Killer Whale Lifespan

HOW LONG DO KILLER WHALES LIVE?

The data we do have show that killer whales at SeaWorld are living as long as their counterparts in the wild. 

A complex issue

What we do know

A look at the most recent research

Why it is important to take a careful look at numbers

Looking to the future

A complex issue:

The issue of killer whale lifespan is one that is often misconstrued and overly simplified. The simple truth is that no one knows.

  • Only a small percentage of the world's wild killer whales — a few populations off the coasts of Washington, British Columbia and Alaska — have been studied long enough to produce statistically valid research. 
  • Killer whales live all over the world in distinct populations—some very different from each other – and we do not have enough adequate science to know if different ecotypes have different lifespans.
  • Additionally, when attempting to compare the lifespan of wild populations vs. those that live in zoos, the data are limited. There is a relatively small number of killer whales in our care, and these limited  numbers make direct comparisons tenuous and misleading. 

What we do know:

The data we do have show that killer whales at SeaWorld are living as long as their counterparts in the wild. 

In peer-reviewed studies, scientists estimate that the average, or mean, life expectancy for a female is 30 years and a male is 19 years in the Pacific Northwest.[1].  For whales in southeastern Alaska, the maximum longevity appears to be in the 50s for females and late 30s for males.[2]   So, in those two areas of the world, female killer whales live around 30 to 50 years and males live around 19 to 30 years.

SeaWorld has several killer whales in their 30s and one that is close to 50.

A look at the most recent research

Because it can be misleading to compare life expectancies between whales in the wild and those in captivity, scientists believe that the most accurate comparison to use is the "Annual Survival Rate" (ASR).  ASR is an estimate of the percentage of whales in a population expected to survive each year.[2],[3]

For instance: if  we were studying a specific community of humans, this method takes into account that – in that specific population -- the number of children that are expected to survive another year is high, and the number of senior citizens expected to survive is low.

According to recent studies, the current ASR of SeaWorld’s killer whales is similar to that of the Alaskan Resident whales.[2]  The study determined that the overall average ASR for that population is 0.976. (This means that there is a 97.6 percent chance that a whale in that population will live another year.)

SeaWorld compared the study’s results to the ASR’s of its killer whale population. To take into account advancements in medical care and knowledge, we looked at four different time spans (1968-1983, 1984-1993, 1994-2003, and 2004-2013).  Not surprisingly, the trend improves over time. The fairest comparisons are the two most recent 10-year periods from 1994 to present, during which the whales have had the opportunity to benefit from advancements in our knowledge, facilities, and husbandry and veterinary practices.

For both of those most recent periods of time, there is no significant difference between the ASR of our whales and the ASR of wild populations.

Why it is important to take a careful look at numbers

Statistics used to determine longevity can use a few different methods, and can be manipulated to mislead people into false assumptions. 

For instance, many animal rights activists will mix different types of studies when comparing the lifespan of wild vs. captive whales – citing side-by-side the maximum longevity for wild whales, but the average longevity of captive whales. 

Using a human analogy: if one man in Japan happened to live to 116 years, but the average life expectancy for a male in the U.S. is 76 years, it would be false to say that “Living in the U.S. causes early death. People have a lifespan of 116, but in the U.S. they die early at age 76.”

Let’s look at some statistical results that can be generated and questions that can be asked which have often led to confusion or misrepresentation during population comparisons.[4]

1. What results are we comparing?

Different studies examine:

- The oldest a whale can get, which is maximum potential life-span.  Since individual killer whales in the wild have only been followed for 40 years, the oldest known-age animal cannot exceed this value. All other proposed maximum-age projections are simply estimates.

- The average age at death of a whale that lives past its first year of life. This statistic creates bias against animals that are currently alive by excluding them from the analysis. It is not considered an accurate representation of population longevity.

- The life expectancy of a whale. This further must be defined as whether that includes any animal from moment of birth, or only those that survive to a particular known “starting age.”

2. When comparing results, what variables have been taken into account?

Because of different variables, comparisons among different populations are often unreliable. This applies to comparing wild whales that live in different regions of the world, and also when comparing wild whales vs. those that live in zoological facilities. 

For whales in the wild, those variables include different whale population life histories and environmental stressors: variations in food availability, shifting climactic conditions, and pollution. All affect wild whale health and mortality, and especially over short periods of time, can significantly skew statistics.

 Other variables that affect comparisons include:

- Are young calves included?  Studies of killer whale longevity in the wild generally exclude mortality of whales less than six months of age. They do this for a very practical reason: killer whale calves often do not become known to the scientists studying them in the wild until they are at least six months old.  

So, to accurately compare the results of studies in the wild (which exclude these very young calves that have a high mortality rate), with the results of studies of captive whales (which typically include every birth), one should make a similar exclusion. This ensures that both sets of results are comparable.  This is something animal activist groups almost never do.

Any comparison of research on young killer whale calves – even with the concern noted above – still shows that calves at SeaWorld have a much greater rate of survival than calves in the wild. But for the purposes of this discussion, and our best effort to equate variables, we have left calves younger than 6 months of age as a separate group, and out of both sides of this equation.

- Are unusual exposures included?  In studies of wild whales, scientists will sometimes exclude animals exposed to a specific unusual event. For example, a study of Southern Alaskan resident killer whales excluded those that had been exposed to the Exxon Valdez oil spill.[5]  Although this was an appropriate way to structure that particular study, it also can be argued that these data then underestimate the risks faced in the wild and therefore unfairly skews any comparison with animals housed in zoos.

- In facilities, do you include whales that arrive already in compromised health?  Whales that come to a facility in a compromised state of health, such as from beaching and/or illness, should be excluded from zoological whale studies, because these whales would not be alive in the wild.

- In facilities, do you use data that reflect current conditions and the evolved state of medical knowledge and care? We know that care of killer whales has improved immensely – thanks to research made possible by maintaining a population of killer whales that we work with on a daily basis. For this reason, the studies that best reflect the longevity of SeaWorld’s killer whales are those that have taken place since the 1980s .

3. How many whales are we studying?

As we mentioned previously, in any study, it’s important to have a statistically valid sample size, and captive populations tend to be small, allowing individual aberrations to skew the numbers and distort comparisons with studies of larger populations. There is no simple solution to this problem, so we need to consider this effect when evaluating our results.

Looking to the future

Moreover, life in the wild for killer whales is getting more difficult, as recent research shows. A study released in October 2013 by the Orca Relief Citizens’ Alliance found that among Southern Resident killer whales, the number of reproductive-age males has declined 26 percent since 2009 – reaching the lowest number of breeding-age males since 2003, and a total population of only 80.[6] These studies are a reminder that the hazards and hardships of life in the wild should not be ignored or idealized when making comparisons with captivity, and they underscore the critical role that SeaWorld researchers are playing in helping to understand, protect and preserve those wild populations.

Independent of the complexity of the subject is our motivation, our mission, our expectation that longevity by any measure of the whales that we are privileged to care for in our parks will continue to increase and will one day outpace that of wild populations.  It is important to remember one thing: NO ONE cares about the health and well-being of our killer whales as much as we do.

Conclusion

Discussions of longevity can become surprisingly complex, and it is easy for people to be confused or misled. As we have seen, a careful look at the data supports the view that the survival rates of killer whales at SeaWorld are comparable to those of the wild.

 



[1] Olesiuk, P. 2012. Population biology of the resident ecotype of killer whale in British Columbia. Materials of the killer whale workshop, Suzdal, Russia.

[2] Matkin, C.O., J. Ward Testa, Graeme M. Ellis and Eva L. Saulitis. 2013. Life history and population dynamics of southern Alaska resident killer whales (Orcinus orca). Marine Mammal Science: 10.1111/mms.12049

[3] Small, RJ and DP Demaster. 1995. Survival of five species of captive marine mammals. Marine Mammal Science 11:209-226.

[4] For a more comprehensive and technical look at the complexity of this subject, see van der Toorn, “Survival Guide to Survival Rates,” Marine Mammals: Public Display and Research, 3(1) 27:38 (June 2000). The paper demonstrates the many pitfalls of comparing wild and captive populations, as well as invalid comparisons between “life expectancy” and “longevity.” It recommended using survival rates instead.

[5]  The Matkin, et al., study excluded whales it believes had been exposed to the Exxon Valdez oil spill.

[6]  “Breeding Male Orca in Collapse, Total Down 26% from 2009 – Lowest Count Since 2003,” Orca Relief Citizens’ Alliance, Oct. 22, 2013, http://www.orcarelief.org/newsroom.php. A study released the previous month on females produced reported similar findings. http://www.orcarelief.org/research.php