An Ocean Warming: Atlantic Cod and Northern Shrimp Search for Colder Water

Perhaps no other New England species has felt the effects of the Gulf of Maine’s rapid warming like the fabled Gulf of Maine cod. An iconic species since its discovery centuries ago off of New England’s coast, cod profoundly impacted the way our region developed, and has shaped our coastal economies.

Today, however, the state of the species looks much different, with cod stocks in the Gulf of Maine hovering around three percent of what scientists say are sustainable levels. In an attempt to quell the overfishing of cod, restrictions on fishing quotas have been enacted. However, instead of seeing the cod stocks rebound, the numbers have continued to plummet.

There are two reasons for this: First, continued fishing pressure hasn’t allowed for enough of an opportunity for cod populations to recover. The other reason? You guessed it: drastic warming due to climate change.

Cod’s home is no longer the comfort zone

Climate change has led to warming ecosystems all over the world, but the Gulf of Maine is experiencing this warming trend faster than most. Cod, like every species, has a range of temperatures at which they can live comfortably, which in turn makes a range of geographical areas suitable for them. Historically, the Gulf of Maine has been at the southern boundary of their range. But, with Gulf temperatures rising due to climate change, cod are now starting to move north in search of cooler temperatures.

Because of this shift, restrictions on fishing quotas, even if effective on their own, have failed – as they didn’t account for what would happen due to warming waters.

As scientists and fishery managers have begun digesting this information and its implications, they are increasingly calling for something called “ecosystem-based management,” a management principle that considers the environmental factors in play in a given ecosystem. With widespread use, this broader understanding of what’s happening, and why, could provide a brighter outlook for the future of Gulf of Maine cod.

Northern shrimp headed further north

Another Gulf of Maine species, northern shrimp (pandalus borealis), face a similar situation. This small crustacean is an integral part of the Gulf of Maine food web. It’s unique because it is hermaphroditic, meaning the shrimp first mature as males at around two and a half years of age, and then about a year later develop into females. Northern shrimp feed on plankton and benthic invertebrates, and are then prey for several important species of fish, including cod, redfish, and hake.

For decades, the northern shrimp fishery thrived, until a few years ago, when stocks showed massive declines and low levels of shrimp reaching the age when they’re large enough to be fished. Particularly warm water temperatures during what is known as the “ocean heat wave” of 2012 caused stocks in the Gulf of Maine to drop even more dramatically. Although heavy fishing pressure is partly to blame for the driving the stocks down, scientists also point to the shockingly low levels of fishable shrimp. As the northern shrimp’s lifecycle is highly dependent on temperature fluctuations – with colder temperatures producing higher levels of fishable shrimp – the decline can be linked to warmer waters.

Northern shrimp, like cod, have a narrow range of temperatures in which they can thrive and, similarly, the Gulf of Maine is at the southern end of their range.

Long-term fishery closure a warning sign

Since 2013, the northern shrimp fishing seasons have been closed entirely. With ocean temperatures predicted to continue their warming trend and the species’ already vulnerable status, it looks increasingly bleak for the fishery.

Little by little, we are losing cod and shrimp to colder waters, and others soon may follow. It’s clear the Gulf of Maine and its composition is changing. That’s why plans to mitigate climate change must pay close attention to oceans and the warning signs they’re giving. And in the meantime, fishery managers must do everything within their power to ensure that management strategies incorporate the best climate science possible.

 

 

An Ocean Warming: Climate Change in the Gulf of Maine

The effects of climate change can be seen all over the world – whether it’s the severe droughts in California, rapid sea-level rise in the Indo-Pacific, or stronger storm systems, the effects of anthropogenic (human-caused) climate change are seemingly everywhere, and the Gulf of Maine is no exception.

Multiple studies have recently shown that the Gulf of Maine, like most of our planet’s oceans, is warming. However, what sets the Gulf of Maine apart is the alarming rate at which this warming is occurring: Scientists say the Gulf of Maine is warming faster than 99 percent of the world’s oceans.

Granted, the Gulf of Maine has been warming for some time, with a steady rate of about 0.05 degrees per year from 1982 to 2004. But we’re now seeing a substantially accelerated rate in warming, about ten times faster than that – warming by approximately a half-degree per year!

How does climate change impact the Gulf of Maine?

Although scientists are still speculating on the explanation for these accelerated warming trends, there is no question about their negative effects.

  • Countless fish stocks have shifted northwards in search of colder temperatures, leaving fisheries struggling in their absence. And as these species migrate out of the Gulf of Maine, other fish, marine mammals, and seabirds that rely on them for food are now left scrambling, in some instances, to avoid starvation. The Atlantic Puffin, for example, once a critically endangered seabird, is now facing a new challenge: species such as white hake and Atlantic herring – both essential elements in the diets for puffin hatchlings – are seeing a shift in geographical range as they move to colder and deeper waters.
  • Diseases that were never before present in the Gulf of Maine have now carved out their place and threaten species. An epizootic shell disease that plagued southern New England waters for years is now cropping up in the Gulf of Maine and poses a serious danger for crustaceans – primarily the American lobster.
  • Non-native and invasive species like green crabs, longfin squid, and black sea bass have been able to move their way up the coast and into the Gulf of Maine, throwing the delicate balance of the entire ecosystem out of sync.
  • Our coasts are under threat from sea-level rise due to changes in density: As water gets warmer, it expands, presenting small towns and major cities alike with an entirely new set of challenges for the future.
  • And the very chemistry of the Gulf of Maine is transforming. Salinity and acidity levels are changing due to increases in precipitation, the rapid melting of Arctic ice, and the rising levels of atmospheric carbon dioxide and other greenhouse gases.

Chemistry? Sea-level rise? Invasive species? If this all sounds overwhelming, you’re not alone. That’s why we’re introducing this blog series, An Ocean Warming, to explore the impacts of climate change in the Gulf of Maine on the species, industries, and people that depend on its health.

Through regular posts focusing on different aspects of this complex issue, we hope to share insights on what the future and fate of the Gulf of Maine will look like – and how we can understand, mitigate, and adapt to this new reality.