Glacier BayNational Park & PreserveNational Park ServiceU.S. Department of the Interior

Pacific Halibut

Can you imagine coming to Alaska and catching a fish that is bigger than your Dad? This could happen to you if you were fishing for halibut in Glacier Bay National Park in Southeast Alaska. That Pacific halibut you just caught could be over 40 years old, weigh up to 400 pounds and be over six feet long.

Halibut

Since the halibut you caught was a big one, researchers could tell you that it was a female since females live longer and grow bigger than males. Few males exceed 80 pounds, are larger than four and a half feet long or live longer than 25 years.

Halibut

But not all halibut are monsters. Most halibut caught by sport fisherman using a fishing rod weigh between 10 -20 pounds. Commercial fishermen catch fish that average 20-30 pounds on long-lines that use a series of 100 or more hooks put down on the ocean floor to “soak” for about six hours.

Halibut

Of course this whale of a fish you just caught started out its life looking much different than your prize fish looks now. It started out as one of up to four million eggs that a female halibut deposited on the ocean floor.

Halibut

Within 6 months the egg was fertilized by a male halibut, and fifteen days later a halibut larva hatched from the egg. The newly hatched larva floated freely in the deep ocean currents. As it matured it moved higher in the water column where surface currents moved it to shallower coastal waters.

Halibut

Your fish started out swimming upright, just like any other fish. But when it was one inch long, it started going through amazing transformations that make becoming a teenager look easy. Its left eye migrated over its snout to the right side of its head and the pigmentation on the left side of its body faded.

Show film clip from underwater film of eye moving

Halibut

Glacier Bay National Park and Preserve

Virtual Visit: Crabs

Glacier Bay National Park and Preserve

DRAFT Virtual Visit: Halibut

Halibut

Can YOU find the Pacific Halibut hiding on the ocean floor?

By the time the halibut was six months old, it had the physical characteristics of an adult; with both eyes on the same side of its head, its belly white and its topside dark brown. It also settled to the ocean bottom of the ocean where it would hunt for its food.

Halibut

But then where did it go? Researchers in Glacier Bay National Park wanted to study the story behind these huge predators of the deep. They were faced with the question: “How do you go about studying a secretive animal living in an environment in which you cannot follow it?”

Halibut

Since animals that live deep under water can’t be studied like land based animals or marine mammals that frequently come to the surface, researchers had to use some novel research techniques. (To see how researchers study and track other animals click on animal photo)

To learn where halibut go, researchers used long-lines like those used by commercial fishermen to catch over 1500 halibut during a five year period. They weighed and measured them and surgically implanted sonic tags into the abdominal cavity of about 100 halibut.

Halibut

Glacier Bay National Park and Preserve

Virtual Visit: Crabs

Glacier Bay National Park and Preserve

DRAFT Virtual Visit: Halibut

Halibut

The sonic tags resemble radio tags used in animals like moose, wolves and bears. Instead of a radio signal, these tags emit a low-frequency sound that travels through water much better than radio signals. Each sonic tag emits a unique number of beeps, which identifies the individual halibut.

The sound from the tags could be received up to a mile away by a hydrophone attached to the front of the researcher’s boat. To find the halibut, the researchers moved their boat toward the direction where the sound was getting louder until they were right on top of the fish.

Halibut

Then they marked the position with a GPS and took other measurements including the depth of the water.

Halibut

When the researchers analyzed their data, they found many interesting new facts about halibut. Scientists used to think all halibut migrated to open water in the winter time to spawn. They also thought that halibut traveled randomly and did not have individual home ranges.

Halibut

By tracking halibut with sonar tags the researchers found that some of the large halibut left Glacier Bay in the winter and returned just like they predicted. But not all the halibut left. Perhaps that large halibut you caught laid its eggs here in the Bay, or maybe it didn’t spawn every year.

The researchers also found that many of the sonar tracked halibut, especially the large mature ones, are genuine “home bodies” who have home territories in Glacier Bay that are smaller than the researchers predicted. Many of the home ranges are less than half the size of a football field.

Halibut

Sometimes the halibut venture more than ten miles away from home, but then they return to their same home area. Some halibut were found by the researchers within a few hundred yards of their original capture location five years after they were first caught.

Halibut

The researchers also found that halibut can find their way back home from places they have never been to before. They learned this when one halibut returned to its home range only three days after the researchers released it in a lagoon about seven miles from where they caught it.

Halibut

Just like people, young fish don’t always act the same as their parents. Juvenile halibut preferred shallow water in areas of steep topography. Adults liked deep flatter areas. Juveniles had bigger home ranges, changed their home ranges more often, and moved around more than adults.

3-d representation of halibut habitat

Halibut

If you caught your big halibut in Glacier Bay when the researchers were doing this study, you could have participated in it. To find out what halibut eat and how they hunt researchers examined the contents of halibut stomachs that were caught by sport fishermen!

Halibut

Researchers learned that small halibut hunt differently and eat different food than adults. The small halibut eat things such as small crabs and shrimp that are found by active hunting. The larger halibut bury themselves in the mud and sit and wait for a fish to swim by and then they grab it.

Halibut

Glacier Bay is a good habitat for halibut and other marine life. Glaciers carved out deep marine basins and created shallow areas filled with rock and rubble. Melt water from today’s glaciers brings fine silt into the ocean that creates mud for large halibut and other bottom dwellers to bury themselves in.

Halibut

Glacier Bay’s cold, nutrient rich waters contain high concentrations of plankton, the small, but very important creatures that make up the center of the marine food web. These are the same creatures that your big halibut ate during the first few months of its life.

Halibut

As researchers learn more about halibut and the environment they live in, they begin to get insights into the complex and amazing world of marine animals. But each new discovery leads to more unanswered questions.

Halibut

Scientists of today and tomorrow will continue to come up with novel research techniques to find answers that will give us a better understanding of the underwater world in Glacier Bay and beyond.

Halibut