Fish Stories

The US is in the midst of a mass migration and it’s not hordes of Latinos storming the Texas border. Rather, it’s sea life – fish and shellfish along our eastern and western coasts.

Why? Because the oceans are getting warmer. As their habitats change, free swimming critters can move. The North Atlantic Ocean has warmed about a quarter of a degree C every decade since the early 1980s. The Gulf of Maine has warmed 3 to 5 times faster and is now 5 degree C warmer than in 1985, according to NASA.

We are witnessing this phenomenon right off the coast of New England. Shrimp have all but disappeared from the Gulf of Maine whereas lobsters are now flourishing there. Conversely, lobsters are rapidly disappearing from southern New England. Warmer waters have increased lobster disease and decreased fertility.

Cod are also moving north from the Gulf of Maine and by 2100, they will be making their home off Newfoundland and Labrador.

Warmer water species are also moving north. Striped and black sea bass are now moving in. They also like to munch on lobsters, furthering the latter’s decline.

A similar story is being told on the West Coast. Mackerel, rockfish, and pollock, are disappearing from the Pacific Northwest. By 2100, predictions are that they will live exclusively in the Aleutians or further north in Bristol Bay.

Why do fish migrate as the waters get warmer? According to an article I read in the New York Times, the reason is oxygen. Warmer waters hold less dissolved gases, including oxygen.

Think about it, when you engage in aerobic exercise, you start breathing harder and faster. Why? Because your body needs more oxygen. It’s also why if you go from sea level to Denver, you may feel dizzy. Your body is not getting as much oxygen in the thinner air.

It’s no different if you are a fish. Some fish, especially fast moving predator species like cod which are higher up the food chain, have naturally higher metabolism. The literally go where the oxygen is.

You may then ask why predator species in the tropics, like tarpon and barracuda exist there at all. Basically, they evolved in the tropics so they are used to it. In addition, at this time, the relative temperature increase in the tropics is currently not as great as it is in higher latitudes.

Warmer ocean temperatures off New England have been implicated as the reason cod populations did not recover even after commercial fishing practices were changed, according to a 2015 study published in the journal Science.

Now here is the interesting, or maybe frightening, thing about the NY Times article. It wasn’t about migrating fish populations.

It was about one of the most devastating mass extinction events of the last 500 million years, called the Great Dying. The geologic record shows that 252 million years ago, 96% of all marine species, and 70% of all terrestrial species died out over a span of a few thousand years, a blink of the eye in geologic terms.

Recent research also published in Science concludes that greenhouse-gas driven global warming during that extinction raised temperatures in the atmosphere and ocean by more than 10 degrees C and depleted global marine oxygen levels by almost 80%. Terrestrial life baked and ocean life suffocated.

Jump forward 252 million years to the 21st century. Worldwide ocean temperatures are increasing. We are already seeing a decrease in ocean oxygen levels. Average air temperatures have increased by 1 degree C and because we are doing just about nothing, they will go up by about 4 degrees by 2100.

The authors of the Science article concluded that current trends in ocean oxygen loss suggest we may already be at the beginning of another oceanic extinction event.

The story of the Earth’s history is found in its rocks. With a lot of hard work scientists have been reading that story for centuries. Today, the fish migrating north along our coasts are telling us a new story. We need to start listening.

Published in the Westborough News, January, 2019