Farming the open sea

Tom Sephton

Back in 1957, Arthur C. Clarke published " Deep Range" a book describing a future where the open seas were zoned into huge whale farms.

While this idea has not taken off for whales, for fish this future seems to be getting closer with the development of plans for offshore fish farms.

In this interview, the Chair of the ICES Mariculture Committee, Tom Sephton, discusses developments in offshore fish farming:



Q)Why is there such interest in offshore fish farming, and what are the benefits?

In a nutshell, offshore fish farms are likely to be much bigger than coastal fish farms. Bigger fish farms will mean more space and less crowding and stress for the fish, which will mean a better quality final product.

In addition, new technology for the long-term storage of feed, combined with remote sensing and automated fish feeding is making the offshore both more feasible and economical. 

Already the Irish have had some recent success in offshore exposed areas that were never before deemed suitable for fish culture. 

And from the inshore coastal marine user perspective, the farms are away from the protected multiple use inshore areas to reduce interactions, and sufficiently offshore so as to not be visible to local land owners.

Q) Which species are likely to be grown in offshore fish farms?

Ones that can take the increased wave action and currents of being in the more exposed offshore areas.  Salmon are a good choice in low to medium velocity areas. 

Cod are being considered along with different halibut spp.

Q) Is it a realistic idea, for instance are there cages strong enough to withstand offshore storms, or is it still at the untried/drawing board stage?

It is now realistic and something that several international companies are considering on a trial basis.  The mooring systems exist courtesy of the engineering developed for offshore oil drilling and shipping industry.  

A major headache to overcome in some warm water areas is the fouling by marine organisms of all vertical structures placed in the marine environment: cages are perfect areas for marine plants and animals to flourish.

Q) Will the fish need to be fed or will farms be sited near areas with plentiful natural food sources, such as upwelling areas?

Farming carnivorous fish will require regular feeding.  Depending on the species for the geographic location area, there are definite advantages to be gained from mixing natural food with prepared diets, although the wild sources would be seasonal in nature. 

The best of both worlds could very well be the co-culturing of marine plants, shellfish and marine in the same location.    

Q) There is a growing body of evidence that many coastal fish farms are damaging their local environment; is offshore fish farming likely to be environmentally cleaner or is it just a case of hiding the problem offshore?

The offshore environments that have been studied so far respond well and recover quickly from many perturbations. 

Being offshore and in deeper areas, the area of direct impact is lessened due to the drift and dispersal of the material from the farm site. 

It is also possible that the seabed communities in these offshore areas may respond positively to a mild shower of organic food in a normally barren area.  A balance would eventually be achieved. 

Q) If offshore fish farming is practical, do you think there will come a time in the future when nations will lease sections of their 200–mile EEZs (Exclusive Economic Zones) to fish farmers?

It's all part of the discussion of integrated coastal zone management and everything that that entails on the national and international forums.

For most countries, it's making the best decisions based on sound environmental advice and using technology that is both practical and economical.

Interview with Tom Sephton originally published in the ICES Newsletter (Autumn 2004).

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