The Dynamics of Fish Spooking

Updated: 3 days ago



Regardless of your target species, you’re going to spook a fish at some point. This isn't the worst thing in the trout world, but if you’re hunting for carp or bonefish, spooking a fish ruins a valuable opportunity. Let's examine some fish behavior to figure out why a fish might spook.


Bonefish are notorious spooky

Let’s start with conventional wisdom. In the behavioral ecology world, there is a theory known as the 'many eyes' hypothesis that suggests as group size increases, the group should have better predator detection. This effect should entice animals to group together. This is also known as the group-size effect. Bigger groups have greater vigilance against predation; the more eyes watching for the hungry beast, the better. A warning from one individual could save others within the group. In the fishing world, there are situations where this is definitely noticeable. For example, a misplaced fly can spook a group of cruising bonefish. But there are also situations where you would think fish should spook and they don't…


So why wouldn’t a fish spook? You’ve probably seen it when hooking a trout out of a pod of fish. Instead of losing the opportunity to catch other fish from the pod, the rest of the fish continue to feed, unalarmed by the bucking trout on the end of your line. The reason the other fish aren’t spooking? Competition!


Several studies have provided experimental evidence that as group size increases (where fish might congregate for protection) the competition increases, and as a result, individuals within the group increase their rate of foraging. More interestingly, as they intensify their feeding, they also seem to make riskier decisions and forage closer to potential predators or forage outside of their cover. The riskiest decisions are most intense when resources are scarce. Meaning, competition is fierce and food is limited (Grand & Dill, 1999; Hintz & Lonzarich, 2018; Johnsson, 2003). Think a hatch is going off, and each fish is trying to make the most of it.


Let's think through the relationship between group size and foraging success. Initially, as group size increases, the foraging success will likely increase. Fish are starting to compete more but the group isn't large enough to make resources scarce. Eventually, with more individuals within a group, competition will lead to some winners and some losers and individual foraging success will vary. Not only does this suggest there is an optimal density of group size for each individual to have the most