Big Numbers by Jack Getze

Wise-cracking stockbroker Austin Carr is about to be killed by an unknown man in an unusual fashion – by being dragged off a fishing boat to a watery grave by a giant bluefin tuna.

Publisher Description

Flashing back three weeks, Carr then recalls the events and bad choices that got him into his deadly predicament.
We spend the book trying to guess the identity of the unknown man on the fishing boat; not an easy task because Carr’s big mouth alienates about everyone he knows.