rock will change - leading to a game of "musical chairs".

While direct conflict results in sporadic numbers of nymphs and larvae in the drift, intentional migration results in consistently large numbers of bugs traveling with the current. If there is too much competition on a particular riffle, or the resources are being depleted, the most expeditious strategy for moving to greener pastures is to float downstream a ways and explore new areas. These migrations, often taking place in the late evening, are far more common than most anglers realize.

With specific species of nymphs or larvae being more common in the drift as hatch periods approach, trout are more inclined to form search images for, and feed on, the ones they are seeing most often. I often use this to my advantage by fishing the corresponding nymph of whatever insect has been recently hatching during periods when there are no active hatches.