In the zone

Scientists like to name and classify things, so it should come as no surprise that they have names for different zones in our lakes. Mainly they talk about four of them.

The one we think most about, that we interact most with, is the littoral zone. This is the area from the shoreline out to the point where the water is deep (or murky) enough so that there is too little light at the bottom to support rooted plants.

The Minnesota DNR pegs this zone as from shore to a depth of about 15 feet, but that depth can vary a lot with water color and clarity. The width of the littoral zone also varies. Where the bottom slopes down steeply, it may be quite narrow. If the bottom slopes gradually, the littoral zone may extend far into the water. In fact, a shallow lake may be all littoral zone.

Life can be incredibly diverse in this zone. Most fish spend most of their time there (and as a consequence so do anglers). It’s a rich environment, with relatively warm water, plenty of light, and nutrient-rich bottom sediments.

All manner of plants grow here, from emergent species like bulrushes, cattails and arrowhead, to floating-leaf plants like water lily, spatterdock and watershield, to submerged vegetation like pondweeds, wild celery and milfoils. Algae are also abundant, some species clinging to the larger plants. The plants provide cover for young fish, which in turn attract larger predators. Frogs, muskrats, turtles, insects and other creatures populate this zone.

Out beyond the littoral zone lies the limnetic zone. This is the open-water world. It begins where the littoral zone ends; its depth again depends on how deep the light can penetrate. Fish move in and out of this zone, but for the most part its inhabitants are plankton – one-celled algae of various kinds (phytoplankton) and tiny creatures (zooplankton) that eat by filtering algae out of the water. Plankton are critical to a lake’s food web, and the phytoplankton are responsible for most of the photosynthesis (thus oxygen production) that occurs in the lake.

Below the limnetic zone lies the profundal zone. This zone may not exist in shallower lakes. It’s the deep water where light penetration is greatly limited. In essence, this is where dead matter from above goes to decay. It is relatively cold, dark and oxygen-poor. The primary life in this zone consists of heterotrophs – small creatures that eat dead material.

Finally, there is the benthic zone, essentially the lake bottom sediments. Residents include bacteria and fungi that break down organic matter, releasing and recycling nutrients. Life just under the sediment surface can be quite diverse. Most benthic zone organisms are invertebrates. The eggs and larval stages of insects like mayflies and midges can be found here, along with worms and small crustaceans.

Sometimes as you look out over your lake, try to picture these zones. You’ll understand a little bit better how your lake ecosystem functions.

Two Pair

As my canoe came clear of a shrubby patch on a small point here on Birch Lake, there came an explosion of wings.

Mergansers – two males and two females – shot out of the water and arrowed away. The contrast of colors surprised and delighted me. I’m used to identifying mergansers by the female’s slender shape and rusty crest. The male with his green head (when in mating plumage) can fool the unsophisticated, like me, into thinking he’s a mallard.

Those of us who spend time on our lakes in spring get to see a variety of ducks pass through on their migration north. According to Audubon, common mergansers (the kind I saw) breed mostly in Canada and winter mainly south of here, in a swath that includes Ohio, Indiana, Illinois, Iowa, Missouri, Nebraska and Kansas.

I’ve heard mergansers described as early arrivals in the northward migration, though I’ve noted other species on our lake sooner after ice-out. Until the sighting of the two pair several days ago, I had never seen more than two mergansers together.

Now and then I’ve had the chance to watch a female diving for fish, which is mainly what mergansers eat. They vanish faster and surface sooner than do loons – they seem to bring to their “fishing” a greater sense of urgency.

The female’s crest looks pleasantly unkempt. As for the male merganser, he’s pretty easily distinguished from a mallard. He’s similar in overall size but more slender. His green head (not crested) isn’t as bright as a mallard’s. He also lacks the mallard’s chestnut breast and white neck ring. The merganser’s bill is long and red; the mallard’s is yellow.

You’ll also easily distinguish the male mergansers by their sound. Mallards give out the “quack” of the stereotypical duck. Mergansers don’t say a lot but emit a low, harsh “croak.”  All that aside, while mallards carry the taint of park ponds and domestication, mergansers portray the essence of the wild.

If I take any lesson from this sighting, it’s that we can appreciate spring and migration more if we see more than “just ducks” passing through our lake country. While I’m nobody’s birdwatcher, I find a little time spent with binoculars and a field guide book reveals a rich diversity in visitors’ shapes, colors and behavior.

And I must say those mergansers that rocketed off Birch Lake – boy-girl, boy-girl – were among the best two pair I’ve ever been dealt.

Dragonfly riot

It’s mostly over now, but for a couple of weeks dragonflies were everywhere around our place on Birch Lake, and probably around your lake, too.

Maybe it was the happy coincidence of a dragonfly hatch with the emergence of late-May and early-June mosquitoes. All I know for sure is that the air was full of dragonflies, sweeping up mosquitoes like vacuums on wings.

Though routinely spotted over land, dragonflies are without question water insects – they come out of your lake after a long metamorphosis. The adult stage we see in the air lasts a couple of months, really just a sliver of the insect’s life.

Dragonflies mate while on the wing – no doubt you have seen this act above the water on your lake. The female lays her eggs on a water plant or directly into the water. When the eggs hatch in a couple of weeks, nymphs emerge. They really don’t look anything like dragonflies, but they have one thing in common with the adults: They’re voracious feeders.

Dragonfly nymphs eat all sorts of water insects and insect larvae, and yes, that includes mosquito larvae (call wigglers). So dragonflies are putting a dent in the skeeter population long before they can fly. The nymphs are also quite agile in the water. They swim fast and have a jet-propelled “hyperdrive,” ejecting water from the anal opening.

The nymph stage can last as long as a few years. The nymphs live in your lake’s calm water, amid reeds, cattails and other plants. As they grow, they shed their skin several times. Each in-between phase after the skin is shed is called an instar.

Finally, once fully grown, the nymph climbs up the stem of a plant and emerges from its skin as an adult dragonfly, leaving behind a skin called the exuvia. You may at times have seen one of these clinging to a reed in shallow water. 

And now the dragonfly is ready for serious eating. Dragonflies are so agile in the air that other insects, like gnats, midges, mayflies and, of course, mosquitoes, have no hope of escape. They use their legs like a basket to catch bugs on the wing. Then they feed their prey into their jaws (mandibles) and crush it before swallowing.

How much do they eat? Well, according to dragonfly-site.com, they can eat their own weight in bugs in about half an hour. So that’s why, in mosquito season, we can be thankful to see squadrons of brightly colored dragonflies, sweeping the air around and above our homes and piers.

Here’s to Hoover-Mouth

There are species of fish in your lake that you may rarely if ever see, yet are important to the health of the fishery. The white sucker is a classic example.

You may know this fish best as bait. Raised in ponds, it is sold in increasing sizes for walleyes, northern pike and muskies. If like me you grew up on a Lake Michigan tributary, you may have fished for suckers using a dip net hung by a rope from a bridge, in springtime when the fish migrate upriver from the lake to spawn.

If your lake contains suckers, why don’t you see them? Well, because they tend not to take what anglers offer. I’ve fished for more than 50 years and have caught just one white sucker from a lake on hook and line.

Suckers are mainly bottom-feeders and have mouths well adapted to that purpose. The leathery lips aim downward instead of straight ahead, so the fish can cruise along, dining in comfort, casually vacuuming up food like insect larvae, worms, small mollusks and crustaceans, plant matter and fish eggs from the sediment. In turn, suckers are a vital food for favored game fish; they may also be eaten by herons, loons, bald eagles and osprey.

White suckers live in almost any lake and stream here in Northern Wisconsin. In fact, they’re abundant throughout the Northeast and Midwest U.S. and in parts of the Northwest. They do fine in clear, clean waters but also tolerate relatively low dissolved oxygen and so can thrive in turbid urban waterways.

Suckers have fine scales. Sides are dark greenish with a metallic luster; the belly white, and hence the common name. Adults can grow up to 20 inches long and weigh two pounds or more; musky anglers are known to use those at the top of the size range for bait in the fall.

Spawning generally starts when the fish are about four years old (later in colder climates where they grow more slowly). Spawning season runs from April to early May. The fish move into streams or, in lakes, select bottoms of gravel or coarse sand. The actual spawning happens at night. Most often, two males mate with one female. With one male to each side, the female lays 20,000 to 50,000 eggs, which the males fertilize.

The fish do not make spawning nests and do not care for the eggs, which simply sink to the bottom. The eggs hatch in five to ten days, and a week or two later the fry leave the spawning area and disperse.

Thus are born swarms of fish on which your lake’s most prized species may depend for growth. So even if you never see suckers on your lake except in your bait bucket, be sure to assign them a little respect. Here’s to Hoover-Mouth!

How does your lake get its water?

You’ve read here about classifying lakes by trophic state – how poor or rich in nutrients they are. But that’s not the only way to categorize them. Another, just as interesting, is by how water gets in and out.

The number of lake types based on source of water depends partly on who is doing the defining. The Wisconsin Department of Natural Resources lists four types, but there is a fifth that many geologists mention. Here are five basic lake types found in Northern Wisconsin and Upper Michigan:

Drainage lakes. On these lakes, a stream brings water in, and a stream takes water out. That is, the lake has an inlet and an outlet. Some lakes may have more than one of each. The water level in these lakes tends to stay fairly constant. Think of a bowl into which you run a slow flow of water from the tap: An equal amount of water flows in and flows out. I live on a drainage lake and its level is largely self-regulating. In 30 years, through wet times and dry, there has been at most a foot of difference between the highest and lowest levels.

Spring lakes. These lakes have no inlet on the surface, but they do have an outlet. They get their water mainly from groundwater flowing in. Many streams originate in spring lakes, which are quite common in northern Wisconsin.

Seepage lakes. These lakes have no stream flowing in or out. Their water comes mainly from rainfall and runoff, sometimes supplemented by groundwater. Their water levels are therefore cyclical, rising and falling with wet and dry years and their effects on the water table.

Drained lakes. These lakes are like spring lakes in that they have an outlet but no surface inlet. They differ in that they are not fed by groundwater – they get their water almost solely from rainfall, snow and runoff. For that reason, their levels can fluctuate greatly. During long dry spells, the streams flowing out of these lakes may dry up. Drained lakes are uncommon here in northern Wisconsin.

Perched lakes. These lakes are truly landlocked. They have no inlet, no outlet, and no contribution from groundwater. In fact they sit on relatively high ground, above the water table, with dense bottom sediments that hold the water in. Water levels in perched lakes can drop dramatically during long dry spells.

If you want, you can add a sixth type of lake: Reservoirs. These of course are like drainage lakes in that they have a stream inlet and outlet. The difference is that they were created by humans – they wouldn’t exist if not for dams. Here in the northern Wisconsin we have the Willow, Rainbow, Turtle-Flambeau, Chippewa and other smaller flowages.  

Which type is your favorite lake? If you don’t already know, consider doing some investigating to find out.

Minnows? Are You Sure?

Soon after ice-out I do canoe reconnaissance: slow paddle around the shoreline to look for signs of life. When I did that recently here on Birch Lake (at Harshaw), I encountered huge schools of little fish at the far-in end of what we call Indian Bay.

My mind reflexively said, “Minnows!” But of course that was both non-specific and taxonomically incorrect. The vertical black stripes on these guys, anywhere from about 1.5 to 2.5 inches long, clearly labeled them as young yellow perch.

It amazes me how soon fish fry take on the markings of adults. Baby smallmouth bass, for example, have the signature black-tipped tails and red eyes. Largemouth bass have the black stripe along the side, northern pike the oblong oval spots. And so it goes.

The young fish seem to mimic adults in temperament, too. Little muskies, for example, are hyper-aggressive. Last summer, I caught a 4-inch musky that slashed at and grabbed a crappie minnow impaled on my hook.

But back to the matter of minnows: We tend to apply that label to any small fish, especially in schools. That’s probably because we refer to the baitfish we buy at the tackle shop as minnows (again not precise, but a well-accepted term).

Scientifically speaking, the term “minnow” applies to a family of fish defined not by size but by characteristics. Members of the minnow family have one brief dorsal fin with nine or fewer soft rays. They have smooth-feeling scales that may come off when the fish is handled. They do not have true spines in their fins. They have no teeth in the jaw but have rows of toothlike structures on the bony frame that supports the gill tissues. Their teeth are in the throat and help grind food.

Most minnows are in fact small, a few inches long. That’s true of the shiners we use for bait – they are in fact minnows. But the minnow family also includes carp that can grow to three or four feet or longer and can weigh 50 pounds or more.

Chances are the schools of fish you see beside your pier will not be minnows but small game fish or panfish. If you can net a few (not easy, I admit), you’ll get a clue to what’s breeding in your lake. The fish I saw in Indian Bay on my canoe ride assuredly were not minnows; from their numbers I can conclude that our lake’s perch of brought off some successful hatches.

That of course is not the same as successfully reproducing: Hatched fry do not a large or stable population make. Those little perch have a tough gauntlet to run before they reach adult size. All I can do is wish them well.

Waiting for Water

Just before hamburgers were served to son Todd and me at Birch Lake Bar a week ago, co-owner Ed stopped by our table and lamented the lake’s condition.

I’d been enjoying the extended thaw – greatly, I might add – but to Ed the lake’s surface of deep slush meant the end of snowmobile season, the end of ice fishing, and so a tough time for business. I can certainly sympathize: an early thaw means different things to different people.

Now the question of the day is: When will our lakes open up? That depends on how the weather behaves from here on, though the past two weeks of well-above-average temperatures have given the thaw a nice head start.

Last year and the year before, the ice went out here on Birch Lake a few days after the official fishing opener (first Saturday in May). It went out a great deal earlier in 2010, the first year we had our land here – I remember wading in the lake, quite comfortably, in mid-April.

2011 was a different story. On April 16, when our family held a ceremonial groundbreaking for the cabin that has since become our year-round home, the lake was still frozen solid, the day cold, wind-blown snow stinging our faces. We drank our champagne huddled inside the RV trailer that served as our first shelter.

As for 2012, I have written evidence of an early ice-out. An entry elsewhere on this blog says I put the pier in on April 7, the Saturday before Easter. Are we due for another early open-water season? Signs point that way, but we can’t forget what April and May were like last year: Cold, cold, and more cold, with a couple of April blizzards tossed in.

Right now, as I write, on Sunday, March 15, it’s pleasantly mild, about 50 degrees, and the forecast, if it can be trusted, calls for highs well into the 40s for the next several days. The snow has melted off the metal components of our pier, arranged neatly on shore, and off the cedar pier board sections I stacked and covered with a tarp last November.

If you’re like me, you’re aching for the ice to be gone and for the start of whichever open-water recreation you prefer. It’s a wondrous time – the days getting longer, the clock sprung ahead, loons on their way north, the long months of spring, summer and fall awaiting, full of promise. We could do worse than to have an early ice-out bring that promise forth sooner.