Aging Sea Monsters

By Steve Midway

Many of you may remember back in October 2013 a giant oarfish was spotted just off of a beach on Catalina Island, California. Despite being one of the largest fish in the sea, giant oarfish remain one of the most elusive. And so when one finds its way to shore, it’s not only a spectacle for its size—this one was 18 feet!—but also a very unique find. It can often take hundreds or thousands of individuals of a species to simply begin to understand basic biology (age, growth, reproduction, etc), and while only so much can be concluded from an individual, a single oarfish represents a substantial opportunity to collect information.

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18 foot giant oarfish that was found in the waters off Catalina Island, CA in October 2013 (Photo: Catalina Island Marine Institute)

Shortly after its discovery, scientists arrived to sample tissues—stomach, gonads, muscle, etc. And some of the information was quickly beginning to shine a light on the biology of oarfish, or at least this particular individual. And not too long after the fish’s discovery, I found my way on a flight to LA, followed by two boat rides, all in an effort to try and be the first to remove the otolith (earbone) from this sea monster. Fish otoliths are a repository of information; we’ve covered otolith science here, and here, and here. Primarily, the often tell a fish’s age because they accrue rings in the same way a tree does. But for some reason, the otoliths of giant oarfish are not particularly easy to extract, as I was unable to track down any person or work successfully documenting the process.

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Defrosting head section of the oarfish—note that it was already decomposing and had been partially-dissected. They look much better fresh! (Photo: Steve Midway)

With NOAA fishery biologist Bev Macewicz, we let the oarfish head defrost in the warm November sun (the fish had been sectioned and kept frozen over the few weeks since its discovery). But it quickly thawed, and surrounded by a mounting army of bumblebees, I began slicing back the skull as I might do for most fish. The skull was largely cartilaginous—not bone—so it sliced fairly easily. We found the brain, and suspected the otolith would be situated just below it, as it is in many species. We sliced gently. And we gently sliced some more.

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The two cavities in the center of the photo are located just below the brain, and it’s in this area that the otolith was discovered (Photo: Steve Midway)

Fast-forward about an hour and finally, amidst shards of cartilage and bits of various other tissues, my forceps felt something small and bony—an object with promising features. But it was very small. Much smaller than I anticipated. When it was finally removed and in my hand, I had to scratch my head. Why would the otolith of an 18 foot fish be smaller than some otoliths I’ve seen from 6 inch fish? It need not scale entirely with size, but this was one of the smallest otoliths I had ever seen—of any species! Regardless, we safely stored it and took a few other bone samples for age—namely a vertebrae and some fin spines, which may also form annual rings for aging purposes.

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CT scan of a giant oarfish otolith (Photo: Steve Midway)

Because only one otolith was recovered (fish have two otoliths, a left and right one), and it would need to be cut up for analysis, I had it CT scanned in order that the most detailed image of it might be saved. After that, the otolith and the other bony structures were sent to Dr. Steve Campana’s otolith lab. Unfortunately, not all of the pieces of bone suggest the same age, and our results are still in the review process of a scientific journal, so I can’t make any announcements of how old the fish was. But we were the first to successfully collect this important bone and may have the first ever estimate of a giant oarfish age…OK, I guess I can share a little. How many rings do you count in the sectioned vertebrae below? (Please leave your guess in the comments.)

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Sectioned vertebrae of giant oarfish—how many rings can you count? (Photo: Steve Midway)

 

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6 responses to “Aging Sea Monsters

  1. Great article!

    I will guess 23 due to the visible bands. I zoomed in on the image a bit, likely blurring the banding patterns. Also no experience with ageing via vertebrae.
    Can’t wait to read the study, I’m very interested in the results you found from the otolith!

  2. It’s interesting that otolith’s rings indicate the age of fish. I never counted those rings. But from the last photo, I think, there are aprox. 21-25 rings…

  3. You asked why they might be so small? Just wondering if there are other species where this is also the case? Makes me wonder if either they don’t have a significant need to know direction and nature of sounds (e.g., their world is generally very “quiet” and they don’t have to track their food) or perhaps it might create a lot of “noise” and some other sense predominates.

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