To begin to understand why billfish (marlin) are such an excellent sport fish, you need to know their physiology. No creatures are such masters of their natural element as the billfish. They have hardly any natural enemies, except possibly the shark and killer whale.
Blue marlin are the most spectacular and the finest fighters of all the marlin species. When hooked, they give an indescribable performance. They tear up the ocean in a wall of whitewater as they tail-walk across the water in all directions. The twisting and turning as it leaps and lunges demonstrates a power and swiftness seldom seen anywhere on land and sea. Before you know it, the marlin can sound hundreds of yards straight down in a matter of seconds, taking hours to bring to the surface.
When you sit in the fighting chair with one of these great fish, you have settled down to one of the hardest battles you have ever had on any tackle. If you are lucky enough to get it to leader, you will be exhausted, sore and very much impressed with the courage and strength of these challenging and exciting marlin. Your option to either kill or release your catch is up to you.
Blue marlin are confined more to the equatorial high sea regions than any other species. They migrate away from the equator in summer and toward the equator in the winter. The Hawaiian Islands appear to be the most common marlin grounds in the Central Pacific. They are usually found in deep waters of 500 to 1,000 fathoms.
Billfish have a long, thin, bullet-shaped body that gives them the speed to be one of the fastest fish in the sea. They have been estimated at attaining speeds of over 50 miles per hour for a very short period of time.
Billfish rely primarily on speed to overtake and engulf their prey. Marlin will attack a high-speed lure traveling at 15 miles per hour without any problem. Most of the time, they swim along at 3-4 miles per hour. The speed of a human swimmer is about four miles per hour.
The resistance of water is something like 70 times that of air, so top speeds achieved by billfish are just short of fantastic and phenomenal.
Billfish swim also by jet-propulsion, with streams of water ejected swiftly backward through the gills, but the first method of importance is the undulating movement of the entire body. They push against the water laterally with their muscular bodies.
The water in which they live has a specific gravity almost equal to that of their own body. This means that the water holds up most of their weight, and hardly any effort on their part is needed to support them.
A 200-pound marlin in saltwater weighs only about ten pounds, so when it swims along, it has only to lift one-tenth of its body weight.