A lucky catch; from a whalewatch boat a few km offshore. Best guess is Salvin's (a subspecies of Shy Albatross) -- see below.
Re range, according to my field guide (Robertson & Heather, Hand Guide) Salvin's & Buller's would be likely, Thalassarche cauta eremita (Shy, Chatham Is. ssp) much less so.
I am very grateful to Guy on the Field Guide ID Help Line thread and to rasmus_boegh for the following detailed analysis:
"Unfortunately, this is one bird I would be unable to identify with certainty from the available photo. I presume you didn't note the underwing pattern, which easily would lead to an ID to species(-complex). Still, I am willing to give a guess, but this is labeled with some uncertainty, as presumably evident from the following.
First, it should be noted that there is one additional taxon to consider, which seemingly isn't mentioned by you: The so-called "Pacific Albatross". It is often referred to as "platei", but this is incorrect, as the type is a juv. bulleri sensu stricto, rather than the new taxon (and as such, platei becomes a junior synonym of bulleri). Depending on view, the "Pacific Albatross" is a new subspecies of Buller's or a new species in its own right (genetically, the undescribed taxon and bulleri sensu strictu differ to an extend comparable to other taxa which have been split by some, e.g. melanophrys & impavida - with the usual hesitation due to the "issues" on judging species-limits in Procellariiformes by mtDNA). Unfortunately, juveniles of the two are virtually inseparable under normal field conditions. Thus, the taxa that should be considered are bulleri, taxon nov. ("Pacific Albatross"), salvini, eremita & chrysostoma.
Of these, T. chrysostoma can be exclude relatively easily, as also mentioned by "poecile05" on the discussion board you linked to in your email. However, his comment that the bill of juv. bulleri is "Dark enough that it is difficult to discern the darker tip at any distance" is incorrect. I suspect he must have used an old reference for this, as there are good illustrations clearly showing the bill of juv. "Pacific Albatross" in Jaramillo's Birds of Chile and juv. bulleri in Shirihai's Complete Guide to Antarctic Wildlife (latter also includes a photo of a juv. bulleri). The bill-patterns of juv. bulleri (incl. juv. "Pacific Albatross") is very similar to that shown in juv. salvini, except that latter (as all members of the cauta complex) has a darker base to the culmen. I have tried blowing your photo up to see if I could see a dark base to the culmen, but it really is too blurry to say if this is present or not (I see some darkness, but am having trouble seeing if this actually is a dark base to the culmen, a shadow or part of the dark loral region). However, the bill-shape presents an additional clue: It appears to have the rather stubby, heavy bill I associate with the cauta-complex. For comparison, bulleri & "Pacific Albatross" have a noticeanly slenderer and longer-looking bill. This really is pretty striking in the field, but admittedly less clear on photos.
The crown of juv. salvini is described well in Shirihai's The complete guide to Antarctic Wildlife, where it is stated that it has an "ill-defined whitish-grey forehead (or entire crown)". This fits well with my own observations of juveniles of this taxon. For comparison, the crown of juv. eremita completely lacks any white (though it may appear paler, esp. when worn and/or in direct light). This would lead me to guess that "your bird" is a salvini. However, here we are relaying on small details in hues, and that is hardly ideal on anything but the best photo. A crown can easily appear whiter or darker due to back-light, shadows, possible contrast enhancing on the photo, etc. Still, from the available photo, salvini would be my best guess."
If you think this observation is inaccurate, please add an ID, participate in the quality assessment above, or describe the inaccuracy in a comment.