This is a postcard image of an image. If "F Duncan" is Frank Duncan, he did quite a bit of that. According to the Auckland Library's photographer database, "Frank Duncan first came into contact with postcards as a commercial traveller for Tanner Bros. Around 1915 he moved to Auckland and established the firm Frank Duncan and Co, which produced huge numbers of postcards using images supplied by photographers F G Radcliffe and T M Hardy, amongst others. The company went into receivership in 1931."
The white lettering is overwritten, the fin is a hasty sketch onto the image, and although the story of Pelorus Jack appears to have started in 1888, going on for 24 years until around 1912, the card talks of the "fish" being around for 30 years. So, the provenance is dubious.
"Does he come always?"
"Without fail, night and day (at night he is like a streak of phosphorus); he meets every steamer, though this is his favourite. He has done so for many years. Lord Onslow, when Governor hero, had him gazetted, and he is now safe from human enemies; at least, I hope so. We are all quite fond of him."
He lifts his cap, and moves away, and we stand and wait eagerly.
Presently, about a hundred yards away, a darker streak comes on the violet sea.
"How does he first appear?" asked a lady, breathlessly pointing at it. But no one answers her. Then the streak moved; a great, glistening, brown fin broke the water.
"There he is," shouted a dozen excited voices, as Pelorus Jack swam alongside. He made straight for the hull; shouldered it in a friendly way and then went merrily along with us.
We watched with delight his white shapely body, clouded by the deep water to a pale-green color. Sometimes, with a flick of his tail, he shot across the bows but, preferring the sunny port side, he always returned, every now and then rising to blow, shooting again into the water with arched back, through a rainbow edged dazzle of foam, and delighted shouts of appreciative laughter from the gallery. At other times he would swim on his side, his cunning little eye cocked up at the ship's company, as who should say "Take a long look, you won't often see a whale like me. I'm little (only about ten feet in length), but I know a lot." He was indescribably comic as he swam there, his brown dorsal fin stuck out like a short coat-tail, his excellent stomach curving as a city magnate's waistcoat curves.
Suddenly, after about half-an hour of his interesting company, this friendly fish turned, with arrowy speed, disappearing into the foam which curled from the bows.
"He's gone!" we sadly exclaimed in chorus. We saw his glistening fin break the water far behind us, and the crowd dispersed, but a few minutes later the pale green shape swam swiftly along our starboard side, as if loath to say farewell; then turning again, he finally left us.
Helen M Spencer, from the Australasian, via Marlborough Express, 1 February 1902
New Zealand Illustrated Magazine, 1 December 1902
From the 1966 Encylopedia of New Zealand:
"Pelorus Jack, whose sex was never determined, was identified from photographs, probably correctly, as a Risso's dolphin (Grampus griseus), a species not common in New Zealand waters. It was his habit to meet the steamers near Cape Francis and travel with them (playing about the bow and in some accounts rubbing against the plates) as far as Collinet Point near French Pass; or likewise in the opposite direction. In spite of his name he did not frequent nearby Pelorus Sound, and local residents familiar with his habits assert that he never went through French Pass."
Dolphin Pelorus Jack, between 1904-1912 Reference Number: 1/2-026542-G The dolphin Pelorus Jack, photographed by Frederick Nelson Jones between 1904-1912. Alexander Turnbull Library.
Pelorus Jack was one of New Zealand's super stars. Even though he/she (gender was never determined) was protected, there were no further sights beyond the end of 1912. The name, however, has lived on in our folklore.