Our Changing Gulf: When the water rises

Fishermen live by the tides. They know when the high and low tides occur each day. They track the phases of the moon to be ready for the monthly neap and spring tides. The range and strength of the tides and currents is etched deeply in a Maine fisherman’s brain. But what happens when the tides change? As sea level continues to rise along the Gulf of Maine, the tides themselves will become greater. How will sea level rise affect the many commercial fisheries in the Gulf?

The Gulf of Maine is warmer than it was in past centuries. Add heat to salt water and the water itself takes up more space, a process called thermal expansion. Sea level has risen globally due in part to thermal expansion. In addition, a warmer climate also affects land-based glaciers and ice sheets, causing them to melt. Antarctica, for example, has lost 2.7 trillion tons of ice, according to a 2018 study published in the journal Nature. This influx of freshwater into the ocean causes sea levels to rise.
Maine has been keeping track of the tidal range in three ports along the coast for more than a century. Sea level is 7.4 inches higher in Portland than it was in the early 1900s; in Bar Harbor it is 8.7 inches higher and in Eastport 8.4 inches higher. The rise in the level of the Gulf of Maine won’t be stopping any time soon and, in fact, has begun to accelerate. According to a study published by the Island Institute in Rockland, “The Gulf of Maine is especially susceptible to fluctuations in sea level due to changes in the strength of the Gulf Stream and seasonal wind patterns. Sea levels in the Gulf of Maine are projected to rise faster than the global average.”

This image has an empty alt attribute; its file name is sea-level-rise-by-WCHS-1.png

Peter Slovinsky, a coastal geologist with the Maine Geological Survey and the Department of Agriculture Conservation and Forestry, studies sea level rise and its effect on the Maine coast. He has found that in the past two or three decades the rate of rise in the region has doubled, to approximately 3.2 millimeters (0.125 inches) per year. The impact of the rise is made more apparent in part because the Gulf of Maine acts something like a bathtub. Changes in the North Atlantic Oscillation, which affects the strength and direction of westerly winds, and in the pattern of the Gulf Stream are causing ocean water to surge against the coast.

What impact will increased sea levels have on Maine’s fishermen and fishing ports? Higher water levels may, in some cases, afford fishermen additional space in which to berth their boats, turning spots once accessible only at high tide to all-tide access. On the other hand, higher water means inevitable flooding of the streets and docks many depend on to reach their vessels. The effect on the species they fish for is problematic as well.

Coastal wetlands are the unnoticed nurseries for many commercially valuable species in the Gulf. Shrimp, shellfish and certain fish species all spend part of their lives in saltwater wetlands. In addition, wetlands act as a soft protection against storm surges and erosion during major storms. Keeping a healthy stock of wetlands along the Gulf of Maine remains vital to supporting multiple marine species.

Typically, as sea levels rise beaches and coastal wetlands move in response to the higher water. The roots of wetland plants collect debris in a process called accretion, which increases elevation. Beaches “roll” back, steadily moving inland. However, the Intergovernmental Panel on Climate Change Summary for Policymakers 2013 found sea level rise in some cases could be occurring faster than the wetlands’ accretion rate. In that case, the wetlands could be subsumed.

The problem occurs when people and businesses located along the coast take steps to prevent the ever-increasing sea level from flooding their properties. Hard structures, such as seawalls or rock revetments, prevent the beaches and wetlands from moving inland. In those cases, the wetlands drown and disappear. When the wetlands are lost, so too are nursery habitats for many species.

The Natural Resources Council of Maine (NRCM) has produced an online map of the Maine coast based on GIS data to show the impact different sea level rise scenarios could have on coastal communities (https://www.nrcm.org/programs/climate/global-warming-air-pollution/sea-level-rise-maine/sea-level-rise-maps/). The top twenty towns to bear the brunt of sea level rise include fishing ports such as Jonesport, Boothbay Harbor, Vinalhaven, and Harpswell. In a sentence of considerable understatement, NRCM’s web site notes, “Damage to scenic beauty and the livelihood of fishermen and other natural resource-based economies could be devastating.”

Coastal wetlands will suffer from a rising sea level, which in turn will impact Gulf of Maine fisheries. Bates College photo.