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Entries in vegetation (2)


Milfoil Hybrid Could Cause Even More Problems for Northern Fisheries

Management of problematic aquatic vegetation could get even more difficult, especially in northern bass waters. Recent findings in Minnesota's Minnetonka and Christmas lakes lead researchers to theorize that a milfoil hybrid could be more invasive and tougher to control than the Eurasian variety.

The hybrid is a cross between Eurasian and northern watermilfoil, a native plant.

Using cutting-edge genetic screening techniques, scientists from the University of Minnesota and Montana State discovered that the hybrid was more prevalent in areas treated with herbicides than those with little management. The Minnehaha Creek Watershed District (MCWD) said that herbicides might actually promote hybrid growth "and some hybrids may show greater tolerance to treatment."

Additionally, MCWD's Eric Fieldseth said, "As a pilot study, this research gets the ball rolling on understanding hybrid watermilfoil, its impact, and how it can better be controlled. These findings are an important first step toward developing more effective milfoil management strategies."

Researchers also found multiple, genetically distinct genotypes of invasive, hybrid, and native watermilfoil. That underscores the need for understanding the genetic makeup of invasive plants in a fishery before devising a plan to manage them and then following up with more genetic screening to guide future management, MCWD explained.

"With this much diversity in the population, a successful milfoil management strategy may not be a 'one size fits all' approach," added, Ryan Thum, professor of plant sciences and plant pathology at Montana State.

"We're looking forward to seeing how these results compare with what's happening in other parts of the region," he said. "This research could have broad implications for managing milfoil in lakes throughout the Upper Midwest and beyond."


Bass Appearance Influenced by Habitat, Other Factors

Bass might have big mouths, but they don't exaggerate.

In fact, black bass are masters of understatement, at least in regard to their appearance. Boasting brilliant hues and/or electric highlights, some fish are among nature's most spectacular creatures. But in a world of green water with green vegetation, largemouth bass evolved as green fish. Likewise, their brown cousins, smallmouth bass, molded to a watery world of gravel and rock.

This camouflage helps protect bass from larger predators and enables them to more easily ambush prey. And Mother Nature didn't stop there. Like aquatic chameleons, bass can alter that shading, which has helped solidify their reputation as North America's most versatile game fish.

"Bass adapt to their surroundings. If they didn't, they would starve," said Ben Beck, director of the U.S. Department of Agriculture's Aquatic Animal Health Research Unit at Auburn University.

"Bass don't think about it. They just do it," added Gene Gilliland, national conservation director for B.A.S.S.

But color change  doesn't occur spontaneously in bass as it does in other species. "The chameleon and the octopus can rapidly change," Beck said. "Bass can adapt. We're just not sure how fast the process works."

Florida's Wes Porak, a black bass genetics expert, added, "These responses are fairly rapid and affect the color patterns when the changes occur. A fish can change color within half an hour if placed in a lighted or dark tank after being collected from a lake."

Savvy anglers are quick to turn this adaptive ability to their own advantage (See related story.), but fisheries scientists still have much to discover about the biological mechanism for change in bass, as most research has focused on colorful reef and tropical fishes. That's understandable too, when considering how monotonous the black bass is in appearance, even compared to its cousin the bluegill, especially during the spawning season.

"Not a lot is known about bass, and it's tricky to get a scientist to anything definitive," Beck explained. "They're still under study."

Porak admitted that he has "a limited understanding about how the intensity of a fish's pigment can change based on the amount of light striking parts of the retina and also the skin of a fish."

But before exploring what little is known and/or suspected, let's look at the basic coloration of a largemouth bass. The Florida Museum of Natural History (FMNH) describes it this way: "The back and head are dark green to light green in color with lighter sides and a whitish belly and underside of the head."

It adds that a prominent lateral stripe runs from the snout through the eye to the base of the tail. "Towards the tail, there is a series of blotches of varying sizes. These blotches evolve into a solid, even stripe on the caudal peduncle (narrow part of the body) . . . Vertical fins lightly pigmented, paired fins generally clear; caudal fin alike in young and adult."

Whether they're in Lake Okeechobee, the Mississippi River, or the California Delta, largemouth bass share that same basic color pattern. But as any angler who has fished all three will tell you, they don't look the same.

"Genetic components (See related story.) influence appearance some and food does a little," Gilliland said. "But water color, clarity, and habitat have a bigger influence. That's why fish will blush out in muddy water and look more camouflaged in vegetation."

Hormones seem to be the key to these variations, according to Beck.  "Photo receptors (in the eye) set the biological clock," he said. "They tell light from dark, and they tell the hormones to change colors."

He added that "generic stressors," such as confinement in a livewell, also can cause change, typically making the fish look more washed out, just as it would from living in turbid water. Either way, hormones likely trigger the alteration, with bass turning lighter when pigment granules aggregate deeper in the skin and darker when they disperse nearer the surface.

In general, the deeper a bass and/or the muddier the water that it lives in, the lighter it will be because of less penetration by sunlight, even to the point that the lateral line will seem to disappear. The shallower and/or clearer the water, the darker the fish will be. Additionally, more alkaline water--- usually indicative of fisheries with no vegetation--- can make a bass less vivid.  By contrast, bass in vegetation-filled waters--- more acidic--- often boast sharper camouflaging.

In tannic (brown) water, fish still can be dark if it doesn't block light penetration, Gilliland said. But in black water, often caused by decaying vegetation, bass will be more washed out.

And this from the FMNH:  "Adults from mud-bottom lakes are dark olive brown to black, with markings hardly distinguishable. Males in breeding condition tend to be darker in overall color." 

Plus, researchers noted that Lake Erie smallmouth bass transform from a mottled color when they are resting at night to a more uniform pattern when they are moving. That's because a contrasting pattern works as camouflage when a bass is near the bottom, but makes it more visible, and consequently less efficient as a predator, if it is moving, they hypothesized.

Gilliland concluded, "Color changes in bass are evolutionary advantages. If a smallmouth is feeding in shallow water, he will color himself to blend into the bottom so shiners don't see him when they look down. It's all part of the predatory process."

Angler's Advantage

If you understand how water depth and clarity, as well as vegetation, can alter a fish's appearance, you'll have a good idea of where to fish next when the bite stops.

For example, you catch bass on a topwater in open water. If its sides are dark, it 's likely a shallow schooler and you'll have to move to find the fish again. But if the sides are pale, it probably came from deepwater to grab your bait, and there probably are more where that one came from. Only most, especially the big ones, aren't willing to expend the energy to chase food on top. Try working the depths with a crankbait or soft plastic.

Or what if you're catching fish along a dropoff near a weedline?  If the color is especially rich and sharp, the bass probably came out of the grass to eat your bait. That could suggest that you'll catch more fish nearer or in the grass, where that camouflage makes them effective ambush predators. If the color pattern is not as clearly defined, a deeper presentation closer to the dropoff might be better.

It's also important to remember that forage species also use camouflage to help them avoid bass and other sport fish. Often they use "countershading," which means a dark back, to better blend into the bottom, and a white belly to better match the lighter background above, especially if a predator is looking up. Generally, anglers believe that they should "match the hatch" with baits that have dark backs and light bellies to make their offerings more natural looking. But a counter argument holds that if you use a bait with coloration that is just the opposite, bass will more readily see and strike it. The jury is still out.

Odd Balls

Did you hear about those "gold" bass caught in Canada and Florida recently? This condition, known as "xanthism," is the most striking aberration in bass appearance. It also occurs in other fish, as well as reptiles and birds.

Considered a genetic mutation, the bass doesn't have the ability to convert white light to blue in its molecular structures. That blue normally combines with yellow to make green.

"It's rare, but not unheard of," said Gene Gilliland, national conservation director for B.A.S.S. "I've seen it in other sunfish. But talk about a target. A fish that color has little chance of survival and, if it does, it beats some crazy odds."

Meanwhile, bass with black blotches aren't quite so rare, especially in clear, northern waters.

"What literally is happening is accumulations of melanin-producing cells are aggregating in the dermis and epidermis of the fish," said Geoffrey Smith, Susquehanna River biologist for the Pennsylvania Boat and Fish Commission. "The bigger question is why and is it really happening more frequently, or just being observed more frequently."

Smith is especially interested in learning more about this condition because anglers often report catching smallmouth bass with black blotches from the Susquehanna, a river troubled by water quality problems and a declining fishery.

Some scientists suspect that endocrine disruption might be a cause of the blotches, and that could be caused, at least in some cases, by pollutants.

Disappearing Act

As with bass, other fish, especially forage species, have evolved with appearance adaptations to help them survive.

"Some juvenile fish have colors that help them hide from prey," said Auburn's Ben Beck. "Some fish have false eye spots to trick predators. And some baitfish are iridescent, which allows them to communicate with each other and move in unison."

This makes it much more difficult for bass and other predators to target individual fish.

As described previously countershading also helps. When seen from the top, the darker dorsal area of the fish blends into the bottom or darkness of the water below. When viewed from below, the lighter ventral area blends into the light filtering down from the surface.

Appearance also helps protect some species because of what the predator has learned to associate with a particular color. For example, bass show a decided preference for the tadpoles of spring peepers, which are brown, over similarly sized tadpoles of toads, which are black.

(This article appeared originally in B.A.S.S. Times.)