Net-Pen Aquaculture in the Pacific Northwest: Frequently Asked Questions

What is net pen aquaculture?

A net pen or sea cage is an enclosed floating cage. The structure holds farmed fish or fish used to enhance commercial and/or recreational fishing and allows water to flow through the pen freely. Although designs vary, net pens in Puget Sound have often been constructed of a floating frame with walkways and an underwater cage surrounded by another cage/net to keep predators out and minimize the risk of fish escaping. 

The inner layer of a pen is typically made of a net containing the fish being reared. The net's mesh size is small enough to prevent fish from escaping but large enough to allow water to flow freely through the pen. The external layer is a stronger net secured to the frame. It is designed to keep predators such as seals out of the cage. The top of the net pen is also typically covered with bird netting to prevent bird predation.

Commercial or enhancement net-pen operations may secure multiple net pens together. The array of pens may include other floating structures that allow service boats (well boats) or barges to attach for various operations such as feeding, net-pen maintenance, harvesting, or periodic sampling to assess fish growth and health status. Net-pen design varies depending on the site but often includes anchors to secure the pen in the permitted location.

What prevents fish from escaping?

The size of the fish when they’re stocked determines the mesh size of the net. The mesh should be small enough to prevent escapes. The outer anti-predator nets provide a second layer of stronger, more rigid net material. This layer also prevents large predators from tearing holes in the inner nets. Generally, handling of fish in the net pens before harvest is minimized to reduce the risk of accidental escapes.

Are escapes common?

Commercial salmon farming began in Puget Sound about 35 years ago. Since then, there have been four structural failures of net pens large enough to allow fish to escape. Fish produced for enhancement in net pens are intentionally released into the wild to contribute to commercial and recreational fisheries.

Escapes from fish farms are uncommon but may occur when fish are transferred to the pens during stocking operations or when they are removed from the pens at harvest. As noted above, escapes have also occurred due to structural issues, tears in the containment nets, or due to the top edge of the nets dipping below the water surface. However, specific permit requirements aim to minimize structural or net issues that could result in fish escaping, and any incident must be immediately reported. Aquaculture operators have a financial incentive to prevent escapes, which would represent an economic loss.

What is required to prevent escapes?

The Washington Department of Ecology issues National Pollutant Discharge Elimination System (NPDES) permits, which require strict measures to prevent net-pen failures and fish escapes. These may include:

• Underwater video monitoring of net pens.
• Regular inspections of the structural integrity of the net pens, with reports certified by a qualified marine engineer.
• Regular net cleaning and maintenance procedures to prevent nets from deteriorating or being damaged by the growth of barnacles and other marine organisms.
• Preparedness training and site-specific response plans if fish do escape.

If fish escape from the pens, will they breed with wild fish?

Depending on the species of fish being reared in net pens, the goals may differ. If fish (salmon or trout) are held in a net pen for sport or commercial fishery enhancement, then they will all be released into the environment with the intent of later commercial or recreational fisheries harvest. In these cases, the fish can breed with wild fish, and depending on the specific program, that may be the goal. Alternatively, the fish may be collected at a weir or hatchery for breeding and production of additional hatchery fish.

NOAA Fisheries and partners produced models to assess risk and develop management approaches and regulations that balance the aquaculture industry's needs with protecting wild stocks.

One way to minimize concerns over escapement is to reproductively sterilize fish. This is done by producing  “triploids,” which is similar to polyploidy used in producing many seedless agricultural products (e.g., watermelon, grapes, bananas). Putting fertilized fish eggs under pressure right after fertilization causes retention of a third set of chromosomes within the egg. After embryo cell division occurs, the resulting cells are triploid, and the fish are incapable of sexual reproduction. Therefore, female triploid rainbow trout/steelhead are sterile and cannot reproduce. The efficiency of this procedure is 99.8% effective. A 2020 analysis of 397 fish sampled by Cooke Aquaculture Pacific, LLC found that 100 percent of the fish eggs treated this way were triploid and reproductively sterile. Farming sterile fish is a way to drastically reduce the potential for escaped farmed fish to interbreed with wild fish, thus mitigating genetic risks to wild populations.

In Washington State, commercial marine net-pen fish farming was restricted to farming only native fish species, but the State’s Commissioner of Lands recently introduced an order to eliminate this aquaculture method from State waters.  Cooke Aquaculture was the only remaining company producing fish in net-pens in Puget Sound, and in 2023, the State denied renewal of their leases despite their shift from farming Atlantic salmon to farming sterile, all-female steelhead (ocean-going rainbow trout), which essentially eliminated the potential for escaped farmed fish to interbreed with wild fish. This was done to mitigate any genetic risks to wild populations. Commercial finfish production operations along the west coast of the US are currently limited to pilot-scale production involving tribal-federal partnerships; however, inland net-pen production does occur in the upper Columbia River.

Is a triploid fish genetically modified?

A triploid fish is not considered a genetically-modified organism. The fish's genes have not been manipulated or changed in any way. A triploid fish has three sets of chromosomes: two from their mother and one from their father. A typical diploid or wild fish has one set of chromosomes from each parent. While having three copies of chromosomes disrupts the formation of fertile eggs, other parts of the fish can function with three copies.

Will escaped fish compete with wild fish?

While escaped fish could pursue the same prey and habitat as wild fish, studies have shown that triploid (sterile) steelhead show less aggressive behavior and have lower survival in seawater. In addition, studies have shown that farmed fish demonstrate poor foraging and competition for food compared to wild fish. 

Are other species are being proposed for aquaculture in Puget Sound?

Sablefish, or black cod, is a deepwater, benthic marine species with a wide distribution throughout the northeastern Pacific Ocean from northern Mexico to the Gulf of Alaska and westward along the Aleutian Islands into the Bering Sea. Fish from these areas comprise two stocks: one off the Pacific coast and one in the Eastern Bering Sea, Aleutian Islands, and the Gulf of Alaska. Juvenile sablefish can be found in nearshore habitats, but numbers in Puget Sound are generally low, although recreational fishers occasionally catch some. Adult sablefish spawn in deeper water of about 1,200 to 3,000 feet off the continental slope.

Research on sablefish aquaculture is ongoing and includes work to evaluate net-pen and land-based production efficiencies through a partnership between NOAA’s NWFSC and the Jamestown S'klallam Tribe. Sablefish have been produced using net-pen aquaculture in Canada (Vancouver Island) since 2006, and fish are typically produced from wild adult parents collected off the Pacific coast. They are generally reared in captivity for 18 to 24 months before harvest. Since females do not mature until ~6 years old, they are harvested four years before they would likely reach sexual maturity.

Given the absence of adult sablefish and suitable spawning habitat in Puget Sound, if such fish were to escape from a net pen, they would likely pose little genetic threat to wild sablefish populations. Any escaped sablefish would have to survive for at least four years and migrate to deep water off the Washington Coast to breed with wild fish, which is unlikely. 

More on Jamestown S’Klallam Tribe’s sablefish aquaculture

Is feeding farmed fish sustainable?

While all animals need to eat and, likewise, all farmed animals need to be fed, aquaculture represents a very efficient method to convert feed to edible protein. Research at NOAA labs and through the NOAA–USDA Alternative Feeds Initiative (2007) has contributed significantly to progress toward reducing fishmeal and fish oil use in aquaculture feeds. Most current commercial aquaculture feeds have low fishmeal concentrations, and some strains of carnivorous species (such as rainbow trout) have been developed to grow on all plant diets (i.e., vegetarian trout). This has been accomplished without sacrificing the important human health benefits of seafood consumption. Such progress in developing alternative protein sources for fishmeal has substantially reduced the reliance on wild fish caught for this purpose.

Please see NOAA’s page on fish feeds for aquaculture

Can farmed fish transfer disease to wild fish?

Research indicates that the risk of farmed fish introducing new pathogens to native salmon and steelhead populations or other fish species is very low. In most cases, disease in farmed fish in net pens originated from wild fish infected with a disease-causing pathogen (virus, bacterium, or parasite). Aquaculture operations incorporate many prevention and control measures to reduce disease risk. These include: 

• Net pens are thoroughly cleaned and left fallow for at least 42 days between harvest and stocking the next group of fish.
• Eggs used to produce fish are certified as “disease-free” through testing and are disinfected multiple times before hatching. Smolts (young seaworthy salmonids) may also be tested again before being transferred to net pens.
• Footbaths and barrels containing disinfectants are required for equipment and divers to immerse themselves in to maintain high levels of biosecurity. 
• Farmed fish are often vaccinated to prevent the most common diseases affecting their species.
• Any sick or dying fish are assessed for physical damage and signs of disease, and a post-mortem necropsy is conducted to determine the cause of mortality. A trained fish health technician performs this assessment, and if abnormal results are identified, the Veterinarian of Record (VOR) is consulted.

Commercial freshwater and marine facilities are subject to inspections by state and federal agencies to ensure proper biosecurity, fish health, and pathogen sampling. 

Can farmed steelhead transfer parasitic sea lice to wild fish?

Atlantic or Pacific salmon and steelhead reared in net pens in Puget Sound have not typically had problems with parasitic sea lice. This may be due, in part, to the lower salinities of surface waters in Puget Sound, which reduce the survival and reproductive success of sea lice. Sea lice are undesirable for quality farmed fish, and frequent inspection for sea lice is required. Increased sea lice burdens must be reported to the appropriate agency. In Washington, such detections would be reported to the Washington Department of Fish and Wildlife and the Washington Department of Ecology within a week.