by Bruce Carlson, Larry Cofer, Ralph Manns & Steve Quinn

A muskie with an injured backbone--a fish handling injury?

CONSERVATION SCIENCE -- HOLDING BIG FISH
Is there evidence to suggest that holding a big lake trout, muskie, pike, or catfish by its jaw or gill plate, without supporting its belly, can be injurious? Rob Swainson, who manages Ontario's Lake Nipigon and Nipigon River, says anglers need to handle big trout differently than small ones. Swainson remembers landing his first big trout. He gloved it by the tail and lifted it out of the water--that's when he heard a popping sound--as the vertebrae separated in the fish's backbone.

If holding a heavy fish vertically by its gill plate, without supporting its belly, can result in damage, why do we catch so few fish with obvious injuries? Swainson says he's only seen one or two large lake trout with deformed backbones. "I'm not surprised," he says, "because popping vertebrae likely means death for big fish. They swim away, but I doubt they survive.

"Big fish need extra body support," he says. "If someone were to lift you up," he asks rhetorically, "would you want to be held by the neck? Or would you rather be lifted by putting both arms under your body?"

As an assistant hatchery supervisor, Ohio biologist Elmer Heyob sees more fish with deformed backbones than most field biologists see. Most of the fish he sees with crooked spines are survivors of genetic defects. You don't see them in the wild, he notes, because they never make it past the fry stage.

Like Swainson, Heyob is an avid angler, with muskies a particular passion. He says one problem with holding a big fish vertically is that the fish appears to calm down. Heyob says the fish are calm only because they're nearly paralyzed from vertebrae strain.

Bass Go Sleepy-Bye -- When we filmed television footage with Captain James Jackson, a Lake Toho, Florida, bass guide, he surprised us by demonstrating a technique for putting largemouth bass into a stupor. It's a simple method, as you see here--a curiosity, even if it serves no particular purpose. Curiosity also compels us to try the method on smallmouths this year. -Doug Stange

Heyob: "We have an Ohio-based muskie club annual tournament that Ohio Division of Wildlife personnel often attend. We keep a redwood measuring board handy that we also use in our research. One of the contestants caught a muskie that they hung from a hook at the marina. When they measured it with a tape it was 51 inches long. When we remeasured it on the board it had shrunk back to 49 inches." The extra length was from vertebrae separation.

If you must measure a fish, Heyob and Swainson recommend doing it while the fish is in the water alongside the boat. "In a perfect world," Heyob says, "we'd just look at the fish in the water and remove the hooks. But many anglers want a picture or two and sometimes the actual weight of a big fish."

When lifting a large fish out of water, it's essential to support most of its weight with one hand under the belly. It's the same for using one of the new tools that grips a fish's mouth and contains a built-in scale. A more fish-friendly weighing method, according to Heyob, is to lift the fish in a knotless net turned on its side, using the gripping tool to hang onto the hoop to get the weight (subtract the net weight).

Gord Pyzer

BASIC BASS BIOLOGY -- NEW RESEARCH ON HOW BASS STRIKE
Bass and many other fish capture prey by inhaling them, using a mechanism called suction feeding. Sophisticated research techniques are now providing a clearer picture of how this happens. Understanding the basic elements of how a bass feeds can give insight to anglers, especially those who use plastic baits.

A recent article by Dr. Christopher Sanford and Dr. Peter Wainwright* described how the use of a technique called "sonomicrometry" provides a detailed picture of how a largemouth bass ingests prey by suction feeding. Two fundamental elements are at work in suction feeding. The first is an increase in volume of the mouth and throat by a rapid expansion of the surrounding structures. This creates a negative pressure, which in turn causes a rapid inflow of water (and prey) into the mouth of the bass. The negative pressure is caused by a sequential set of complex muscular actions, which result in first opening the mouth, then depressing the throat through the displacement of the hyoid bone (the bone that forms part of our Adam's apple), and finally the flaring of the gill covers.

Just before producing suction, a bass slightly increases the pressure in its mouth by reducing the size of its oral cavity. This, combined with the subsequent production of negative pressure, permits a greater velocity of water flow as the suction producing phase begins. These actions occur within a fraction of a second. The rapid expansion of space in the mouth and throat is the key to the generation of the negative pressure (suction), and this occurs in less than 0.2 seconds.

No wonder that a good worm fisherman has to have hair-trigger reflexes. What has not received much attention by biomechanics researchers is the mechanics of rejection of an object that is not deemed edible by a bass. Most worm fishermen have sometimes found that it's difficult, almost impossible, to strike back quickly enough to set the hook when a bass rejects a bait.

Bruce Carlson

*C.P.J. Sanford and P.C. Wainwright 2002. Use of sonomicrometry demonstrates the link between prey captured kinematics and suction pressure in largemouth bass. J. Experimental Biology 205:3445-3457.


HOW MUCH DIFFERENCE DOES LURE COLOR MAKE?
Experienced bass anglers know that lure color sometimes makes a difference in their catch. At times, lure visibility and its contrast against backgrounds, in addition to a lure's resemblance to natural forage, appear to influence the catch. But we have little scientific data measuring such differences.

Biologists Gene Wilde, Kevin Pope, and Bart Durham of Texas Tech University* compared catch results with "blue shiner," "brown trout," "fathead minnow," and "firetiger" 3-1/2-inch-long Rapala minnowbaits. Fishing in a lightly fished 10-acre private pond, they rotated lures among four anglers until 183 bass from 5 to 17 inches were caught.

Comparison of catch rates revealed that firetiger lures took fewer large bass than the other three color patterns, but the difference was not statistically significant. In the fairly clear water of this heavily vegetated lake, firetiger lures caught only 3.88 fish per hour. Brown trout colored lures took 5.88 bass per hour, while both the blue-shiner and fathead-minnow imitations caught 6.25 bass per hour.

In this environment, matching a specific baitfish species didn't seem necessary. But baits with a more natural appearance were more effective and took slightly larger fish than high-visibility firetiger lures. Had the water been murky, the results might have been reversed.

Ralph Manns

*Wilde, G. R., K. L. Pope, and B. W. Durham. 2003. Lure-size restrictions in recreational fisheries. Fisheries 28(6):18-24.

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