On a dark night in the middle of a wide marsh near Tuckerton, N.J., a team of Rutgers University researchers lowered a net over the railing of an old wooden bridge.
Then they turned off their flashlights and waited. Below, in Little Sheepshead Creek, the incoming tide was washing hundreds of tiny fish larvae into the net.
By now - 24 years after these weekly surveys began - Rutgers ichthyologist Ken Able is seeing the unmistakable effects of warming oceans and climate change.
Especially in the last decade, the researchers have been seeing more southern species, including the larvae of grouper, a fish common in Florida.
At the same time, they've been capturing fewer northern species, such as winter flounder.
The changes Able is recording at Little Sheepshead Creek, near Great Bay, are reflected along the East Coast and worldwide. They have the potential not only to alter ecosystems, but also to change the seafood on our dinner plates.
Out on Jersey's beaches, where Atlantic croaker catches used to be a rarity - this was considered the northern end of the fish's range - anglers now commonly reel them in.
"As far as fishermen are concerned, climate change is here. This is a reality," said Tom Fote, of the Jersey Coast Anglers Association. "We're going to have to change the way we fish."
Mackerel, once an important species for Cape May's commercial boats, have moved north, out of reach.
Within the last two decades, New Jersey's renowned surf clams, once common just off the beaches and harvested for chowder and fried clams, have moved 40 miles offshore into deeper, cooler water.
"The environment is changing. Our critters are moving because they have to," said David Wallace, who heads Wallace & Associates, a consulting firm to the fishing industry.
Many factors could be at work, fisheries experts say. Ocean currents and fishing pressure itself affect where fish go. And as anyone who chases fish for fun or a paycheck knows, huge natural variability is a given.
But what tells researchers that climate change is likely a significant factor is much simpler. It's temperature.
Temperature is one of the most important environmental influences for marine organisms, affecting their metabolism, growth, and other factors.
"A couple degrees of difference will cause fish to move," said Jeff Kaelin of Lund's Fisheries in Cape May, whose boats target 20 species. "There are very narrow niches where they survive."
While Able has been collecting his larvae, other researchers have been monitoring the water temperature at a nearby boat basin. Amid year-to-year variability, the overall trend is clear: The water is warming. For 12 of the last 15 years, temperatures have been above average.
The same thing has been happening out on the northeast coast's continental shelf. In 2012, sea surface temperatures hit their highest in 150 years of recorded history.
Able, bearded and friendly, started the larvae project because he hoped to learn more about summer flounder, a valuable commercial species.
What he now sees is a steady progression of newcomer fish.
"Things are changing. People who spend a lot of time on the water know this," he said. Anglers are catching Atlantic trigger fish and sheepshead. "Big schools of cow-nosed rays are here," he said.
Some of the fish Able and his researchers collected were just oddities, swept northward by the Gulf Stream, and didn't survive the winter.
"Now, our winters are milder. They're surviving," Able said. "And they're growing up to reproduce and be harvested."
It's not just New Jersey. More broadly, a 2009 study found that about half the 36 fish stocks off the northeast coast of the U.S. were shifting northward or seaward, into deeper, cooler water.
What was important about the paper, said NOAA fisheries expert and coauthor Jon Hare, is that it charted not only commercial fisheries - since fishing itself has an effect - but also fish that were not.
In a study in the journal Nature in May, scientists analyzed global catch data and found that hauls were already changing, favoring warm-water species.
"Climate change is suddenly an unexpected guest at dinner," wrote Mark Payne of the National Institute for Aquatic Resources in Denmark in an accompanying commentary.
Overall, the effects on New Jersey's $200 million-a-year commercial fishing industry aren't as dramatic, the exit of mackerel and surf clams notwithstanding. The state is a midpoint for the range of a lot of fish, so even if they shift, New Jersey still has the species.
But at $3.60 a gallon for fuel, adding extra miles to get to the fish - or finding them in the first place - is significant.
Many commercial species have been overfished and are subject to management plans aimed at rebuilding their stocks. Without adequate rebuilding, some experts have predicted an end to commercial fisheries - and readily available seafood - within the century.
Fisheries managers already dole out state-by-state allotments, a political as well as a scientific challenge.
The industry worries that regulations will change in response to conditions that, evidently, are very much in flux.
In recent discussions on mackerel, said Lund's Kaelin, "we argued strenuously that we not have our quota reduced because of climate change. With a few cold winters, the fish could come back."
Black sea bass, common in New Jersey waters, are now being seen far to the north. "Potentially, Rhode Island or Massachusetts may be arguing for a bigger piece of the pie," said Patrick Campfield, director of fisheries science for the Atlantic States Marine Fisheries Commission, one of many coastal management agencies.
When officials started assessing summer flounder distribution in the 1970s, it was found mostly from South Jersey into Virginia. Now, the core is off northern New Jersey, and the fish have extended their range into New York. Juveniles have been caught off Rhode Island.
Not all species will be winners like croaker, whose juveniles need warm water to survive. Cod, whose productivity declines at higher temperatures, will be a loser.
Also, other effects of climate change - all of which could affect fish - are becoming apparent. Changing ocean temperatures have influenced blooms of fish food - plankton - and the range and abundance of fish predators.
Data show the waters off the northeast continental shelf are becoming more acidic. The northernmost waters are becoming less salty, suggesting the influence of melting Arctic and Greenland ice.
In August, the published results of a three-year worldwide project showed that warming oceans are causing not only shifts in fish ranges, but also changes in breeding times.
"What it reveals is that the changes that are occurring on land are being matched by the oceans," said British researcher and lead author Camille Parmesan, of Plymouth University. "And far from being a buffer and displaying more minor changes, what we're seeing is a far stronger response from the oceans."
Awed by the potential
Late at night, back in the Rutgers lab near Tuckerton, heads bent over clear casserole dishes, researchers sort through the night's haul with forceps, plucking out tiny creatures that are little more than two eyeballs atop inch-long transparent bodies.
Able and his team have amassed the most comprehensive data set of its kind on the coast, Able said. It's crucial to understanding the long-term trends.
At the beginning, Able struggled to find the money. "Everyone wants long-term data, but no one wants to fund it," he said. Then, as the trend began to emerge, he knew he had no choice but to continue.
In a room at the lab, an old Coast Guard station deep in the marsh, are hundreds of vials of larvae, preserved in alcohol. In a nearby warehouse are thousands more: Each specimen they've ever caught in a quarter century.
Able isn't sure of the count. But he's awed by the potential.
Even on something as small as a larvae, scientists can examine the otolith - akin to an ear bone - and can tell how old the fish is. They can analyze the organ for substances showing where it has been and whether the waterway was polluted.
To him, the collection is a vast time series, and potentially a road map to climate changes we're already experiencing, just waiting to be understood.
THE SEAS' CHANGE
Northern fish species becoming less abundant in larvae surveys:
Southern fish species becoming more abundant in larvae surveys:
*Economically important species
SOURCE: Ken Able