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
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