Summer Trout Bod

My office has a nice view

It seems like I was just out in Loyalsock, but the calendar doesn’t lie. Two weeks had come and gone and it was time to head back out and collect more blood samples. A full day in the woods, avoiding the ever-increasing traffic around town, handling native trout in the clear, cool stream?  A pity, my life.
 
It’s been a fairly wet summer, especially compared to the severe drought of last year. Nonetheless, streams flows have really dropped in the last few weeks and are reaching summer lows. Yet, I continue to be surprised with some fairly large brook trout in some pretty crappy habitat.  But, hey, no complaints here. Work smarter, not harder, right?  Or, more accurately, thank you field Gods for blessing me with good fortunes.
 
But, it’s not just stream flows that have been changing.  Over the last few weeks, the trout have put on their summer figures: long, lean, and almost unhealthy looking. How could this be?  Just a few months ago I posted about how fat and “football-like” the trout were.
 
The answer is simple. They’re starving.
 
It’s a common misconception I often hear about stream trout. In the summer, we’re constantly getting bit by bugs, we see a bunch flying around, and we may even flip rocks and see various aquatic invertebrates crawling around. Insects are everywhere, and so it would make sense that summer would be buffet season for trout.  

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Far from the worst I've seen, but the fish this week were noticeably more skinny than sampling events prior. Usually it's the area around the tail that starts to loss weight the fastest.

But, not all insects are created equal.  Think about the type of bugs that you see in summer and those you might see during a spring hatch, the time of year when many invertebrate species are transitioning between aquatic larvae and terrestrial adults. Spring hatches may be brief, but the number of bugs swimming and flying around is unmatched.  And, many of these bugs are floating on the surface of the stream or in the middle of the water column, making them easy targets for trout. In spring, almost all of a brook trout’s diet is comprised of these aquatic prey forms.
 
Now, think about the bugs you see in summer.  Hatches are over, and most of the invertebrates that are left in streams are difficult for trout to eat because they are glued to the bottom, hiding between rocks, and, in cases like caddisflies, armored is shells. By summer, stream trout are feeding almost entirely on terrestrial insects.  But, this food source doesn’t come easy. Most terrestrial insects aren’t buzzing around the water surface for too long, and it takes a lot of energy for trout to jump out of the water to capture their prey, especially when most attempts are unsuccessful. In all, these terrestrial insects are much harder to capture, and in many cases offer fewer calories than the spring hatches.
 
Making matters worse, as stream flows recede, habitat starts collapsing down giving fish fewer places to forage, but also fewer places to hide from increasing predation pressure. Given the choice between eating and hiding, trout will usually choose hiding until they are at the extremes of starvation. 

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The degree of summer food deprivation certainly varies by region, and even by stream. Lakes and large rivers go largely unaffected, but in smaller streams, there is often not enough food available for fish to maintain basic metabolic functions. When this happens, fish growth stops and condition factor (the ratio of length to weight) takes a sharp drop. That’s when fish get that long, lean appearance I’ve dubbed “summer trout bod.”
 
Long-term food deprivation can of course result in death, but can also have long-term effects for survivors. As brook trout are fall spawners, summer is the time they should be devoting calories to production of gametes (eggs and sperm).  When fish are barely meeting basic metabolic demands needed for survival, they are can’t devote energy towards gamete production.  As a result, they produce fewer and lower quality gametes, leading to fewer and lower quality eggs and juveniles.  It’s a vicious cycle.
 
So, when you head out to your favorite trout stream this summer, the fish might bite like crazy. But, it’s not because they are having a alive and well.  It’s probably because they are in desperate need of calories and willing to take more risks and eat a larger variety of prey than they normally would. There’s some controversy in angling if it’s ethical to take advantage of fish when they are in heightened states of vulnerability. Usually this centers around discussions of “bed fishing” (targeting bass on their spawning nests) and targeting coldwater zones that attract fish during high temperatures. But, you could certainly argue that summer trout fishing starts edging closer towards the category of giving humans the unfair advantage.  I’m not here to play fishing police (I was fishing just the other day, in fact), but just something to think about next time you grab your fishing pole.