STRIPER BOILS - Background

Surface feeding activity occurs as 100-5000 striped bass roll and porpoise in unison. These "boils" can simmer or boil over as striped bass trap shad schools against the surface. Water spouts and crashing splashes mark the spot. Disturbance by fishing boats cause striped bass schools to sound and then reappear a few hundred yards away as feeding resumes in a different direction.
As shad grow in size and develop stronger swimming ability the surface action gets more intense as striped bass corral shad against the surface or trap them near shore. The tendency for shad to "ball up" in a tight school when predators approach allows striped bass to herd and trap shad schools. The trapped shad school is repeatedly probed by striped bass working together to eat, injure and kill as many shad as possible. Shad are often slashed by the jaws and stunned by the powerful caudal fin during such encounters. Striped bass capture most shad at the surface creating a highly visible disturbance with water spouts and a boat wake-like wave as stripers line up shoulder to shoulder to feed. When the attack commences the surface activity is intense and visible for many hundred meters as water is thrown high in the air. Surface feeding boils last from a few seconds to as long as three hours. Duration is probably determined by shad abundance. Many shad allow a longer feeding period while few shad may be consumed or lost from sight in a few seconds.
Surface boils only occur when shad are present. In years when shad numbers are limited and eventually eliminated from the open water, no striper boils are seen. When shad are abundant boils are common and predictable. Striped bass often feed at the same time in the same location on a daily basis. Striped bass habitually return to a successful feeding spot every day until the forage is consumed or escapes.
Both shad and stripers are tightly bunched as they begin the daily feeding ritual. Normally, about one-half hour after first light shad form schools after spending the night randomly distributed in the water column. This shad schooling behavior attracts striped bass and feeding begins. As shad schools are repeatedly attacked, large schools fragment into smaller groups. Fragmentation of shad schools also causes striped bass schools to break up as groups of striped bass chase after small groups of shad. An original feeding event, one-acre in size, can dissolve into scattered striped bass feeding in many different directions over a square mile. When feeding ceases both shad and striped bass regroup.
If striped bass are satiated they may not eat for the rest of the day. More likely they will randomly feed again near mid-day and then again in the evening just before dark. After dark, shad schools disperse and boils are not likely. Striped bass are effective nocturnal feeders and feed on shad subsurface at night.
In times when forage is very abundant, boils may be rare or half-hearted because shad are easily obtained and schooling efforts are not required to obtain food. Perhaps surface feeding action is at its peak when shad are common but not abundant. Striped bass must now work hard to corner shad for effective feeding opportunities. As shad become scarce, surface feeding opportunities decrease.
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