Fish Facts

FISH FACTS: Atlantic cod lessons

Atlantic cod. Image: Patrick Linehan

THE story of the rise and fall of the Atlantic cod (Gadus morhua) fishery in the northwest Atlantic Ocean is a famous cautionary tale. The coastal upwellings and bottom features of this part of the world generated a highly productive “groundfish” fishery which sustained native people living in Iceland, Greenland, and North America for thousands of years. The Atlantic cod fishery was legendary for its seemingly inexhaustible supply of fish. Explorer John Cabot first officially documented the fishing in the waters off Newfoundland for the English aristocracy in 1497. Such were the sheer numbers of cod at that time, his sailors reprovisioned his ship by simply scooping up cod in baskets weighted with stones and raised from the bottom. However, this was still not a virgin fishery, as he arrived several hundred years after Norwegian and Basque fishers had first established international trade in dried and salted cod (known as stockfish). With its low fat content and delicious, firm flaky flesh, cod could be dried outdoors and after salting it stored for months, allowing stockfish to be transported long distances to be sold in markets throughout Europe.

However, once the technological innovations of the latter half of the 20 th century emerged, it was all over. The fishery was gone. Atlantic cod populations are divided in several genetic stocks, but the Atlantic northwest fishery off the east coast of North America peaked in 1968 with a catch of over 800,000 tonnes, representing nearly 25% of the record global cod catch that year of nearly 4 million tonnes. This was an increase of over 400% in landings since the late 1940s as industrialised fishing power in the area rose dramatically. The development of more powerful boats, better nets, sounders, freezers, and other equipment during the post-war era, combined with government subsidies lead to massive industrialised overfishing of the Atlantic northwest fishery for the next several decades. Despite the undoubted resilience of Atlantic cod to fishing (female cod historically grew up to 2 meters long and 210 lb (96 kg) in weight, while a 80 lb (36 kg) fish could produce nearly 10 million eggs), after years of ignoring warnings by fisheries scientists about signs of overfishing in the 1980’s, the stock collapsed. The fishery was halted in 1992, but only after the once indescribably abundant Atlantic northwest cod stocks had been depleted to less than 1% of their original biomass.

The collapse of the fishery had enormous economic effects and put over 30,000 commercial fishers and processors out of work. But many thought that the fishery closure would only be temporary, that cod stocks would quickly recover and that they would be back fishing in 3 to 5 years. However, the collapsed cod stocks did not recover. Indeed, they have still not recovered even 25 years after industrial fishing ceased. Because Atlantic cod were the most important apex predator in the northwest Atlantic, they ecologically dominated the seascape with their feeding, keeping stocks of baitfish, lobsters, crabs and other crustaceans in check. So the extirpation of cod by commercial overfishing lead to “trophic cascades” which included increased abundance of these various prey species and other ecological changes including reduced zooplankton (which was eaten by the larger schools of plankton-feeding baitfish) which reduced food supply for larval cod. The heavy fishing pressure also caused fisheries induced evolution which destroyed spawning migrations and aggregations and resulted in cod maturing at younger ages and smaller sizes, reducing egg production. The natural mortality rate of cod eggs and larvae also appears to have increased because they were being eaten by the much enlarged plankton-feeding baitfish population, while mortality rates of juvenile and even adult cod have also increased dramatically in recent years due to a massive increase in seal populations (from 8000 in the 1960’s to over 500,000 by 2014). All of this is evidence of what scientists call a “predator driven Allee effect” where predation drives a species’ reproductive potential so low it cannot rebuild its population, once its numbers are decreased below a certain population size. Which is bad news for Atlantic cod.

The hard lessons from the Atlantic northwest fishery are still being learned today. Recent modelling suggests that recovery from the Allee effect could have been enhanced by immigration of even a relatively small number of codfish from unfished populations. These fish would be more genetically diverse (not having been subjected to fishery induced evolution), which would make them able to reproduce faster and more effectively, allowing cod to reach the critical population size which would allow rebuilding of the stocks to begin. Alas, there were no unfished Atlantic cod stocks left in the Northwest Atlantic, so the results of this modelling effort are moot. But they do tend to lend support to suggestions that marine protected areas can serve as “emergency savings in the bank” if a fishery is so poorly managed that it “becomes seriously overdrawn”.

But if you think these problems are restricted only to commercial fishing, it’s time to think again. Over the past 10 to 15 years we have seen similar magnitudes of increased fishing power fall into the hands of recreational anglers. I mentioned this earlier this year in a previous column where a study found that anglers in bass tournaments in the USA had become 3 times more efficient at finding and catching fish in the 10 year period between 2005 and 2015. This threefold increase in angling efficiency was put down to “improvements in sonar systems, satellite communications, global positioning systems, fishing gears and information-sharing technologies”. With today’s technology, for the first time in history, fish truly no longer have anywhere to hide. Even the most remote little rock outcrops can be detected in deep water by powerful sounders, pinged by GPS and effectively fished using modern gear. This also means there are no longer any natural marine protected areas left.

This subject has been further explored in a recent scientific review article entitled “Technological innovations in the recreational fishing sector: implications for fisheries management and policy”. The reviewers found that new technology has led to “rapid and dramatic changes in how recreational anglers interact with fisheries resources. From improvements in finding and catching fish to emulating their natural prey and accessing previously inaccessible waters, to anglers sharing their exploits with others, technology is completely changing all aspects of recreational fishing.” The upshot is that today, more than ever before (and particularly since and the increase in recreational fishing effort since COVID), recreational fishers in Australia are capable of imparting increased pressure on fish stocks through improved gear (e.g. tackle), and use of technology to locate fish (e.g. sonar, GPS, weather, catch predictions, forums). In addition, “the use of smartphone apps can lead to ‘crowd fishing’ wherein anglers are using apps to identify current hotspots”. This is something I can definitely relate to, given how I have been crowded out of several spots recently in Moreton Bay which I have previously fished unmolested for decades. Is the antidote for these never-ending technical innovations more marine protected areas, or tighter fisheries management? Or do recreational anglers need to work harder on restoring and enhancing damaged fisheries habitats to improve fish stocks and increase the size of the fisheries pie? Perhaps we need a little of all three? Or at least a lot more of the last one.

For more on the recovery (or lack thereof) of Atlantic cod, see:

For more on the effects of technological innovations on the management needs for recreational fisheries, see:

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