During a day of fishing on Long Island Sound earlier this month, Richie Nickerson of Niantic caught 10 legal-sized scup, a black sea bass and a northern kingfish — all species he wasn’t likely to land when he first started angling in these waters 30 years ago.

Tony Murphy of Berlin, who fished from the Black Hawk charter boat with Nickerson, also reeled in a haul of scup, also called porgies, as did most of the other 38 fishermen on board that day.

“It used to be we’d strictly catch bluefish and striped bass,” Murphy said. “But now, there are just so many porgies.”

Scup, black sea bass and northern kingfish are just three of the species once more prevalent in warmer mid-Atlantic waters that are now becoming abundant in Long Island Sound.

As the warmer-water species move in, they compete for food and habitat with cold-water species, such as winter flounder and cod, that are now becoming scarce.

“Everything’s changing,” said Greg Dubrule, owner and captain of the Black Hawk, which takes daily boatloads of anglers into the Sound from its docks on the Niantic River.

“There’s no question that, because of the warmer water, we’re seeing more scup and black sea bass, which had always been a New Jersey and southern Long Island fish," he said. 

"Our mainstay used to be winter flounder and cod, but now it’s sea bass, scup and fluke," he added, "and we’re catching a lot of trigger fish, which we never used to see.”

The firsthand experiences of these fishermen are no surprise to Penny Howell, senior fisheries biologist with the state Department of Energy and Environmental Protection.

This spring she completed a research project documenting how the Sound has changed since the 1970s and projecting how the trends are likely to continue through 2080 as the effects of climate change intensify.

That research is among the first to project how Long Island Sound will respond as the buildup of greenhouse gases in Earth’s atmosphere further warms the planet.

Among other findings, the data showed that year-to-year fluctuations in the Sound's water temperatures mirrored the patterns of Pacific air currents, with warming of the Sound occurring in response to effects of the jet stream in the Pacific.

“Long Island Sound is usually left out of the climate modeling,” Howell said.

Done with colleagues at the Stevens Institute of Technology in New Jersey and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service, the research showed that as water temperatures have been creeping steadily higher, the Sound is looking more like the habitats off the New Jersey, Delaware and Maryland coasts and less like a classic New England marine habitat.

The scientists compared six cold-adapted fish and six warm-adapted ones counted in DEEP's spring and fall trawl surveys over the past three decades, pairing the species abundance data with the records of temperatures in the Sound.

Significant correlations were found between rising bottom water temperatures and declines in numbers of cold-water fish, matched by rising numbers of warm-water fish.   

“Cold-water fish aren’t doing as well. They’re losing their competitive advantage to the incoming species like black sea bass and scup,” Howell said.

The research shows that, since the 1970s, the surface and bottom temperature range in the Sound have risen about one-half a degree Fahrenheit per decade, or about 2.8 degrees total.

“That sounds like a little but it makes a big difference,” said Howell, who presented the findings at a Long Island Sound conference in May.

For the cold-adapted fish species, she said, this means fewer days at the cooler temperatures when they spawn, and lower survival rates for the young fry as they are preyed on by the incoming warm-water species.

For warm-water species, it means a longer optimal season for spawning and growing in the Sound.

And the Sound’s remaining lobsters, already in a serious decline since the 1999 die-off, are finding ever-reduced areas and fewer days with the colder temperatures they prefer.

“The size of the area and the amount of time that’s stressful for lobsters will almost double, going forward,” Howell said.

According to data compiled as part of DEEP's trawl surveys, the most dramatic temperature increases are occuring in the spring at the bottom of the Sound, which is an important habitat for many species.

Average temperatures went from about 44 degrees in 1991 to about 47 degrees in 2014, Howell said.

A longer data series collected at the environmental lab at the Millstone Power Station in Waterford shows a similar trend.

Spring temperatures at the lab averaged about 45.5 degrees to 49 degrees in the 1970s.

Now, more than four decades later, the spring temperatures are ranging from about 48 to about 51 degrees.

According to the research done by Howell and her colleagues, the western end of the Sound is warming most dramatically, along with areas closest to the Connecticut coast across the estuary.

Another change of note is the increase in freshwater inflows from the Connecticut, Housatonic and Hudson rivers into the Sound, causing a drop in salinity overall.

The portion of the Sound east of the Connecticut River is experiencing the greatest shift, Howell said, since virtually all the water from that river — which contributes more than half of the fresh water that enters the entire estuary — flows eastward after it empties at the river’s mouth between Old Saybrook and Old Lyme.

The volume of water flowing from the Connecticut River has increased by an estimated 17 percent from 1981 to 2013, the researchers found. 

Howell said the exact cause of the increasing freshwater flows is unclear, although higher levels of precipitation in the large Connecticut River watershed — which extends into eastern Canada — as well as land use changes that send more runoff into the river are probable explanations.

Looking forward to 2080, it is uncertain whether the changes in freshwater flows and salinity will continue.

The trend for rising water temperatures, and with them more warm-water species, however, shows no sign of abating.

By 2080, the research shows, the average bottom temperature will be as much as 5.5 to 9 degrees warmer across the Sound in the winter, and as much as 3.5 degrees warmer in the summer.

“This is a new world,” Howell said. “The baselines are shifting.”

These shifting baselines must now be factored in to decisions about how species are managed for recreational and commercial fishing, according to David Simpson, DEEP director of marine fisheries.

Multistate panels determine when seasons are open for particular species, minimum sizes and maximum catch.

But the bureaucratic process can be lengthy and not as adaptable to ever-changing conditions as it should be, Simpson said.

“This whole shift in species distribution has created all sorts of issues for fisheries management,” he said. “We have to use a more flexible approach.”

j.benson@theday.com