How do you like these odds?

I wrote recently about seeing near my Birch Lake pier a school of hundreds of what I believed to be smallmouth bass fry. Looking at all these tiny fish and envisioning many more such schools around the lake’s perimeter, one could assume the lake will soon be chock full of smallmouths.

The reality is far different. The odds of survival for these fry are exceedingly long. One scientific study used DNA tracking to estimate the success of spawning smallmouth bass on a lake in Ontario. To make a long story short, the study found that only 27.7 percent of male bass that acquired eggs (it’s the male who guards the young after the eggs hatch) had at least one offspring survive to the fall young-of-the-year stage. Just 5.4 percent of all the spawning males produced 54.7 percent of the total number of the fall young-of-the-year, which range in size from 1 1/4 to 3 inches.

To look at it another way, consider that female smallmouth bass deposit anywhere from 2,000 to 10,000 eggs on a spring spawning bed. Even under the best conditions, most eggs don’t survive. They’re vulnerable to changes water temperature and oxygen levels, flooding or sedimentation, disease and predation (as from panfish and crayfish).

When the eggs hatch, the larval fish live off a yolk sac attached to their bodies. Once the yolk sac is fully absorbed, the young fish, called fry and about an inch long, rise from the bed and start eating on their own. For a time the male bass protects the school, but eventually he leaves and the fry scatter. They survive on tiny crustaceans until they are big enough to eat aquatic insects, then larger crustaceans and fry of other fish species that spawned later. As the fish grow, they face the same threats as the eggs – in addition to which all manner of predators feast on them.

When they’re small, they get attacked by bluegills, perch, pumpkinseeds and sunfish. As they grow, they become prey for walleyes, northern pike and muskies. Other enemies, again depending on the fishes’ size, include kingfishers, loons and herons, mink, frogs, and some snakes. The end result is that only a tiny fraction of the eggs laid in a spawning bed, and only a tiny fraction of the fry I see near my pier, ever become adult bass that I try (with limited success) to catch. Yes, nature can be a cruel mother. I am certainly glad the odds of survival for my new grandson, Tucker, are considerably better than for a newly hatched smallmouth bass.

They're not just minnows

Judging from what I saw while uncovering the boat on return to Birch Lake yesterday, some fish have pulled off a highly successful spawn. A large school of fry skittered off as I waded into the water to untie the boat canvas. They were about an inch long and, individually, looked like little more than slender shadows cast against the sandy bottom.

We're tempted to label any small fish we see, especially in schools, as minnows. In reality, minnows are a family of fishes defined not by size but by body characteristics. For example, carp that can grow to 50 pounds belong to the minnow family, as do the shiners, only a few inches long, that we use for bait. 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: The teeth are actually in the throat and help grind the fishes' food. Most minnows are in fact small -- they reach a few inches to perhaps a foot long. 

So, what did I see in the shallows near my pier yesterday? My guess is that they were smallmouth bass, since those fish were on the spawning beds just two or three weeks ago. I am not aware that any other fish species have spawned since then. I wished I'd had a little dip net with which to scoop a few up and examine them. When I have done this, it amazes me how much even tiny fish fry resemble the adults they will become. There is no mistaking them. Smallmouth fry, for example, have the signature black-edged tails and red eyes. Largemouth bass have the black stripe down the side, perch the vertical black bars, northern pike the oval spots. And so it goes.

Have you seen fish fry (not minnows) in your lake? Try netting a few and taking a close (brief) look. It will allow you to see what's breeding successfully. Of course, success is a relative term -- hatched fry do not a large or stable population make. The odds of fry survival are long indeed -- a topic for another time.

About those midges

My last post mentioned that midges, besides mayflies, were hatching on Birch Lake recently. Midges of course are tiny white flies that when on the wing look like mobile bits of cottonwood fluff. Believe it or not, trout fishing enthusiasts (or should we say fanatics?) actually tie flies small enough to mimic these things.

While the mayflies at Birch were hatching a week or so ago, the midges were, too. One day hundreds of them clung to the screens of our lakeside porch; a tap on the screen sent them flying; in a few moments they were back. The next day only a few remained. I’ve been down on the lake when midges were thick, a swarm hovering around my head, and if I listened carefully I could hear a faint, collective buzzing.

These were non-biting midges, from the insect family Chironomidae, and often called chironomids. Some call them “blind mosquitoes”; others call them “fuzzy bills” because of the males’ bushy antennae. As with mayflies, if your lake has midges, that’s a sign the water quality is pretty good. Midges are an important link in the food chain in and around a lake. Fish and predatory water insects eat them, and the midge larvae help keep the water environment clean by eating organic debris.

Like mayflies, midges have interesting lifecycles. The adult flies lay gelatinous masses on eggs on the water surface, each holding as many as 3,000 eggs, which sink to the bottom and hatch in about a week. The larvae dig into the mud or, in some species (and there are many) build small tubes to live in. They feed on organic matter suspended in the water and mixed with the bottom mud. As they grow, they turn pink and eventually dark red, at which point they are known as bloodworms. The color comes from hemoglobin, the same compound that makes our blood red; it allows the larvae to “breathe” in the mud, which of course is low in oxygen.

After two to seven weeks (largely depending in water temperature) the larvae become pupae. About three days later, they swim to the surface, and adults emerge within several hours. The adults then mate; they live only three to five day and do not feed. In the heat of summer, midges may complete their lifecycle in as little as two or three weeks. Fall larvae do not pupate but instead remain in the larval stage until spring.

Have you seen midge hatches on your lake? Watch for them throughout the summer – several generations may hatch before the season turns to autumn.