The Spawning Urge
Is it based on temperature? Whereas many
anglers often ask each other if they think the bass are ready to
spawn on this or that full moon, most biologists do not look up
at the night sky, but rather look at the seasonal thermometer.
What Scientists Say
I do think the moon phase means something, but
it's just not something bass biologists are prone to experiment
with or study. True, the moon the sun, other planets and their
relationship to our spinning earth can and do exert forces that
influence life here, but bass biologists are often in
laboratories, and even in the field, they typically focus on more
down-to-earth causes and results, such as trying to determine
what influence the spring weather, water temperatures and water
levels will have on the bass spawning in this lake or that
So yes, I do think
"more" bed fish will be found on the moons after
a certain water temperature is achieved, but like I said,
scientists do not care about the moon, they care about other more
measurable factors to which they can attribute the year's
spawning success or failure.
Are you having your photoperiod yet?
There are also occasional discussions of photoperiod (length of
daylight and angle of sun in the sky) among anglers, as if there
is a magic day on the calendar when bass wake up that morning and
begin spewing milt and eggs. True, I have occasionally heard of
the photoperiod cited as a factor in many fish movements
(spawning, mustering, migration) for a number of differnet
species, however, it was not in my notes of the studies that I
came across when preparing this article for black and brown bass
spawning. However, since seasons, temperatures and weather are
all results of earth's orbit, I do believe photoperiod is
probably mixed in there somewhere. It's kinda like when my wife
asks me why I love her: "No big reason, honey, but many
countless small ones that all add up!". That seems to
But...most studies see spawning
primarily as a function of water temperature - the stability
and duration (taken together, the persistence) of the
average daily water temperature over time, the velocity of
the season's overall warming water trend over time, the average delta
of daily low and high temperature extremes, the frequency
of sudden changes in water temperature. All these temperature
factors have measurable effects on spawning success.
And while temperature seems to be the biological controller
here, studies also indicate that oxygen, PH, salinity and other
factors can measurably affect spawning. This article will tell
you a bit about all these factors. Are you interested? Please
Green versus brown. In the field,
you may find smallmouth and largemouth spawning in different
places and at different times. In general, smallmouth nest
building may start a few degrees colder on average, and may be in
slightly rockier areas on average than largemouth. These factors
are different - but not different enough - to warrant much
special mention in this article. Most studies have not indicated
a major difference between largemouth and smallmouth spawning in
terms of temperature, nest substrate, dissolved oxygen, PH, etc.
North versus South. Studies do
not show dramatic differences based on water temperature, areas
used, oxygen, PH, etc. In general, bass in the deep southern
ranges may get their urges a few degrees warmer than their far
Nest Building. Studies show that
the urge to build nests occurs in males at lower temperatures
than when females are ready to lay eggs. Most studies indicate
bachelor males will begin to build nests in water temperatures as
low as 54° - 57° and surely by 60°. There is a "magic
number" above 60° when females begin to reveal their
interest in the boys and the nests that they've built!
Males dig nests by dishing out the softer top layers of
sediment with their tails to ideally get down to harder
ground. After sweeping it out vigorously, the bottom of the nest
may be scoured down to clean chunk rock, gravel, roots, etc.
Where the bottom is sand or dirt, the sweeping will tend to
remove all the finer granules, leaving behind a slightly raised
floor of pebbles, twigs, shells, rubble, etc.
The nest-building urge in males is thigmotrophic. Given
a choice, they will build nests that are protected on one or more
sides by "things" - logs, rocks, pilings, stumps,
ledges, etc. This may provide partial protection from predators
and egg robbers, or a break from wind or water current.
can spawn in main lakes and rivers or ascend tributaries to
spawn. They typically migrate up the tributaries on periods of
high water levels. This makes navigation easier, and allows bass
to claim the highly-preferred gravel, stone and hard sand bottoms
that have been flushed clean of silt by the high water's passage.
Both smallmouth and largemouth bass nests are commonly in
shallows, backwaters or tributaries of either streams or lakes.
Nests are commonly close to shore in protected bays and creeks,
or on the sides and tops of mid-water shoals. Nests are usually
in areas of quiet water. Nests are usually in areas of very slow
current. Nests are usually on the leeward shore or sheltered from
Male bass instinctively prefer not to build nests
wherever turbidity may be a concern. Not only may a soft bottom
composition (mud, silt, clay) be avoided if possible, but areas
that are prone to have wind disturbance or water flow are also
avoided, since both wind and water action can induce fluctuating
temperatures, raise turbidity and deposit silt that can suffocate
Bass may spawn on depth breaks (edges of pools, cliffs,
ledges, etc.), provided these areas should have minimal wind and
current exposure, and at a depth sufficient so that wave action
will not destroy the nest.
Water levels. Some studies
indicate that a high water period may trigger bass migrations
towards the spawning grounds. Once they've arrived on the scene,
then relatively stable water levels are preferred before bass dig
nests, drop eggs and hatch fry. Dropping water levels can result
in poor spawns for various reasons including desertion by males,
wind-driven wave destruction, and nests ending up high and dry.
Rising water levels (barring floods) usually do not have major
negative consequences, although quickly rising waters may usher
in cold or turbid water that stalls egg or fry development.
Depth. Most studies indicate
highest spawning success off nests covered in from 1 to 3 feet of
water, but deeper nests may occur in very clear warm water.
Although uncommon, studies done on clear, deep-sided impoundments
report males still maintaining nests from 20 to 27 feet deep that
were covered with slowly but steadily rising warm water. I do
believe there is a concept of bass becoming "committed"
to a nest that is covered by rising water, and so long as the
bass feel the nest has a chance to draw females or hatch eggs,
they'll stick with it.
More depth. Although shallow
nests are "scientifically" more successful, nests down
to 6 or more feet are not that uncommon, particularly for
smallmouth in deep, clear impoundments. Rationales for deeper
nests include that:
Mating. The actual laying and
fertilizing of eggs can range higher or lower, but it usually
takes place when the water temperature is stabilized above 60°
and rising slowly between 60° and 70°. Dropping water
temperature will tend to keep females off the nests, and rapidly
rising temperatures have been reported to delay spawning until
the warming trend slows down and stabilizes too.
1) Deep clear lakes simply have very little littoral benthos
(shoreline bottom) in the 1-3 foot range. Often just a small rim
that smallmouth in such lakes do not normally live in anyway,
except to visit for brief feeding periods at those magic moments
of half-light at dawn and dusk. If there is any livable littoral
benthos...other species will usually dominate it if they exist -
largemouth, panfish, pike, pickerels, muskies, etc.) Smallmouth
cannot compete against largemouth or even panfish for food in
such areas, and they'll be heavily predated by the water wolves.
2) Deep clear lakes characteristically have more wind surface
(which causes stronger waves and more forceful underwater
turbulence) that would upset shallower nests. So, the added depth
3) Deep clear lakes often have rock sides and bottoms which
amplify any heat gain/loss as sun (or lack of it) is transmitted
easily into the nearby water. Hence, deeper nests are buffered
better from some of this daily temperature fluctuations in such
areas. So, the added depth provides stability, but also causes
the incubation and hatching process to take longer than in
Sharp drops in water temperature, followed by increases,
will cause repeated waves of mating, but that doesn't
necessarily mean multiple crops of viable eggs or fry. Sharp
drops in temperature will also kill eggs, and studies report
increased frequency of males deserting eggs in water dropping
I had no notes of studies detailing how long females lay, but
I have seen plenty of them doing it in the wild. The act itself
is beautiful and fleeting, often under ideal environmental
conditions...water like glass, pleasant day, flowers blooming on
shore and all that. Maybe I'm romanticizing here, but both bass
seem to appear to have heightened body colors...Dare I say an
aura? She lays on her side and shudders with the male also, then
moves off the nest. It's not long! She'll often do some
inspecting and tidying up the nest when she comes onto it and she
often acts more aggressive to intrusions by nearby egg-robbers
like sunfish than will the male at that moment. The male seems
more intent on keeping her there, and will often circle her and
positon himself to cut her off from leaving him. She'll do a lot
of enticing lingering near the nest both before and after,
usually at the nearest weedline or slope, sometimes slipping back
up for another quickie or two or three. She'll usually be present
in the area for days, especially so if there are several males
with nests nearby. I might add she'll often "smoke" a
smoke-colored finesse bait (tube, etc.) after the act when she
returns to the weedline, and she'll often snap it right off the
nest before the male if you interrupt them during the act.
Incubation. Fresh eggs need time
to "harden" and become acclimatized after
fertilization. Studies show eggs will become temperature tolerant
after 12-15 hours. Then the males will become fathers and
caretakers of the egg clutches. Males defend their clutch from
predators and fan eggs with their tails to keep a small flow of
aerated water circulation and to keep sediment from settling and
suffocating the eggs. Clutches can also get infected by fungus
that destroys them, and fanning also prevents fungus from getting
into the eggs.
Once acclimatized to moderate temperature fluctuations,
desertion of the male is the factor most harmful to eggs.
Hatching. Studies usually
indicate optimum incubation and hatching temperatures to be from
66° to 72°. More eggs will hatch, and they will incubate
quicker in this temperature range. For instance, almost all eggs
will hatch in 3 to 4 days in this temperature range. That seems
to be the ideal. Far fewer eggs will hatch and will take much
longer to do so at lower temperatures.
Dissolved Oxygen. DO must exist
in all life-giving waters. Normally, there is a saturation point
- how much oxygen can remain dissolved - which rises or falls
based on water temperature, water/air pressure, altitude, depth,
PH and other factors.
Some lab studies have pumped up DO levels far above what's
reasonably expected in nature. These lab results have not seemed
very stressful to adult bass, although eggs and fry clearly
thrive best when oxygen stays near nature's normal level - the
"saturation point". In fact, normal, healthy
levels of DO can reduce the bad effect of other adverse
conditions. For example, if water temperatures rise rapidly and
get too hot, it is not as harmful if DO also climbs higher. The
difficulties arise when there's not enough oxygen. As other
survival factors worsen (too low/high temperature, PH, etc.), DO
becomes critical. Low DO will dramatically worsen the effects of
other bad conditions. There is also a problem anytime when DO is
reduced suddenly. For instance, there is a marked difference
(called the "diurnal DO flux") between oxygen levels
from day to night. If this daily change is severe, it can hamper
the ability of fry to hatch or grow.
In summary then, studies show bass (adults, fry, eggs) better
able to handle other stressful factors when DO remains high or
increases. A higher percentage of eggs will hatch and fry will
grow quicker in optimum, well-oxygenated water. Keep in mind that
well-oxygenated water usually occurs as a result of when
all other conditions (temperature, depth, etc.) are also optimum
for egg incubation and fry development. On the other hand, when
DO is unfavorable, eggs will take much longer time to incubate,
many eggs will not hatch, and fry will develop more slowly or not
at all. This problem is compounded in that low levels of DO are
usually associated with other unfavorable factors (too low/high
temperature, PH, etc.).
PH. Yes, some of us may have
learned about PH back in school and biologists are always talking
about it as one of the factors for life. If PH is too high
(alkaline) or too low (acidic), an environment cannot support
life easily if at all.
As we mentioned about oxygen above, there is a normal range
that can be tolerated by adults, eggs and fry. PH that is too low
or too high can be avoided by non-spawning adults who will move
to better conditions. But spawning adults, eggs and fry will be
stressed by PH above or below the normal range. As we also
mentioned above, there can be a diurnal flux in PH levels from
day to night. In areas where vegetation becomes far too abundant,
the PH can become very high in daytime as plant photosynthesis
peaks. The dramatic daily change, plus the daily peak in PH can
both badly affect the urge to spawn, and affect the survival of
bass eggs and fry.
Salinity. Although adult bass may
live in brackish water environments, studies show it is not
always the best environment for adult bass to prosper. As for the
more vulnerable bass eggs and fry, studies indicate that even low
levels of salinity (far below an adult's tolerance) will greatly
impair the survival of bass eggs and fry. Therefore, it is
presumed that adult bass in brackish water will seek out fresher
tributaries and headwaters for spawning purposes.
Turbidity. Clear water is
preferable for spawning. Studies have shown that there is limited
survival and success in moderately turbid water, and eggs may not
hatch in highly turbid waters.
Hatchlings. Fry are usually
better able to survive temperature changes that would destroy
eggs. Fry become independent from their father and optimal growth
metabolism for fry is achieved during early summer at water
temperatures between 78° - 85°.
Predation. The above are just a
few of the more commonly-recognized factors that have measurable
effects on bass spawning. Many studies also show that predation
on bass eggs and fry can be critical to the year's spawning
Food availability. As a final
factor, studies also show that the timing and availability of a
food supply is also critical to fry.
Preferences. This article, and
the studies it is based on, deal with preferences and optimal
factors. Keep in mind that preferences may not necessarily be
limiting factors. For example, most studies indicate that bass prefer
to spawn and live in clear water, however, studies also show that
although turbidity is not preferred, it is not necessarily a
limiting factor in bodies of water where it is the only option.
That's what's so great about bass! Between largemouths and
smallmouths, you can usually find them everywhere!