In the following article, Dr. Robert Butler, former head of the Pennsylvania Cooperative Fisheries Unit at Pennsylvania State University, discusses the known facts concerning elusive nocturnal brown trout known as rogues and offers an incredible explanation as to why they are never taken, or even seen, during daylight hours.
Rogue Trout
By Dr. Robert Butler
Anglers who routinely fish the same brown trout stream during the day quickly become aware of the size of fish that typically hold in that stream. However, when they fish the same area of the stream at night, they often catch much larger trout, which are commonly referred to as rogue trout. The explanation usually given for this phenomenon is that rogues are trout that have adapted to feeding primarily at night and have no home range or preferred foraging sites; they move at will and feed anywhere they wish. However, this explanation falls short for several reasons. First, it implies that rogue trout are always somewhere other than where anglers are fishing during the day, for not only are they not caught by anglers, they are rarely ever seen by them. More importantly, rogue trout are rarely, if ever, taken by biologists using electro-fishing equipment. Where, then, are these big browns during the day? Two independent studies - Dr. Robert Bachman's observations of the daytime movement of wild browns in Pennsylvania's Spruce Creek, and my underwater observations of wild browns in California's Sagehen Creek - combine to debunk the notion of freely ranging browns and offer an amazing alternative explanation. Bachman spent 3,000 hours over a three-year period observing the daytime activities of Spruce Creek's wild brown trout population. He noted that each trout's home range was very small, often confined to one side of a very short section of the stream, and that they utilized these home ranges throughout the duration of the study. But if brown trout are essentially homebodies, as Bachman's study indicates, where are the large rogue browns during the day? Trout, like other animals, have only two objectives in life - to feed and reproduce. To maximize these objectives, they must learn the characteristics of their environment by sight, smell, hearing, lateral line detection, and touch. Based on this information, the trout can then exhibit behaviors that are bioenergetically efficient, such as where and when to seek safety, and where and when to feed. Rogue brown trout must also feed and reproduce, and they, too, must exhibit behaviors that are bioenergetically efficient. If they forage at night, they must rest during the day in a place where they would be safe from predators such as raccoons and anglers, as well as be sheltered from the water's current and the biologist's electric current. But where could they hide so effectively that they couldn't be seen or detected by anglers, raccoons, or fisheries biologist? The answer may lie in a truly surprising behavior that I witnessed during hundreds of hours of observation from an underwater observation tank at Sagehen Creek. In the early morning, before sunrise, large browns in the observation area were seen to swim to the bottom of the stream, head first, and literally burrow themselves into the gravel bed of the stream, not unlike a pocket gopher on land! There they lay all day, free from anglers, water currents, and electrical currents. Observations of the site were made throughout the direct sunlight period, but not once did these trout emerge during the day. But at dusk, the large brown trout would literally explode from the depths of the gravel, swim rapidly around the observation area, and then settle down for a night of hunting. I am convinced that rogue trout are old resident brown trout that have developed a different survival strategy. After years of experience, they have so thoroughly integrated the information from their nonvisual senses that they can freely and efficiently forage at night.
