Cooler Than #SharkWeek: Bulking Up On Bull Shark Testosterone?

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Discovery Channel has pissed off tons of its viewersincluding meand Wil Wheatonby launching shark week with the mockumentary Megalodon: The Monster Shark That Lives. With so much awesome shark science out there, its sad that they had to stoop so low for ratings. In response to the outrage, Brian Switek started Cooler than #SharkWeek on twitter, highlighting actual research on sharks. Im continuing the movement by posting or reposting a blog entry about sharks every day this week.So instead of watching Shark Week, tune into Science Sushi all week for real shark science! Today we have an updated version ofmy 2012 Science Sushi post busting the myth that bull sharks are constantly raging on roids

This startling image of a 1,000 pound bull shark circulated the internets, but what really caught my eye was a (mis)quote from the lead researcher. According to news outlets, he said that bull sharks have the most testosterone of any animal on the planet, so that should tell you a little something.

It wasnt the first time Id heard this whole bull sharks and testosterone bit. Indeed, all over the internet, you see claims that bull sharks are so aggressive because of their insane testosterone levels. But it was the character Bruce Kibbutz in Grand Theft Auto IV that really got people talking about bull shark testosterone. During the game, the roid-raging fitness freak explains how he juices on testosterone taken from Chilean bull sharks. Suddenly, extreme body builders and skeptics wanted to know if you could really bulk up on bull shark blood.

The rumor, as Id heard it in college, is that the fierce attitudes of these large and aggressive sharks is due to unfathomably high circulating levels of testosterone. Specifically, these menacing monsters supposedly have higher serum testosterone levels than any species on the planet, land or sea, and that even a female bull shark has higher levels than a testosterone-raged male elephant in musth. I know Im as much to blame as anyone, as Ive repeated that line myself. But when I was asked about it, I realized that I didnt know if its true. How do the circulating testosterone levels compare between bull sharks and other species? Could you procure enough testosterone by catching and eating bull sharks to beef up your body?

Lets start with that elephant. In the red corner, standing up to 11.5 feet tall and weighing in at up to 20,000 lbs, we have the African Bush Elephant (Loxodonta africana). Whats the testosterone level in this whomping beast? During much of the year, not much. Male elephants, on average, have less than 2 ng/ml ciculating in their plasma. But wait! Big boy wants to get his groove on, and he is getting ready for a season of fighting and fornicating. So whats the male elephant in musths testosterone level? As high as 64.4 ng/ml! About a 60 fold increase in average circulating testosterone1. Ai! Thats a lot of anger-pumping hormone.

Is this bull shark experiencing roid rage? Not likely. Image by Albert Kok

How about his opponent, the every day female bull shark (Carcharhinus leucas)? In the blue corner, weighing in at around 505 lbs and stretching almost 12 feet long, is our large and in charge girl. Shes bigger than her man, no doubt, but she still has to keep her femininity about her. After all, as a girl, if her testosterone levels are too high, she might have reproductive issues. Surely her circulating levels are lower than the male elephants?

According to the only, extremely obscure published reference with testosterone levels in a female bull shark, actually, yes, they are2. Her circulating testosterone level is right around 0.1 ng/ml, a whole lot lower than that angry elephant. Sorry to burst bubbles, but she aint gonna give anyone roid rage. Her man, though My oh my. One of the two male adult bull sharks in that study had a circulating testosterone level of 358 ng/ml. Yeah, thats one roided out shark. Problem is, the other male bull shark in that study only had 2.7 ng/ml of testosterone in his serum which is probably less than you male readers out there have pumping in your blood right now. So not all male bull sharks are running around roided out of their minds. To be fair, these were just single sharks, caught once and tested once. Without a more complete study of the average hormone levels in bull sharks, by size, season, etc, we cant really say that bull sharks have abnormally high or low testosterone levels.

Of course, there is a more complete study. Not a super detailed one, but a study none the less. Rasmussen & Murru3 studied androgen levels in a number of captive sharks over time. They found testosterone levels of 10 ng/ml to 20 ng/ml in two captive bull sharks when they measured every June for three years, just after the sharks normal breeding season. Not too impressive, boys not too impressive, but of course, that is in captivity, and its unknown how captivity may affect their hormone levels.

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Cooler Than #SharkWeek: Bulking Up On Bull Shark Testosterone?