Scientists estimate that at the current rate of decline, most of the world's fish stocks could collapse within our lifetimes. There are a number of efforts in place to combat this.
Governments regulate fishing with an individual fishing quota and fisheries mustn't take more than a certain amount of fish from the sea. This enables the species to maintain its population without adverse effect on them or other species.
The method in which fish are caught matters too. High seas drift nets, trawling and dredging should always be avoided. Fish that have been caught by handline, rod and line, pole and line, potting, diver-caught, hand gathered or using organic farming methods are best.
But it's clear that the sustainability rating given to fish species might change, as seen with mackerel earlier this year.
Phil Macmullen, head of environmental responsibility at Seafish, says: "Sustainability can be time-limited because of environmental conditions and because natural predator/prey relationships are dynamic and unpredictable. Modern fish stock management is adaptive in that it tries to anticipate and accommodate these natural variations but a sustainably managed fishery is only that for as far as we can see ahead. Some stocks may almost disappear for many years in response to big cyclical changes in the marine environment, and then return in abundance."
WHAT YOU CAN DO
"If you live anywhere near the coast, you may want to support the local industry by going local," says Macmullen. "Always be a curious consumer and ask, 'where's that from?' and 'how was it caught?' You'll often find that the fish counter staff don't know all the answers but if we all keep asking questions they'll start to know more too."
James Simpson from the Marine Stewardship Council (MSC) stresses that consumers have more power than they know. "Shoppers have a huge power over their supermarket, if you choose a sustainable fish with the MSC label you are sending a message to them and they will listen," he says. "The more people buy these fish, the more the supermarkets will stock them."
The big five of the sea world are cod, haddock, tuna, salmon and prawns but we're too reliant on these.
"Cast your net wide by trying different sorts of seafood," says Macmullen. "It's the same as varying the fruit and veg you eat; you'll get a better range of nutrients if you vary your diet and buying different fish helps to take the pressure off the most popular species."
If you can't access these while you're out shopping, look for the blue MSC labels with the white tick on more than 15,000 products to show that it's certified sustainable seafood. If in doubt, your fishmonger should always able to help.
SUSTAINABLE FISH RECIPES
Handline, driftnet caught or mackerel fished from the North Sea are the ones to look out for when buying mackerel. It's such an easy and versatile fish to cook with, just take a look at our recipes, which include Tana Ramsay's nicoise substituting tuna for mackerel, James Martin's mackerel en papilotte and Aaron Craze's linguine with leeks and mackerel.
Seabass is one of the best fishes to eat from the UK as long as it is line-caught. Our favourite recipes include Uyen Luu's sweet and sour sea bass soup, a simple Chinese-style sea bass with bok choy and James Martin's pan-fried sea bass with chorizo.
Keep an eye on your food miles at the same time as eating sustainably as sardines (or pilchards) from Cornwall, which are mainly caught by driftnet, are the best to eat. As well as simply served on toast, we love this recipe for grilled sardines with tomato salsa and this Italian-inspired bucatini with sardines - a pasta dish with fennel and pine nuts.