Scientists release thousands of hatchery-raised halibut in Mission Bay, boosting population

The Hubbs-SeaWorld Research Institute is releasing up to 5,000 juvenile California halibut in Mission Bay this week to bolster their population.

On Tuesday morning, a small cohort of scientists carried thousands of fish via water coolers into the bay of Ski Beach, releasing them just beyond the shoreline where they will likely remain until they’re mature enough for deeper waters.

Not to be confused with the Pacific halibut, the California halibut is a flounder — a type of flatfish — that lives on the sea floor, camouflaged in the sand.

“They’re really bizarre,” said Mark Drawbridge, a senior researcher at the institute and the director of the Sustainable Seafood Program. “When they’re about three weeks old, they’re in the water column like a regular fish, and they have eyes on both sides of their head. Then they settle down, and whichever side they lay on, their eye migrates up over the bottom to the top, so two eyes are facing up.”

These particular groups of funky fish were bred and hatched at the Hubbs-SeaWorld headquarters at Perez Cove on Mission Bay. They are just over a year old, split into two size groups measuring 4 to 8 inches in length. Adult halibut have the potential to grow up to 5 feet, making them a popular catch among people who fish for sport and commercial purposes.

Although they are not considered an endangered or threatened species, halibut are important in the realm of aquaculture; keeping them robust and thriving is, according to researchers, a crucial component of sustaining the local fish economy.

“The population particularly in southern California are just a fraction of what they used to be,” said Drawbridge. According to their best estimates, the halibut is currently at 14% of historic population levels. “We’re trying to give mother nature a boost,” he said.

Back in 1983, the Ocean Resources Enhancement and Hatchery Program under the California Department of Fish and Wildlife selected the California halibut as a second priority species to support and research, with white sea bass being the first. The Hubbs-Seaworld institute, which has been conducting research on replenishing local white sea bass populations for decades, established a program in 2014 to apply their research methods to the halibut. They have been conducting controlled spawning and releasing since then.

“The goal is to see if we can grow these fish on land through their first months, when they’re most sensitive, to restore their wild population and eventually restore seafood production,” said Danielle Haulsee, a chief science officer at Hubbs-Seaworld.

Supported by private and recreational fishers from the community, the institute has been able to collect dozens of adult male and female halibut over the years to induce natural spawning in their research tanks.

“Under the right conditions, we get millions of very, very small eggs,” said Drawbridge. “We’ll set those up in our culture tank in a very controlled environment and monitor them through their stages.”

During their last halibut release in 2020, just 500 juvenile fish were introduced to Mission Bay. This year, they have upped the effort tenfold. The institute are technically authorized to release up to 20,000 fish, and Drawbridge suspects that they’ll continue working up to that number.

“We don’t want to just put the fish out here and call it good,” he said. “We want to understand how many are surviving, how they’re moving, and ultimately we want them to enter the fisheries to be caught.”

Each fish is tagged with a small coded wire in their cheek muscle so researchers are able to keep tabs on them. Though it may seem counter-intuitive to encourage capture while trying to bolster this fish’s population, Drawbridge emphasized the importance localizing aquaculture in a sustainable way.

“This is a conservation program,” he said. “People who like to eat seafood — and they should, because it’s good for you — might not realize over 85% of seafood in the United States is imported. Of that, over 50% is farmed. … So we’re trying to help provide locally produced and sourced product.”

On Wednesday morning, they will release 2,500 more fish at Ski Beach.