When you hear the name “barracuda”, the first thing you might think of (or start singing) is a very popular tune of the late 1970’s, a little song called “Barracuda” by Heart. With lyrics such as “You lying so low in the weeds, bet you gonna ambush me”, it’s hard not to conjure up images of huge 6-ft long barracuda, looming in the shadows and decorated with enormous teeth protruding in all different directions from a monstrous mouth (Fig. 1). But are barracuda really that scary? Do they really ambush prey? The short answer is yes!

Figure 1 – Stuff of nightmares? Maybe this great barracuda is for some small reef fishes! (Source: Jaroslav Kaspar via divetheocean.net)

Barracuda may not be frightening to humans (as they pose little threat to us), but for fish that are a potential meal – they can definitely come across as scary! There are a few species of barracuda found throughout the world’s oceans, but this article focuses on great barracuda, a species common to the western central Atlantic Ocean. Great barracuda can grow over 6-ft in total length, weigh upwards of 110-lbs and live to 14 years [1]. A new paper [2] suggests that to certain species of reef fish, even the presence of barracuda can be enough to alter behavior, movement, habitat use and when and where they eat. In this study, the two species of prey fish – schoolmaster snapper and white grunt (Fig. 2) – stayed very close to structured habitat (i.e. reef and mangroves) during the day and moved into open channels at night, a time that coincided with a reduction in the abundance of barracuda. Under the cover of darkness, fish altered their behavior and moved into high-risk areas with less protection to look for food in seagrass habitats. Why would fish move away from the afforded protection of reef and mangrove habitats? And why would they do it at night? This may seem counterintuitive to many people as we tend to be afraid of the dark! However, in this study, scientists observed a decrease in predators at night and thus prey fish did not perceive any risk of being eaten. Perhaps schoolmaster snapper and white grunt were more active at night because barracuda are visual predators that utilize ambush tactics [3] and moving around at night would hinder the ability of these predators to see and capture their prey.

Figure 2 – The two species of reef fish (left: schoolmaster snapper, right: white grunt) that were observed avoiding the presence of barracuda. (Sources: right, John Maraventano via Science Source; left, Frederick R. McConnaughey via Science Source)

Many animals on earth will experience fear at some point in their lives. For example, have you ever watched a horror movie alone or been on the top floor of a skyscraper? You may have experienced heightened senses during these moments and behaved differently than you would under normal circumstances. In ecology, this phenomenon has been termed the “Landscape of Fear” (for additional reading on the LOF see [4,5]) and can be observed across species inhabiting both terrestrial and marine ecosystems. In simple terms, the LOF describes the way in which individual animals perceive their environment based on the cost-benefit tradeoff between food and safety (Fig. 3). 

Figure. 3 – A visual representation of what a Landscape of Fear (LOF) could theoretically look like. The x and y axes are referring to the geographic space that this individual animal occupies. The z (or vertical) axis shows the level of predation risk with dark colored (blue) peaks indicating higher predation risk and light colored (green) troughs indicating less perceived predation risk. (Source: [5] Laundré et al. (2010))

In our example, two small reef fishes perceived daytime to be a more likely time when barracuda would hunt or target them for an easy meal. These fish made decisions to stay near or on reef structure during the day (i.e. an area they perceived as safe as there are more places to hide and seek shelter if a predator is around) and only at night, did they move into open areas to feed on seagrass. Here, the fish determined that the risk of moving into the open water during the day was too great and instead employed the trade-off to eat at night. Yet, it is important to understand that predators do not necessarily impose a LOF [4], and many other factors contribute to how certain species interpret the environment around them. 

So the next time you watch a scary movie and then purposely avoid certain areas of your home (perhaps near closets or windows), just remember you are not alone and that there are animals around the world that share your heighted sense of fear in their own environments. 

References

1. Aiken, K. A., et al. “Sphyraena barracuda great barracuda (errata version published in 2017).” The IUCN Red List of Threatened Species (2015): e.T190399A115319634.
2. Rooker, Jay R., et al. “Seascape connectivity and the influence of predation risk on the movement of fishes inhabiting a back-reef ecosystem.” Ecosphere 9 (2018): e02200.
3. Almany, Glenn R. “Differential effects of habitat complexity, predators, and competitors on abundance of juvenile and adult coral reef fishes.” Oecologia 141 (2004): 105-113. 
4. Bleicher, Sonny S. “The landscape of fear conceptual framework: definition and review of current applications and misuses.” PeerJ 5 (2017): e3772.
5. Laundré, John W., Lucina Hernández, and William J. Ripple. “The Landscape of Fear: Ecological Implications of Being Afraid.” The Open Ecology Journal 3 (2010): 1-7.