Behind the Catch
Sea Surface Temperature Increases in the Gulf of Maine
This is the first blog in Talking Fish’s new series, Behind the Catch, in which we’ll explore New England’s waters and fisheries from a scientific perspective. By examining the region’s fundamental ecology, we can better discuss and tackle marine conservation issues.
Clayton Starr is a guest writer for Talking Fish. He is a recent graduate from Bowdoin College where he earned a bachelor’s degree in Environmental Studies and English with concentrations in Marine Science and Creative Writing. Clayton hopes to communicate science to spread understanding and, ultimately, to inspire climate action.
It’s no secret that all over the world, average annual temperatures are rising.
The entire planet is heating up and has been for almost 200 years. Unfortunately, the ocean is no exception. In fact, in the Gulf of Maine, sea surface temperatures are increasing faster than almost any other ocean region. This blog unpacks the mechanics behind that trend and some of the specific challenges facing New England’s fisheries.
A Runaway Trend
To understand the Gulf of Maine’s changing oceanography, it helps to first think globally. In part, the region is warming for the same reason that oceans everywhere are warming: the runaway greenhouse effect.
As everyone knows, heat on Earth comes from sunlight. Naturally occurring greenhouse gases (GHGs) trap heat within the atmosphere and insulate the planet. This greenhouse effect is completely natural. Actually, it prevents Earth from becoming a snowball. Without GHGs (carbon dioxide, methane, nitrous oxide, etc.), much of the sunlight and heat would bounce off Earth back into space.
It’s the runaway part that’s unnatural. Since the industrial revolution, cars, infrastructure, factories and land use changes have polluted the atmosphere with a surplus of GHGs. Human emissions—mostly in Western countries and especially in the United States—have raised the amount of carbon dioxide in the atmosphere to over 400ppm, the highest concentration in three million years. With more GHGs, more heat is trapped. As a result, ice cap melting increases, and heat that would normally reflect off the poles is retained, as well. This cycle is why the entire planet and its ocean waters are warming.
But why is the Gulf of Maine warming so much faster?
Upping the Hot, Downing the Cold
In the last decade, the Gulf of Maine’s sea surface temperatures have warmed by ~0.04ºC per year, which is 4x the global average rate and faster than 99% of the global ocean. The cause is the region’s unique circulation pattern, specifically the interplay between two currents: the Labrador Current and the Gulf Stream.
Typically, the cold Labrador Current flows south from the Arctic while the warmer Gulf Stream flows north up the eastern seaboard. These two systems balance each other out and help to regulate the region’s temperature.
The Labrador Current is a very dense water system that forms in the Arctic annually when sea ice freezes. Sea ice, like all ice, is frozen fresh water and does not contain salt. So when sea ice freezes in the Arctic, salt accumulates in the surrounding unfrozen water, and a very cold and salty water mass is reborn every winter. The Labrador Current sinks far below the surface and acts as the region’s predominant south-flowing current.
Yet, man-made global warming has disrupted this process. As the poles melt, more fresh water from sea ice and from Arctic landmasses enters the ocean. This added fresh water dilutes the Labrador Current’s salt content, making it less dense. The result: less cold water from the Labrador Current sinks and flows into the Gulf of Maine.
With a weakened Labrador Current, the warmer Gulf Stream is becoming the dominant circulatory system in the Gulf of Maine. Think of the region as a bathtub with the cold tap turned down and the hot tap turned up. This lop-sided tug of war is causing the Gulf of Maine to warm rapidly.
Implications for Fisheries Management
The ecological consequences of sea surface warming are manifold: changes in fish distributions, predatory relationships, and disease transmission to name a few. As Colin Woodard reported for the Portland Press Herald just days ago, “Warming within the swirling ocean depths of the Gulf of Maine has implications for all life and livelihoods within the ecosystem.”
Commercially valuable fish stocks—including lobster, red and silver hake, yellowtail and winter flounder, and Atlantic cod—have already started moving northward or further offshore in search of colder waters. The challenge for fisheries management is not just to be able to adapt to these changes but also to anticipate them.
Take the Maine Lobster industry for instance. According to the state’s DMR, landings have risen over the past thirty years. However, in 2012—the warmest year on record in the Gulf of Maine—more lobsters were caught than the industry could process, let alone sell. Supply exceeded demand, and ex-vessel prices dropped. Ex-vessel prices (the price that fishermen receive at docks) fell to $1.25, which was 70% below average. To compensate for this bumper harvest, an unusual amount of Maine lobsters had to be sent to Canada for processing.
Yet, the industry learned from this year.
To reduce mortality, fishermen made efforts to keep lobsters cool and oxygenated on their boats during warm spells, and more processing facilities opened in the state. When 2016 brought another ocean heat wave in the Gulf of Maine, the industry was ready, hauling in 133 million pounds of lobster and $533 million. At the time, those were industry records for both landings and value.
With climate change and ocean warming, we are entering a new world order. But if we invest in fishing infrastructure, practices, and policies that account for these changes, perhaps we can stay ahead of climate impacts.
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