Life History of a Fish: Atlantic Cod

By Scotty Kyle

I am an Atlantic cod, most important and largest member of the genus “Gadus”, which contains several other cods. All “true” cod are medium to large-sized, demersal (bottom loving) fish found around the cold, northern oceans of the world. Many other fish, unrelated to me but also called “cod”, are found throughout all the oceans and some freshwaters, of the world. Human scientists named me Gadus morhua hundreds of years ago but well before that humans have used me for food, barter and medicine. I enabled creation of new settlements, caused wars, contributed to growth and collapse of economies, fed millions, and cured diseases. 

We cod are torpedo shaped, elongate fish with characteristic prominent single barbles below our “chins”. We have large eyes, to assist us find food in deep, dark and murky waters and a big mouth with which to gulp in worms, crustaceans and, as we grow older and larger, an increasing proportion of other fish – including our own young. We don’t have any prominent teeth, but simply swallow our food whole. Our colouring can change with depth, but we are usually grey, green or reddish brown on our upper side and creamy below. 

In terms of size, we can attain 2 meters (78 in.) in length and 100 kilograms (220 lbs.) in weight, but are more common around one meter (39 in.) and most fish caught are in the range 5-12kilograms (11-26 lbs.). Generally, our maximum sizes in most areas are greatly reduced, due to sustained overfishing, but really large individuals still survive in isolated areas. Although we are sometimes still abundant, we are usually dispersed, but congregate towards spawning time when aggregations can develop from January to April each year. These shoals develop in fairly deep water and then pairs of fish swim off and, while the female swims slowly in circles, the male swims vertically very close below her and fertilises the eggs as they are produced.

A plate of fish and chips.
Fish and chips is how most of us make our first acquaintance with cod. Learn more about this amazing species from our blog.

We are possibly the most fecund fish species, in that a 34 kilogram (75 lbs.) female cod is estimated to produce a record 9 million eggs, while one of 5 kilograms (11 lbs.) produces a paltry 2.5 million. We spawn within a limited temperature range of about 4-6 degrees Centigrade (39-43 degrees Fahrenheit) and the eggs drift and develop for about 3.5 months before sinking into deeper water. We grow rapidly and mature at about 50 centimeters (20 in.) and an age of 3-4 years. Some of us have been known to attain 25 years of age. 

In terms of range, we are a complex species. Our distribution extends from Massachusetts, up and round the USA Atlantic seaboard past Newfoundland, Greenland, Iceland, Norway, past the UK and as far south as Portugal. This range is, however, composed of at least nine almost separate sub-populations and this has caused much of the turmoil in terms of fisheries management. Although we can be found in shallow waters, we are most abundant offshore in fairly deep areas and yet are most common, obvious and targeted by fishers in shallow ocean areas. Everyone must have heard of our past amazing abundance on the Grand Banks off Newfoundland and the Dogger Bank in the North Sea.

The Vikings, who crushed local peoples, established new villages, and even reached North America, couldn’t have survived their long trips and extended stays in inhospitable areas withoug eating my species. Another sea-faring nation, Portugal, developed a vibrant dried cod economy and market at the same time. In many areas during the centuries of “western” colonisation, cod were a very important part of local economies and indeed survival. Many towns were initially placed at harbours that were developed for cod fishing. One of the visual tokens of how significant I was to humans is the “sacred cod of Massachusetts”, a carved wooden cod hung in a place of honour in the state’s House of Representatives. 

For many, many decades exploitation of my species grew slowly and facilitated the establishment, survival and growth of many north-eastern American cities. In the end, however, the continual growth and demands of the humans could not be sustained by some of my populations.

A commercial cod catch
In spite of Atlantic cod’s excellent fertility, overfishing can cause a collapse of population.

Probably the most spectacular and well documented collapses of fish stocks were those of cod and wars were fought by humans over remaining stocks until there were simply not enough fish left to fight over. In the 1960’s, the Newfoundland cod fishery, based exclusively on my species, had climbed to about 800 000 tons per annum. By the 1980’s it had fallen to 200 000 tons, due to overfishing and by 1992 a moratorium on fishing had to be installed. This was a “managed” fishery and yet it ended as an economic and social disaster as it simply ran out of fish almost overnight. Perhaps the most important reason for the collapse was that people assumed there existed one integrated population of cod across our range, while in fact there was very little recruitment from neighbouring stocks.

All fish live in ecosystems and are part of food webs that are complex and interconnected systems. The effective and cumulative removal of so many tons of biomass, of fish in this case, was simply too much for the ecosystem and it effectively ceased to function normally. The removal of so much nutrient from the system resulted in not enough food for the remaining fish and so, despite the incredible numbers of eggs produced by each female cod, recruitment almost stopped completely. Recovery of cod stocks in this situation has been slow and is still erratic. 

Another human upheaval created around my species was the series of three “cod wars” fought between Iceland and the United Kingdom between 1958 and 1976. Iceland was dependent on cod fishing, but the United Kingdom and other countries had become used to fishing very close to Iceland and job opportunities depended on it. To protect its cod stocks, Iceland proclaimed a “12 mile” limit of no foreign fishing around its shores and began to enforce it. It came to actual naval clashes between warships of both nations. Iceland won; not because it had a better fleet (it hadn’t), but because it had nowhere to retreat, while for the UK the issue was not important enough to fight an all-out war over, against the world’s opinion at that. 

Cod fisher with catch
Atlantic cod offers an excellent recreational fishing opportunity as well.

Commercial fishing remains a serious threat to my species but, in many areas and sub populations, appropriate and strict limits are now in place and some cod populations are recovering well and others are being sustainably used. Almost all commercial fishing is carried out using nets, usually trawled along the bottom of the sea, but almost all true recreational angling is carried out by rod and line. There are very few examples of line fishing anywhere in the world severely damaging fish stocks and recreational line fishing, often targeting large fish, can only succeed and be popular where stocks are good and large fish are still available. 

There has always been local rod and line fishing for food and recreation almost everywhere that there were inshore cod stocks available. People can often fish, very easily and inexpensively, from the shore or from small private boats, using baits or artificial lures to catch cod and some other species. While this suits many people, especially beginners and casual anglers, those seeking more excitement and a greater challenge now have excellent opportunities to go after really big cod. 

In many harbours, particularly along the rugged far northern Atlantic coast, specialized fishing operators provide excellent access, equipment and advice to facilitate the keen angler to put his skill and strength against the larger members of my species. From the Fjords of Norway and the islands off Scotland to the north-eastern seaboard of the USA there are many excellent charter operations able to take anglers to the right place at the right time and give guidance on how to fish. The weather can be foul and conditions difficult, but the results can be excellent and well worth the effort and expense. 

These operators are no threat to my species and, as mentioned, can only thrive if the fish stocks are well managed. As general management of cod improves there will be increasing scope for greater numbers of operators and new destinations will be added. While, in the far past, man scarcely impacted our stocks and then there was a long and progressively worsening period when he simply killed too many cod to satisfy his own greed. Hopefully there will now be a period of improved balance between exploitation of our species and the needs and wants of man.  

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