A bait ball is a spherical formation that a school of fish make when they are being threatened by larger predators, such as dolphins, sea lions, and bigger fish. This instinctual behavior is a defense mechanism so that fewer fish are exposed during this feeding frenzy. When a school of fish has no protection from rocks and crevices they must use their vast numbers to their advantage. Bait balls typically do not last longer than ten minutes due to the vast amount of energy it takes to make this tightly packed ball. It is typically a fishes last ditch defensive measure because it can draw the attention of other predators like birds and sharks.
Each fish coordinates with its neighbor through visual site and the use of their lateral line. The lateral line is an organ located along both sides of the fishes body. Noted by faint dots along their scale, this lateral line can sense subtle pressure changes in the water and help direct them instantaneously.
Here at Catalina Island you can see a bait ball almost everyday, in varying sizes and species. Here are the most common species of fish that make up bait balls around Catalina Island.
Pacific Sardine:
- 1`aqA
distinctive flashy quality - release air bubbles as they swim
- freckles on back
- greatest body width underneath pelvic fin
Northern Anchovy:
- appear glittery or sparkly
- random solitary fish open their mouths wide and flare their gill covers in order to feed
- dark on back with no markings
- jaw shifted farther back
- elongated body that is straighter and thinner than sardines
Jack Mackerel:
- often hover motionless as if they were frozen,
- can mix in with other species of fish
- lateral line bends down due to longer pectoral fin
- back is blue green or brassy brown
- symmetrical dorsal and anal fins
Sources:
https://www.nwf.org/Magazines/National-Wildlife/2017/Feb-March/Conservation/Forage-Fish
https://daily.jstor.org/how-do-fish-schools-work/
https://ocean.si.edu/ocean-life/fish/bait-ball
https://www.pierfishing.com/jack-mackerel/
Video Content from Gretchen Beehler and Anthony Julien
