Trout have an acute sense of hearing that is well worth understanding. Trout have two sound receptors. The first one runs along the length of the fish’s body. This receptor picks up frequency vibrations – such as the banging of rocks or oars against a boat. A second receptor, located inside the trout’s ear, is used to detect the movement of the aquatic insects the trout eats. This receptor is extremely acute, allowing the trout to hear sound frequencies well outside the human hearing range. This hearing receptor of the trout is what allows the fish to find food even in very murky water.
Because trout have such acute senses of hearing, anglers need to keep several things in mind when fishing for trout.
First, trout can’t hear human voices outside of the water. Thus, having a loud conversation about something along the bank of a river will not spook the trout.
Second, trout are acutely aware of vibrations and sound that occur in the river. Banging oars on the side of a boat is a wonderful way to alert the trout to your presence, thus spooking them. Likewise, great care should be taken when wading. Loud wading, either caused or by the splashing of the water or the movement of rocks beneath the angler’s feet, is easily heard by a trout – especially in slow moving water. In fast water, these vibrations tend to get drowned out by the current and rapids. But in slower water, such as runs or spring creeks, it is crucial that an angler take care when wading.
Third, trout are easily able to hear things that fall into a river. A nearby trout can readily hear a grasshopper or other bug that falls into the river. Because of this, care must be taken in casting to prevent the fly line from making a splash in the water or from having the fly itself strike the river at full force. A gently dropping fly is far more likely to attract the attention of a trout than one that gets slammed into the river due to a bad cast or too heavy of a fly or fly line.