Hitchhikers: Free Rides on Gray Whales

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Reading and Writing Connections


Look at those barnacles!
Keith Jones

Gray whales are more heavily infested with a greater variety of parasites and hitchhikers than any other cetacean. Imagine carrying a load of hitchhikers on your back that can weigh several hundred pounds! Gray whales do this all their lives. Who's riding, and why?

Big Batches of Barnacles
Those patchy white spots you see on gray whales are barnacles. Grays carry heavy loads of these freeloaders. The barnacles are just along for the ride. They don't harm the whales or feed on the whales, like true parasites do. Barnacles don't serve any obvious advantage to the whales, but they give helpful lice a place to hang onto the whale without getting washed away by water. Barnacles find the slow-swimming gray whale a good ride through nutrient-rich ocean waters.

Photo Keith Jones

As larvae, the whale barnacles swim freely in the ocean. But they time their reproduction so the larvae are swimming in the water of the nursery lagoons when the baby whales are born. Then the larvae jump aboard the whales arriving in the lagoons--as well as the newborn calves—to start their lives as hitchhikers. The most common barnacles on gray whales are host-specific, which means they occur on no other whales. One type of barnacle, Cryptolepas rhachianecti, attaches only to gray whales. Once this type of small crustacean has settled on "its own" gray, the barnacle spends its whole life hanging onto that whale.

Life is good if you're a barnacle. Snug inside their hard limestone shells, the barnacles stick out feather feet to comb the sea and capture plankton and other food for themselves as the whales swim slowly along. As the young whales grow, the barnacle clusters grow too. Gradually the barnacles form large, solid white colonies. The colonies appear as whitish patches, especially on the whale's head, flippers, back and tail flukes.

Whale biologists look at the pattern of barnacle clusters in order to tell individual grays apart. This is possible because no two barnacle clusters, like no two human's fingerprints, are alike! (See more about barnacles here.)

A Look at Lice
Whale lice are another type of whale hitchhiker. Unlike barnacles, lice are true parasites. They feed on gray whale skin and damaged tissue. The lice gather around open wounds or scars. See Photo.

Whale lice may spread from mother whales to their calves during birth, nursing, or other bodily contact. Up to 1000 of these parasites have been found on a single gray whale.

Luckily for the lice-infested whales, other creatures go after the lice. Topsmelt are silvery fish that school in the breeding lagoons. Normally they feed on marine plants, tiny shrimps and other miniscule creatures of the lagoons. But when the whales are around, the topsmelt dine on the whales. How? Schools of these small fish pick at the barnacles and whale lice crusting up a whale's skin. Topsmelt groom whales in the calving lagoons. By ridding the whales of some of their parasites and old, flaky skin, topsmelt may be helping to cut down the resistance, or drag, that grays create as their huge bodies move through the water. The whales have a smoother ride and the topsmelt groomers get protein-rich food.

Try This! Journaling Questions and Activity
  • Why do you think gray whales have more hitchhikers than any other whales? (Look for clues in the text above.)
  • How would you describe the connection between the whale, the whale lice and the barnacles?
  • If you were a gray whale biologist trying to figure out which whale is which,you'd have to be able to spot differences in the unique clusters of barnacles on each whale. Give it a try! Dr. William Megill gives you step-by-step help, with lots of photos for practice in the lesson: Who is That Whale? Gray Whale Photo ID Matching.