geelstert.com - Fishing adventures on the Agulhas Banks

Are marlin color-blind or color-perceptive? The answer is both. When you and I look at something, the image forms on the backs of our eyeballs. That's where early researchers looked for color sensors in the eyes of marlin. When they found only blue receptors, they concluded that marlin could only see blue and then constructed a persuasive argument for why blue vision is best in the blue-water world they inhabit. Over the past several years, however, Australian vision experts located the seat of billfish color vision in the bottom of the eye. Scientists from the Vision Touch and Hearing Research Centre at the University of Queensland say the lower part of a marlin's eye contains two differently shaped cone photoreceptors. That's where the image forms when a marlin looks up into the bright light, according to researcher Kirsten Fritsches, who conducted the study along with Professor Jack Pettigrew and Dr. Justin Marshall.

"The upper part of the retina, the part that looks into the deep water, does not see color but contains mainly receptors specialized in working under low-light conditions," the report stated, which gets the proponents of the advantages of color-blindness off the hook. "Color vision requires bright light, so billfish only seem to use a region of their eye for perceiving color that is likely to have good light conditions."
Feel assured, then, that billfish do see the colors of your trolling lures as they pass overhead. On the other hand, a live bait fished on a downrigger is just a blue object against a blue background, even for a creature that could see all colors if the light allowed.
Vision is a marlin's primary feeding asset.

The Australian vision specialists identified two areas of highest billfish vision, one that points along the bill in front and one that points backwards. That duality means that it simultaneously sees what is in front of it and what is behind it. Without moving its eyes, it can track prey without sacrificing the ability to keep track of enemies sneaking up from behind.
Human eyes focus sharply because both eyes see the same exact image with a slight shift to aid depth perception through triangulation. The opposite-facing eyes of billfish don't have that advantage.
Still, marlin eyes are larger than those of most animals on land or sea, which suggests that they should have better vision than most other fish. The team's studies of blue and black marlin, however, found that at best they could resolve an object of roughly 4 inches at approximately 50 yards, which was "surprising, considering that the large size of the eye ... should have allowed for a much better acuity."
Further studies solved the mystery by showing that marlin handle visual information through a process that may reduce acuity but improves sensitivity. As a result, say the researchers, marlin may not see as much detail, but they are better equipped for "the demands of seeing while moving at high speeds and traveling or hunting in dim light conditions." For you, the angler, this means you are not wasting your money on those brightly colored skirts. However, intricate lure details are probably just a blur to billfish. And when a marlin swims up right next to your lure, it's not staring sideways at it for a closer look.

It's inspecting your leader.