The Northern Cod are Coming Back

ResearchBlogging.org The Atlantic cod offshore of Newfoundland are at this point the stuff of legend and fable. For five hundred years, they supported one of the largest fisheries in the world, until, in the latter half of the twentieth century, a tangle of new technology, greed, and mismanagement caused the population to crash. In 1992, with enraged fishermen trying to batter down the door, Canada’s Minister of Fisheries declared a moratorium. The fishery was closed.

The closure was expected to last a couple of years, maybe a few, giving the cod population time to rebound. But the rebound didn’t come. For twenty years, cod remained scarce, virtually extinct in ecological terms. Hypotheses were proposed to explain this lack of recovery. Maybe the cod had been selected for smaller size by centuries of net meshes. Maybe other species had filled their niche. Maybe the ecosystem had flipped into an alternate stable state, and was no longer capable of recovery. The northern cod became the canonical example of overfishing and collapse. The history took on mythical overtones. Moses striking the rock. Gilgamesh killing Humbaba, and felling the cedar forest.

Six years ago in the fall of 2009, when I was a brand-new grad student at the University of Washington, a scientist from the Memorial University of Newfoundland named George Rose came to give a seminar. He argued that the collapse of the northern cod had been accelerated, and their recovery hampered, by poor ocean conditions. And he presented tentative evidence that these conditions might have begun to relent, giving the cod their first chance in two decades to succeed. In 2008, acoustic surveys showed that cod were more abundant in certain areas, and, for the first time in twenty years, were forming large spawning aggregations. A few pieces of the old ecosystem were starting to pull themselves back together.

Cod spawning aggregations

Echogram from March 2008 showing cod spawining in massive “haystack” aggregations. The dark red line is the sea floor, and the blobs extending above it are schools of cod. This aggregation is over a mile long and 100 m tall in some places. (From Rose and Rowe 2015.)

I didn’t hear much more about the northern cod until this month, when Rose and another scientist at Memorial, Dr. Sherrylynn Rowe, published an open-access paper showing that 2008 was not a fluke. Over the past few years, cod biomass has increased modestly. Cod have continued to spawn in large aggregations, including in two northern channels that they abandoned during the collapse. Most importantly, they argue, capelin—the small schooling fish that were historically the cod’s most important prey—are rebounding after a collapse of their own, probably related to cooler ocean temperatures in the early 1990’s. Cod in survey trawls are older, longer, and fatter today than they have been in a long time.

The cod are by no means recovered. Their population is still small compared to historical levels, and it is too early by far to reopen a large-scale fishery. But if current trends continue, the cod may be poised for their first sustained population growth in decades. This is not a guarantee. There is a lot that can go sideways in the ocean, not to mention in human affairs.

But it is still really important to know that an environmental disaster of this magnitude—the disappearance of one of the largest populations of fish in the Atlantic, the end of a 500-year-old fishery, the overnight gutting of Newfoundland’s traditional economy—has a chance of reversal. Fish, given the slimmest chance and enough time without human exploitation, can actually start fighting their way back.

Testify, Dr. Malcom.

To me, this is reason for profound optimism, and profound gratitude.

Rose, G., & Rowe, S. (2015). Northern cod comeback Canadian Journal of Fisheries and Aquatic Sciences, 1789-1798 DOI: 10.1139/cjfas-2015-0346

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