We can look at another human being and estimate their age pretty easily—but it’s not so simple with octopuses. Scientists haven’t yet found a reliable way to identify the age of giant Pacific octopuses (or GPOs), since no part of the animal’s body, even the beak, shows any growth rings or other measures. Even size isn’t an indicator of age, since GPO growth is highly dependent on food availability when the animals are young.
Determining GPO maturity—the point at which the animals are capable of reproducing—isn’t a simple matter either. Various studies have attempted to gauge GPO maturity at anywhere from 1.5 to 3 years of age but these are estimates; anatomical studies are more accurate. Such studies of female and male GPOs show that females are mature when they have well-developed eggs in their ovaries; males when they have mature spermatophores in their internal storage. Needless to say, that’s not something that can be determined while looking at an octopus on exhibit at the Seattle Aquarium, or while diving in Puget Sound!
As we mentioned above, size isn’t an indicator of GPO age—and it’s not a measure of maturity either. The average weight of a sexually mature GPO varies broadly, from about 15 pounds to over 60 pounds. Males tend to mature at smaller weights than females. Females and males smaller than 22 pounds or so tend to be immature but, complicating matters, some considerably larger animals may still be immature.