When high-powered seabirds like albatrosses go to sea, they could easily fly far enough to meet up at sea with strangers from the same species but from different islands. Good places to feed might have birds from more than one, even many different, islands. Still, members of these two populations sometimes feed in the same places between the two island groups. If a ship-based biologist recorded these petrels in water near Hawaii and distant from Galapagos, if would be hard to know which islands those birds called home.
Same problem applies to the albatrosses.
We want to know where Hawaiian birds go to feed, but just seeing Laysan and black-footed albatrosses at sea and recording the locations is not good enough.