But how do we really know how old J2 is?
The honest answer is that we don’t know for sure!
There are several factors that the 1911 birth date is based upon. According to Bigg et al (1990), the age of a mature female (based on relative size) was determined by the age of her first viable offspring. The birth date of the mother was estimated by a complicated equation that included the following variables:
1. The age of her oldest offspring (probable or known)
2. The average age a female gives birth to her first calf-12 to18 years.
3. The average interval between calves – 4 to 6 years.
4. The probability of a female loosing a calf.
5. The average number of calves a female will have in her lifetime - 4 to 6
6. The age at which females stop reproducing- about 40 years.
For J2, her probable offspring is J12, who was estimated to be born in 1935. If you extrapolate backward using the parameters above, the earliest date J2 could have born is 1911. It has also been suggested that J2’s age is based on a possibility that J1 was her last-born son. Based on his size, J1 was estimated to be 21 years old - the age that most males reach physical maturity- in 1972 when he was first photographed. That makes his birth year 1951. So if J1 was born in 1951 and J2 was at least 40 at the time - the age females typically stop reproducing - that would make her birth year 1911 (1951-40 years).
As you can see, there are a lot of assumptions here! Most obvious is the assumptions about probable offspring could be incorrect. Association is not always enough to determine a real genetic relationship. Just think of L87 and his recent association with J8. If the study had started last year, we would have assumed that L87 was J8’s son! In the few encounters with J pod this year, L87 has been seen traveling with J2 now that J8 is gone. J2 could very well be younger than her estimated age. She could have been J12’s sister? Any way you do the math, she is still above the average age for a female orca in the wild or in captivity. Of course, there is also the possibility that she is older than our estimate!
Excerpt from the initial Photo-Identification study of the SRKW published in 1990 by Bigg, et al showing the original age estimations of J1 and J2.
Like J2, estimates on all the whales born before the study began are based on the same parameters. There are only two whales left, J2 and L25, that were estimated to be born long before the study started. This is exactly why our goal at the Center for Whale Research is to keep the study going through an entire generation of whales. Then we will have a much more accurate picture of the average lifespan of wild killer whales. This is not only important for conservation, but it has become important in the arguments against captivity. For those of us lucky enough to see killer whales frequently in the wild, we know that their beauty and majesty in their natural setting doesn't compare the choreographed shows performed in theme parks.
Wouldn’t it be something for J2 to live through the lifespan of seeing her species in captivity? Will J2 outlive the captive killer whale industry?
We will talk more about that in our upcoming newsletters! Stay tuned!
From the Center for Whale Research
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