I keep seeing these cute “guess the shark species” slideshows l on tiktok, but they always show a pelagic thresher shark and just call it a “thresher shark,” so I realized not a lot of people might know there are three species of thresher shark. I’m going to introduce you to all of them and give you some certified marine biologist (tm) tips and tricks to notice species-specific features to look for once you see the long tail that indicates it’s in Alopiidae (since even google images messes it up sometimes).
This is a pelagic thresher shark (Alopias pelagicus). It is the smallest of the three species, and usually the one everyone thinks of. Some of the most distinguishing features to me are the slender body shape, a smooth head with no noticeable ridge, and eyes that are still somewhat large, but not noticeably so. But the most important distinguisher to me is its coloration, the white on the shark’s ventral side forms a border with the grey on it’s dorsal side, and this border goes *under* the pectoral fins, not *over*. They can be found to at least 150 m.
The common thresher shark (Alopias vulpinus) is the one that’s the most annoying to find on google images, because half the images are of the pelagic thresher. It is the largest species of thresher shark. As you can clearly see, these guys are a bit chunkier and also don’t have a noticeably large eye, and they have a smooth head that lacks a noticeable ridge. But the most important distinguisher for these guys is also related to their coloring. As you can kind of see in this photo, the border between the white of the ventral side and grey of the dorsal side goes well above the pectoral fin, so they have a spot of white that goes *above* their fin. This is the easiest way to distinguish them from pelagic thresher sharks, since you might see them within the same size range, so going off of body shape and size alone isn’t the most reliable.
And lastly, we have the bigeye thresher shark (Alopias superciliosus), so hopefully now it’s clear why I was harping on the eyes so much for the last two. Their gigantic uwu eyes are definitely a distinguishing feature, but the most prominent feature you want to look for during identification is the large ridge between the top of their head and their body. It’s super noticeable in person as well, and is not a feature shared by the other two sharks. These are the most easily distinguishable from the other two, and can be found to a depth of up to 723 m.
All thresher sharks are ovoviparous, so they give live birth! And they’re all cutie patooties who deserve to be appreciated.
