Killer Whale Testosterone Surges Documented by SeaWorld

Tilikum, the male killer whale that fatally injured trainer Dawn Brancheau in front of a horrified audience at SeaWorld in Orlando Wednesday, was a breeding "stud" that sired his first first calf when he was just 8 or 9 years old. According to the American Cetacean Society (ACS), most killer whales become sexually mature between the ages of 10 and 18 years, but Tilikum was no ordinary whale. 

Footage from October of last year showing how Tilikum's performances normally began at SeaWorld.

Over the years, the sexually charged marine mammal has sired a record 17 calves, 10 of which are still alive. Such offspring are extremely valuable to marine parks, and Tilikum's progeny have gone to other SeaWorld parks and even to facilities outside of the U.S. 

The hormones that make Tilikum such a good breeder, however, may have also turned this killer whale into a human killer.

A few years ago, Todd Robeck, corporate director of theriogenology at SeaWorld and Busch Gardens' Reproductive Research Center, conducted a study with Steven Monfort of Smithsonian's National Zoo on testosterone levels in male killer whales. The study was published in the journal Theriogenology.

For the study, the researchers analyzed both serum testosterone concentrations and semen production in killer whales.

"Serum testosterone concentrations were higher (P<0.05) from March to June than from December to February in pubertal animals (4.2±3.4ng/mL versus 1.4±2.6ng/mL) and than from September to December in sexually mature animals (7.2±3.3ng/mL versus 4.0±2.0ng/mL)," the scientists determined.

While the March to June spring surge was linked to males younger than Tilikum, the researchers acknowledged that male testosterone concentrations fluctuate as a result of age and that there is "reproductive seasonality in the killer whale."

Yesterday, marine biologist and killer whale expert Nancy Black of Monterey Bay Whale Watch told me that Tilikum may have even been exhibiting mating behaviors during the attack. (To read more about that, please read today's Discovery News story concerning the incident.) 

Robeck and Monfort's paper was the first comprehensive research on male killer whale testosterone, so clearly research on this matter is in its infancy. If these marine mammals are like others in the animal kingdom, however, then there is probably a genetic component to their hormonal makeup. A parent with unusually high testosterone, or a predisposition to hormone swings, could pass that on to offspring, so whales like Tilikum that are particularly good breeders could be producing whales with a tendency for behavioral problems.

Environmental influences can also contribute to behavior in all animals, including humans. This too was problematic for Tilikum, according to Black.

(Image: A killer whale in the wild; Credit: NOAA)

"It is not natural for whales to be kept by themselves," she told me, adding that it was her understanding that Tilikum is often housed alone. And "he was kept in small tanks from the beginning." SeaWorld's Shamu Stadium has a 7 million gallon tank, an improvement on Tilikum's earlier tanks, but even that amount of water is probably a drop in the bucket for a whale and other large marine dwellers.

According to the ACS, in the wild, "orcas generally live in pods (groups) consisting of several females, calves, one or more males, and/or juveniles. Some pods consist of a mother and her offspring who stay with her for life."

Black told me, "Once in a while, a male killer whale will go off by itself, but that is unusual. The orca at SeaWorld would have been living in an unnatural state."

Captivity itself is, of course, unnatural, but habitats for some animals can be replicated from the wild better than others. Ken Peterson, communications director at the Monterey Bay Aquarium, told me that even that impressive facility decided "not to devote a lot of space" for marine mammals like killer whales, so he and others there instead urge the public to go on whale watching excursions, where these animals can be admired in the wild.

Tilikum was captured swimming in waters off of Iceland. In more recent years, the emphasis has been on breeding programs instead of acquiring whales from the oceans. While Black admits whales born in captivity may be less wild, and therefore less of a threat to trainers, it is not a risk free solution. She, the ACS and many other experts also believe that no whales should be in captivity.

"My hope is that staff at these facilities will not continue to breed killer whales," Black said. "The existing whales in these programs should be allowed to live out their lives," but after that, she told me, the programs should be terminated.