The biology of the bass spawn

It’s March, so the bass will begin spawning in southern Mississippi. By the end of the month, assuming normal warming trends, the bass spawn will be in full swing in central Mississippi.

It seems like a good time to provide a summary of the biology of the bass spawn.

Largemouth bass spawn at 64 to 68 degrees. Yes, I’ve heard angler reports of bass spawning in cooler and warmer water.

Undoubtedly some do, but it is very few.

If you use your temperature gauge to decide whether to go looking for spawning bass, where do you measure the temperature? At the boat ramp? At the back of a shallow cove? In the main lake? At the surface or the bottom? In the morning of afternoon?

The spawning water temperature of 64 to 68 degree is largely based on observations in shallow hatchery ponds that have pretty uniform temperatures end to end and top to bottom. Some bass spend most of their time in shallow water, so expect some spawning activity to begin when the afternoon temperature in the shallow water climbs to 64 degree.

Will bass spawn at temperatures above 68? Yes. The spring sun is powerful and quickly warms shallow water. By the time the water temperature in the main lake reaches 64 to 68 degrees, afternoon temperature in the back of a spawning cove could easily reach the mid 70-degree range, maybe even warmer.

It should be apparent that largemouth bass appear to spawn at a far wider temperature than 64 to 68 degrees, and indeed they do, depending on when and where you monitor temperature.

Every lake warms differently, but individual lakes have warming patterns that are consistent from year to year. You might want to develop a consistent method for measuring water temperature so you can predict the spawn in future years.

For example, note the temperature in the main lake early in the morning when the bass spawn first starts. It might be different from the 64- to 68-degree range, but it will be a good predictor in years to come.

Largemouth bass build nests — shallow depressions that can be 1 to 2 feet in diameter — on hard bottom. The nests are built on clean gravel, hard sand or clay — or they might be in an area where bass can fan away silt to get to hard bottom.

Don’t waste your time fishing for spawning bass in areas with a thick layer of soft sediment or decomposing plants. Yes, bass will spawn on the thick tubers of water lilies to have a hard surface in an area with an otherwise soft bottom.

A nest will be adjacent to a single object like a stump, log, dock piling or rock if available. Nesting near a large object makes it easier to guard against intruders with an appetite for bass eggs and larvae.

Conversely nests are not built near complex cover like brush piles that would make detection of nest predators more difficult.

The male courts the female to attract her to the nest and stimulate her to spawn. This might involve a little dancing and  nipping.

On the nest, the male might nudge or nip the female near the vent or gill cover, presumably to stimulate egg release. Contrary to some accounts, head butting is not necessary to loosen the eggs — female bass spawn just fine without “tough love.”

Usually the female spawns in only one nest and the male spawns with only one female.

The female leaves after she has spawned, and the male guards the eggs. Yes, this disagrees with anglers’ reports of two bass guarding a nest.

Nest guarding by both the male and female (biparental guarding) has been documented for a bass population in a North Carolina stream but is infrequent in other studied populations. If you see two bass on a nest, you can bet one is a female (a male bass would chase another male from its nest), but most likely the female is yet to spawn.

Bass eggs hatch in three to four days at 64 to 68 degrees, and in slightly less time at warmer temperatures. The yolk sac larvae remain on the nest for another three to four days before becoming free swimming.

Thus, you can expect a spawning bass to occupy a nest for at least six days. However, a bass will abandon a nest if egg predators are successful at removing a large number of the eggs.

Bass have been reported to abandon nests after a severe cold snap. I think this is questionable. It might happen, but bass invest a lot of energy in their reproductive effort and ecological theory would predict that cool but not injurious water temperatures would not trigger them to abandon their investment.

Largemouth bass spawn a relatively large number of eggs. The number of eggs carried by a female bass is call “fecundity.” Fecundity generally increases with size of the bass, so biologists measure “relative fecundity,” which is the number of eggs per pound of female.

Relative fecundity estimates range from 2,000 to 15,000 eggs per pound of female, but 6,000 to 8,000 eggs per pound is a good average range.

The ovary weight of a mature female bass immediately before spawning averages about 5.5 percent of body weight, 7 percent max. Despite the excited claims of many anglers about “what she would have weighed if I caught her before she spawned,” bass only lose about 5 percent of the weight when they spawn.

Many anglers claim that the biggest bass spawn first. Although one biological study refutes this, several others support anglers’ claims.

And a thought for you to ponder while fishing during the spawn: Nest predators can quickly flock to a nest when the guarding male is gone — and the longer you handle a bass, the slower it is to return to the nest

So handle spawning bass carefully and release them quickly. The successful spawn of a few large pairs of bass can provide more fry than a quarter-acre hatchery pond can handle.