Ishmael decides to explain the reason that Flask "waifed" a whale (in Chapter 87) by sticking a special marker-pole called a "waif" into it.
Because whaling ships often cross paths, and sometimes one whaling ship will attack but fail to kill a whale that’s later killed by someone else, some basic rules have developed among American fishermen about how to decide who has the right to the whale.
The rules are simple: "A Fast-Fish belongs to the party fast to it" and "A Loose-Fish is fair game" (89.4-5).
A Fast-Fish can be alive or dead as long as it’s attached somehow to something belonging to the ship or boat that lays claim to it—by a harpoon, a rope, or a marker pole like a waif.
Ishmael describes a court case from "fifty years ago," in which one group of men set out to hunt a whale but had to abandon their boat, and then a second ship came along and slaughtered the whale and collected it, along with their boat and equipment.
The crew of the first boat sued.
The counsel for the defense, Mr. Erskine, argued that this whaling case was just like the divorce case he’d argued recently, comparing the men who were forced to abandon their whale because it was too vicious to the husband who abandoned his wife because of her vile temper.
The judge didn’t quite buy this, and awarded most of the possessions at stake in the case to the defendants.
Ishmael regards this decision as just. After all, he says, all the laws of the world pretty much come down to this issue of Fast-Fish and Loose-Fish: the world usually supports those who, through greater strength, can take possession of something, be it a slave, money from a sinecure (an office or job with little or no actual responsibility), or even land.