Lined Seahorse- Hippocampus erectus

Cool Fish, Hot Water: Seahorses Swim North

New England’s ocean is getting warmer—and the fish are headed north.

In 2012, water temperatures in the Gulf of Maine reached record high temperatures. NOAA reports that sea surface temperatures in some areas were as much as 11 degrees Fahrenheit above long-term averages, while deep waters were about 3 degrees  higher than average. Temperatures in the first half of 2013 were less extreme, but remained unusually warm. The high temperatures of the past two years aren’t a new development, either—the Gulf of Maine has experienced a long-term warming trend for well over a century.

While these balmy temperatures may be nice for swimmers and surfers, their effect on marine life might not be as positive. The impacts of climate change on the health of marine species are still uncertain, although scientists are beginning to understand how warmer temperatures cause plankton to bloom earlier, help invasive species like green crabs thrive, may cause fish to grow to smaller sizes, and push commercially important species like cod to cooler, deeper waters.

One effect of warming waters in New England has been very clear, though. As ocean temperatures around Cape Cod and in the Gulf of Maine reach record highs, fishermen have started to notice some unusual species on their lines and in their nets—species more typical of warmer waters in the mid-Atlantic or even the tropical ecosystem of the Caribbean. Over the next several posts in this series, we’ll introduce you to some of these new faces.

Our first species—perhaps the most startling example of a once-subtropical species showing up in the Gulf of Maine—is the common seahorse, Hippocampus erectus (also known as Hippocampus hudsonius). Although their range does extend as far north as Nova Scotia, these familiar fish were once only common from the Chesapeake Bay to the Venezuelan coast, and were almost never found in the Gulf of Maine. Most people probably associate these fish with snorkeling on a reef or the tropical tank at the aquarium. But last summer, at least one Maine lobsterman, David Cousens, pulled up several seahorses in his lobster traps—something he’d never seen before.

The evidence for warm-water fish species moving north isn’t just anecdotal. Several scientific studies over the past five years have shown strong evidence that fish distribution is changing in response to climate change. In 2009, scientists from the National Marine Fisheries Service tracked the center points of the populations of 36 fish stocks and found that between 1968 and 2007, nearly all of these species moved north or shifted to deeper water. In 2012, a group of scientists developed an index called the Mean Temperature of Catch, or MTC, which is calculated as the average “preferred temperature” of the species caught in an area. Worldwide, MTC has increased steadily since at least the 1970s, suggesting that global fisheries are catching more species that prefer warmer water.

Most recently, an article published in Science shows that the direction and speed at which the distribution of species changes closely tracks the direction and speed of the effects of climate change. This does not always mean that species move north—off California, for example, stronger winds have pushed cooler waters south, and fish have moved south, too—but it does mean that marine species are redistributing to follow cooler water as temperatures change. In New England, cooler waters are moving north and offshore, and that’s where the fish are headed, too.

Stay tuned over the next several weeks as we introduce you to some of the species that have started calling New England home as our water temperatures rise. These profiles will just skim the surface of the fish moving in to this region—everything from grouper to vivid tropical species like filefish has been spotted in this area in the past few years, and these changes may just be beginning. Whether a beachgoer, a diver, or a fisherman, we will all have to adapt to the changing environment and new species in the Gulf of Maine.