The science of buying sustainable fish

Buying fish can be a slightly daunting experience. At a fishmonger’s, salmon and shellfish are sometimes the only species discernible from the filleted corpses laid out on beds of ice.

The scenario is further compounded when a sustainable buy is on the agenda. Picking up a pack of frozen fish sticks is a quick way to avoid those tough questions about provenance and sustainability that we might otherwise feel compelled to ask. And for the majority of the population who are neither marine biologists nor fisherman, the answers risk tipping us into even greater uncertainty.

Sustainability is a growing priority for consumers, but knowledge of fishing and how it is regulated is not always accessible. Globally, the Food and Agriculture Organization of the United Nations estimates that more than a third of fish stocks are overfished, meaning they are depleting at a rate that is impossible to recover.

A recent wave of documentaries and books have portrayed harsh views on the fishing industry, but the reality may be more nuanced. Fishing is complex, with boats pursuing their careers over vast stretches of ocean that are difficult to interpret and manage.

Determining what is sustainable currently relies on a rigorous mathematical approach, says Dr Anne Marie Power, marine biologist at NUI Galway. “The way we solve or explain this overexploitation [of fish] often uses the analogy of a bank account. You have the capital, which is your healthy stock, and the capital grows because they raise, and what is added every year through breeding is interest. So to fish sustainably, you only fish the interest, you don’t eat into the capital. »

Data collected from fish catches and population surveys are fed into numerical models that generate trends and forecasts. It is an audit based on methodologies developed at the turn of the 20th century, when industry, capital, interest and growth took their place in our common vocabulary.

The fact that a dynamic ecological system can be understood through the prism of economic calculation is quite shocking, but it is currently the only method on which political decisions can be based.


Sustainability is determined only in terms of the fish as a stock and whether the current rate of fishing allows that stock to maintain a stable capital. Quotas are the method of management, says Dr Ciaran Kelly, director of the Marine Institute of Galway. Constantly reassessed based on current fishing data, they distribute the stock of each species of fish between the fisheries and their boats.

“[Quotas] limit the industry’s impact on the environment, ensure the sustainability of the fish stocks themselves and ensure continuity of food supply in a secure market,” Kelly adds.

Stock assessments and quotas look at sustainability in terms of maintaining an exploitable fish population. But a more holistic approach must be taken to ensure the longevity of local small-scale fishing economies, says Alex Crowley, secretary of the National Inshore Fishermen’s Association,

“One of the problems we would have as small-scale boats is that a lot of the quota is allocated mainly to the bigger boats,” says Crowley, while acknowledging that “there are certain species, certain stocks , you need boats to harvest, so it’s appropriate in some cases”.

Mackerel is considered Ireland’s most important fishery in terms of economic value, with 48.3 million landed in 2020. Most of it was caught by larger boats, says Crowley, which is often necessary to ensure a sufficient yield that maintains food security. But he adds that the share given to smaller boats could be increased, doing more to support local communities.

It may be easy to assume that huge fishing boats are plundering the oceans and ruining the livelihoods of small-scale fishers, but the intricacies of creating a fair and sustainable industry make it difficult to draw hard lines between this what is sustainable and what is not.

“It’s an oversimplification when you’re talking about small-scale fishing,” says Kelly. “Are we talking about the fish stock or are we talking about the fishing fleet, or are we talking about the fishing vessel?”

Larger variables

The way fishing quotas are determined makes sense in the context of a market economy, but it is perhaps a dangerous simplification with insufficient consideration of broader variables. And whether or not the method is comprehensive enough, how scientific findings are put to use ultimately comes down to a variety of demands from anglers, consumers and policy makers.

A 2020 analysis by Birdwatch Ireland found that there was a tendency for policy makers to go against scientific advice for the allocation of fish stocks, often in the interest of political expediency.

The same report revealed that fishing in Ireland was highly dependent on a limited variety of stocks, leaving the sector vulnerable to crises. Like any wild harvest, focusing on a limited number of species will reduce their numbers disproportionately.

It is true that many of our fish stocks are in a precarious situation. According to the Marine Institute, the stock of whiting in the Irish Sea has collapsed, while cod in the North Atlantic is listed as “threatened” by the International Union for Conservation of Nature.

“Cod is a problem in a lot of cases,” Power says, adding that “a lot of cod that you see in chippers isn’t really cod because cod is overfished and very expensive.” The fact that another white fish could be disguised as cod demonstrated some interesting points; we have a preference for such a restricted selection of fish species that they have been driven to exhaustion; and our preference is potentially superficial.

“What is a desirable fish as opposed to what is not a desirable fish is totally artificial,” says Power – arriving at the fundamental principle that “the market price is determined by the fashion and the ideas of the consumers” .

The factors determining the durability of what we buy are perhaps as numerous as the fish in the sea. Everyday shoppers cannot be expected to keep up with the vast amounts of data produced by researchers in the field of fishing.

Power recommends taking a look at the MSC Good Fish Guide, which distills masses of scientific information into a simple traffic light system for fish species. Harnessing the power of consumers through this handy booklet could be one way to influence fishing fashion.


Sustainable is a fluid term, and each buyer may have different priorities, including the geographic origin of their purchase, the resulting carbon footprint, and their contribution to local economies. “No type or method of fishing can be simply described as sustainable or unsustainable,” says Crowley.

What is certainly lacking in selling fish is the availability of consistent information on which buyers can make their selection. “Seafood traceability is very low,” adds Crowley. “You can go to a supermarket, get your fish and they’ll just tell you it’s caught in the northeast Atlantic. And that will tell you the type of fishing method, but it won’t really tell you more than that.

It is perhaps the lack of interpretable information that makes buying fish responsibly so difficult. We know that connecting with our food breeds familiarity, which in turn can inspire informed choices.

“We want to give them a choice: if it was caught by a small fisherman in Donegal or Galway…let’s label it for what it is and then look at the sustainability,” says Crowley.

Power reflects that familiarity is a key trait that our relationship with fish lacks. “Ideally we would all go out into the ocean…we would develop a respect for it and then we would eat a diversity of seafood…there’s a lot to consider and it’s confusing.”

We don’t need any more information. This will only add to the confusion and there are already extensive fisheries databases. Fish buyers are increasingly aware of sustainability. What they need is appropriate access to key facts, clearly presented, that buyers can interpret. Only when sustainability makes sense can it be achieved.

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