FISH FACTS: Atlantic cod course
By Dr Ben Diggles | 28 October 2021
The story of the rise and fall of the Atlantic cod (Gadus morhua) fishery in the northwest Atlantic Ocean is a famous caveat. The upwelling coastal waters and bottom features of this part of the world have generated a highly productive “groundfish” fishery that has supported the indigenous peoples living in Iceland, Greenland and North America for thousands of years. years. The Atlantic cod fishery was legendary for its seemingly endless supply of fish. Explorer John Cabot first officially documented fishing in the waters off Newfoundland for the English aristocracy in 1497. Such was the considerable number of cod at this time, his sailors restocked his vessel by picking up simply cod in baskets weighted with stones and lifted from the bottom. However, it was not yet a pristine fishery, as it happened several hundred years after Norwegian and Basque fishermen first established the international trade in dried and salted cod (called stockfish). With its low fat content and delicious, firm, flaky flesh, cod could be dried outdoors and after salting could be stored for months, allowing the stockfish to be transported long distances to be sold. in markets all over Europe.
However, once the technological innovations of the second half of the 20th century appeared, it was all over. The fishing was gone. Atlantic cod populations are divided into several genetic stocks, but the Northwest Atlantic fishery off the east coast of North America peaked in 1968 with a catch of over 800,000 tonnes, representing nearly 25% of the world’s record cod catch that year, or nearly 4 million tonnes. . This was a more than 400% increase in landings since the late 1940s, as industrial fishing power in the region increased dramatically. The development of more powerful boats, better nets, depth sounders, freezers and other equipment during the post-war period, combined with government subsidies, led to massive industrialized overfishing of the Northwest Atlantic fishery over the years. next decades. Despite the undoubted resilience of Atlantic cod to fishing (the female cod grew up to 2 meters long and 210 lbs (96 kg), while an 80 lbs (36 kg) fish could produce nearly 10 million eggs), after years of ignoring warnings from fisheries scientists about signs of overfishing in the 1980s, the stock collapsed. The fishery was halted in 1992, but only after the once indescribable Northwest Atlantic cod stocks were reduced to less than 1% of their original biomass.
The collapse of the fishery had enormous economic effects and put more than 30,000 commercial fishermen and processors out of work. But many believed that the closure of the fishery would only be temporary, that cod stocks would rebuild quickly, and that they would resume fishing in 3 to 5 years. However, collapsed cod stocks have not recovered. Indeed, they still have not recovered, even 25 years after the cessation of industrial fishing. Because Atlantic cod were the most important predator in the Northwest Atlantic, they ecologically dominated the seascape with their diet, controlling stocks of baitfish, lobsters, crabs and other crustaceans. Thus, the extirpation of cod by commercial overfishing led to “trophic cascades” which included increased abundance of these various prey species and other ecological changes, including a reduction in zooplankton (which was eaten by the most common prey species. large schools of plankton-feeding baitfish) which reduced the food supply for the larvae. Cod. The strong fishing pressure also caused a fishery-induced evolution that destroyed spawning migrations and congregations and resulted in the maturation of cod 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 eaten by the much larger population of plankton-feeding baitfish, while the mortality rates of juvenile and even adult cod have increased. also increased dramatically in recent years due to a massive increase in seal populations (from 8,000 in the 1960s to over 500,000 in 2014). All of this is evidence of what scientists call a “predator-driven Allee effect” where predation reduces a species’ reproductive potential so low that it cannot replenish its population, once its numbers are reduced. passed below a certain population size. Which is bad news for Atlantic cod.
The hard lessons of the Northwest Atlantic fishery are still being learned today. Recent modeling suggests that recovery from the Allee effect could have been enhanced by immigration, even of relatively small numbers of cod from unfished populations. These fish would be more genetically diverse (not having undergone any evolution induced by fishing), which would make them capable of reproducing more quickly and more efficiently, allowing the cod to reach the critical size of the population which would allow to start restocking. Unfortunately, there were no longer unfished Atlantic cod stocks in the Northwest Atlantic, so the results of this modeling effort are irrelevant. But they tend to support suggestions that marine protected areas can serve as “emergency savings in the bank” if a fishery is so poorly managed that it “goes into serious deficit”.
But if you think these issues are limited to commercial fishing, it’s time to think again. Over the past 10 to 15 years, we have seen similar magnitudes of increases in fishing power fall into the hands of recreational fishermen. I mentioned this earlier this year in a previous column where a study found that anglers in bass tournaments in the United States became 3 times more efficient at finding and catching fish over the period. 10 years between 2005 and 2015. This three-fold increase in the efficiency of angling was attributed to “improvements in sonar systems, satellite communications, global positioning systems, fishing gear and technology. information sharing ”. With today’s technology, for the first time in history, fish really have nowhere to hide. Even the most remote small rocky outcrops can be detected in deep water by powerful sounders, cracked by GPS, and effectively fished with modern gear. It also means that there are no longer any natural marine protected areas.
This subject was explored in a recent scientific journal article entitled “Technological innovations in the recreational fishing sector: implications for fisheries management and policy”. The reviewers found that the new technology has brought about “rapid and dramatic changes in the way recreational fishermen interact with fishery resources.” From improving the search and catching of fish, mimicking their natural prey and accessing previously inaccessible waters, to anglers sharing their exploits with others, the technology is completely changing all aspects of recreational fishing. The result is that today, more than ever (and especially since and the increase in recreational fishing effort since COVID), recreational fishermen in Australia are able to put increased pressure on fish stocks through improved gear (eg fishing gear) and the use of technology. to locate fish (for example, sonar, GPS, weather forecast, catch forecasts, forums). In addition, “the use of smartphone apps can lead to ‘mass fishing’, in which fishermen use apps to identify current hot spots.” This is something I can certainly relate to, considering I have been kicked out of several places recently in Moreton Bay, where I have fished without worry for decades. Is the antidote to these endless technical innovations more marine protected areas or stricter fisheries management? Or do recreational fishermen need to redouble their efforts to restore and improve damaged fishing habitats in order to improve fish stocks and increase the size of the fishing pie? Maybe we need a little of all three? Or at least a lot more of the last.
For more information on the recovery (or lack of recovery) of Atlantic cod, see: onlinelibrary.wiley.com/doi/full/10.1111/faf.12470
To learn more about the effects of technological innovations on the management needs of recreational fisheries, see: link.springer.com/article/10.1007/s11160-021-09643-1