Gaspereau Aggression Towards Trout

The gaspereau (or alewife as they are known elsewhere) run has been going on for a few weeks now. The run happens every spring when the gaspereau come up river to breed. The gaspereau have a reputation among local fishermen for creating poor fishing conditions for brook trout. I’m inclined to agree, as for the duration of the gaspereau run, trout fishing always seems to slow down for me. This year I’ve taken some time to observe these smaller members of the herring family, and think I’ve found out why.

I should actually clarify, and say that there are two main reasons why brook trout fishing slows down when gaspereau are breeding. The first reason isn’t all that surprising, and I think many anglers are aware of it. The gaspereau keep the brookies very well fed. At 10″ average size they’re to big to be a meal themselves for brook trout, but their eggs provide a bountiful feast!

The brook trout actually sit just down stream of the spawning gaspereau and eat their eggs as they drift by their noses. The plentiful gaspereau eggs keeps the trout very well fed, and usually quite uninterested in other offerings.

The unfortunate thing about it is that you probably won’t be successful attempting to “match the hatch” with egg patterns because gaspereau eggs are much smaller than most egg flies. I suppose if you want to get into extremely small hook sizes like 28+ you might have some luck. You can still get the odd take with nymphs, streamers, and even dries on the right evening, but it’s much slower fishing then when the gaspereau are not there.

The second major reason the gaspereau turn the trout off is that they are literally attacking them! Like most fish, gaspereau are very active and get quite aggressive when spawning, often chasing other fish away with trout being no exception.

Last weekend I sat on a bridge at a popular trout fishing hole, and watched a river teeming with gaspereau, trout, and a healthy amount of small salmon parr, all clearly visible on a bright sunny day in water no deeper than 2-5 feet deep.

At first I saw what was to be expected, gaspereau zipping about chasing each other, with trout sitting right behind them waiting for any stray eggs to drift by. As I watched more closely, I noticed that the gaspereau weren’t just chasing other gaspereau, they were actually chasing (and biting!) trout as well. The chase typically consisted of 3-4 gaspereau nipping at a similar sized trout and chasing it away. One of the more remarkable things I saw was two gaspereau squish a 13-15″ brook trout between their two body’s and push it away from the spawning site. I attempted to take a video of the behaviour, but the glare from the sun proved to make it impossible to distinguish trout from gaspereau.

I suppose the gaspereau behaviour shouldn’t come as any surprise. The trout are eating the gaspereau’s eggs and fry after all, the gaspereau are quite wise to chase the trout off whenever possible. It’s just a shame it has a negative affect on the angling. I will mention that if you are set on fishing trout during a gaspereau spawn, streamers seem to have some effectiveness. The trout are agitated and you can often trigger a defensive/reactionary strike with an oversized streamer.

Even if you don’t hook into a trout, the gaspereau themselves are tons of fun on a fly! They are quite strong for their size, and will even jump when hooked. Size 8 and smaller streamers in colours appropriate for the time of day seem to work well if your targeting gaspereau. I’ve caught plenty on my confidence brook trout streamer the Mo-hair leech.

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The gaspereau run occurs after most of the sea run brook trout are already in the river, and the gaspereau’s aggression seems to push much of the trout further up river. The gaspereau will only go so far up river before they start spawning, meaning trout can go even further up river to escape their enthusiastic mating. If you want avoid the gaspereau when trout fishing, just go further upstream. This obviously depends on the specific river system, but it’s what I do most of the time this time of year.

For those unfamiliar with the fish, gaspereau are a smaller species of the herring family. Gaspereau share their range and mating waters with blueback herring, and the two can often be found schooling together. They are quite similar to shad in appearance, albeit much smaller.