It seems that the bigger species live longer. Is this true?
Generally speaking, yes. The Giant Pacific Octopus has about a 4 year lifespan and there are reports (accuracy not clear) of at least one living 6 years in captivity. Of the ones you will have access to from the wild in FL the vulgaris will have the longest natural lifespan guestimated at about 18 months (a small egg species for age at capture even as a small animal has requires adding a month for drifting in the plankton, not possible to raise from egg so actual is hard to determine). As a rule of thumb, O. mercatoris live 8-10 months with some males raised in captivity exceeding 12, O hummelincki is small egged and hard to know the age at capture (again, it can't be raised from hatchling in a home aquarium) but the expectation is 12 months (I suspect it is a longer since I have kept a few over 7 months that appeared to be adult when they arrived but it is an odd species and may be more than one lumped together), O briareus is a confirmed 12 month (large egg species with a minimal amount of success being tank raised) norm with the males living a little longer and the females a bit shorter, brooding at around 8 months.
Most likely found in the crabbers traps will be O. briareus, O. mercatoris or O. vulgaris (in order of commonly bought by licensed collectors to resell but I don't know about actual frequency or if the location makes a major difference). It appears that O. briareus has had several very good hatching years and are quite plentiful (to the chagrin of crabbers). We have not seen many O. mercatoris for about two years but are now seeing them show up again. O. hummelincki for sale were most commonly purchased from collectors in Haiti but they are common to the Keys (not sure about north of there though and I suspect not). Since the earthquake, very few have been available. I was very lucky to have kept
Octavia last year (in tank 9.5 months, captured in the FL Keys) and am hoping we will start seeing more of this species.
There is one other Caribbean (or new to the Caribbean)
that I have had the honor of keeping. I am not sure of its lifespan (I kept him for 10 months and have no clue on the species but I keep trying to find out). I may have kept
a female recently but she closed herself into a den within two days, would not eat and I expected hatchlings. She died without offspring and I could not tell if she ever laid eggs. The male was a wonderful animal and I was extremely excited to have had the chance with the female and majorly disappointed that she was not with me long and that I did not get to see if it was a small or large egg species. One way to id this one is the presence of a pair of circles (called ocelli or eye spots) below the eye on at the top of the web. O. hummelincki has a similar pair of eyespots but the outer ring is yellow and the inner a bright blue (when displayed) this one has a tan/brown outer ring (you can see it in some of the photos) and a brown to black (that may even reflect an almost midnight blue) center. I have no idea if this one invades the crabbers' traps or not
Colder water species (the GPO being one) may as much as double the warm water lifespan (again a generalization) . There may be evidence of some deeper water Pacifics also living longer and some of the very cold water animals (Alaska and Hydrothermal vent animals) are suspected of extended lifespans but they are just now being studied. There are only two Pacifics that we currently see in home aquariums. The most common is O. bimaculoides (commonly called bimac). We have seen a few of these live almost 3 years IF they are kept at temperatures below 68 degrees. At 70 degrees they may live between 12 and 18 months, much like vulgaris. At warmer temps, shorter but more active lives as long as the temps don't exceed about 72 degrees over any extended period. O. reubescens, the other common coldwater animal we occasionally see, needs even colder water just to survive and I don't know its lifespan.