Managing Genetic Risk in Offshore Aquaculture

Aquaculture can sustainably produce seafood to complement wild-caught fisheries. However, like all food systems, aquaculture requires sound science to ensure farmed species don't harm wild species. Scientists at NOAA's Southwest Fisheries Science Center are working to understand the genetic risks in offshore aquaculture.

NOAA has identified 21,000 acres in federal waters of the Gulf of America and offshore Southern California as Aquaculture Opportunity Areas . To support this effort, experts developed three science advice publications outlining considerations for genetic risk for offshore aquaculture in these areas.

What is Genetic Risk?

In aquaculture, genetic risk is the potential harm from farmed species interbreeding with wild populations. For example; when farmed fish-the product of generations of domestication-interbreed with wild fish, the offspring tend to be less genetically diverse and evolutionarily fit. As those fish interbreed, the entire wild population can lose evolutionary successful traits and become more vulnerable to changing ocean conditions.

Genetic impacts from aquaculture can happen in several ways.

Escapes

This happens when species escape their containment systems and breed with wild individuals in the marine environment. Escapes can occur slowly (when a few fish wiggle through a hole in a net over time) or catastrophically (when an entire net collapses and releases the fish inside).

Spawning

Many farmed species, such as oysters and clams, are broadcast spawners. That means they release their eggs and sperm, or gametes, into the water. Since gametes are microscopic, they can flow through nets or cages and potentially interbreed with wild populations. This is also a risk for fish that reach sexual maturity before harvest.

Spores

This occurs when seaweeds farmed on longlines reach maturity before harvest and release spores, or when pieces of the seaweed break free into the marine environment. Spores are microscopic and can travel away from the farm site depending on ocean currents.

Fragmentation

During storms or periods of large waves, broken seaweed fragments can carry spore-releasing tissue even greater distances. Depending on the species, some dislodged fragments may be able to reattach and grow if they find a suitable location. These spores and fragments may settle and grow near or in natural seaweed beds.

Best Practices for Managing Genetic Risk

Understanding the genetic risks for individual species helps farmers make informed decisions. "To manage genetic risk, we want to understand how these risks are specific to each species," said Catherine Purcell, marine resources management specialist at NOAA Fisheries and lead author of these science advice publications. "This helps us develop best practices that both grow healthy seafood while protecting wild populations."

Seaweeds

This publication investigates 16 species of seaweeds and their potential to interbreed with wild populations . Spore dispersal is the primary genetic risk in seaweed farming, but some species can also grow from broken fragments.

For example, sea spaghetti, an adaptable red algae native to the U.S. Pacific Coast, propagates from fragments and grows quickly--making it useful for aquaculture. However, harvesting sea spaghetti can release spores and fragments. This creates moderate genetic risks, which can be reduced by sourcing local seeds and reducing breakage during harvest.

Fish

Most genetic risks from fish come from escapes, but mature fish can also release eggs and sperm into the water. Smaller, and genetically and/or geographically fragmented, wild fish populations are more vulnerable to genetic risk. That is because interbreeding can have a proportionally larger impact on their gene pool.

This publication describes 15 fish species and risks for farming them in Southern California or the Gulf . For example, cobia are fast growing, highly migratory fish native to the Gulf. Their large, stable population shows no genetic differentiation throughout the Gulf of America, which helps protect the wild cobia from genetic impacts of escaped farmed individuals.

Farmers can reduce the likelihood that aquaculture operations impact wild fish populations by:

• Opting for lower risk species
• Using storm-resilient gear
• Implementing sterilization techniques
• Harvesting fish prior to sexual maturity
• Sourcing farmed stock from local areas

Shellfish

When farmed shellfish spawn near wild populations, or when farmed shellfish settle on or near wild populations, there are genetic risks. This publication explores 13 shellfish species that could be farmed in the Gulf or Southern California . Some of the shellfish, like Eastern oysters in the Gulf, are native and have wild populations present. Others, like Manila clams in Southern California, are not native and pose a risk of establishing or expanding non-native populations, which could displace other native shellfish species.

There are multiple methods to reduce genetic risk in shellfish aquaculture. For example, most of the Pacific oysters farmed in Southern California are triploid . These oysters are bred to have three sets of chromosomes, which makes them functionally sterile. This helps oysters grow faster and meatier because they don't dedicate energy to growing reproductive organs. Farming triploids reduces the genetic risk of oyster aquaculture. For other species, farming practices and timing considerations can help reduce genetic risk.

Farming Sustainable Seafood

The offshore environment presents great opportunities to expand our domestic seafood production. Together, these publications build a strong framework for potential seafood farmers seeking to develop safe, secure, and sustainable aquaculture operations.

When managed sustainably and guided by best available science, aquaculture growers can manage genetic risks and farm safe, sustainable seafood. This will help the United States continue to grow our domestic aquaculture industry in complement to our wild-capture fisheries.