(09-03-2020, 04:33 AM)GuateGojira Wrote: Body size of the orca (different populations):
When this topic was created very few information was available and must of us only used the often repeated statements in the web. However, through the investigation and with the help of other posters I manage to found more information, which helped me to dig even more on this topic. At the end, I manage to found a good amount of sources and records from several areas that shows that orcas are as diverse as other animal populations, like tigers for example. The only difference is that officially there are not subspecies stated and only one species is recognized. So, based in the information that I found I can make this summary.
Before to start we must take in count these facts:
The sexual maturity of the males is at around 15 years old, although they do not start actually breeding until 21 years; the maturity is also reached when specimens measure over 6 meters in length. For females, the sexual maturity reaches at 10 years but may start breeding normally until 20 years old; the length of mature females is normally over 5.5 meters long.
This information was obtained from Best et al. (2010), Ward et al. (2019) and Cawardine (2001). Best et al. (2010) focused his report of orcas from South Africa. However, during the investigation, I found that some specimens were classified as “adults” at smaller lengths, probably because like any other animals, there are short ones that are adults and shorter ones that are still young, so this must not surprise us.
1 – Southern hemisphere:
Specimens from the southern hemisphere are now classified in five groups, however this was not the case in the old days of whaling and many of the samples have mixed specimens and only with the efforts of Biologist that studied that information we can get a more or less good idea of the size of those populations.
Mikhalev et al. (1981) presented a very good sample of orcas hunted in the Antarctica region, and based in Pitman et al. (2007) it seems that these orcas belong to the Type A, arguably the biggest orca population at this moment (on average at least). The presented figures are these:
* Males: Average 726 cm – n=205 – range: 450 – 900 cm.
* Females: Average 642 cm – n=118 – range= 370 – 770 cm.
It is clear that some immature specimens were included in the lower ranges, which means that the overall average may be somewhat bigger, probably over 750 cm in males and over 650 cm in females, but that is just speculation.
Also Mikhalev et al. (1981) reported average figures for males and females, depending of the regions, but the difference is no more than 35 cm (practically nothing in animals of over 6 meters of length) and the issue that the four forms were not separated completely separated, makes this differences irrelevant, and also by the fact that most, if not all the specimens are probably of type A, as Pitman mentioned.
There is no clear information about the difference of the Type B (large and small forms), so they are just estimated to be smaller than the Type A and bigger than Type C.
Now, about Type C/Ross Sea, Pitman et al. (2007) presented an study using photogrammetry and he got the following measurements:
* Males: Average 560 cm – n=64 – range: 490 – 610 cm.
* Females: Average 520 cm – n=33 – range= 460 – 580 cm.
At this moment, this is the smallest population known, it predates mainly in fish.
Finally about the Type D, I could not found any information, but probably is about the same size than the small form of Type B.
Best et al. (2010) made a full study about the orca population in South Africa, and based in the measurements these are probably from the Type A, he did not presented averages, but mode and ranges, here are the results:
* Males: Range from 290 to 881 cm – n=37 – mode between 750 to 799 cm.
* Females: Range from 300 to 790 – n=16 – mode between 650 to 699 cm.
This means that the average length will be between 770 cm in males and 670 cm in females, close to the figures reported by Mikhalev et al. (1981).
Under this investigation and taking over 470 specimens measured, the biggest male recorded in this area was of 900 cm and the biggest female of 770 cm. Skinner & Chimimba (2006) quote it as 910 cm in males and 760 cm in females, but that is an error. COSEWIC (2008) Baird (2002) quotes these specimens as the biggest reliably recorded and quote the correct figures from Mikhalev et al. (1981)
About weights I could found only 4 figures, two males (one probably immature based in the measurements):
1 - Length of 482 cm and weight of 1,434 kg.
2 - Length of 593 cm and weight of 3,166 kg.
Both specimens were from the southwest region of the Indian Ocean (Skinner & Chimimba, 2006).
There is a record from “Old Tom” from New Zealand that measured 670 cm in total length, Wikipedia says that it weighed 6,000 kg, but with my best efforts, I could not found any source with this figure. The final came from a male of 8,000 kg from Tomilin (1967; in Skinner & Chimimba, 2006), although it seems an estimation and the fact that I could not found the original source, Tomilin also is used for other information about the oil amount obtained from orcas in the Antarctic, which suggest that this could be based in a real figure too.
2 - Northern hemisphere
From the northern hemisphere we have other studies and not from few specimens. Modern studies present three types in the Pacific and two in the Atlantic. The north Pacific population is the must studied of all, specifically the resident ones. One of the best books of orcas (“Orca the whale called killer”, from Erich Hoyt in 1981 and other subsequent editions) is about this population.
Duffield & Miller (1988) mention the following ranges:
* Males: 650 – 750 cm – n=17
* Females: 580 – 640 cm – n=20
However these ranges are a mix of wild-caught specimens in the Pacific coasts of Canada and USA its subsequent growing in captivity, so they are not useful for comparison. The big male of 750 cm reached that size after some years in captivity.
Fearnbach et al. (2011), using photogrammetry got a good sample of animals and several re-measurements of the same specimens, all from the coasts of the Washington state, USA. Using this data, they got an asymptotic average of 6.9 +/- 0.2 m in adult males and 6.0 +/- 0.1 m in adult females. The longest male measured 720 cm and the longest female. Now, using the measurements in the Table one I got the following averages:
* Males over 15 years old: Average 623 cm – n=10 – range: 500 – 720 cm.
* Females over 10 years old: Average 593 cm – n=38 – range= 370 – 640 cm.
These averages seems smaller because some specimens were smaller than the figures reported by Best et al. (2010) for mature specimens, but correspond to the ages of sexual maturity reported by Ward et al. (2019) and Cawardine (2001), showing that the resident orcas from the north Pacific are smaller than those from Type A from South Africa.
Hoyt (2013; reedition of 1981) reported that from 16 adults stranded in the Vancouver Island in 1945, the males average less than 23 ft (7 m) and the females less than 20 ft (6.1 m). And Fing (2016) reported the maximum lengths from males in the region at:
* Resident males: Up to 701 cm – n=38.
* Transient (Bigg’s) males: 760 cm – n=20.
*Offshore males: 620 cm – n=12.
Based in the study of Fing (2016), the transient orcas are bigger than all the populations, while the residents are bigger than the offshore, although the difference is not too big no average. Take in count that the sample mix males and females and even then, the ranges in the transient orcas are bigger in all the cases.
On the other side of the Pacific we found another large sample from the waters of Japan. The study came from Nishiwaki & Handa (1958), but as I was unable to found the original source I used Heptner et al. (1996) and checking other sources where this Japanese study is used the quote from the Russian source is accurate. The values presented are:
* Males: Average 640 cm – n=320 – range: Max 945 cm – Mode between 550 – 760 cm.
* Females: Average 610 cm – n=247 – range= Max 823 cm – Mode between 550 – 670 cm.
This sample shows animals that on average are smaller than the Type A from Antarctica, but the maximum figures are higher. Now, based in the average and the fact that the authors said that most of the kills of this orcas were fish, we can guess that these orcas are probably offshore populations, but the same authors also said that the biggest orcas feed on mammals, which is a characteristic of the Transient ones, so probably we have a mix of populations here, but as far I checked, not even Pitman et al. (2007) presented a clarification on this.
Under this investigation and taking almost 670 specimens measured, the biggest male recorded in this area was of 945 cm and the biggest female of 823 cm, both from Japan. In North America the biggest male reached 760 cm in the transient population.
On the weights, I got two specimens from Japan and two from USA/Alaska Pacific coast:
* Male: 765 cm in length – 6,600 kg – Japan.
* Female: 658 cm in length – 4,700 kg – Japan.
* Male: 604 cm in length – 4,000 kg – North America.
* Female: 635 cm in length – 3,100 kg – North America.
Sources: COSEWIC (2008 - Japan) and Heyning & Dahlheim (1988 – North America).
From the population of the North Atlantic, there are two types, both in the Eastern area. The studies are available, one from Jonsgard & Lynshoel (1970) and other from Christensen (1984). While I could not found the study of Christensen, I did found the one from Jonsgard & Lynshoel, both studies were made in the Norwegian region and Iceland.
The study of Jonsgard & Lynshoel (1970), from a sample of 1413, shows the following data:
From 891 males, the mode is of 670 cm (group of 135 specimens). Also from this sample only 4 specimens exceeded 30 ft (920 cm), the largest was of 32 ft (980 cm).
From 494 females, the mode is of 579 cm (group of 84 specimens). Also from this sample only 2 specimens exceeded 26 ft (790 cm), the largest was of 28 ft (850 cm).
Now, the study itself clarify that some of those measurements are actually estimations and they found that the deviation between the real measurements and the estimations made was +/- 2 feet (61 cm). However, the fact that most are estimation can’t be ruled out and Baird (2002) reported that those two extreme measurements (980 cm for male and 850 cm for female) are not real measurements. Finally Hoyt (2013) put the final stone in the grave, corroborating that the biggest orcas on record are a male of 31.5 ft (960 cm) and an estimated weight of 9 tons, while the biggest female was of 27 ft (820 cm) and an estimated weight between 5 to 6 tons, both specimens from Japan; interestingly these are the same maximum figures quoted by Nowak (1999) in Walker’s Mammals of the World.
Check this graphic from Jonsgard & Lynshoel (1970), showing all the specimens, probably the average will be about the same than that of the Antarctic Type A, if we include the other adult specimens:
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*This image is copyright of its original author
*This image is copyright of its original author
The information that I got from Christensen (1984) came from AMMPA (2017) and Guinet & Bouvier (1995). It only mentions that the average male measure between 580 to 670 cm, while the average female is between 490 to 580 cm, with a maximum of 700 cm. Until I found the original source I can’t provide other details.
I could not found any weight from this area, but certainly the Eastern North Atlantic Type 2 is one of the biggest orcas, and may match the Antarctic Type A. However the issue here is that the record male and female are not real measurements but estimations and there is a possibility that the male and female could have measured as low as 919 cm and 789 cm respectively. Interestingly the biggest orca from this region, accepted by Pitman et al (2007) is a male of 920 cm from Norway.
Conclusion:
In the Antarctic region, the biggest male recorded was of 900 cm and the biggest female of 770 cm. From the North Pacific region the biggest male recorded of 945 cm and the biggest female of 823 cm, both from Japan; in North America the biggest male reached 760 cm in the transient population. And from the North Atlantic, the biggest male recorded of 980 cm and the biggest female of 850 cm, but both could be a low as 919 cm and 789 cm respectively as were estimations. However let’s remember that Jonsgard & Lynshoel (1970) found that from 1413 specimens only 6 specimens surpassed the 30 ft and the 27 ft, so the existence of this large specimens is comparably rare, while normally most of the specimens of the large populations (Antarctic Type A and Pacific Type 2) will be over 7 meters in males and 6 in females, like Hoyt (2013) believed. The smaller population, Type C of Antarctic, with 560 cm in males and 520 cm in females, represent the lowest values, and all the other populations range between these figures.
About the weights, all the specimens that we have are below the averages except one (male of 765 cm and 6,600 kg), which means that an average male will weigh about 6,000 kg and an average female about 4,000 kg.
So just by mere curiosity, applying the isometric escalations that we have used for other mammals, and using the few specimens available with actual measurements and weights (4 males and 2 females), the figures that I got for the largest specimens are these:
Male 900 cm – 11,096 kg
Female 770 cm – 6,529.5 kg
Male 945 cm – 12,845 kg
Female 823 cm – 7,972.7 kg
Male 980 cm – 14,325.8 kg
Female 850 cm – 8,783.4 kg
Personally I think that in this case the figures are too high, especially by the fact that the maximum weights normally quoted range between 8,000 kg to 10,000 kg in males and between 5,000 to 6,000 kg in females. But this just gives an idea of how heavy an orca may be.
So this is the summary about all the sized and weights of wild orcas that I could found, hope this help to clarify the question.
Greetings to all.
