Steelhead Net Pen Aquaculture in Puget Sound: Frequently Asked Questions

Find answers to some frequently asked questions about net pen aquaculture.

West Coast

Commercial salmon farming in net pens began in Puget Sound about 35 years ago. Companies initially raised Atlantic salmon, which is the most common type of salmon farmed worldwide. Salmon farming in Puget Sound and the Salish Sea is the only example of marine net pen salmon farming on the U.S. West Coast.

Following the failure of an Atlantic salmon net pen in 2018, the Washington Legislature decided to phase out Atlantic salmon net pens by 2022 and prohibit new aquaculture operations with non-native fish in state waters. Cooke Aquaculture, which operates net pens in Puget Sound, has proposed raising sterile native steelhead. Steelhead are rainbow trout that migrate to the ocean and back like salmon. In addition, the Jamestown S'Klallam Tribe is developing net pen aquaculture with sablefish (also known as Black cod), a species native to the Pacific Northwest.

We provide answers to some frequently asked questions about net pen aquaculture below.

What is net pen aquaculture?

A net pen or sea cage is an enclosed floating cage. The structure holds farmed fish and allows water to flow through the pen freely. Although designs vary, net pens in Puget Sound are typically constructed of a floating frame with walkways and an underwater cage with two layers.

The inner layer is made of a net that contains the farmed fish. 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 net pen is also typically covered with bird netting to reduce bird predation.

Commercial farms may secure multiple net pens together. The array of pens may include other floating structures that allow service boats or barges to attach for various operations such as feeding, net pen maintenance, harvesting, or periodic sampling to assess growth and health status. The design of the net pen array 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 anti-predator nets provide a second layer of stronger and more rigid net. This outer layer prevents large predators from tearing holes in the inner nets. Generally, fish handling in the net pens before harvest is minimized. This reduces the risk of accidental escapes.

Are escapes common?

Commercial salmon farming began in Puget Sound about 35 years ago. Since that time, there have been four structure failures of net pens large enough to allow fish to escape.

Fish may escape due to spills during transfer to the pens during stocking operations or removal from the pens at harvest. They may also escape due to structural issues. For example, tears in the containment nets, or the top edge of the nets dipping below the water surface, have allowed fish to swim out. But staff frequently check them to minimize any losses of fish. Aquaculture operators have a financial incentive to prevent escapes, which would represent an economic loss.

What is being done to better prevent escapes?

The Washington Department of Ecology has issued updated National Pollutant Discharge Elimination System permits for proposed net pen operations. These permits require increased protective measures to prevent net pen failures and escapes in Puget Sound, including:

Increased underwater video monitoring of net pens.
Regular inspections of the structural integrity of the net pens, with reports certified by a qualified marine engineer.
Improved 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 steelhead escape from the pens, will they breed with wild fish?

As proposed by Cooke Aquaculture, 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.

Cooke Aquaculture Pacific, LLC plans to rear only female triploid fish in its Puget Sound net pens. As background, female trout gametes (eggs) contain two sets of chromosomes, and after fertilization with the single chromosome containing sperm, the fertilized egg sheds one of the chromosomes during the first cell division process. This results in diploid cells and a reproductively capable fish. By putting the fertilized egg under hydrostatic pressure right after fertilization, that extra third chromosome is retained within the germ cell. After cell division occurs, the resulting cells are triploid and the fish are incapable of sexual reproduction. Female triploid rainbow trout/steelhead are sterile and cannot reproduce. Making the fish triploid is expected to be 99.8% effective. An analysis in 2020 of 397 fish sampled by Cooke Aquaculture Pacific, LLC found that 100 percent of the fish treated were determined to be triploid and therefore 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.

Will escaped steelhead compete with wild fish?

While escaped fish could pursue the same prey and habitat as wild fish, studies have shown that triploid steelhead show less aggressive behavior and have lower survival in seawater. In addition, studies have shown that farmed fish demonstrate poor foraging and competitive abilities for food compared with regular fish. As a result, they are unlikely to survive long in the wild.

Is a triploid fish genetically modified?

A triploid fish is not a genetically modified organism. The fish's genes have not been manipulated or changed in any way. A triploid fish has three chromosomes: two from their mother and one from their father. A typical diploid (wild) fish has one copy 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 sablefish pose a risk to wild fish?

The 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 are composed of 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 have declined, and few are occasionally caught by recreational fishers. The adult fish spawn in deeper water of about 1,200 to 3,000 feet off the continental slope.

Sablefish used in commercial net pen aquaculture in Puget Sound come from wild adult parents from the Pacific coast stock captured from coastal Washington. They are generally reared in captivity for up to 24 months before harvest. Since females do not mature until age 6, 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, fish that might escape from the net pen should 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. They also would not interbreed with any other fish species in Puget Sound. Sablefish occupy a much different habitat than native salmon and steelhead and should not compete with them in Puget Sound.

Is feeding farmed fish sustainable?

Cooke Aquaculture, Inc.'s Pollution Prevention Plan includes strategies to minimize uneaten food that falls to the seafloor. This includes feeding the appropriate size food and not overfeeding the farmed fish. Also, feeding rates are adjusted based on weather and water conditions. These conditions may affect fish appetite and feed consumption. Underwater cameras observe the feeding to help minimize how much uneaten food falls through the pens to the seafloor. The feeding rate is then immediately adjusted as needed to reduce excess food.

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 is very low. While there will always be some level of disease risk associated with rearing fish in nets pens, Cooke Aquaculture has incorporated prevention and control measures into its proposed operations to reduce any risk, including:

Net pens would be left fallow for at least 42 days between harvest and the next group of fish and would be thoroughly cleaned.
The hatchery-raised steelhead eggs would be disinfected and tested for regulated pathogens before and after hatching and again before being transferred to the net pens.
Footbaths to disinfect shoes will help maintain biosecurity, while any equipment moved between sites will be disinfected.
Any dying fish would be assessed for physical damage and signs of disease, and a post-mortem necropsy would be conducted to determine the cause of mortality (Cooke 2018, disease plan). A trained fish health technician performs this assessment, and if abnormal results are identified, the Veterinarian of Record (VOR) would be consulted.
Farmed fish would be vaccinated against several of the most common diseases that affect their species.
Cooke's freshwater and marine facilities are subject to inspections by WDFW to ensure proper biosecurity, fish health, and pathogen sampling. WDFW can modify sampling levels in response to pathogen findings.
Smolts would be tested for disease before they are moved to net pens.

Can farmed steelhead transfer parasitic sea lice to wild fish?

In the past, Atlantic salmon net pens in Puget Sound have not had problems with parasitic sea lice. This may be due, in part, to the lower salinities of surface waters in Puget Sound, which reduces 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 Washington Department of Fish and Wildlife and Washington Department of Ecology within a week. It is in the best interests of the aquaculture operator to reduce or eliminate any sea lice. Consequently, the risk of transfer of parasitic sea lice is expected to be low.

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Last updated by Northwest Fisheries Science Center on 09/07/2022