The Pros and Cons of Aquaculture
If you've been shopping for a fish supper lately, then you've almost certainly been offered both farmed and wild fish. Fish farms are found all over the world and can be really a good way of reducing reliance on wild stock. But there are also some very real environmental concerns. To find out more about aquaculture in all of its forms, Ben Valsler spoke with Dr. Kenny Black, from the Scottish Association for Marine Science, to find out what fish farming involves...
Kenny - Fish farming is a kind of "catch all" as you say for aquaculture which is essentially the culture of any species, plant, animal, invertebrate, vertebrates in an aquatic environment. Essentially, in the sea, we've got everything from seaweeds, a whole variety of species that are cultured are seaweeds, used for a whole range of purposes. Through invertebrates, things like sea urchins, mussels, bivalves, up to the higher trophic level of carnivorous fish.
Ben - So it really is a broad range of things that we're farming here and it doesn't all have to be at sea, it doesn't all have to be in real rivers. Quite a lot of it is also happening on land in huge tanks.
Kenny - Yeah. There's a lot of tanks. Not so much tank stuff if you look at it in the very big picture. I mean, a lot of the actual big numbers as from which things are dominated by the far east. China particularly has a 2,000 year history - at least that long - of culturing carps in ponds, and that's still probably the biggest single aquaculture animal species cultured. There's a variety of different carp species in China.
Ben - So, how does this compare to wild fisheries? Thinking particular of food, how much of our fish food is supplied by aquaculture rather than just wild catching?
Kenny - Well, the trouble with aquaculture is it's increasing at approximately 7% across the board per annum compared with wild fisheries which are - if anything stagnant, possibly in some sectors, declining. So it's difficult to know that absolute up to date figures because one of these is increasing very rapidly. But I've got some figures back in 2004. It seems like a long time ago, but it's actually - the data are quite hard to collate on an up to date basis because the data take a long time to collect. But at that time, in terms of freshwater and marine animals, there was about 46 million tons grown in cultured systems, compared with about 96 million tons extracted from the sea and traditional fisheries. So about - roughly speaking, 50% at that time, but at 7% growth rates, it doesn't take very long and people are suspecting that in terms of just animal production, you might find that we get more from aquaculture than we do from fisheries which represents our incredible paradigm shifts in the way that we use water. Instead of hunting and gathering, we will be using it for culture. That has never happened before in history.
Ben - Are there certain species that we're seeing a very large proportion of and then others that are still really a minority? I get the impression there's an awful lot of farmed salmon and that's just from walking through a supermarket.
Kenny - Farmed salmon is a really big deal. It's not the biggest product. As I said before, carp is probably biggest product, but we don't use so much carp here. So, what we can grow very well in the northern temperate areas of the world are Atlantic salmon. A very easy fish to grow in many respects. It has large eggs, so it's very easy to culture and traditionally it's seen as a luxury food, so there's a ready perceptive market there. So, you will find salmon is rapidly increasing in its overall annual production with a few minor blips, particularly the collapse of the Chilean industry a few years ago - or near collapse, I should say.
Ben - I mentioned earlier that there are some environmental concerns with regards to this. So if we can sort of break that up a bit, people are concerned about the way that farmed fish may interact with wild fish, be it genetically or with regards to things like parasites. What are the big hot button problems there?
Kenny - Right. I think these are two of the key areas. If we're going to look at salmon particularly, some of these things don't apply to other species, but for salmon which is important to the UK, particularly in Scotland, these are very contentious issues.
Taking sea lice first. There is evidence to show that sea lice from the farmed fish interact with wild fish and of course, vice versa, and that wild fish probably suffer as a consequence of that in terms of population. It's usually quite hard to disentangle specific cause and effect, for example, for declining salmon population because there's probably lots of interacting things, for example climate change is a big driver probably of salmon population numbers. For sea trouts which are more coastal species, probably the sea lice issue is more important one.
So a lot of effort is going on at the moment to try to reduce lice numbers on farms, and manage farms in such ways that they limit their interaction, but I think we're quite a long way from cracking that one myself.
Ben - If you have a concentration of fish, does that also affect the sort of the local food web and that normally, there wouldn't be so many fish here, they wouldn't be adding as many nutrients back into the water, they wouldn't be eating as much of the food that's there? Can it have that sort of environmental impact as well?
Kenny - Well they don't eat any natural food that's there, or very little natural food. They almost entirely eat what they've been fed. So, the output therefore are dissolved nutrients excreted and wasted feeds in particulate matter, faecal matter. So you'll have a potential for an impact in terms of increasing the amount of nutrient in the sea water which might be thought to lead to increased primary production and you will see profound effects on the seabed.
Just going back to the nutrients though, in terms of overall budgets if you're looking at nutrient run off from agriculture, that massively outweighs nutrient contribution from aquaculture. So, although there's a potential for some effect, at the moment, the levels of farming don't really realistically make that very likely. And also, for enclosed systems, there are government guidelines which have been calculated to try to reduce the possibility that fish farming will contribute to any change in the phytoplankton community, for example.
On the seabed, though, the story is different. We know a large amount now about the effects that fish farming has on the seabed, the changes to the benthic communities there and the profound biogeochemical changes that you get from essentially dumping a huge amount of organic matter onto a very small patch of seabed. Just to finish that point though - and I could talk all day about the profound changes because that's one of the things I'm interested in - it is a limited amount of seabed. It's generally restricted to a very small area around the farms, and it doesn't spread a huge distance.
Helen - We've touched on the fact that we have to give these fish something to eat and one of the big reasons we think that farmed fish is good is because it means you don't have to catch them from the wild. But isn't it true that actually, we are all going out and catching fish to feed to the farmed fish, and therefore, the problem is still there.
Kenny - Well, absolutely right. In the past, I think that everybody, particularly the feed companies and the farmers have recognised this now and there's a tremendous drive underway to substitute both fish meal protein and fish oil in salmon diets. Salmon are eaten, one of the great advertisings for healthy eating with salmon is their omega-3 fatty acids which have a huge range of human health benefits. They are delivered to the fish in terms of their fish oil. We are now substituting a large amount of fish oil. It varies by country and also by company, but we're substituting a lot of that from plant derived materials, and then using the fish oil, the more expensive and more healthy if you like, fish oil, to top up the fish at the end of their growing cycle, so that their fatty acid profile still gives us the health benefits. Similarly for protein, protein is pretty much protein and substituting protein from terrestrial plant meals is a big deal at the moment, and I think we can look forward to a time where a very small proportion of the diet is actually fisheries derived. Particularly if you end up with - fish oil is the big deal - but I suspect in the future, we will crack (and there's quite a lot of signs of it) a GM plant which will produce essentially fish oil with many of the same benefits, which you could either eat directly or you could feed to fish. Obviously, the GM issue is quite a sensitive one in Europe, but I think - my own belief in this particular one is that that will be one that we will see perhaps in a decade or two. But there's huge resistance from both consumer and producer at the moment to anything that has the word GM on it.
Ben - I believe the omega-3 fatty acids themselves actually come from algae. So rather than they're being something that the fish itself produces, if we could actually find a way of farming the algae, then we would be able to have this apparently very healthy oil without actually needing the fish at all.
Kenny - Absolutely and there's a lot of work going on in growing algae generally. At the moment, macroalgae are the other biggest single class of organisms that are cultured, China produces, I think it's something like 14 million tons per year of cultured macroalgae. They have farms that you can see from space. However, these algae are not particularly rich in fatty acid. You get the fatty acids from microalgae. They're now being grown in large amounts, huge amounts of money are being poured into culturing microalgae, particularly as sources of biofuel.
You will see that the biodiesel that we put in our cars I think 8% comes from a plant source, usually terrestrial oil seed derived, but there's a huge potential for using microalgae. Now these microalgae can also be harvested for their oil or other purposes, and you're right to say that you could then use them as components of animal feeds.
Ben - So actually doing this would also help reduce our reliance on the rainforest and so on, that are being cut down for things like palm oil, and other oil producing plants that may feed in to biofuel.
Kenny - Absolutely. The key thing with aquaculture is, it will never really mature and become a really big contributor until it separates itself from the terrestrial system entirely. The terrestrial food production system has big problems over the next 30, 40 years, in terms of feeding the world's growing population. These problems are to do with land area, to do with nutrients and fertiliser, very highly energy intensive, and of course, to do with freshwater supply. So if you can make aquaculture essentially close its production cycle and grow its food in the sea, then you obviate a large amount of these problems.