Wednesday August 20, 2025
Seafood Source —
Kelp aquaculture operations are rapidly expanding in Alaska and coming into increasingly greater contact with wild marine species.
In an attempt to limit some of the interactions between Alaska’s aquaculture operations and wild species, researchers have outlined strategies to prevent Pacific herring from spawning and laying eggs on kelp farmed at aquaculture farms along the state’s coast.
The study, “Strategies to deter Pacific Herring from aquatic farm infrastructure,” was conducted earlier this year in partnership with NOAA to determine methods that help ensure the aquaculture subsector can expand harmoniously in Alaska alongside the healthy growth of wild species.
“Herring spawn is an ecologically, economically, and culturally important resource in Alaska. As kelp aquaculture is poised to expand in the region, developing strategies so kelp farming and spawning herring can coexist is critical for the sustainable growth of both. In this study, we explored safe and effective deterrence methods that keep herring off of farms and don’t harm herring or harass marine mammals,” Jordan Hollarsmith, a mariculture research lead at NOAA’s Alaska Fisheries Science Center and an author on the study, said.
In the fall months, Alaskan kelp farmers plant kelp seeds on long lines, which are then suspended about 10 feet below the water’s surface. By late spring, the kelp is ready to be harvested, but the harvest season happens to coincide with the spawning season of Pacific herring.
Pacific herring deposit eggs on intertidal and subtidal vegetation, such as kelp, and Alaska regulations prevent kelp farmers from harvesting their kelp if herring have spawned on the farm.
In the spring of 2020, a herring spawning event cost an Alaskan kelp-farming operation USD 300,000 (EUR 260,000) in losses, according to NOAA.
“The easiest solution [for kelp farms] is avoidance, achieved by siting outside of known spawning areas, including areas that were historical spawning grounds, and harvesting before spawning season. The Alaska Department of Fish and Game provides information on current and historic herring spawning locations on its website,” Hollarsmith said. “However, avoidance can be difficult given the variable nature of herring spawn sites and timing between years.”
To ensure farmers do not sustain such heavy losses and wild populations remain healthy, the study tested four different deterrent methods to prevent herring from spawning on kelp farms: underwater LED lights, an aeration system using bubble curtains, banana pingers, and commercial fishing flashers – both moving and stationary.
Among the tested methods, researchers found that only the aeration system using bubble curtains elicited a clear behavioral response from the herring.
“Our results strongly suggest that bubbles are the only effective deterrence method of those we tested. Questions remain about the most efficient and effective way to set up a bubble net system, including optimum duration and spatial coverage of bubbles,” Hollarsmith said. “Deterrent methods were chosen based on reviews of available literature, the ease of access to materials, and to test different biological mechanisms. In addition, we purposefully selected deterrence mechanisms that would not inadvertently harm or harass protected species.”
Although aeration seemed to create the only clear behavioral response in herring, the study was completed two months after the spawning season ended in a sheltered environment during daylight hours. As a result, spawning herring may respond differently to the aeration and other deterrent methods during spawning season, nighttime, or even in a high flow area where the bubbles could more rapidly dissipate, the study cautioned.
Practical implementation of such a technology at farms also poses significant challenges, so the researchers who participated in the study are waiting on responses from stakeholders to determine whether there is interest in new research.
“We are getting feedback from the aquaculture industry and regulators to gauge interest in next steps. The challenge of testing during the spawning season is less regulatory and more logistical, as the herring can move unpredictably between spawning areas year to year. We would need to carefully design an experiment that could account for that natural movement,” Hollarsmith said.
Besides the Alaska Fisheries Science Center, researchers who contributed to the study also came from NOAA’s Alaska Regional Office, the National Centers for Coastal Ocean Science, and Florida International University.