SEAMI tells us (Works, p. 246) that this play was written by Enami no Sayemon. "But as I removed bad passages and added good ones, I consider the play to be really my work"--(p. 247).
On p. 245 he points out that the same play on words occurs in Ukai three times, and suggests how one passage might be amended. The text of the play which we possess to-day still contains the passages which Seami ridiculed, so that it must be Enami no Sayemon's version which has survived, while Seami's amended text is lost.
It is well known that Buddhism forbids the taking of life, especially by cruel means or for sport. The cormorant-fisher's trade had long been considered particularly wicked, as is shown by an early folksong: 1
"Woe to the cormorant-fisher
Who binds the heads of his cormorants
And slays the tortoise whose span is ten thousand æons!
In this life he may do well enough,
But what will become of him at his next birth?"
This song, which is at least as old as the twelfth century, and may be much earlier, seems to be the seed from which the Nō play Ukai grew.
127:1 Ryōjin Hisshō, p. 135.