The old saying goes that “the cod were so plentiful that you could walk across the water on their backs”. Nowadays cod populations in New England are nearly gone. Not only is this bad for people who want to eat fish… or walk across their backs, but it’s driving ecosystem loss and climate change.

It’s clear that when mass amounts of fish are removed from the ocean, certain ecosystems are lost. But how does overfishing contribute to climate change? Large boats burn massive amounts of diesel, releasing carbon dioxide; while on land trucks and planes burn fuel to deliver seafood to restaurants and grocery stores. Additionally, trawling (dragging a net along the seafloor) disturbs ocean sediments where carbon is stored. Yearly, trawling releases almost the same amount of carbon as the global aviation industry. Removing fish from the open ocean, particularly large fish, prevents the carbon in those fish from eventually sinking to the ocean floor and becoming sequestered. Instead the fish-based carbon is actually added to the atmosphere as people eat them, convert them to energy in our bodies, and then exhale CO2. 

These are the hidden costs of fishing.  Yet, fish are often considered the “sustainable” option, especially compared to meat like beef which is notorious for contributing approximately 7% of annual carbon emissions. So in addition to eating less fish (and meat overall) more regulations must be put into place and enforced that set clear and ecologically informed limits to fish catches.  

Nowadays, a major method in regulating fisheries is setting limits based on the MSY or Maximum Sustainable Yield. This number estimates the allowable harvest, based on historical catch data that includes the amount and size of the fish being caught. 

MSY is based on what we think are healthy stocks; but people have been fishing the oceans for centuries before catch data and regulations were a thing. That means the starting point for many MSY calculations are wrong: the baseline is not a healthy population, it is a population that has already been fished for centuries. This is called “Shifting Baseline Syndrome”. For example, historical records from the early 1800s show that Dogger Bank, in the North Sea, was a much more productive cod fishery than it is now.  Yet, modern regulations don’t reflect that because MSY calculations are based on data collected after the cod were already overfished. Regulations should prioritize the restoration of fish populations to historic levels which will help restore degraded ecosystems and keep more carbon in the ocean.

Currently, overfishing is evident in almost every major fishery. Each year fish are smaller and less numerous; boats have to go further and fish longer to catch the same amount, requiring more energy and harming fisheries. On Georges Bank off of Cape Cod fisherpeople are catching less than 1/3 the pounds of cod in each net than they were catching just 2 years ago. Cod stocks have crashed many times across fisheries in the northern hemisphere. For example, in 1993 the Northern Cod fishery off the coast of Canada was completely shut down because populations were unthinkably low. 

So, why is this current decline so concerning? Well, unlike in the 1990s when cold water temperatures combined with overfishing were to blame; climate change is now the culprit.  

As ocean temperatures increase, female fish have less babies and those young fish have less of a chance of survival. So now more than ever it’s urgent to decrease catch limits to below MSY to give cod, and all fish a fighting chance to rebound. 

It’s hard to imagine how many fish swam through the ocean before the advent of modern fishing technology just 300 years ago. Enforcing catch limits that prioritize the fish rather than profits might change that.  Not only could that restore the potential of the oceans, in turn it will help in the fight against climate change and create a more resilient planet.