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Posted by Peter Mathiesen on December 6th, 2011
Schooling baitfish are a critical food source for bass in large impoundments and are key to ensuring healthy populations of sportfish. Consider this fact, no artificial bait is better represented on the shelves of your local tackle store than shad. In big water it’s the meal of choice for bass.
My first largemouth bass was caught in Missouri on Bull Shoals Reservoir in late October with a Storm Silver ThinFin Shad. My guide pointed to a school of shad boiling on the surface and instructed me to throw on the outside of the school. My cast was not stellar and he anxiously told me to crank the bait as fast as I could – they didn’t say “rip” in 1969. The choppy retrieve was crashed by a 4-pound largemouth that, to an 11-year-old kid, seemed to walk on water. That shad-imitating moment, still vivid 35 years later, left me bass-bitten for life.
In Part Four of the Bassmaster Forage Series, we examine threadfin and gizzard shad and offer strategies on how to net more big bass by understanding those schools of darting baitfish.
Freshwater shad are arguably the most numerous of all baitfish in America. In many lakes, the shad population accounts for more than 50 percent of the total fish biomass. There are two primary freshwater species, threadfin shad (Dorosoma petenense) and gizzard shad (Dorosoma cepedianum). Other common shad, American, Hickory and Alabama, are migratory species that commonly invade freshwater estuaries or rivers to spawn, but live most of their lives in saltwater.
In the spring, shad school together to release massive amounts of eggs, with a single adult female releasing more than 200,000 eggs during the spawn. The eggs are fertilized as they fall to the bottom of the lake, and the tiny fry emerge in less than a week.
Like most fish, a shad’s first meal is microscopic zooplankton and protozoa. Later, the primary food source becomes free-floating algae (phytoplankton), and in many watersheds, insect larvae. In very clear northern lakes with sterile environments, desperate adult gizzard shad have been known to actually suck algae and decaying matter off the bottom.
Although life begins with great similarity for both species of freshwater shad, their journey to becoming a bass dinner is very different. Gizzard and threadfin shad are saddled with notably contrasting growth rates and temperature ranges.
Threadfin shad have little tolerance for low temperatures. “Forty-five degrees is about all they can take,” said Ken Weathers, biologist for The Alabama Department of Conservation. “When the temperature falls dramatically, we have seen large shad kills in northern Alabama on the Tennessee River, although their numbers quickly recover.”
Despite their sensitivity to temperature, threadfin shad flourish throughout warmwater southern reservoirs and into some midwestern lakes. As you move farther north and west, threadfin become less numerous and are often stocked to maintain a viable food source for bass.
Growth rates for threadfin are surprisingly different than gizzard shad. Most of the young-of-the-year threadfin are 2 inches by late summer, the perfect bass meal. They will reach 3 to 4 inches by October in most of the southern impoundments. Topping out at 4 to 5 inches, a threadfin will remain a potential bass food its entire life, particularly where fish in the 7-pound-plus category cruise.
Weathers is documenting the relationship of threadfin shad and largemouth bass in Alabama lakes. “Shad are a clear barometer of water quality and bass populations. We are seeing parallels that we are just beginning to understand in bass numbers and growth, relating to threadfin reproduction on Lake Eufaula. When the shad numbers are strong, the bass are thriving. When the shad crash, the bass numbers fall,” said Weathers.
You can find gizzard shad in most large impoundments in the United States, but bass only chase them for a limited period of time. “After the spawn, the gizzard fry just explode,” said Elmer Heyob, fisheries biologist with the Ohio Department of Natural Resources. “They will be 1 1/2 to 2 inches in midsummer, but by late fall, they’re often 5 inches long and a little too large for the majority of our Ohio largemouth bass. When conditions are perfect, gizzard shad can actually spawn a second time,” said Heyob.
Visiting the shad zone
To find shad much of the year, you need to visit the pelagic zone – open water, where light penetrates above the thermocline. During the day, shad will move deep enough to stay out of direct sunlight, yet the water must have enough light to produce algae and plankton.
These depths vary dramatically based on the clarity of a lake and the amount of algae bloom. “The spot to fish in the summer on many lakes is where the thermocline in low light meets with structure like a dropoff or hump. Shad will stay there during a hot, bright summer day, and so will bass,” said Weathers.
Weathers has tracked shad’s nocturnal movements in the summer. “We wait until evening to net shad – as soon as it’s real dark they move into shallows and coves en mass.” He noted that a shad’s reaction to fall temperature changes on Lake Eufaula is less dramatic. “Shallow southern lakes are not as sensitive to the lake turning over as are the deeper northern lakes. Once shad school up in a fall pattern, they will stay fairly consistent,” said Weathers.
It may not be popular to find bass in open water, but trolling can be efficient. “Set a couple of rods with different depth crankbaits, motor slow, and watch your depthfinder for schooling baitfish. Once you establish a couple of hits at the same depth and see baitfish on your screen, mark the spot, note the depth and start casting. Key on diving birds and where shad are breaking water, and then fish under the school of bait. Most of the action on top is from smaller bass. The larger fish will usually hit the school from the bottom,” said Weathers.
Finding them requires a similar game plan. As you travel to more northern latitudes, gizzard shad, due to temperature range and colder lake temperatures, will frequently occupy more swallow depths than they would in the South.
Throughout the summer months, depthfinders can be the key to establish and zone in on schooling baitfish and to help narrow where you need to pitch your baits.
By mid to late fall, gizzard shad in most impoundments are just too large to eat for all but the biggest bass in the lake.
Roll it over
Around Labor Day, much of the Midwest will experience a big wind, and a cool, heavy rain will turn the lakes over, creating dramatic changes in gizzard shad behavior.
As the lake turns over you’ll find baitfish more evenly spread out on your depthfinder. In lower light conditions, they will quickly congregate in shallow coves and protected water. Look for areas where a flush stream or creek empties into the lake. The turbid water and large amounts of silt and organic matter can create food for schooling baitfish.
“We’ve seen these coves black with gizzard shad. Largemouth will quickly maraud their way in and attack anywhere there is an edge or dropoff to deep water. It can be explosive,” said Heyob.
Keep in mind that if there is a low shad population, bluegill or perch (on far Northern Lakes) will play a much stronger role in summer and fall patterns and replace shad in the food chain.
The next time you’re reaching for a shad-imitating bait, think about the lake you’re fishing and its population density of threadfin and gizzard shad. Locate where the thermocline meets the structure and spend some time idling, watching your screen to establish a schooling pattern. If you’re in a primary gizzard shad lake, don’t wait for the fall temperature change; you’re already in the prime bite.
This article has been reproduced on OzarkAnglers.Com with the permission of the author, Peter Mathiesen.
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