The Gulf of Maine is astonishing. Captain John Smith, Rachel Carson with her nephew Roger, and many others have found it wondrous. Many of the marine life connections beneath the waves remain a mystery. Efforts to look at the inner-clock workings, the causal gearing of ecosystems, are frustrated by changes in wind, weather, currents and seasons unseasonable. Understanding the ocean is paradoxical. The more observations made, the more questions arise. The more that’s discovered, the more mystery remains.
Why do authors of a recent Science article, citing empirical evidence that the cod stock collapsed due to climate change, believe that a 100% reduction in the cod catch (instead of the 78% cut taken) would have enabled the cod stock to have “kept up with the climate changes?”
When essential fish habitat goes south, temperature-wise, cod move north to better conditions, regardless of fishing pressure. In fact, Newfoundland is experiencing what George Rose calls a remarkable comeback of cod.
Clearly, cod are suffering from degradation of habitat due to more than global warming. The Science article acknowledges up front that climate change is “contributing” to the problem, not determining it.
The damage from hypoxia and ocean dead zones is expanding due to nitrogen washing, flowing and seeping from the land to feed harmful algal blooms. Could cod reproduction be down due to toxins as well as warmer water?
The evidence, as reported in the Boston Globe, is that “between 2004 and 2013, the mean surface temperature of the Gulf of Maine rose a remarkable 4 degrees.”
Last year’s “rise in temperature exceeded those found in 99 percent of the world’s other large bodies of saltwater.”
The rapid warming is linked to a northward shift in the Gulf Stream and “the warmer water coursing into the Gulf of Maine.”
Water temperature is the most measurable factor for predicting cod reproduction, the colder the better. However mean surface temperatures are not much of a factor because cod are demersal fish meaning they live near the ocean floor, as far from the surface as possible. Undersea valleys fall to depths of 1,500 feet.
A four degree Fahrenheit temperature spike in surface water, exceeding 99 percent of the world’s other larger bodies of saltwater, is less surprising than is the finding that there are 99 other large bodies of saltwater. (The seven seas have been busy.)
The Gulf of Maine is unique. It excels at greatest tidal height, fetch, slosh, and marine life biomass. The Grand Banks may have more biomass but it’s not a saltwater body. The Gulf of St. Lawrence is and has less biomass with warmer waters.
The Gulf of Maine is a sea beside the Atlantic Ocean. It is separated by Cape Cod, Georges Bank, Browns Bank and Nova Scotia. While the Gulf Stream meanders about towards the Denmark Straits off Greenland, spinning off warm core eddies of Sargasso Sea water that drift into Rhode Island. The Labrador Current flows inshore from the Arctic Ocean bringing fog to the Grand Banks. Flowing south of Nova Scotia, rounding Browns Bank cold Labrador Current water enters the Gulf of Maine through the sixty mile wide deep water channel to the north of Georges Bank. Cold nutrient-rich waters from the Labrador Current enables more cod to live in the Gulf of Maine than in the waters around Prince Edward Island to the north or in the warm sandy shoaling waters south of Cape Cod.
The amount of cold Labrador Current water entering the Gulf of Maine varies greatly from year to year. The technical terms for this oceanographic phenomena are “barn door open,” “barn door closed,” and “barn door ajar.” Barn door open years have the coldest deep water in the Gulf of Maine and are associated with good reproduction by cod. Cod will have more than 200,000 eggs per fish per year. Every year need not be a good reproduction year when cod live for decades. If the barn door is closed for a couple of years cod will get by.
From the cod’s perspective, down below, a four degree temperature spike in surface waters does not a rapid warming of ocean waters make.
Marine life abounds in the Gulf of Maine because it is nearly a closed ecosystem. Fresh water from the Saint John (the “Rhine of North America”), Penobscot, Kennebec, Saco, and Merrimack Rivers reduces the salinity to 34 parts per thousand. Salinity nearby in the Atlantic Ocean is 36 ppt. Fresh water stretches out across the sea surface and drives a counter clockwise gyre around the Gulf.
Unlike marine life living south of Cape Cod, marine life born in the Gulf stays in the Gulf, generation after generation. Unfortunately, pollutants swirl around and do not dilute like elsewhere.
Given the great extent and massive volume of the Atlantic, for the surface waters of the estuary known as the Gulf of Maine to warm more rapidly is not surprising. Here, surface water temperature changes, how the currents run and gyre turns, are more related to seasonal weather than to climate. There’s much movement in the spring and much less in the winter.
Knowledge of the Gulf of Maine waters runs deep. Henry Sinclair and his crew of Scotsmen began catching cod in the Bigelow Bight north off Newburyport in 1398. Like the cover of a book, it is best not judge a fishery by temperatures found on the sea’s face.
In 1638, the Pilgrims passed the first fisheries regulation banning the use of cod and striped bass to fertilize fields. It was obvious to those that had left behind the cod bereft waters of Great Britain that cod habitats were not what they were on arrival what with all the clearings, roads, constructions and river damming.
Rather than lay blame on fishery management, we must clean up our act. Stop polluting land, waterways and atmosphere. We must practice responsible stewardship and restore essential cold-water fish habitats. Ours is the only Gulf of Maine we’ve got.