This bird is sometimes known as the dusky-backed shearwater;[2] its specific epithet honours the French naturalist Félix Louis L'Herminier.

[2] It can be confused with the Manx shearwater (P. puffinus), which has white undertail coverts and in direct comparison a longer bill.

Other similar-looking species are usually completely allopatric, though the largely subantarctic little shearwater (P. assimilis) may occasionally range into waters where P. lherminieri is normally found.

If not split into several species, the Sargasso shearwater ranges across the Indian Ocean north to the Arabian Sea, throughout the north-west and central Pacific, in the Caribbean, and parts of the eastern Atlantic.

It is a species of tropical waters; only some Atlantic populations and Bannerman's shearwater of the Ogasawara Islands occur farther north.

Unlike other shearwaters, it is not commonly a ship-follower, though it may attend small fishing boats; it is also sometimes met with as part of a mixed-species feeding flock.

[2] The species is colonial, nesting in small burrows and crevices in rocks and on earthy slopes on atolls and rocky islets.

Possibly, they do form a distinct species separated from the third clade by a different circannual rhythm, as is known from other procellariiform birds.

There appear to be no significant genetical or morphological differences between these birds, which is quite amazing given that the Pacific and Indian Ocean subpopulations must have been isolated for a fairly long time, and that no less than three unequivocally distinct subspecies (bailloni, persicus and temptator) occur within the range of Indian Ocean dichrous.

Clearly, some mechanism blocking gene flow is at work, but what this is exactly remains unknown – though as remarked above, separate breeding seasons seem a reasonable assumption and are tentatively supported by the available field data.

The case of gunax seems fairly straightforward – as certainly as this can possibly be said in the absence of new data, it belongs to the bailloni clade either as a distinct subspecies, or, more likely, as yet another synonym of dichrous.

In the absence of more recent data to investigate this claim, its status continues to be altogether unresolved, though the case for it being at least a distinct subspecies in the bailloni clade seems good.