December marks the beginning of my favorite time to be bass fishing. No, I don't like the challenge of being so cold it hurts, being stuffed into so many layers of clothing that it's hard to move or the thrill of falling into 45-degree water. But my time on southern waters makes it clear that December through February is the best time to catch a big bass. Here's some biology that might explain why.

Catchability and fishing

Research completed at Mississippi State University demonstrates that angler catch rates in ponds declines rapidly, even when the fish are released. Eight ponds were fished from May through October in two successive years. These ponds had been fished little or not at all before the study started.

Each pond was fished weekly for one angler hour per acre. An angler hour is one angler fishing for one hour.

Averaged over all ponds and both years, the catch rate declined from more than six bass per angler hour in May to less than one bass per angler hour by the end of October.

I analyzed catch stats from national Bass Angler Sportsman Society tournaments during the last 30 years: Neither catch rates (measured as bass weighed in per angler day) nor average weight of bass weighed in changed significantly over three decades.

So if catch didn't change, how is that evidence of declining catchability? If you were a statistician, you would conclude that catchability didn't change.

But if you are a bass angler, especially one with a little gray in your beard, you might be more likely to agree that catchability has declined.

My first bass boat had a 10-horse outboard, a 12-volt trolling motor and a Lowrance "green box." Today, I can move five miles down the lake in less time than it takes to retie a Carolina rig, stop exactly on a waypoint marking a structural feature in the middle of a large reservoir and turn on the side-scan to see if any fish are present.

Yet catch rate is the same.

If failure to catch more bass despite changes in technology that make anglers more effective doesn't convince you bass are getting harder to catch, think about the tackle innovations - more-sensitive rods, less-visible line. Add to that the advances in presentations - bass jigs, jerkbaits, stick worms, drop shots and shaky heads, just to mention a few. Top that off with a steady supply of new lures - tempting morsels that bass haven't seen.

Despite all the advantages available to and used by anglers, bass catches haven't changed. It appears that the bass have changed, too.

Hook learnin'?

Most bass anglers I know tend to agree that fishing pressure reduces catchability. Twenty or 30 years ago, bass were harvested, so more fishing meant fewer bass to catch. The prevalence of catch and release in modern bass fishing makes removal of bass a less-likely explanation for declining catches. This is clearly demonstrated by the declining catches in the eight ponds where all bass were handled quickly and gently, and released.

The common reasoning for declining catchability is that bass "learn" to avoid capture. Hooking, fighting and handling qualify as strong punishment, and therefore the bass avoid making the same mistake. Or so the reasoning goes.

Studies by Dr. Keith Jones at Berkley's lure-testing lab support this form of learning - bass quickly learn to avoid striking a certain lure.

But there is more to declining catchability than the few fish that get "educated" by striking a particular lure.

In the Mississippi State pond study, only 55 percent of the bass were caught. With 45 percent of the bass never caught, learning by being caught does not completely explain the decline in catchability.

Regardless of how fishing affects bass catchability, winter is a time of very low fishing pressure, and a time when your odds of catching a big bass increase.

I have my own hypothesis, supported by fundamental biology, for why catchability declines with fishing effort. I'll leave it to you to ponder how fishing effort might affect bass catchability.

Something to think about on a cold but calm and sunny winter day on your favorite lake.