Jim,
Indeed there are a number of variables that can come into play when trying to determine when certain species of fish spawn. Of course, water temperature is one of the more important factors, but one must remember that “consistent” water temperatures is a key element! If your daytime weather is warm, but night-time temps dip low, the “consistent” water temperature may not be high enough to induce spawning. I’ve seen temp swings of several degrees in the shallow waters that bluegill typically prefer to spawn in with the passage of strong cold fronts and/or cold nights.
Now, other factors that come into play when trying to determine when fish spawn include latitude, photoperiod, and water clarity. Many folks think moon phase plays in this, other folks don’t think that theory holds much water. Personally, I think moon phase affects when the majority of the individuals of several Centrarchid species when spawning. For example, here on Kentucky Lake, my 30-some years of experience with white crappie have me believing the majority of the fish spawn the week of the nearest full moon when “consistent” water temps are at or first go above 56 degrees.
“How does latitude play in fish spawning?” some may ask. Easy enough! Water temperatures reach preferred ranges earlier in more southern climes. Notice I said “ranges”. These ranges appear to vary with latitude, perhaps explaining the discrepancies between researchers on spawning temps noted in an earlier post. Also, in the more northern latitudes, many waterbodies do not EVER reach temperatures that may be found in southern zones. This is where photoperiod may come into play a bit more. Even though water temps may not be at the optimum for the species, because of its actual location in more northern waters, the fish go on and spawn at less than optimum temps because that is the way Mother Nature adapted the fish to ensure their reproductive success along the more extreme northen edges of their native ranges.
Next, allow me to address water clarity for a brief moment. If the water in your local lake is clearer than “normal” during spawning season, you can bet fish such as crappies, bass, bluegills, and redears will spawn in deeper waters. Of course, water clarity is a factor of rainfall, runoff, and wind-induced stirring of sediments. (I’m discounting man mucking in the water with dredging, etc!)
Some additional observations from 30 years of being a “Fish-Head” include the following: Usually, the first Centrarchids to spawn are crappies, followed by smallmouth bass, spotted bass, largemouth bass, redear (very slightly behind largemouth bass), and bluegill. Of these, bluegill will get off several (multiple) spawns, especially in more southern waters, throughout the summer. Typically, the larger individuals of each species spawn first, selecting the best spawning sites. Also, typically with Centrarchids, the males come into the spawning areas first to prepare the nests. Now, crappie are the poorest nest builders, usually making only minimal efforts at fanning beds, if at all. But they don’t need to as their eggs are adhesive, sticking to the roots of flooded bushes (buttonbush here on Kentucky Lake) and other aquatic vegetation. Bass, redear, and bluegill do much better jobs of nest construction, evidenced by the round, saucer depressions everyone is probably familiar with. Finally, in my experience, redears usually spawn deeper than bluegill. So, back off the banks a little more for them than you do for bluegill.
That is probably way more than anyone wanted to know of my opinions on this subject!