Aquaculture: Predator Resistant Cages

By April 17, 2013Ocean Solutions

hawaiian aquaculture

Aquaculture has been going on since possibly as early as 6000 BC, when the Gunditjmara people in Australia raised eels. It has also been observed to be used as a method of growing food throughout the world all through history, from Japan and China to Polynesians to Romans. In modern times, techniques for aquaculture are growing more sophisticated, and people are growing concerned with the impact of aquaculture facilities on the surrounding environment.

pond aquacultre

When people do aquaculture on land typically it involves digging out large ponds, which are then filled with salt or freshwater depending on the species to be raised. For saltwater, the easiest way to fill your pond with water is to build it close to the sea. Now unfortunately often times the land close to the sea is very important as nursery habitats, flood abatement, nutrient filtering, etc.

So, by building on these sites people are destroying very important habitats that provide ecosystem services, which are either impossible, or extremely costly to replace (beyond the simple inherent value of these sites). With these problems in mind in the 1970’s, NOAA brought together a bunch of scientists and engineers to try and figure out if there was a way to perform aquaculture in the open ocean. This is now called offshore or open-ocean aquaculture.

Aquaculture effects

There are still environmental issues with offshore aquaculture such as increased nutrients, addition of medications, the logistics of transporting food and workers from land to the aquaculture pen, and the fact that oceanic predators (sharks, seals, sea lions etc.) like to break into these pens and get a meal (part 2 of this article by the Pew Oceans Commission).

In this blog I’m going to focus on that last problem with predators breaking into offshore aquaculture pens. There are a number of environmental effects, which can lead to the introduction of invasive species; introduction of genetic traits that are valuable in aquaculture but harmful in the wild into wild stocks of fish; and, the altering of predator behaviour which could have effects that ripple down the food chain. There is also the somewhat obvious economic impact that happens when an aquaculture facility loses thousands of fish to predation or escapement.

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This is where DSM Dyneema and NetSystems come into play. For any climbers out there you may recognize Dyneema as that really strong rope fibre that is one of the common ropes climbers use since it’s hard to break/tear. So these two companies decided to try and make a type of netting that could be used in offshore aquaculture that would withstand a shark trying to get in, to eat the fish. So working with their engineers and scientists at the Cape Eleuthera Institute (CEI, which has an experimental offshore aquaculture system that grows cobia) they designed a net which mixed Dyneema with steel fibres. To test this the researchers at CEI used nets with different proportions of steel to Dyneema in the netting fibres and attracted sharks to bite the netting by baiting a small cage and filming the shark response to each cage and photographing the resultant holes (or hopefully lack there-of!).

And low and behold it actually worked (check out the videos below to see the experiment in action!).

Fish_production

There is now a type of net that can be used to prevent predators from getting into aquaculture pens, dubbed the Predator X. This is fantastic news because it helps to reduce the risk of invasions by commercially raised fish species into new ecosystems.  Now there are plenty of other problems that need to be addressed with aquaculture to make it sustainable and more economically viable than traditional fishing, but this is one important step towards meeting those goals.

In order to feed the 7 billion people that live on the planet today (and conservatively 9 billion in 2050!) we will need aquaculture and we will need it to be sustainable if we want the planets oceans to remotely resemble what they look like now.

Do you think aquaculture is a solution to decreasing over-fishing and increasing food production?

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