Changing Planet

Can New Shark-Resistant Nets Spur Responsible Aquaculture?

Divers install a Predator-X shark-resistant net for an aquaculture pen. Photo courtesy of DSM Dyneema

Around the world, more than a billion people rely on seafood for a significant part of their protein. And yet the United Nations has projected that by 2030, there will be a 40 million ton seafood shortage.

Some experts have therefore been pointing increasingly to aquaculture as a means to provide protein, while reducing stress on native fish stocks. Aquaculture has not been without its problems, however, from fouling waters with waste to spreading disease (and genetic material) to wild fish populations. Some developers have also ripped out mangrove forests in order to site fish pens.

Despite past problems, it seems likely that aquaculture will play an even bigger role in the seafood industry, as production continues to ramp upwards. Recent years have seen some laws around the world to regulate the growing industry and minimize impacts. There have also been some technological advances. (See “Farmed Fish Now More Popular Than Beef Worldwide.”)

Royal DSM, a Dutch life-sciences company, has produced a new shark-resistant netting called Predator-X, which is being marketed for aquaculture in open-ocean, warm water settings. Previously, there has been more aquaculture in cold water than warm, in part because warm water often has more sharks (see more on this issue below).

Predator-X was developed by a DSM subsidiary called DSM Dyneema, with a net manufacturer called NET Systems Inc., and the Cape Eleuthera Institute, a nonprofit marine research center in the Bahamas. The new net is made of polyethylene fibers and stainless steel wire.

According to a release, “Field tests at the Cape Eleuthera Institute have shown that the netting is resistant to bites, and has successfully withstood attacks from tiger sharks, hammerheads, black tip, reef, lemon and nurse sharks, as well as bull sharks.”

The company says locating fish pens in open water means the waste produced by the animals can be more readily diluted than if they were concentrated closer to shore.

Ocean Views spoke with Ken Robertson, a chemical engineer and the Application Development Technical Service Engineer at DSM Dyneema, about the product and aquaculture in general. Robertson is also a vice president at the Ocean Stewards Institute, an aquaculture industry group.

What impact does such netting have on sharks? Can they get caught in the nets? There have been media reports of sharks getting caught in beach-protecting nets off South Africa.

The mesh size in an aquaculture cage must be small enough that the fish can’t get out, therefore it is too small for the sharks to get trapped in the net.  NET System’s Predator-X netting, made with Dyneema, is strong enough to keep the sharks from biting through the net and entering the aquaculture cage.

Nets typically require a lot of maintenance, because they get encrusted with marine life that eventually weighs them down. How does your product handle that issue, and can it impact other marine life? 

While anti-fouling coatings are still used on a large-scale and these coatings do not have the best reputation in terms of their environmental friendliness, most countries have strict guidelines on the use of these products and laws in place to dampen the impact on the environment.  Many farmers are also leading the way to reduce the use of these coatings and have started to use specially designed high-pressure washers to keep the netting clean.  More and more, these machines are being used to control fouling rates on the nets allowing them to use less coating.

These washers have been used for years with great success and no known adverse impact to the fish.

How large can the nets be? Any limits? Typical sizes?

The aquaculture cages come in many different shapes and sizes.  From cylinders, to rectangular prism, to sphere, even diamond-shaped cages. While there is no “common” size of cage for all farmed species, cages can vary from 40 meter diameter (131 feet) x 4 meter depth (13 feet) to 160 meter diameter (525 feet) x 30 meter depth (98 feet). (The size is usually limited by the ability to engineer a large frame that can withstand the dynamic forces in an ocean environment.)

Predator-X shark-resistant net and divers
Photo courtesy of DSM Dyneema

You have advertised your nets as being a boon to would-be warm water aquaculture growers. Why has aquaculture been relegated primarily to coldwater places up to this point?

Aquaculture has not been relegated primarily to coldwater per se.  The Mediterranean has large production of species like seabream and seabass.  However, coldwater regions of the globe, at the extreme northern and southern ends, do tend to have more sheltered areas more suited for fish production; steep rocky shorelines that are not typically inhabited by a lot of people; deep water  close to shore; and tend to have more coves, inlets, and fjords that offer protection from the elements and currents.  Salmon, a popular, healthy, and high-value species, also grow in cold water.  So it was natural that coldwater aquaculture would develop in less populated regions with a popular and valuable species.

Warm waters have less steep shorelines that are also much more densely populated by people, who don’t want a fish farm near their homes.  Also, warm waters are typically shallower close to shore, forcing a potential fish farmer to locate the cages further offshore, and more exposed to extreme weather conditions like hurricanes (there are submersible aquaculture cages that allow the fish farmer to lower his cages far below the ocean’s surface to avoid damaging winds and waves).

What would be the benefit of expanding aquaculture to other areas?

The USA imports 90% of the seafood we consume.  A marine aquaculture industry could provide much needed U.S. jobs as well as enable U.S. consumers to purchase local fresh fish.  We raise chickens, pigs, sheep, goats, and cows because they do not exist in the wild in quantities sufficient to feed the population.  We have the same challenge with providing fish to the marketplace.  Aquaculture is the solution.

Would the nets help prevent spread of nonnative species used in aquaculture beyond the pens?

Most new aquaculture regulations stipulate that aquaculture species must be native to the area.  Properly designed aquaculture cages made with Dyneema, the world’s strongest fiber, are an excellent option to prevent the possibility of farmed fish escaping into the wild.  This is the case is countries like Greece, Turkey, and Spain, where Dyneema is used to prevent escapes due to fish biting holes in the cages in their attempt to each the organic material that grows on the nets.

Would the nets help prevent any of the other problems associated with some aquaculture, such as spreading of disease (or genetic material) to native animals, or fouling?

There is no evidence that a net in the water either promotes or inhibits naturally occurring diseases in wild fish populations.

Will you be providing information to buyers to help make sure they are using your product in an environmentally benign way?

My personal experience with fish farmers is that they love the ocean much like a farmer loves his land.  Our industry trade group is called “The Ocean Stewards.”  I think that name captures the intent of the pioneers in this industry.

While DSM Dyneema does not routinely advise fish farmers on environmental stewardship, we do promote that if fish farmers have to use anti-fouling coatings that they take into account that by using Dyneema there are big savings; not only financially to the fish farmer by having to pay for less coating, but to the environment, by having less coating be introduced.

What should people be doing to minimize environmental impacts of aquaculture?

The U.S. government is now developing aquaculture regulations and procedures to align with the president’s aquaculture policy.  As with most U.S. land-based industry, U.S. aquaculture will be operated in an environmentally safe way.  U.S. consumers, and consumers worldwide, can protect wild species and the ocean by purchasing products raised or grown locally or in countries that demonstrate the same commitment to the environment.

  • Capt. Lee L. Gottwald

    On the subject of sharks, and the preservation thereof.

    I believe in preservation as much as possible but what about culling the shark population down a bit?

    Obviously we are eating our way through this planet but realistically, since this overpopulation of humans is not about to change quickly enough and…. obviously we must feed our children and….. obviously the sea is our last resource until we get our expanding population under control. Is it not also obvious that one of our greatest competitors for seafood is the shark?

    I do not say exterminate the shark, like the wolf, the shark has an important job to do culling the weak and infirmed. Lose him and you lose an important factor in natural selection.

    However, we humans are depleting the seas so quickly that sharks are being forced to not only continue feeding their own population, and thusly, reducing the seas populations further, but are now targeting humans as a new source of food.

    I strongly believe we must reduce the number of sharks that feed in and around areas frequented by humans. This can be managed in a positive way so as not to upset the delicate balance of nature.

    Sharks have never been considered a good source of meat only the vitamin E and the fins have been seriously used for food.

    Thus, while we continue to overfish the oceans in order to feed hungry mouths all over the world, the shark population has outstripped it’s usefulness. It needs to be culled back to where it was in terms of ratios or two things will happen.

    The first is that with a dwindling supply of their usual diet and the easy presentation of so many humans in their feeding grounds they will, and are, beginning to target humans as a possible food source.

    Secondarily, with the dwindling resources of the sea and the non fishing of sharks, the ratios are now so out of whack that they, the sharks, will further deplete already short stocks of food.

    It is all very fine and idealistic to say “save the shark” but when there is not enough food to go around and your own children are dying of starvation or being eaten alive and/or dismembered as they play in the surf, isn’t it time to do something about the shark problem?

    The alternative is to do something about the “People Problem.” So whom do you put first when push comes to shove? The shark or your own children? This “save the shark” delirium is ridiculous.

    The shark is not some “Teddy Bear” or cute cuddly Koala, it is a near mindless, top predator and feeding it from cages or by hand is among the stupidest things I can imagine, this only trains sharks to relate to people as a food source.

    We must cull the shark back to normal ratios or lose both valuable seafood as well as miscellaneous limbs and appendages.

    Thank you,
    Captain Lee L. Gottwald

    PS/ and yes, I am aware that there are some sharks that are quite tasty and I am not in favor of some mindless slaughter and complete waste of the shark carcass, there are many ways to properly use the remnants of the shark that is not wanted. The shark population is out of balance and should be brought back into previous limits. Otherwise through preservation we are causing another unfavorable imbalance in nature.

    • Thanks for sharing, interesting perspective. I tend to think that natural systems do best when we interfere with them as little as possible, and let ecology run its full course, which tends to lead to the greatest abundance.

  • Neil Anthony Sims, President, Ocean Stewards Institute

    Generally a very pleasing story, Brian. We appreciate you focusing on positive developments in open ocean aquaculture.

    But come on: “Some developers have also ripped out mangrove forests in order to site fish pens.” Please provide a citation for this, or else publish an apology. Fish net pens require very deep water, and excellent water quality. Mangrove swamps provide neither. We expect better from Nat Geo.

    And while “Recent years have seen some laws around the world to regulate the growing industry and minimize impacts.” such developments have been sadly lacking in the US, where much of the technology innovations originate. It is as if, after the first flight at Kittyhawk, America told Wilbur and Orville to take their contraption to Canada.

    Thanks, and aloha,
    Neil Anthony Sims, President, Ocean Stewards Institute

  • Neil Anthony Sims, President, Ocean Stewards Institute

    Brian, This ppt is all about shrimp farming in ponds. It is not in any way germane to fish in net pens.
    And it is also woefully out of date. The most recent citation is 1999, and the ppt speaks of capture of wild post-larvae – a practice that has long been supplanted by hatchery-produced PLs. Similarly – to my understanding – depletion of mangroves for shrimp farming is now considered neither sustainable nor desirable for the industry.

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.

Voices director: David Braun (

Social Media