On Tilikum & Statistics

While so many of us were busy thanking our respective deities that the fiasco that was 2016 has passed, the new year is already off to a heartbreaking start – at least for the animal care community, and especially for SeaWorld Orlando’s zoological team.  On January 6, 2017, the infamous killer whale Tilikum passed away from a chronic lung infection at an estimated 36 years old.

Tilikum’s death represents a huge loss—literally, he was over 20 feet long and weighed in at more than 12,000 pounds. On an even larger scale, though, this whale inspired millions of people to care for all marine mammals by connecting them to the beauty, intelligence, and pure majesty of nature.  His impact on the trainers who worked with him, the guests who connected with him, and the wild whales who now benefit from a more passionate society will continue long beyond his last breath. 

Photo of Tilikum by SeaWorld.

While it is certainly worth just taking the time to recognize Tilikum’s enormous lifetime impact on humans and animals alike, the main reason I wanted to write this post was to address a long-standing misunderstanding that has resurfaced with this tragedy: do killer whales (and all cetaceans) in zoos and aquariums live shorter lives than their wild counterparts?  A few subtle factors make answering this question much more complicated than it seems.

First of all, lifespan statistics are generally difficult to accurately assess because it takes a lot of time, and a little luck, to collect truly representative life history data on any whale population.  Due to cetaceans’ long life cycle, decades of research may be required to develop a thorough data set on any given pod.  Additionally, if a population resides in formidable climates (such as Antarctic subtypes), migrates long or unpredictable distances (e.g. transient whales), or lives far from coastal regions (for example, offshore ecotypes), it is nearly impossible acquire consistent, representative population data.  As a result, not all life history statistics are well-understood – including those of the Icelandic population that Tilikum was born into.  However, although information from one ecotype does not necessarily represent all others, it certainly gives us a better idea of the species’ general survivorship patterns than no data at all. 

Arguably the best-studied killer whale pods are the two "resident" populations off the coast of Canada.  While their lifespan parameters may differ somewhat from those of Icelandic whales, the residents are considered some of the longest-lived due to one female nicknamed "Granny" who was estimated to have survived somewhere between 90 and 105 years.  Therefore, data collected from these animals represents a liberal estimate for other populations, making it an ideal set for comparison. (Sad side note: a few days ago, scientists announced that they haven’t seen Granny recently and are therefore assuming her deceased.  It's been a rough week for Orcinus orca.)

Photo of J2 "Granny" in 2010 by the Center for Whale Research.

From 1973 through 2004, Olesiuk and colleagues collected data on the aforementioned resident populations in the northeast Pacific.  Their research estimated the female average lifespan to be between 30 and 50 years, depending on the group and time period, and approximated males between 19 and 31 years (see Table 14 in Olesiuk report).  Tilikum passed at 36 years of age, five years older than the upper average male estimate deduced by Olesiuk et al. (2005).

It is important to note that maximum longevity is different from average longevity.  The same study also estimated that males in these populations have a maximum longevity of somewhere between 40 and 70 years, but of course this doesn’t imply that every individual is expected to live that long.  It’s kind of like saying that although the oldest human ever recorded was a 122-year-old female in France, the average male lifespan in the United States is estimated around 76 years, and we obviously wouldn’t consider an American man who passed at 85 years old to have “died young” since he didn’t surpass the world record.  Similarly, no unbiased observer would consider Tilikum to have passed prematurely since he didn’t live up to the 100-year record estimated for a female, but exceeded the 19-31 approximation for average male lifespan.

Okay, so maybe you'll agree that Tilikum didn't die young in this one case, but what about all of the other whales in human care?  If you take the average age of all whales in zoos and aquariums and compare it to the wild, you will find that those numbers look different.  However, consider that Granny may have survived past 100 years, but killer whales have only been in human care for about 50 (and our ability to care for them has improved exponentially during that time).  Therefore, it’s impossible for the zoological population to mirror the dynamics of a wild one, making the comparison of average member age inherently inappropriate.

Additionally, even well-studied populations aren’t visible during certain times of the year, and as a result calves are usually first spotted around six months of age.  The problem is that if a calf dies before they’ve been recorded, they will never make it into the calculation for average lifespan – and this is significant since upwards of 40% of calves are estimated to die within their first six months (nature is brutal, people.).  However, of course we have all data for populations in zoos and aquariums, so any young calves that die in human care are usually included when calculating average age of death.  The result?  Many people wind up comparing statistics between uncontrolled groups (the zoological one including deaths of calves aged less than six months, the wild one excluding them).  And that, my friends, is what we call bad science.

Another side note: because they receive world-class health care and protection from natural threats, calves in human care have a significantly higher chance of surviving to two years of age than those in the southern resident population (.966 versus .795, p < .04; excluded zoological calves that survived less than 40 days to control for sighting bias) (Robeck et al. 2015).  Pictured here is Kasatka with her fourth calf Makani at SeaWorld San Diego.

All of this is to show that a lot of the statistics you’ve probably seen in the popular media are—and excuse my language here—baloney. So, how can we accurately compare these two necessarily distinct populations to see if there actually is a significant difference?  One way is to look at year-to-year survival rate, or what percentage of each population survives on average to the next year. Luckily for us, a group of researchers have already crunched those numbers: Robeck and colleagues (2015) calculated the southern and northern resident populations' annual survival rates (0.966 and 0.977, respectively) and found that these numbers were not significantly different from that of SeaWorld's whales from 2000 to 2015 (0.976).

These survival statistics are indicative of the quality of care that animals receive in accredited zoos and aquariums today, and the stimulation and health care provided for Tilikum during his nearly 25 years at SeaWorld Orlando was no different.  While he has been portrayed in the media in a very negative light, his trainers say that he had a fun-loving personality and enjoyed relationship-building sessions.  If you want to know more about this, I recommend checking out one of SeaWorld’s publications or this video from one of his former trainers.

Tilikum with trainers during an enrichment session.  Photo by SeaWorld.

Animal rights organizations are aggressively spreading false statistics and emotionally-compelling (but not accurate) claims that threaten the well-being of all cetaceans in human care today by pushing for their release, which would likely have lethal consequences (just as it did for Keiko).  This movement is based on emotion, not logic, and because of this ignorance, its propaganda is actively hurting the animals that it's claiming to help.  Although you may choose not to go to a zoo or you may disagree with the idea of animals in human care, I hope everyone will critically consider statements made in the media and by extremist groups.

One of the biggest impacts Tilikum had was inspiring millions of people to care about killer whales, and we desperately need that passion to continue beyond his passing.  The same southern resident population that I've referenced several times throughout this post is rapidly declining because of severe food shortage, boat traffic, and pollutant bioaccumulation.  Other populations of whales around the world are also facing myriad threats from global warming and human activity.  Learning about killer whale conservation initiatives, consuming sustainable seafood, and disposing of waste appropriately are just a few doable things that can make a huge difference for the lives of wild whales and the entire natural world, and in my opinion it is one of the best ways to honor Tilikum's memory.

My condolences are with the SeaWorld Orlando training team and all those whose lives were touched by this magnificent whale.