Farming Thinking

How Do I Know I’m Buying Sustainable Fish? 7 Questions To Ask Your Fishmonger

24th July 2018

We’ve often heard the phrase ‘sustainable fish’, but what does it mean? And how do we know if what we’re buying was caught with the future of our oceans in mind? First thing’s first, ask the right questions! Sustainable fish collective, Sole of Discretion, are on a mission to protect our seas and connect shoppers with the fishermen operating in the most sustainable way. Founder, Caroline Bennett, helps us get to the bottom of these murky waters.

A Sole of Discretion diver about to take the plunge

A Sole of Discretion diver about to take the plunge


It is nigh impossible for most people to be able to differentiate at the checkout the fish that has been caught with minimal impact to the marine ecosystem and those that have wreaked considerable damage. Knowing where to start in an incredibly complex marine world is tricky.

It’s well-known that to limit damage on the seas hand-line-caught fish are some of the best. On the other end of the scale, it doesn’t get much worse than dynamite (outlawed and yet still practiced in some parts of the world). But what about the rest? The vast majority of fishing lies somewhere in the middle of these two extremes. In this 99% ‘grey’ fishing area, there are some practices that are significantly better than others, and here at Sole of Discretion, our aim is to help you navigate your way through.

Here are some questions to ask your fishmonger to be sure you’re always buying the most sustainable fish on offer.

1. How was it caught?

Ask this question to try and get to the bottom of whether or not the fishing method was ‘low impact’ or not. ‘Low impact’ means the fishing gear did little damage to the marine environment from a number of perspectives. Firstly, the seabed wasn’t churned up and delicate seagrasses or corals were not damaged.

Aaron Lidstone on his boat Happy Days, its named coined from the catchphrase of a fellow fisherman who had positive outlook each time he set off for a catch

Hand-lined versus trawling

The best fishing methods in this context are static-netted, hand-lined or potted. In other words, they were caught in a net that is static rather than moving across the seabed, caught with a fishing line, or in a trap. On the other end of the scale is trawling, whereby industrial boats drag nets across the sea floor, picking up whatever’s there along the way. One of the most damaging industries is the prawn trawl fishery, which trawls the area the size of two football pitches for just one kilo of prawns! The amount of other, unwanted species they pick up at the same time is enormous. These fish are then thrown overboard – dead – because they have either little value or are not the target size. It’s estimated that on average 30% of fish landed are discarded in this way.

There are also light trawls, which can be fine. Soft, sandy beds are generally okay so ask questions on where they are trawling and how heavy and big the trawl is. You’ll have to trust your fishmonger on this one!

2. Small boat or big boat?

Under 10m in length is the UK definition of a ‘small boat’. The advantages of small boats are many. They discard virtually nothing, whereas the big boats catch plenty of untargeted fish in their nets, and because they have low commercial value, throw them back in the sea, dead (as mentioned above). The small boats have limited impact on the sea bed, even when they use trawls in some places. The fish caught per litre of fuel is low and lastly they are usually caught by the skipper who owns the boat (as opposed to the often foreign-owned conglomerates of industrial trawlers), so the social impact on local communities also tends to be better.

Sustainable fishing with Aaron Lidstone's Happy Days boat

3. Does ‘day boat fish’ mean it was caught sustainably?

‘Day boat’ is a term commonly used now. It means little. Day boats can be damaging trawlers as well as tiny rod and line boats. Day boats can be poorly managed and not take ice out to sea, so quality isn’t necessarily guaranteed. It’s better to ask what type of fishing gear was used to catch the fish (i.e. how it was caught) rather than just knowing it was a ‘day boat’ .

4. The fresher the fish, the better the quality?

Well, yes, generally. It’s best to eat fresh fish within a day of it being caught. But quality is equally determined by other factors. For example, how much bruising the fish suffered in the catch, which is most common when they’re trawled, or how long the fish was left in the net in the water (also known as the ‘soak time’). When caught on a small-scale, they’re less likely to be bruised because the nets favoured are static. 

filleting fish

Sole of Discretion fishermen don’t leave fish in the net any longer than 12 hours. During processing, too, minimal handling of the fish and keeping it at a low temperature throughout are also important factors behind quality. There’s also the debate on freezing fish, versus keeping it fresh…

5. Is frozen fish best avoided?

Not necessarily. One of the difficulties that small-scale fishers face is their inherent vulnerability to poor weather. The odds are stacked against the small-scale fishers in the modern food system. They are unable to fish when the weather is poor or go offshore to find fish when they are not in season. This is because they’re in smaller boats and because you need more consecutive days of good weather to catch fish in a static net as opposed to trawlers. As the modern food system requires volume, they are often unable to meet the demands of the processors on a consistent basis. This means small-scale fishers are often unable to command better prices, in spite of their fish’s often superior quality. 

Freezing fish is a solution that is two-fold: blast-freezing fish usually within 24 hours of landing allows a continuity of supply even when the weather is poor or fish are not in season. We’ve done numerous blind tastings, and in many of them people preferred the blast-frozen fish! There was no question that freshly frozen fish is preferable to five to 10-day old fresh fish. Iceland actually have an interesting video to illustrate this point.

6. Is farmed fish ever okay?

Badly managed farms are all too common, and the biggest threat to wild fish stocks and fishing communities today is aquaculture. Why? Unlike sheep and cows that are vegetarian, fish eat other fish. When farms take sand eels for fish meal, they are disturbing the ecosystem for wild fish trying to find food. Farms are trying to rely less heavily on fish content in fishmeal as it is expensive, so instead rely on vegetable oil, insects, worms and algae, but this has an impact on the flavour and texture of the fish. Badly managed salmon farms, for example, can be detrimental to the environment and ultimately our health.

Loch Duart is a good example of a well-managed salmon farm. Their methods involve leaving sea lochs alone for one in every three years to allow regeneration. The fish food they feed their salmon is certified as coming from sustainable sources from Iceland and is predominantly capelin, rich in omega 3. The result? Better tasting, healthier salmon.

It must be noted though that farming exacerbates wild stocks and in no way helps preserve wild fish stocks because farmed fish eat a lot of wild fish that are often caught in countries that have fewer regulations than, for example, the EU or the US. There are a few exceptions. Farmed mussels, for example, are great as they aren’t fed anything.  

sole of discretion

7. I’m still confused. What should I do?

Above all, ask questions. And if in doubt, try to always buy fish that was caught by small-scale fishers. They often offer superb quality fish, from boats that do little damage to the marine environment, use less fuel and employ more people than the larger boats. Currently there are few places offering these fish for sale with full traceability, and there is little knowledge of where to go to find these fish to buy.

Through Farmdrop, we are able to provide absolute transparency – including method of catch, location of catch, and the name of the fisher and their boat. Working alongside Farmdrop to create a fairer and more environmentally sensitive food system has been a blessing. Your purchasing power provides impetus for continued improvement in many other fisheries so consider yourselves part of this great journey!

Find Sole of Discretion’s wonderful, sustainable fish here at  

Want to know more about Britain’s forgotten fish, and why it’s important to eat them? Read on here


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