Science Spotlight

WARC diver Shelby Kawana assesses habitat at one of the CDFW red abalone stocking sites located off the coast of southern California.


WARC diver Armand Barilotti assesses habitat at one of the CDFW red abalone stocking sites located off the coast of southern California.


Octopus are a top abalone predator and therefor pose a threat to newly stocked juvenile red abalone populations. Researchers catch and relocate octopus when they are found hiding in crevasses near stocking sites.


A rediscovered stocked red abalone was found clinging to the underside of a rock during a one year post stocking survey.

Harvesting abalone for dinner used to be as fundamental to a Southern California lifestyle as fish tacos and flip-flops. But by 1998, a combination of overfishing and disease led to the closure of all abalone fishery south of San Francisco. By 2001, the white abalone was listed as an endangered species because populations continued to decline despite protection from fishing pressure. Population numbers are so low today that the only option for recovery is believed to be through a robust captive breeding and stocking program.

Scientists from the California Department of Fish and Wildlife (CDFW) White Abalone Recovery Project and their partners in the White Abalone Recovery Consortium (WARC) are working to bring back the iconic white abalone from the brink of extinction. Since 2016, CDFW and partners have been working to actively restore abalone populations through stocking of young captive-reared abalone. Successful stocking is the critical next step to reestablishing self-sustaining wild populations of this culturally and ecologically important mollusk. The early stocking studies have aimed to perfect the methods that will be used to restore wild white abalone populations in the future by using red abalone as a test case. Red abalone, a sister species of the white abalone, lives in the same deep kelp forest habitats, and their populations in Southern California have also been very slow to recover.

Every few months, scientific divers on board the CDFW research vessel Garibaldi wrestle into thick neoprene wetsuits and load heavy steel tanks onto their backs in order to check on the stocked abalone. As the divers descend deeper into the kelp forest, they enter the world of the white abalone. Sunlight streams through the towering giant kelp, briefly illuminating the shiny sides of the small fish taking cover in the kelp blades. Lobsters and octopuses are tucked into the crevices of rocks, and abalone and urchins shelter in the shadows. Many of those abalone are adorned with small brightly-colored numbered tags that identify them as the new additions to the neighborhood. After a few months in the wild, the stocked abalone can show an extensive amount of growth which speaks to the quality and abundance of resources in their new habitat.

Since restoration stocking began in 2016, the partnership has stocked close to 10,000 red abalone off the coast of southern California. These studies are helping scientists understand how stocked abalone interact with their new environment in the wild. Researchers are increasing the effectiveness of future stocking work by teasing out the risk factors that abalone face in their new environment. For multiple years after releasing the abalone, divers track the number and identity of each abalone, and assess the ecosystem health and predator abundances at each site. The divers also collect any abalone shells encountered to determine the effects of different predators at each site through time.

Octopuses, lobsters, sea stars and fish are all major predators of the young abalone, and care is taken to introduce the abalone during times of the year when the predators will be least abundant. All of the data from these early studies are aimed at lessening the risks that stocked abalone face, and to improve long-term growth and survival.

The WARC understands that abalone are at the heart of coastal California’s identity and culture. The return of red and white abalone to the wild marks the beginning of a new chapter in the love story between California and this amazing mollusk. This is true for the ecosystems that rely on them as well as for the humans that cherish them. Please stay tuned for updates on the lessons learned from these studies, and plans for upcoming white abalone stocking work!

For more information, please visit the following pages:

• UC Davis Bodega Marine Laboratory’s White Abalone Captive Breeding Program
• Journal of Shellfish Research, Vol. 35, No. 3: “Implementing a Restoration Program for the Endangered White Abalone (Haliotis Sorenseni) in California”

CDFW Photos. Top Photo: Newly tagged red abalone that are ready to be released into the ocean during a WARC stocking study in 2016.

Working late, Mojave River hatchery staff apply FDA-certified epoxy coating to hatchery rearing ponds.


CDFW fish transportation truck at Fillmore Hatchery


Acting Mojave River Hatchery Manager Forest Williams at work


A hatchery crew releases trout into the Feather River


A fishy view of trout planting on the Feather River

The beginning of trout fishing season in Southern California is just around the corner, and CDFW biologists and hatchery staff are striving to maximize hatchery trout availability for the many anglers who will cast lines in coming weeks. Trout angling in lower-elevation waters of Southern California generally begins in November and continues through April, to correspond with colder water temperatures that can sustain stocked trout.

Precise temperatures are just one of the criteria that must be met before trout stocking begins. Currently, these conditions are approaching optimal levels, but CDFW is running about two weeks behind schedule due to unforeseen circumstances at Mojave River and Fillmore trout hatcheries, two of CDFW’s southernmost facilities.

The Mojave River Hatchery, built in 1947, raises and stocks a ten-year average of 340,000 pounds of catchable trout per year. Beginning in June of this year, extensive maintenance and facility upgrades necessitated turning off the water for a six-month period. While the completed upgrades will ultimately result in better and more efficient trout production for Southern California, the project ran about two months behind schedule. Water is scheduled to flow again at Mojave River Hatchery in late November and the hatchery will be populated with fingerling trout for fast growth. Mojave’s year-round water temperatures yield fast trout growth resulting in maximized yield in minimal time.

While the Mojave River Hatchery was closed, Fillmore Hatchery, built in 1941 on the Santa Clara River, experienced a significant loss of trout inventory intended for Southern California angling due to gas bubble disease. Gas bubble disease is a result of supersaturated gasses (oxygen, nitrogen and carbon dioxide) present in well water pumped from a deep aquifer. While Fillmore Hatchery is equipped to aerate this water and make it suitable for trout, an unknown variable (possibly a drought-depleted and then recharged aquifer) overwhelmed that ability. In an average year, Fillmore Hatchery produces about 400,000 trout for lakes and streams in Southern California. To reduce fish losses from gas bubble disease in the last several weeks, catchable fish were stocked from Fillmore to appropriate waters, and some fish were transferred to other hatcheries. Ultimately, the gas bubble disease at Fillmore resulted in a loss of about 50 percent of inventory. While emergency measures taken by Fillmore staff and

CDFW fish pathologists resulted in better conditions and lower gas super-saturation, the hatchery must be depopulated so that the issue can be addressed entirely. As soon as all trout are removed, hatchery staff and scientists will increase the gas diffusion capability of aeration towers at Fillmore, in order to handle supersaturated well water for the short and long term.

The status of these two hatcheries presented a substantial problem for trout stocking in Southern California that was solved in part by hatcheries in Central and Northern California. These hatcheries have sufficient catchable size trout to supply Southern California’s approved waters immediately and in coming weeks. Thanks to strategic planning and trout production at a statewide level, Northern and Central California can supply fish to Southern California without impacting originally scheduled trout releases in their respective areas.

Trout stocking for Southern California waters will begin this week and hatchery trucks are on the move. Hatchery staff will work quickly to distribute trout to as many approved waters as possible. Trout stocking to Southern California will initially be lighter than usual, but will likely pick back up in 2018. As Mojave River Hatchery comes back online, fish transferred to that facility will be fed and reared to maximize daily growth. We anticipate another large batch of catchable trout available for Southern California toward early spring 2018.

Hatchery staff will be doing everything possible, statewide, to maximize trout production and releases to approved waters in the coming months. Staff work diligently for the angling public and appreciate their continued support.

The statewide planting schedule is updated in real time online.

CDFW photos. Top: Steelhead trout at Mokelumne River Hatchery