At least one authority thinks your fragment is in fact Pindar: this turns up in the Snell/Maehler Teubner edition of Pindar, as fragment 52wi of the Paians. See http://www.poesialatina.it/_ns/Greek/testi/Pindarus/Fragmenta01.html
Luckily, we can see the Teubner on Google Books: https://books.google.com.au/books?id=rWAgAAAAQBAJ&pg=PA68&dq=δέρκεν&hl=el&sa=X&ved=0ahUKEwj3ztnHo5TdAhVCIIgKHW0mD60Q6AEIWjAH#v=onepage&q=δέρκεν&f=false
The app.font. says "Π^26 fr. 87 (olim P. Oxy. 1787 fr. 9)". Fragment 52wh is also "Π^26 fr. 86 (olim P. Oxy. 1787 fr. 8)".
I don't have the full book, to tell you what Π^26 is, but clearly it's a reconstruction of a book of Pindar's from papyri, and scholars have been at work gathering fragments into that reconstruction.
... No, strike that: https://books.google.com.au/books?id=mXdzAAAAIAAJ&q=π26+pindar&dq=π26+pindar&hl=el&sa=X&ved=0ahUKEwi3u9qdpZTdAhWO-mEKHbZ2BMw4ChDoAQg0MAI , snippet from the Teubner edition:
Π^26: nondum edita, cf. Lobel P. Oxy. 26, p. 31
So Lobel has gone through Oxyrhynchus, worked out that a hundred-odd fragments from Oxyrhynchus are Pindar, and published his handiwork in Vol. 26 p. 31 of the Oxyrhynchus volumes. But noone had put together all the fragments he has gathered together into a single published source as of 1997.
P. Oxy. 1787 was published in vol. 15, in 1922. Vol. 26, when Lobel published that Π^26 was a thing, came out in 1961. Since Lobel decided this was a fragment of Pindar, he did not include it with the other fragments of P. Oxy. 1787 which he thought were Sappho (already published in 1955). And since Lobel had deemed that P. Oxy. 1787 fr. 8 and 9 henceforth belong to his Π^26, sometime between 1922 and 1955, they've been withdrawn from the online publication of P. Oxy. 1787 ("8&9 missing"; "olim" = "formerly" P. Oxy. 1787 fr. 9).
Papyrology. The more I learn about it, the dodgier it seems. :-)
I think I've tracked this down in an online catalogue; assuming Π^26 is "Snell P26", which is reasonable: https://www.trismegistos.org/ldab/text.php?tm=62564
Publication: P. Oxy. 75 5039 (Maehler, Herwig; 2010; transcription); P. Oxy. 26 2442 (Lobel, Edgar; 1961; transcription)