July 10, 2014
Bass Facts & Figures -- Anglers have long believed that lunar phases affect fishing results, but there has been little catch data to test that assumption. Data presented by Lake Fork biologist Kevin Story at the Texas Chapter, American Fisheries Society, Bass Management Symposium showed graphically that in March 2003 and March 2004, lunker bass catch rates at Fork were apparently linked to moon phase.
March is Lake Fork's most productive month for bass over 7 pounds. Catches go up when bass are in or near spawning areas, and large bass tend to spawn earlier than smaller adults. Large bass, presumably on or near spawning areas, were caught most often on the full moon. Secondary peaks occured around new moons if water temperature was 61F to 63F. The lunar-tied cycle of bass catches then fades until the spawn is over.
Biologists postulate that moonlight illuminates shallow nests and allows bass to more easily lay eggs and later to guard the nest against raiders. Thus, spawning on the full moon with a clear sky may aid fry survival. Once the temperature has exceeded about 65F at nest depth, the light of the full moon doesn't appear to be as important, since subsequent spawns were scattered around the intervening new moons (dark nights) and next full moon.
Severe cold fronts can change this pattern by dropping the water temperature below spawning minimums (about 60F). If the first wave of bass fails to spawn, they may start over on the next full or new moon. If eggs were killed by weather, females may not have enough eggs remaining to support a second attempt, although multiple spawning is possible when an ample food supply allows additional eggs to develop. Unless they're already physically spent, male bass may nest again but the timing of later spawns is more variable.
There were also catch peaks near the two half-moons. These peaks don't match any theories of bass spawning. But they match postulates of some lunar theorists who report that catches of lunker bass increase on these specific half-moon days.