The Ones That Get Away: How Predatory Fish Pursue Evasive Prey
Whether it’s stripping streamers for trout, trolling plugs for mahi mahi, or reeling in a spinnerbait for bass, we have all had fish follow our lures all the way in. We hold our breath, waiting for the strike… but it never comes, and the fish turns away. Furthermore, I’m sure you’ve had a fish strike your bait, but miss (more often than not, if you ask me). Why do predatory fish sometimes miss and why don’t they strike sometimes when pursuing prey? I asked Dr. Matt McHenry, a biology professor at the University of California, Irvine, these same questions after his presentation on “How fish predators pursue evasive prey” at the Society for Integrative and Comparative Biology’s Annual conference a few weeks ago.
To understand how a fish pursues lures, we first have to understand how they pursue and capture evasive prey. I discussed how fish capture their prey in a previous post, so I will focus on the pursuit here. On land, predators mostly have to pursue prey in two-dimensions, which can make chasing after prey easier since most prey has to stay on the ground and cannot go down or up.
Fish, on the other hand, live in a highly three-dimensional (3D) world, and can move in any direction, which makes pursuing prey a bit more challenging. Despite this fascinating complication to pursuing prey in an aquatic environment, Dr. McHenry was shocked to find out that very little research exists in this field. In order to find comparisons for fish hunting in water, he turned to examples from another 3D medium: air.
Many aerial predators, like dragonflies and birds of prey, use a pursuit strategy known as parallel navigation (PN). According to Dr. McHenry, PN requires predators to sense the heading and speed of the prey relative to the predator, so that they can intercept the prey. However, it doesn’t appear as though fish use PN, as that strategy “may be difficult for vision underwater, especially when the water is murky and the prey offers a poor contrast to its background.”
Instead, as Dr. McHenry explains, fish use a deviated pursuit (DP) strategy, which only requires predators to sense the position of the prey and the direction it’s moving. Think of DP like chasing a friend in a game of tag, while PN is like a safety trying to predict where a running back with the ball is going, to make the most of his one chance at tackling him. DP is likely the most robust strategy for fish in aquatic environments, where predators try chase and out-swim evasive prey before they can evade, like the lucky mummichog below.
So, you have a fish following your lure. What can you do to improve the odds of the fish continuing to pursue your lure and for it to make a successful strike? If you slow down or stop your lure and keep it at the same position, that would make it easiest for the predator to intercept it, says Dr. McHenry, but that doesn’t look natural and may not entice a wary predator to strike.
If you keep the retrieval at a constant speed, that would be the next easiest way for the fish to intercept your lure, but again, this may not look natural to the fish. It’s a trade-off: you want your lure to seem like an evasive prey to entice a strike, but you don’t want it to be so evasive that the fish misses your lure. Personally, when a fish follows my bait, I slow the retrieve, give a couple of sudden twitches, and then a half-second pause after the last twitch, at which point, BAM!
For more information on fish predator-prey interactions, check out these recent research articles from the McHenry lab:
Nair, A., Changsing, K., Stewart, W.J. & McHenry, M.J. (2017) Fish prey change strategy with the direction of a threat. Proc. Roy. Soc. B 20170393. doi:10.1098/rspb.2017.0393.
Nair, A., Nguyen, C. & McHenry M.J. (2017) A faster escape does not enhance survival in zebrafish larvae. Proc. Roy Soc. B 20170359. doi:10.1098/rspb.2017.0359.
Soto, A., Stewart, W.J. & McHenry, M.J. (2015) When optimal strategy matters to prey fish. Integrative and Comparative Biology. doi:10.1093/icb/icv027
Stewart, W.J., Nair, A., Jiang, H. & McHenry, M.J. (2014) Prey fish escape by sensing the bow wave of a predator. Journal of Experimental Biology 217: 4328-4336. doi:10.1242/jeb.111773.