Moving on up – Vertical migrations of Nautilus

If you like nature documentaries, you’ve probably seen the following clip (from the BBC’s “Planet Earth“):

Nautiluses are really cool – they’re misfits among cephalopods, having many tentacles and external shells while their fellow squids and octopodes are squishy and eight- or ten-armed. In this clip, at least, they come across as sort of mysterious, spending most of their time floating about in the abyss and only coming up to where it’s easy for us to see them at night. In fact, daily vertical migrations are common in the ocean, with a truly enormous number of organisms moving from shallow to deep waters and back again each day. The nautilus takes part in this migration, probably for its own safety – it’s harder for predators to see you (and eat you) if you stay where it’s dark.

Now I love learning new things about cool animals, but there’s something that I’m more interested in: how do we get that information? Presumably, biological facts are not true just because Sir David Attenborough says they are. How do the producers of that clip (or anybody, for that matter) know that this is what Nautiluses do?

It turns out that the answer is pretty simple: we monitor some of them for a period of time and see what they do. We can’t actually follow them underwater and visually watch them (because it would be difficult and expensive to do this for very long), so we have to use some sort of remote communications device (a radio or ultrasonic transmitter) to see what they do.

This is just what a group of researchers from the University of Queensland, have been doing for some years. Following up on reports about the possibility of daily vertical migrations in Nautilus, they attached ultrasonic transmitters to eleven nautiluses they caught around Osprey Reef in Australia. They kept track of each animal’s vertical movement, and described what they saw.

Nautilus fitted with ultrasonic transmitter - from Dunstan et al. 2011

As far back as 1899, a naturalist by the name of Arthur Wiley made note of the depths at which Nautilus live, both because it made them hard to study, and it meant that they were only be caught in shallow-water traps at night (although to be fair, he provides us no proof of this, only his word.) There are several other reports that support the idea that Nautiluses make vertical migrations (for example, a report published in Nature about the daily migrations of Nautiluses in Palau by Peter Ward et al. in 1984, and a report by Bruce Carlson et al. published in the journal Pacific Science about the same population of Natuiluses.)

Enter Dunstan and co-workers, the group of scientists at the University of Queensland that I mentioned earlier. They followed eleven individuals for up to around 80 days each and also used information from remote-operated vehicle dives to get a clearer picture of what Nautiluses spend their time doing. It’s easy to get an impression of their data from the following graph (click on it to see a bigger version):

Graph of individual recordings of Nautilus depths from Dunstan et al. 2011

Each line is one recording – there are multiple recordings from each animal. The “depth” of the line at the time of day shown at the top of the graph indicates the depth of the recording.

So what do we learn from this? Basically, we learn that it’s not as simple as “shallow at night, deep during the day” – just look at that graph! It doesn’t look like the movement of nautiluses is coordinated very well, either between animals or with times of the day. The authors note that the nautiluses often spend the daytime resting in relatively shallow water, and at night are found in all sorts of depths. In summary, it looks like there are several factors that influence where a nautilus ends up hanging out; purely physically, they can’t go deeper than about 800 meters (2600 feet) due to the high pressure (their shells implode at depths greater than this) or shallower than about 100 meters (320 feet) due to higher temperatures near the surface. During the day, nautilus appear to rest in shallow water or forage in deep water, while at night they are active and move through a whole variety of depths – this is probably influenced by things like food availability, the type and number of predators around, the conditions of the water, and the size and age of the animal. These results don’t contradict earlier results, although the authors note that different populations of Nautilus have been observed to have different patterns of behavior, and chalk this up to differences in their environments.

On a final note, I’d like to mention a study by Kanie and coworkers in which they determined what depth of water would cause a nautilus’s shell to break. To do this, they put a nautilus in a tank of water, and pressurized the tank until the nautilus imploded, all the while measuring its ventilation rate (how quickly it was “breathing”). From this, they came up with a maximum depth for nautilus of 785 meters. At first, this sounded like a cruel experiment to me, but on second thought, it was done very well. They used a single animal (although one might criticize them for that, it means that they only caused harm to a single animal) and in doing so adequately and rather elegantly answered a basic question in cephalopod biology that has implications not only for the ecology of living nautiluses but also for the study of nautiloid fossils and their distribution.

Thanks for reading!

NOTE: This post has been edited from its original form in response to Dr. Peter Ward’s comment (see below). As I did not have access to the research he mentions when I wrote this post (and still don’t), it was inappropriate of me to comment on the state of the field as I did. I’d like to sincerely apologize to Dr. Ward and his coworkers for any disrespect I may have shown to them and their work. I’ll do my best to bring myself up to speed on the research he mentions and include a more detailed discussion of it in a future post, so that I’m accurately representing the field. The text of this post before it was revised is available at this link.

ResearchBlogging.org BRUCE A. CARLSON, JAMES N. McKIBBEN, AND MICHAEL V. DEGRuy (1984). Telemetric Investigation of Vertical Migration of Nautilus belauensis
in Palau Pacific Science

Yasumitsu Kanie, Yoshio Fukuda, Hideaki Nakayama, Kunihiro Seki, Mutsuo Hattori (1980). Implosion of Living Nautilus under increased pressure Paleobiology, 6 (1)

Dunstan AJ, Ward PD, & Marshall NJ (2011). Vertical Distribution and Migration Patterns of Nautilus pompilius. PloS one, 6 (2) PMID: 21364981

Arthur Willey (1899). On a Zoological Expedition to the South Seas Proceedings of the general meetings for scientific business of the Zoological Society of London

Ward, P., Carlson, B., Weekly, M., & Brumbaugh, B. (1984). Remote telemetry of daily vertical and horizontal movement of Nautilus in Palau Nature, 309 (5965), 248-250 DOI: 10.1038/309248a0

11 Comments

  1. Pat Bowne says:

    How did the researchers determine that the transmitters weren’t affecting the animals? The one in the picture looks pretty large compared to the shell size.

    • Scanning the article again, they don’t seem to have done anything to check for this. It seems like it would be a big deal, though. They made sure it wouldn’t affect their buoyancy, and it looks like it’s outside of their range of vision (so they wouldn’t see it and get alarmed), but it still might have affected their movement.

  2. Mike, you are only one animal too.

    • The point I wanted to make is that the use (and death) of one animal to gather a useful piece of information in a well-recorded and clearly communicated study is less wrong that the use of many animals.

      I did not mean to imply that there are no ethical problems with the use of animals in research – there are significant ethical problems to deal with when using animals for any purpose. I don’t think that the way to resolve these problems is to equate the lives and experiences of non-human animals (like nautiluses) with our own. Even if this approach makes arguments for not using animals our of empathy persuasive, it is ultimately wrong (or at least incomplete.)

  3. Danna Staaf says:

    How neat! Thanks for sharing–I love that figure with all the depth tracks. One thing always jars me about nautilus vertical migrations: the fact that “shallow” for a nautilus is still deeper than a human can dive! I’m so used to thinking of “shallow water” as the space from the surface to 20 or 30 meters . . .

    I noticed at least two of the studies you mentioned are about different species of nautilus. I wonder if there’s much difference in migration behavior between species–and in particular, I wonder if anyone’s ever looked at Allonautilus?

    • The scarcity of data is a problem here – its possible that various populations of a single species have different patterns of movement depending on their local environment, let alone different species.
      As far as I could tell from a quick search, the information available on allonautilus specifically is all phylogenic or anatomical, not behavioral/ecological.

  4. Dr. Peter Ward says:

    You are so full of crap. Get your damned facts straight. My “crew” followed 6 Nautilus in Palau, three in New Guinea, and 7 in New Caledonia for a total of a month (see Ward et al, 1984; Ward, 1987

    If you are going to spout off about something you know nothing about, get it right. One man died doing this work. He deserves better than your drivel.

  5. pj says:

    Nautili, dude. I just heard a talk including some research about why they don’t live more than 2-3 years in captivity. Most die immediately after capture. Their shells show a shock pattern at that point and show degraded chemical composition in their growth pattern after that. Sounded like they aren’t making the synthetic ocean water properly for one thing. Personally I think it’s cruel to take them out of their natural habitat. A fascinating creature.

  6. Peter Ward says:

    Great job and I am really sorry I was so harsh in my comment above. You are doing a service.

    I WOULD like to answer one comment above. You are so right about the size of the transmitters being so large relative to the animal. We do not know what to do about that. The size constraint as in all things electronic is the battery.

    Peter Ward

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