Coelacanth: Behavior

Summary: What are those coelacanth doing in the deep water of the ocean? Join Kiersten as she discusses some of the coelacanth’s behavior.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show Notes:

 Coelacanth, Smithsonian, https://ocean.si.edu/ocean-life/fish/coelacanth

“New Insights About the Behavioral Ecology of the Coelacanth Latimeria chalumnae Video Recorded in the Absence of Humans Off South Africa” by Jiro  Sakaue, Kazuhiko Maeda, Micheal J. Miller, Ryuichi Sakai, Koh-ichi Tahara, Hideki Abe, Kazuya Made, and Hitoshi Ida, Front. Mar. Sci., 10 November 2021, https://www.frontiersin.org

 

Music written and performed by Katherine Camp

Transcript

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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

 

This episode continues coelacanths and the fourth thing I like about this enormous fish is their behavior.

Once again, I’m going to  state that we are still learning new things about the coelacanth everyday, so what I talk about in this episode is what we currently know, but the future may bring different information.

As I mentioned in the last episode, coelacanths are a deep water fish. They are typically found between 250 feet to1300 feet below the surface. We can see them using specialized scuba diving equipment called ‘rebreathers’ and by using submersibles. This technology has allowed us to study live individuals instead of the dead specimens that wash ashore or are, most often, caught as by-catch by fishermen. Because of this we know a lot about their anatomy, since many of the dead specimens have been dissected, but we don’t know as much about their behavior.

In the 1980’s studying coelacanths with deep sea vehicles became the common practice in the Comoros Island area. Between 1986 and 2009 we studied this population with submersibles and remote operated vehicles, or ROVs. Using their spot patterns we determined that this population contained approximately 300 to 400 individuals. We also observed their basic day to day pattern. 

A day in the life of a coelacanth consists of resting in caves at a depth of 500 feet to 800 feet during daylight hours. They will share caves with other coelacanths and smaller species of underwater life. The caves are carbonate caves formed during underwater volcanic eruptions. During the night, coelacanths leave the caves to hunt in even deeper waters. At least one individual was seen hunting in waters approximately 2000 feet deep. That’s a third of a mile under the surface of the water! I can’t even imagine the pressure these fish endure.

In the Fall of 2000, a few individuals were encountered by divers in another area near South Africa called Jesser Canyon. This encounter actually was the first direct contact between humans and a live coelacanth. We then began focusing on this area, as well, to study the coelacanth. Between 2002 and 2004 submersibles were used to watch this area. Here they observed 21 individuals in 16 different locations in canyons off the coast of Sodwana Bay, South Africa. These individuals were seen at depths of 300 feet to 450 feet. These studies revealed that the coelacanths in this area were traveling between two canyons, Jesser Canyon and Wright Canyon.

Research begun in 2018 wanted do something that had never been done before, study coelacanths without the influence or interference of humans. If you noticed in all the research I’ve detailed so far, the common thread was the presence of a submersible, human diver, or mobile ROV. We have no idea how these things might change the behavior of the coelacanths observed. We do know that the presence of unknown stimuli, meaning divers or ROVs, can alter the natural behavior of wild animals. 

These researchers used fixed cameras set up in a known coelacanth resting places to record the fish’s behavior without the presence of humans. They also wanted to record the ocean conditions such as temperature and current direction and velocity. To do this they placed two oceanographic recording devices near the study site. The main focus of this study was on the folding or unfolding of the first dorsal fin. 

Now you might think, wow that’s a lot of work to look at one trivial little fin,  but we’ve learned some of the most ground breaking things about animals by looking at one tiny little behavior, such as the eye movement of gorillas and the tongue flicking of snakes. This research actually shone a light on coelacanth behavior that we didn’t even know we should be looking for!

Okay, let’s take a moment to look at the iconic coelacanth image. If you haven’t yet googled the coelacanth, do so now and look at a few different photos of live coelacanths. Go ahead now, I’ll wait. Unless you’re listening to this podcast in your car. Do Not try to look up an image of the coelacanth if you are driving. Eyes on the road! 

For those of you able to safely pull up images, look at that first dorsal fin. What do you notice about it in 98% of the pictures? It’s unfolded and standing up right, correct? I’m actually looking at the cover of the book A Fish Caught in Time by Samantha Weinberg right now and the first dorsal fin is erect in the illustration of the coelacanth on the cover.

Up until the 2018 research project, we thought this was just how the coelacanth naturally carried this fin. Now we did know they were capable of folding it up and down and we assumed this fin was used for stabilization during swimming. We might have been wrong about that. According to the data collected in the absence of human interaction, the dorsal fin raises when the coelacanth encounters a stressor. 

In this research it was a sand tiger shark. They got great video of a coelacanth and a sand tiger shark in the same cave during the day. The shark showed no antagonistic behavior toward the coelacanth but while the shark was in the cave with the coelacanth, that first dorsal fin was raised. When the shark left the cave, the fin relaxed. They were other species of fish in the cave with the coelacanth as well and the fin was lowered while they were present. 

This sand tiger shark was larger than the coelacanth and might have posed a threat to the coelacanth. There isn’t any evidence that sand tiger sharks eat coelacanths but when you’re a potential prey item you’re not going to ask the shark if they going to eat you, you’re going to take action. Raising the dorsal fin may be a way for the coelacanth to look bigger and ward off predators. This type of behavior has been well documented in other species of fish.  

This observation floored me. It means that the presence of humans and ROVs is considered stressful to the coelacanth and our presence was probably changing the behaviors we observed. If we want to know more about them, we’re going to have to come up with some unobtrusive methods of observation. 

This research also studied temperature and currents near where the coelacanth were seen. Does this impact their behavior? It was observed that the coelacanth were present in the caves when the temperature of the water was between 59 degrees Fahrenheit and 71 degrees Fahrenheit. This has been seen in past research, as well. The researchers postulated that this is the optimal range for oxygen uptake in the coelacanth. The current direction was frequently southward and low in velocity when the coelacanths were seen at the study site, but more research will need to be done to determine if this is of any significance.

Wow! I don’t know about you but the coelacanth continues to amaze me. I’m glad you spent some time with me to learn about coelacanth behavior because it’s my fourth favorite thing about this ancient fish.

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another episode about the coelacanth.  

 

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.