How Many Fish Are in the Sea?

It sounds like a rhetorical question, but figuring out how many fish are in a given area of the sea is hard work—and important for everyone.

It’s often said that there are plenty of fish in the sea. But in the same way that soon is not a time, and some is not a number, plenty cannot offer adequate context for making reasoned choices about harvesting wild fish.

In Newfoundland and Labrador, the concept of “plenty of fish” is further complicated by the long, sordid history of Atlantic cod.

"Cod is fish and fish is cod." (George Rose)

Here, when people refer to “fish,” they mean “cod” (indeed, “cod is fish and fish is cod” is how fisheries scientist George Rose and colleagues once put it). It’s a sore spot because the same cod fishery that built many communities along these coastlines also shuttered them when cod stocks collapsed and the fishery closed. It’s now thirty years since the Canadian government put a moratorium on cod, sixteen since it resumed a smaller scale cod fishery, and nearly two since releasing the first-ever rebuilding plan for Northern cod. Once one of the world’s largest fish stocks, the latest science from Fisheries and Oceans Canada (DFO) puts the stock in the critical zone. With so much at stake for the fish, fishery, and communities that depend on it, calculating how many fish are in the sea has arguably never been more important.  

That’s where stock assessments come in. Stock is a fisheries management term referring to a group of fish of the same species in a given area. For example, take Northern cod within 2J3KL, a Northwest Atlantic region, which extends from Hopedale in southern Labrador to the northern part of the Grand Banks. A stock assessment is an evaluation of the status of a stock, based on past, present and future life history characteristics including age, growth, natural morality, reproduction or productivity, feeding habits, habitat, and fishing pressures.

“The most sustainable harvests today tend to be those blessed with the greatest amount of data,” wrote the late fisheries biologist Jeffrey Hutchings in A Primer of Life Histories (2021). Hutchings argued the “gold standard” includes data on the numbers of individual fishes at each age, the probabilities of their surviving from one age to the next (based on natural and fishing mortality), and the numbers of offspring produced by the average individual at each age. But he also contended this gold standard rarely exists in fisheries management, which “makes it challenging to determine harvest or catch levels that are sustainable, i.e., able to be maintained at the same levels for the foreseeable future.”

In Canada, "the health status of a third of stocks remains uncertain, due to insufficient data." (Oceana Canada)

In Canada, “the health status of a third of stocks remains uncertain, due to insufficient data,” argues the non-profit Oceana Canada in its 2021 Fishery Audit. The audit is the fifth report of its kind and is arguably the most comprehensive current-state assessment of fisheries and fisheries management practices in Canada. 

On the plus side, the audit finds DFO is making modest progress in tracking natural mortality estimates (the rate at which fish naturally die), articulating limit reference points (the point below which a stock is considered in serious danger, in the critical zone), and using upper stock references (the boundary between a healthy stock and one in a cautious zone). But the audit also finds most stocks in the critical zone are managed without a rebuilding plan. For those few with a rebuilding plan, such as Northern cod (released in late 2020), the plans lack targets and timelines for rebuilding stocks to healthy levels.

“DFO is operating mostly in the dark when it comes to critical decisions about these fish—like how much fishing to allow,” reads the Oceana Canada report.

Fisheries scientists Jeff Hutchings, George Rose, and Peter Shelton went further than that—calling the cod rebuilding plan “sufficiently riddled with weaknesses from a science and policy perspective [and that] it’s unclear whether it will help or hinder a cod recovery.”

"The most sustainable harvests today tend to be those blessed with the greatest amount of data, but what would be considered the 'gold standard' of data rarely exists in fisheries management." (Jeffrey Hutchings)

Fast-forward to the middle of March 2022, when DFO announced it could not undertake its annual fall offshore trawl surveys due to its aging marine research fleet. The same mechanical failures also hampered data collection of cod’s primary prey, capelin—a small foraging fish crucially important to fish, whales, and birds (that is also critically depleted). All told, DFO says that means they have insufficient data this year for stock assessments for Northern cod and capelin. 

“It’s just another symptom of how unimportant fisheries are in the priorities of this country. It’s very disappointing,” says George Rose, of the recent DFO decision. Rose has extensively studied Northern cod, perhaps spending more time on the water undertaking surveys of the species than any other scientist. He says the existing capelin survey does not cover the full stock range, nor give estimates of potential spawning biomass (the part that will be fished).

For its part, Oceana Canada has once again called to halt the capelin fishery and invest in capelin research to develop reference points and a rebuilding plan for its fishery.

“The last 30 years have not only been a time without the commercial cod or salmon fisheries but also 30 years of austerity, cuts to the government, gutting, so that there is no capacity left to do single stock assessment let alone ecosystem-based management,” says Dean Bavington, a Memorial University geography professor and author of the 2010 book Managed Annihilation: An Unnatural History of the Newfoundland Cod Collapse

“At the best of times we don’t have a roadmap for what ecosystem-based management would look like,” says Rose. “A step in the right direction would be to use environmental factors, such as prey abundance and ocean conditions, in projections of what the stock is likely to do in the coming years. But this is beyond current practice or knowledge.” 

“DFO should definitely use every precautionary approach measure they can,” argues Petty Harbour fisher Kimberly Orren. Orren also co-operates an award-winning fishing social enterprise called Fishing for Success, which teaches handline cod fishing.

Crucially important to sustainable fisheries are the trawl and acoustic surveys, which provide real-world data that informs assessment models. A recent Evidence Commission defines modeling as relying on mathematical equations to simulate scenarios (i.e., what is likely to happen) and real-world options (e.g., what happens if various approaches are taken) in a virtual environment. In fisheries management, Rose says the most important outputs from models are the past and present state of the stock (numbers at age and biomass) and the impacts of various levels of fishing. He also cautions: “forecasts are always questionable.”

Once one of the world's largest fish stocks, the latest science from Fisheries and Oceans Canada (DFO) puts Northern cod in the critical zone.

“The stock doesn’t live in some kind of a vacuum, though sometimes the models that come out of fisheries tend to look at it that way,” says Rose.

But even when relying on comparable real-world data, different models—each with their own limitations and assumptions—produce different results. That’s exactly what happened when Rose and colleague Carl Walters examined the same data DFO used in its stock assessments, but using a different assessment model to the federal fisheries department scientists.

In The state of Canada’s iconic Northern cod: A second opinion (2019), Rose and Walters’ alternative modeling supported overfishing as having a substantially greater role in the population decline of Northern cod than had been estimated in the DFO stock assessments. Unreported catches of foreign fleets and discarding of small fish by Canadian vessels may have contributed to cod’s decline in the early 1990s, argued Rose and Walters—adding DFO’s inference that fishing had little impact on subsequent stock growth likely led to the department’s increasing annual fishing quotas in more recent years. Then, as now, DFO contends natural mortality (due to, for example, lack of capelin prey and warming waters) is mostly responsible for the decline of cod leading up to the moratorium and in its slow rebuilding ever since.

Graphs from the Rose and Walters (2019) study comparing various measurements estimating the number of fish in the sea.
Estimates of historical changes in stock biomass and mortality rates from the model used by Rose and Walters (2019)—what’s called a Virtual Population Analysis (VPA) model—with comparisons to the model used by Fisheries and Oceans Canada, the Brattey et al. (2018) state-space model, the Northern Cod Assessment Model (NCAM). Comparisons are shown by: a) trends in biomass; b) trends in fishing mortality rate; c) trends in natural mortality rate M. Republished with permission. Source: Rose GA and Walters CJ (2019), The state of Canada’s iconic Northern cod: A second opinion. Fisheries Research.

Of that DFO finding, Hutchings, Rose and Shelton (2019) argued that the proposed pattern of naturally caused mortality “if real, would be without precedent for a fish with the life history of Atlantic cod.” 

“It would be optimal and reassuring if differing model approaches gave similar results, but when they do not, as here, it calls for increased management caution,” Rose and Walters argued in 2019. 

“The impact on the stock’s ability to produce is what fisheries management is all about and it’s how you have to frame overfishing. Taking a certain amount like a quota is not the whole story. Taking the same quota at a time of high productivity might be fine. Taking that same quota at a time of low productivity becomes overfishing. My view of this—you can’t easily separate overfishing from the environment,” says Rose today, arguing DFO’s assessments have consistently suggested the stock is stronger than what it is. 

So, exactly how many fish are in the sea? 

At its peak, the spawning biomass of northern cod reached 1.6 million metric tonnes (that was in 1962—in fact, that’s the first year for which these figures are available). Thirty years later, in 1992, the year of the collapse, the biomass then dropped to between 72,000 and 110,000 tonnes. In 2015, DFO reported a total end-of-year (fall or post-fishery) Northern cod biomass estimate of 500,000 metric tonnes. But based on Rose and colleague Sherrylynn Rowe’s independent survey in the spring of 2015 (prior to the fishing season), Rose argues that number was likely closer to 310,000 t. Both estimates are well below the lower reference point for Northern cod (800,000 t).

With DFO foregoing its annual cod survey, Rose says it means fisheries managers will have to base their decisions on two-year-old data, at a time that could be argued is a critical time for determining whether the stock will continue to grow, or whether mortality from fishing and other sources will continue to prevent any growth. 

“Everyone wants the stock to grow so this is a key question,” says Rose—adding a year-to-year growth trajectory is key when trying to rebuild a stock.

“There’s a real data gap. If we don’t know anything about these cod and capelin stocks, then making predictions is really hard to make unless you know what those fundamental driving factors are,” says Rose, who argues fisheries managers need more data today than ever before.

As one example, Rose offers: “What is the effect of climate change on the stock? We need specifics.”

Seasplainer is The Independent’s monthly fisheries and oceans explainer series by journalist Jenn Thornhill Verma. Canada is a country of coastlines—the longest on the planet. The magnitude of that coastline is only overshadowed by the knowledge of those who call these coastlines home. Seasplainer travels to the boots and boats in harbours of the Northwest Atlantic to relay the best-available evidence on fisheries and oceans in Canada. Our explainer series covers a range of topics relevant to fisheries management, marine biodiversity, ocean climate, environment, natural resources, and more. Each issue is reviewed by those with on-the-ground, bench or policy strengths and expertise. This issue was reviewed by: Dean Bavington, George Rose, Kimberly Orren, and Robert Rangeley.

Follow Jenn on Twitter.

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