Welcome to Dear Shark Man, an advice column inspired by a ridiculous e-mail I received. You can send your questions to me via twitter (@WhySharksMatter) or e-mail (WhySharksMatter at gmail).
Dear Shark Man,
Are Daddy and Grandpa sharks really morphologically bigger than Mommy and Grandma sharks?
Addicted to “Baby Shark” in Arizona
Thank you for a great question, which allows me to continue teaching science from things that go viral on the internet. First, let’s make sure that everyone’s on the same page about what precisely you are inquiring about.
You’re referencing the viral song “Baby Shark,” which has been made popular recently by the online educational company Pinkfong. (Though, let’s be clear here, the song is much older, I remember singing it at summer camp 25 years ago). The Pinkfong version of the song is an undeniable hit, inspiring remixes, educational parodies, clothing, food, and even the baby shark challenge.
In case you haven’t seen it yet, you’re welcome:
Anyway, in the song and associated dance, a series of shark age classes are named, and the dancer moves their hands and arms progressively larger to signify an increased gape size (size of open mouth) associated with changes in shark life history. Baby shark is the smallest, mommy and grandma shark are the next largest, and daddy and grandpa shark are the largest. Additionally, both grandma and grandpa shark are shown to have no teeth.
So let’s get back to your question, Addicted. How accurate is the dance associated with “Baby Shark” in terms of portraying the relative dimensions of gape sizes associated with different life history stages of sharks?
Is the gape size of a reproductively mature shark (male or female) larger than that of it’s newborn offspring, which are called either “pups” or “young of year ” or “neonates”? Yes, because the whole shark would be larger. This makes intuitive sense, I hope! Indeed, a mommy or daddy shark would have a dramatically bigger mouth than a baby shark. The size disparity becomes a little blurrier when you’re talking about not-quite-reproductively-mature juveniles and have-just-become-reproductively-mature young adults, but the difference between baby and mommy or daddy sharks is noticeable.
Are reproductively mature adults old enough to have reproductively mature offspring going to be approximately the same size as their reproductively mature offspring? In other words, are grandma sharks the same size as mommy sharks, and are grandpa sharks the same size as daddy sharks? No. Sharks have what’s called “indeterminate growth,” which means that they continue growing throughout their lives. Therefore, grandma sharks would be larger than mommy sharks, and grandpa sharks would be larger than daddy sharks. This difference in size (and associated gape size) would not be as drastic as the difference in size between that of mommy/daddy sharks vs. baby sharks, however, because growth rate slows down as sharks age.
Next, are reproductively mature adult male sharks larger than reproductively mature adult female sharks? In other words, are daddy sharks bigger than mommy sharks, and are grandpa sharks bigger than grandma sharks? Typically not! In many (I’m always hesitant to say “all” because sharks are weird, but I don’t know of a counterexample) species of sharks, the females are larger than the males. The reasons for this are complex, but if you think of it in terms of how much energy and effort and space it takes to make sperm vs. eggs (or how much energy and effort and space it takes to have pups grow inside you), it makes some intuitive sense. In some other fish species, the smaller younger individuals are all males, and they *turn into* females when they age and grow, a phenomenon known as protandrous sequential hermaphroditism. (This happens with clownfish, which would have made Finding Nemo a very different movie if they paid a little more attention to scientific accuracy).
Finally, would older grandma and grandpa sharks have lost all their teeth as they aged? In reality, many shark species can continually regrow new teeth throughout their lifetime (sometimes going through thousands of teeth per individual shark). This is good, because when you’re a wild predator and you don’t have any teeth, you can’t eat and you, um, die.
So in summary, Addicted, “Baby Shark” is catchy as hell, but is not a new song, and the associated dance is not scientifically accurate. Put another way, the song is not quite right, doo doo doo doo doo, not quite right, doo doo doo doo doo, not quite right doo doo doo doo doo, not quite right.