The author caught this brook trout, in full spawning condition, Lyman Brook in Stratford.

THE IMPULSE to reproduce can have some very strange effects on an animal. Some birds will dance around until they pass out, snakes will gather in the hundreds and coil into a ball, and bull moose will respond to these urges by simply trying to kill one another.

Nature can be a harsh place and, for those organisms that reproduce only once a year, the drive is incredibly strong.

In the world of fish, some species migrate thousands of miles to find the right mate or location. Some stop eating during the spawn and some complete the process in such a state of complete exhaustion that they keel over and die.

As September turns to October in New Hampshire, brook trout experience this crucial part of their life cycle. The process is triggered by water temperature, the amount of daylight, and other subtle conditions.

Male brook trout begin the ritual by corralling females into the preferred spawning habitat. Small gravel and gentle flows provide the location that females will build their nest or “redd.” As she does this, the male really kicks his courtship into high gear by darting around and under the female in an anxious and spastic dance. This ritual looks comical to the casual observer as the male trout will actually quiver and shake.

As the nest is being constructed, the male does his best to ward off other males with similar amorous intentions. Most trout mature at age one and even the smallest fish are part of this process. As if he doesn’t look ridiculous enough already, the protective fish will charge other males regardless of the size difference. A five-inch male brook trout will give everything he has and instigate physical altercations with much bigger fish.

Once the spawning has occurred, the female will whisk some gravel over the redd where the eggs will remain protected until they hatch sometime in February. I imagine the males spend the rest of the year recovering and rebuilding their manly image after such an embarrassing display.

In addition to their strange behavior, the males also undergo physical changes during the spawning period. A change in color takes place as their bellies become deep red and orange. It seems like quite a coincidence that they take on the color of the fall foliage that surrounds the landscape during late autumn.

While the females remain, for the most part unaffected, males will develop a hook in their lower jaw known as a kype. It is unclear what the function of this strange growth is but some scientists theorize that it might aid in holding on to a female during spawning. It is also thought that it may symbolize virility and reproductive prowess. I’m not sure why they grow a kype but I have caught some trout in the fall with this condition and it seems to bolster their image and spirit.

Even though they seem to be totally wrapped up in the process of reproduction, trout continue to feed and are frequently caught in the fall. A responsible angler will recognize both the sensitivity of individual fish and the implications to the fishery by reducing their impact in a few ways.

Careful not to walk on redds and not casting near spawning fish is a good start. As the days get shorter and cooler, landing a colorful brookie on a fly rod brings me great pleasure. The cycle repeats itself every year and reminds me why I love fishing in the fall.

Adventures Afield appears in the New Hampshire Sunday News. Contact Andy Schafermeyer at troutandsalmon1@gmail.com.