From Business Insider:
Interestingly, the animals seem to have just one global population. This has never been seen before in ocean-living species. Usually animals that live in the oceans end up genetically segregating into sub-species over time as they spread out around the globe. Not so for the enigmatic giant squid.
... The researchers studied 43 specimens from from all over the world — New Zealand, South Africa, Florida, California and more — to analyze their DNA. They relied on the genome of the mitochondria — the cells' powerhouses — to compare individuals. These genomes live outside of the nucleus — the brain of the cell — and are passed down from mother to offspring.
They found that no matter where the animals washed up they seem to be very similar, genetically.
The researchers think that the squid might live in shallower waters while they are younger, floating the global ocean currents. When they get old enough they sink down to deeper waters to mate and live and feed off of larger prey, releasing their offspring into the global currents once again to repeat the cycle.