This article estimates at a 40kg sailfish uses about 2.7 megajoules per day of energy when hunting. That's about 650 kcal.
An 80kg human weighs about twice as much and needs about 3 times the energy, without even exertion.
Warm blooded animals spend a lot of energy just maintaining body temperature. Plus water doesn't have very much oxygen in it, compared to the atmosphere.
The "Stan Kelly" persona itself is a fictional satire. The work is actually done by cartoonist Ward Sutton, whose standard political cartoons under his own name criticize the right wing directly.