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We're often told we need more fish in our diet, but determining which fish to eat is increasingly an environmental minefield. The oceans, once considered a bottomless source of seafood, are now "more akin to a watery desert," according to a team of international researchers.

As shallow waters become depleted of fish stocks, scientists from the non-profit Marine Conservation Institute, based in Bellevue, Wash., say commercial fisheries have resorted to overexploiting the deep seas, the last refuge of many vulnerable species. In a study recently published in the journal Marine Policy, the researchers compare deep-sea fishing with mining operations that exhaust resources and move on. They propose a controversial and drastic solution: to shut down deep-sea commercial fishing altogether and redirect efforts to rebuild fisheries closer to shore.

Professor Rashid Sumaila of the University of B.C. Fisheries Centre and a co-author of the study says deep-sea fishing accounts for only 1 per cent of global catches,yet, as it relies mainly on bottom trawling, it has a devastating impact on the environment. He says until the waters can be properly managed, deep-sea fishing is simply not worth the lasting damage. He spoke to The Globe from Vancouver:

Why are deep-sea species more vulnerable than fish in shallower waters?

The deep sea is not that productive, and you can understand why – there's very little sunlight, so the normal processes of growth in animals is very slow. They also live very long. Some of them live up to 150 years, if you can believe it. So the growth rate in a year is less than 1 per cent for most of them. This makes them very vulnerable to fishing because they're almost like non-renewable resources. When you fish them, chances are you're going to overdo it.

Your paper mentions that without government subsidies, deep-sea fishing would be operating at a loss. So why do governments subsidize it?

The key thing is governments are looking for jobs for people. And some also argue it's to ensure food security. So there are socio-economic reasons for pushing for this. This used to work when we had lots of fish in the ocean, like after the Second World War. But now, the fish stocks are so weak, that kind of thinking only makes things worse.

What kind of deep-sea fish are Canadians most likely to see in grocery stores and restaurants?

Orange roughy is one of them. The name for them used to be "slimehead." Years ago, nobody would to touch them because they don't look pretty, but now we're beginning to go for them. Then there's alfonsino. Then, you have Chilean sea bass. These would be the three most popular ones you see.

Should consumers simply be advised not to eat them?

This is a tough one for some of us because we don't want to be telling people what to do and what not to do. But really, for this kind of species, if you are really concerned about sustainability and conservation, I think it's advisable to avoid eating them. There's a colleague of mine, who says, "Don't ever eat anything that is as old as your grandma."

If deep-sea fishing has become problematic because shallow areas have become overfished, how would it be possible to return to coastal waters?

From the individual to the state, we need to [take the necessary steps]to rebuild depleted stocks. People say they may not come back to previous levels, but in general, if you leave things alone, they come back. We don't know how quickly.

In the interim, there is an issue there because to rebuild means you have to actually reduce fishing for some time, and that is where we have a challenge.

Does that mean consumers should be eating less fish in general?

The thing is, maybe we need to differentiate a little bit. For people in the developed world, we have lots of options to meet our food requirements, so one could try to eat less fish than before … But if you move to the developing countries, for some, they either have fish or they starve, and that's where we have real problems because it's so hard to tell them to let the fish grow when they can't survive today.

Locally and globally, we need to find ways to help people to pull back, and one of the ways is actually to convert the subsidies we now give out and help people find alternative livelihoods.

What else can consumers do?

There are some efforts, like [guides and labels for]seafood choices. Some of us in academia are very skeptical about them because it's very difficult to implement them. But if the consumer is conscious, and they go to the supermarket and try to find fish with a label that says, "from all that we know, this is coming from a sustainable source," that would be a good thing. Just do the best we can. I know it's tough for consumers to have to do all this nitty-gritty work, but the more we can do that, the more it helps.

And I also say that it's good to vote carefully. Your values and what you care about, if you let that guide your voting - that should help. I think most Canadians care about making sure that the environment is there for future generations.

What would you say to those who argue an outright ban on deep-sea fishing is too extreme?

Even economists advocate bans on things. What we do is a cost-benefit analysis. The gain and the losses are broad. You're thinking of jobs, you're thinking of dollars and conservation goals and so on. Once you do that, if the cost of continuing to fish is higher than the benefit, then a ban is okay.

This interview has been condensed and edited.

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