you're reading...


Scaredy Fish: How Timid Fish Could Skew Research

Emslie, M. J., Cheal, A. J., MacNeil, M. A., Miller, I. R., & Sweatman, H. P. (2018). Reef fish communities are spooked by scuba surveys and may take hours to recover. PeerJ6, e4886.

We named her Wendy, the unofficial mascot of the driven and intelligent students at my school. A long, silver flash in the water, Wendy was the largest barracuda I had ever seen.  She had piercing eyes that observed every movement, and she loved to watch me and my classmates as we surveyed the reef for fish. After a week of being followed, we got used to what had originally been unnerving. But while Wendy would come up to us and stare us in the face, the smaller fish we were seeking would dart away, finding cover in little crevices of the coral. By the end of the week, we hadn’t all seen the same types of fish, but we had all seen Wendy. But what about those other fish? What if we had been looking for them specifically? A new study about fish communities in coral reefs explains how fish react differently to divers. The results have serious implications for how we study fish populations in coral reefs and how we understand the information we already have.

The paper, written by scientists at the Australian Institute of Marine Science and Dalhousie University, critically analyzes the process by which we study how many fish are in coral reefs. Underwater visual surveys (UVS) are one of the most common methods for doing this. During a UVS, a diver swims through a section of a coral reef, counting the number of fish they see, identifying them, and sometimes estimating how large the fish are. It takes an experienced diver who can identify a number of fish. However, the diver can only record the fish they see. If some species of fish are shyer or better at hiding, it is possible that the diver will underestimate how many of these fish are living in the reef, no matter how experienced they are. What Dr. Michael Emslie and his colleagues found was not only are some fish warier of divers, but they may hide long after divers have come into the reef.

Figure 1. The seven groups of reef fishes identified by the divers: A) Surgeonfishes, tangs, and unicornfishes (Acanthuridae); B) Butterflyfishes (Chaetodontidae); C) Wrasses (Labridae); D) Snappers (Lutjanidae); E) Parrotfishes (Scarinae); F) Sea basses and groupers (Serranidae); G) Rabbitfishes (Siganidae); and H) Moorish Idols (Zanclidae). All images from Wikimedia Commons.

In order to investigate how accurate these surveys are, the researchers decided to focus on five sites off the Great Barrier Reef. The areas, while not completely remote, were visited only infrequently be tourists and fishers. At each site, a lead diver would swim through counting and identifying fish, while a second diver followed, laying down the transect to mark the path the first diver followed. They did this ten times at each site. After waiting for a variable amount of time, the divers would come back, perform another survey, and count and identify the fish they saw once more. Fish were categorized within seven different groups (see Figure 1). The counts were then compared between the first and second surveys performed at each transect. The rates at which fish returned after the first divers were inferred from the relation between the two surveys.

Figure 2. Laying a transect for a dive survey. Image from USEPA by Charles Lobue.

What they found was that fewer fish and fewer species were identified on the second round of the surveys.  The total abundance of the fish, the number of species identified, and the abundance of four of the families of fish were all smaller than what was estimated from the first survey. The most anxious fish groups that took the longest to recover included surgeonfishes, rabbitfishes, predatory wrasses, and parrotfishes. Not only this, but it could take hours for the number of fish seen in the survey to return to normal. Predatory wrasses, for example, returned to their original numbers after 222 minutes, but the total fish abundance wouldn’t recover until after 1022 minutes.

These findings have important ramifications for how we study coral reefs and assess fish populations. While some groups, like sea basses and snappers, may be less impacted by divers, other species are likely to be underestimated simply because they get scared and hide. Coral reefs will need to be monitored going forward as the threat of climate change looms, but just because we are monitoring closely doesn’t necessarily mean we are getting good data. If the reefs are in areas where tourism is more popular or fishing more extensive, it is possible that some of the shyer species will never be fully estimated. This could leave us bemoaning the loss of fish before they are even gone. Additionally, some studies will lay down tape along their study transect before they survey the fish. This small action alone could skew their results. If researchers want to gather the best data possible, they will need to keep these more bashful fish in mind. Otherwise, they may end up seeing all the Wendys, but miss the parrotfishes.

Figure 3. A large barracuda, much like Wendy. Photo from Wikimedia Commons.


No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com