Evaluate Slot Limits As Your Fishery Matures

Everyone has heard the standard harvest policy–cull bass under 14-inches.  That’s appropriate for some management scenarios, but slot limits must be evaluated and revised as the fishery develops.

Here’s why!  Long before sculpting a lake bottom with bulldozers and pond management was cool, a 50-acre lake southwest of Fort Worth was built with a goal of producing giant bass. It had the right cover, including creek channels, standing timber, flooded humps, brush piles, the works. When completed in the Fall, the food chain foundation was stocked with fathead minnows and coppernose bluegill. Next Spring, 2,500 pure Florida bass were air freighted from a Florida hatchery to DFW Airport.  Average size, just slightly larger than one-inch.

The little creatures were carefully placed in their new home. Fathead minnows were everywhere. Bass grew extremely fast.  Within two-years, those tiny bass topped four-pounds. A few football-shaped females pushed six-pounds.  The lake owner established a slot limit to remove any bass less than 14-inches. Gizzard shad, stocked two-years earlier, schooled all summer and provided diverse forage.  Big bass began ruling the lake.  The owner looked like the wizard of largemouth bass, until blindsided by a dramatic change six-years later.  He assumed, once the lake matured, it would stay the same forever.  That’s a wide-spread myth.  Truth is, getting a lake to trophy status is a major task.  Once that goal is attained, there’s no room to become complacent. In this case, 11-years after the lake was stocked, large bass began to lose weight–rapidly.  In one season, 10-pound bass shrank to six-pounds.  The same hungry-looking fish soon weighed five-pounds.  Once huge, the skinny fish looked like victims of a Third World famine.

This was the unhappy results from two different problems.  We quickly ruled out disease and parasites.  A fish pathologist examined 10 fish and found nothing unusual.  First, these aging fish were 11-years-old, moving past their prime.  The gray bearded bass had lived, thrived, and dominated this waterway for years, but the sun was setting on their mottled green backs. Secondly, their food chain had diminished.  How?  Blame it on the slot limit.  By leaving the original slot limit in place so long, two things happened.  One, there were too few rising healthy, young stars to replace veteran trophies. Secondly, big bass eat big bass. A 15-pound bass will inhale a two-pounder and keep it down.  Meanwhile, the gizzard shad population was not maintained. Over a two-year period, shad disappeared, victims of big bass appetites.  Turns out, slot bass became the food chain for big bass.  As trophy classes dominated the population, as much as 80-percent of these ambush experts were 18-inches or longer.  That percentage is too high for long-term management.

Something had to give.  In this case, it was the heroes, not the goats.  So, how to fix this problem?  Nurture young bass.  Grow them into the system.  It took  three-years to resolve the dilemma, but it worked by revising the original slot limit. If the owner had identified effects sooner, he could have adjusted the slot much earlier and groomed young bass for trophy stardom.  This was a classic example of how slot limits must change as the fishery matures.  If you maintain consistent relative weight records and population profiles, fish will tell you when slot policies should be revised.  Have you done a lake survey lately to analyze slot limits?  Spring is the perfect season.