As our planet and our oceans warm, the habits and habitats of marine wildlife change, too. Fish, sharks and crustaceans that are normally found within a certain temperature range are forced to pack up and move. Why is that a big deal? Lots of reasons.
In Maine, for example, lobster fishing is a US$495 million a year industry. But fisherman are catching fewer lobsters (millions of pounds less each year), and the population is expected to continue to decline as these crustaceans migrate toward the cooler waters of Canada. What does that mean for future jobs and state revenue?
In California, sea lions are dying because sardines and anchovies, which comprise their typical diet, are vanishing in the warming waters, leading sea lions to feed on less-nutritious fish. More than 3,000 sea lion pups washed ashore in 2015 - more than 15 times the annual average. One scientist told National Geographic the number was "unprecedented."
From prey to predators, take a look at eight ocean creatures who are now calling more northern parts of the oceans home.
1. Atlantic salmon
The Gulf of Maine is one of the fastest-warming parts of the world's oceans, the Portland Press Herald reports, and water temps are expected to rise another 5.5 degrees Fahrenheit by 2065. While that may seem like a long way off, warming seas are already affecting Atlantic salmon populations in the Penobscot River, Saint Croix River and the Miramichi River in New Brunswick.
"We're seeing declines over very large geographic areas, which points to some sort of factor out to sea, in the marine ecosystem," fisheries ecologist Katherine Mills of the Gulf of Maine Research Institute told the Portland Press Herald.
Mills says salmon likely are heading to deeper waters chasing their food source: capelin, which has seen its own population decline off Greenland and Atlantic Canada, where Maine's salmon go to feed.
2. Humboldt squid
Humboldt squid once called the warm Pacific waters from South America to Mexico home, occasionally going as far north as California. However, the giant squid now migrates so far north it has been found off the coast of Alaska, according to National Geographic.
But occupying cooler parts of the ocean does something odd to these voracious predators. Scientific American reports: "The colder waters...delay their maturation and allow them to survive into the next year, giving them a two-year life cycle. But during this second year they continue to grow fast, meaning that by the end of their two years they attain much larger sizes. In fact, these climate events have triggered the establishment of large bi-annual groups of squid weighing 25 to 40 kg - ten times their normal size."
3. Yellow-bellied sea snake
This exotic and highly venomous snake usually spends its entire life in the tropical waters of the Pacific and Indian Oceans, but in the last few years, a couple of them have made appearances on California beaches. These slithering creatures previously hadn't been seen in California in nearly 30 years, according to Heal the Bay, an environmental group in Santa Monica. The snake, which has a bright yellow belly and a paddle-shaped tail, will drift up to colder latitudes on warm currents, especially when El Niño is strong.
4. Hammerhead shark
Hammerhead sharks are rarely seen in California, yet 2015 brought what one scientist called "an endless parade of hammerheads," reported National Geographic, and several hammerheads were spotted off the Ventura coast this year, too. When this happens, a community's relationship with the ocean changes.
That National Geographic story tells the tale of Richard Shafer, a 58-year-old electrician who free-dives for fish with a speargun. The warming waters had driven game fish like yellowtail north from Mexico. Shafer was off the coast of San Diego in August 2015 and speared a yellowtail. He held it close as he swam back to the boat, worried about a hungry sea lion trying to snatch it. Never did he expect that a seven-foot hammerhead would bite him on the wrist trying to steal his catch.
5. Lobster
Maine has long been famous for its plentiful catches of fresh lobster, and lobster fishing is a major part of the local economy. But will that always be the case? Like salmon, lobsters are migrating away from the Maine coast to colder waters. A 2013 study found these crustaceans moved north about 43 miles per decade between 1968 and 2008. At that rate, Maine lobsters will be entirely in Canada within 30 years, Business Insider estimates.
A new study from scientists at the University of Maine Darling Marine Center and Bigelow Laboratory for Ocean Sciences says baby lobsters might not survive if water temperatures rise five degrees more, which is precisely how much the United Nations’ Intergovernmental Panel on Climate Change expects the Gulf of Maine’s temperature to warm by the year 2100.
The warm water is affecting lobster populations as far south as Connecticut and Rhode Island. A 2015 study from the Atlantic States Marine Fisheries Commission found lobster populations south of Cape Cod, Massachusetts, were at record lows with the number of adult lobsters at 10 million - about a fifth of the total in the late 1990s.
6. Manatee
Manatees are common off the coast of Florida and in the southeast United States. But in August, Cape Cod beach-goers were treated to an unusual sight when they spotted one swimming off the Massachusetts coast.
Their normal range stretches from Brazil to the mid-Atlantic coast, and they normally don't frequent water colder than 68 degrees. However, according to the National Oceanic and Atmospheric Administration (NOAA), the water temperature for Wood's Hole, Massachusetts, at the time was around 75 degrees - unusually warm for that area.
Still, officials are keeping an eye on this sea cow as the weather gets colder. If he doesn't head south on his own soon, the U.S. Fish and Wildlife Service will mount a rescue attempt, the Christian Science Monitor reports.
7. Ocean sunfish
The ocean sunfish, aka mola mola, is the heaviest known bony fish in the world, with some adults tipping the scales at 2,200 pounds. While they're native to tropical and temperate waters, rising ocean temperatures have brought these big boys all the way up to the North Pacific and the Gulf of Alaska.
The same is true on the Atlantic coast in the Gulf of Maine. As the Portland Press Herald reports: "Before last year, lobster fisherman David Cousens of South Thomaston, Maine, had seen only one ocean sunfish in nearly 40 years of pulling traps. [Lately] he's seen a bunch of them, sometimes days in a row."
8. Crabs
For the last two years, swarms of red crabs have been washing up on the beaches of Southern California. In June 2015, hundreds of thousands of these two-inch-long "tuna crabs" came ashore, though 2016 has seen fewer of them - about a thousand so far, according to the Christian Science Monitor.
Pelagic red crabs usually live in waters off Baja California, but the warm currents of El Niño pushed them farther north in recent years. However, when they hit the colder water, they die off and end up on the sand.
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