Tag Archives: Sea Lion

Bait Ball: Have You Ever Heard of It?

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.

Bait Ball marlin

mackerelEach 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.

Bait Ball sea lion feeding

Pacific Sardine:

  • 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







Video Content from Gretchen Beehler and Anthony Julien

Thermoregulation Makes Me Hot – Sea Lions

I want those of you who have ever been cold on a snorkel to raise your hands in the air…No really, raise your hands in air—that’s the best way to stay warm in the water. Don’t believe me? Just ask the sea lions. Sea lions are marine mammals, and therefore endothermic. This means that they control their own internal body heat separate from their ambient environment. Many marine mammals, including sea lions, keep their core around 100 ˚ F. This can pose some interesting dilemmas for marine mammals that live in waters MUCH colder than their internal temperature. There are many adaptations that sea lions have to maintain their core temperature in the water, both physiologically and behaviorally—this process is called thermoregulation.


One behavioral modification that California sea lions enact to stay warm in the water is something called “jughandling”. Have you ever seen a sea lion waving at you from in the water? Maybe you have while on your boat ride to Catalina, or if you kayaked around Bird Rock. What appears to us as an overly-friendly sea lion saying “hello”, is actually a behavioral form of thermoregulation. Sea lion front flippers are not covered in fur, and therefore very susceptible to thermal conduction and convection, meaning they can transfer heat easily with the water and air. If a sea lion is cold in the water, all they have to do is raise a flipper to the sky and have the sun warm up their blood before it transfers back to their core. Vice versa, if a sea lion is too warm on the beach, they will take a dip into the water to cool off.
More than just behaviorally, many marine mammals thermoregulate physiologically as well. Fur is a frequent form of thermoregulation, because it can trap air against the skin keeping it warm. Blubber is an insulator utilized by large marine mammals such as whales, seals, and sea lions. Commonly (and wrongly) assumed to be a thick layer of fat, blubber is actually a complex matrix of collagen and adipose tissue that can both insulate an animal and keep it afloat.
So just like we may get cold in the ocean, marine mammals fall victim to the same tribulation. However, instead of warming up with a cup of hot chocolate or a steaming shower afterwards, they must rely on other adaptations to stay warm in the frigid ocean waters. So take a note out of the sea lion’s book, and next time you’re cold in the water, raise your hands up high and proud.

Author: Max Veenema


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