Warming waters and nitrogen overloads are conspiring to alter the composition of southern New England’s fisheries
By FRANK CARINI/ecoRI News staff
For generations winter flounder was one of the most important fish in southern New England waters. Today, the once-abundant flatfish is hard to find off the coasts of Rhode Island, Massachusetts and Connecticut.
Overfishing is often blamed, and the industry certainly bears much responsibility, as does consumer demand. The winter flounder commercial fishery was once a highly productive industry with annual harvests up to 40.3 million pounds, according to the Atlantic States Marine Fisheries Commission.
Since the early 1980s, however, landings have steadily declined. Total commercial landings for all stocks combined — Georges Bank, Gulf of Maine and Southern New England/Mid-Atlantic — dipped to 3.5 million pounds in 2010, according to the Virginia-based organization.
Overfishing, however, is just one factor in the decline of some once-prevalent species in local waters. The reasons are complicated and diverse, from habitat loss, pollution, and even energy production — the Brayton Point Power Station in Somerset, Mass., pre-cooling towers, played a role in the precipitous decline of winter flounder in Mount Hope Bay — to climate-change impacts such warming water temperatures, shifting currents and less oxygenated waters.
In fact, one of the biggest current threats to domestic fisheries, including those along the southern New England coast, is the impact a changing climate, combined with land-based pollution, is having on water quality.
“When water is polluted, it exacerbates the threats posed by algal blooms and disease,” said John Torgan, director of ocean and coastal conservation for The Nature Conservancy’s Rhode Island chapter. “Our coastal edges and estuaries inoculate the ocean from threats. Our coastal ponds and rivers are breeding grounds for marine life. If we reduce the amount of pollution in our waters, they’ll be able to better cope with whatever challenges climate change brings. The best investment we can make is to address the sources of land-based pollution.”
The former Narragansett baykeeper for Save The Bay said that effort must continue to focus on reducing the amount of nitrogen dumped into local waters from wastewater treatment facilities, septic systems and cesspools. He also noted the importance of rebuilding natural buffering along the coast, and better protecting wetlands.
However, the technology required to remove nitrogen from wastewater treatment plants and septic systems is expensive. In fact, very few wastewater treatment facilities in southern New England possess it. A de-nitrification septic system for a home or building can cost upwards of $40,000, but Torgan noted that one system could serve a number of structures. He said reducing the amount of nitrogen in local waters is an investment the region must make.
“Water quality and the ecological health of our coastal waters and estuaries are the most important drivers for environmental and community well-being in coastal states,” Torgan said. “Clean, healthy coastal waters are the key to environmental protections, public health and tourism. Can you swim? Can you take fish?”
Southern New England’s coastal waters are warming, and key species are disappearing (cod and winter flounder), southerly species are appearing more frequently (spot and ocean sunfish) and more unwanted guests are arriving (jellyfish that have an appetite for fish larvae and, in the summer, lionfish, a venomous and fast-reproducing fish with a voracious appetite).
This biomass metamorphosis will likely transform southern New England’s fishing industry, for both better and worse. But how much of this change is climate related and how much is simply the region’s natural ebb and flow of marine life? A lack of ecosystem-wide data makes that a difficult question to answer. But change is being witnessed and documented.
“Climate change has happened in southern New England’s coastal waters,” Torgan said. “We’ve seen a significant warming on average in water temperatures, especially winter water temperatures. Southern New England’s ocean waters have changed, and this warming triggers fish kills, hypoxia and die-offs."
In 2012, water temperatures off the New England coast hit a record high, and shifts were observed in the distribution of Atlantic cod, a cold-water species, according to a 2013 study. While the region’s biomass diversity is certainly being altered by warming temperatures, species populations also are being changed by prey-to-predator ratios and by overfishing in waters hundreds of miles away.
Jon Hare, director of the National Oceanic and Atmospheric Administration’s Narragansett Laboratory, told ecoRI News that fishing pressures and climate change are the two obvious factors when it comes to changing population distributions.
“Whether it’s climate change or fishing pressures, species distribution is changing and we need to adapt how we manage that change,” Hare said.
Climate change, however, is perhaps the least understood factor. Both scientists and fishermen are just beginning to understand the possible ramifications. For instance, despite ongoing, but so far fairly limited, research it remains unclear how different species will adapt to warming waters, shifting currents and other climate-change impacts.
Species native to southern New England marine waters, such as cod, lobster and winter flounder, which the region’s fishing industry built its fleet around, will either adapt, find more suitable habitat elsewhere or their numbers will decline.
“Numerous studies have now documented changes in species distributions related to climate change,” Hare has written in research papers. “In general, species are moving poleward and into deeper waters. However, it is important to recognize that this is a general pattern and that there are a substantial number of exceptions.”
Winter flounder, which have distinct habitat needs and migrate to estuaries to spawn, may be unable to shift their populations, as warmer-water species such as black sea bass and butterfish move into the void left by the migration of cold-water species northward and/or further offshore.
Challenges and opportunities
Sarah Schumann, president and founder of the Warwick, R.I.-based nonprofit Eating with the Ecosystem, said local fishermen are seeing an influx of black sea bass, and it’s northern expansion is putting native species, such as lobster, at risk.
Black sea bass historically have been found between Cape Cod and Cape Hatteras, N.C., where they are sought both commercially and recreationally and are subject to size restrictions and rigid quotas. However, their numbers here are increasing and they are now being found in the colder waters of the Gulf of Maine, which isn’t quite as chilly as it once was. In fact, according to a 2015 study, warming waters are a major factor in the Gulf of Maine's cod collapse.
The greater abundance and distribution shifts of black sea bass will have environmental impacts and economic implications — both good and bad.
“The predatory impact of this explosion of black sea bass will be significant. They eat lobsters and shellfish,” Schumann said. “Their quota is pretty small, so there’s time and effort associated with catching them by accident and throwing them back. They also get caught up in fishing gear. That’s money lost for fishermen.”
On the flip side, Schumann noted that the increased range of these spiky-finned fish opens up a possible fishery to New England fishermen. “This shift northward of black sea bass will hopefully bring new opportunities, but it also will bring new challenges,” she said.
The change in black sea bass population density and increased range doesn’t automatically mean a changing climate is the reason, according to Schumann, other fishermen and scientists.
Populations shift and change all the time. It’s difficult to spot trends without more significant data sets. For example, there is plenty of data on surface-water temperatures but very little on bottom-water temperatures.
Also, the appearance of southern, warmer-water species off the New England coast isn’t an uncommon occurrence. Atlantic garfish, torpedo rays and cobia, to name just a few, have been randomly appearing here for decades.
However, that doesn’t mean warming waters and shifting currents, being caused in large part by manmade greenhouse-gas emissions, aren’t reshaping southern New England’s fisheries.
“Climate change is happening and we need to deal with it,” Hare said. “Fishermen are seeing the changes every day. They’re used to seeing fluctuations in species from fishing impacts, habitat destruction and a large number of negative impacts, but climate change is having an impact.”
Summer flounder and blue crabs — both of which spawn offshore and are less dependent on specific habitat needs — will likely expand their range because of climate change. In fact, fishermen and scientists here are already seeing blue crabs, a more southerly species, in greater numbers. Summer flounder offshore spawning stock is moving up the East Coast, as coastal waters here become less New England like and more Mid-Atlantic like.
That’s not to say southern New England hasn’t witnessed the return of some classics. Torgan noted that cod, for the first time in years, are biting off Block Island. He also said the region’s Atlantic herring population is doing well.
Southern New England’s lobster population has declined sharply since the late 1990s. The reasons are varied — for example, dredged material from marinas dumped off Prudence Island destroyed lobster habitat, and some believe pesticide use has contributed to the decline — but warming waters are likely shifting these bottom-dwelling crustaceans offshore and to the north.
In fact, last summer, a report by the Atlantic States Marine Fisheries Commission attributed southern New England’s lobster decline to climate change.
“Since the American lobster is highly influenced by temperature, climate change is expected to significantly impact the life history and distribution of the species,” according to the 493-page report. “In the lobster’s southern range, the number of days above 20º C (68 degrees Fahrenheit) is increasing, threatening successful reproduction. Contrastingly, in the Gulf of Maine, the number of days in the ideal range of 12-18º C is increasing, providing a potential benefit to the species. Climate changes are important to monitor and provide a strong justification for the timing of this benchmark stock assessment.”
Warmer water temperatures also can influence lobster vulnerability to disease and reduce their growth rate — a bad combination for the species and for those who make their livelihood catching the popular seafood.
“Lobsters are moving offshore into deeper waters, and it seems to be connected to warming waters,” said Eating with the Ecosystem's Schumann. “But we don’t have data on bottom-water temperatures, so it’s difficult to say that’s the main reason. It’s a complex issue.”
The Nature Conservancy’s Torgan said climate change and pollution, most notably excess nitrogen, are conspiring to destroy lobster habitat.
“We’re losing lobster habitat,” he said. “They’re not dying; they’re numbers are declining because their habitat is.”
Climate change is impacting, and will continue to impact, southern New England’s marine waters. But how fast and in what way is still anyone’s guess. These unknown climate-change impacts pose a challenge for both scientists and fishermen.
With the decline of cod, winter flounder and yellowtail flounder, much of Rhode Island’s groundfish fleet has turned its attention to squid. The Ocean State is now one of the biggest harvesters of squid on the East Coast. Climate change most assuredly played a part in the local loss of those three popular fishery species, but without more data it’s difficult to pinpoint how big a role it’s playing or will play.
But climate change is altering ecosystems, both aquatic and terrestrial. Ocean surface temperatures are expected to increase another 4-8 degrees Fahrenheit by the end of the century, according to Rhode Island’s Coastal Resources Management Council.
“Even a shift of one to three degrees on average can have a dramatic impact on the life cycle and distribution of southern New England’s classic cold-water species,” Torgan said. “It doesn’t necessarily mean it will kill them, but it makes them more susceptible to disease and predation.”
Warmer waters could also lead to changes in the timing of seasonal plankton blooms, disruption in migration patterns, and the disappearance of species at the southern end of their range, such as lobsters.
The world’s oceans also have been steadily acidifying for the past 250 years, fueled largely by rising levels of carbon dioxide in the atmosphere, according to the Woods Hole Oceanographic Institution. Acidifying oceans could dramatically impact the world’s squid species, including the population off the southern New England coast that is being harvested in greater numbers by an adapting local fishing industry.
In fact, about half of 36 fish stocks in the Northwest Atlantic Ocean, which includes the waters of New England, have been shifting northward during the past four decades, with some stocks nearly disappearing from U.S. waters as they move farther offshore, according to a 2009 NOAA study. Many of them are commercially valuable species.
The study focused on the impact of changing coastal and ocean temperatures on fisheries from Cape Hatteras to the Canadian border. The research looked at annual spring survey data from 1968 to 2007 for stocks ranging from Atlantic cod and haddock to yellowtail and winter flounder, spiny dogfish and Atlantic herring. Researchers found many familiar species are shifting to the north, where ocean waters are cooler, or staying in the same general area but moving into deeper waters.
The study’s co-authors, including Hare, selected the 36 species to study because they were consistently caught in high numbers during annual spring bottom-trawl surveys. They also represented a wide range of species known to be commercially and/or ecologically important.
Ocean temperatures have increased since the 1960s and ’70s, and the authors found significant changes in species distribution consistent with warming in 24 of the 36 stocks studied. Ten of the 36 stocks examined had significant range expansion, while 12 had significant range contraction, according to the study.
The study also found that heavily fished stocks appeared to be more sensitive to climate change. Also, each fish species has a particular temperature range in which it thrives. If water temperatures depart from that range, they may experience reduced growth and reproduction, ultimately reducing their numbers in a particular area and changing the species’ distribution.
It also means fisherman will have to travel farther to catch some species, at least until it’s no longer economical.
These climate change-driven shifts in fisheries pose a threat, or at least a challenge, to the industry. It will require fishermen and regulators — like the fish and shellfish they catch and monitor — to adapt. One possible measure that has been proposed is adjusting fishing seasons and allowable catches based on observed population shifts, such as the growing emergence of black sea bass in southern New England waters.
While numerous studies have shown that adult marine fish distributions in the Northeast are changing, few studies have looked at the early-life stages of these adult fish.
A 2015 study by NOAA fisheries researchers, including Hare, has provided some answers, finding that distributions of young stages and the timing of the life cycle of many fish species are also changing.
Hare said most marine fish have complex life histories with distinct stages — much like frogs. Marine fish spawn tiny planktonic eggs that move at the whim of ocean currents. Over a period of weeks to months, while drifting in the ocean, larvae develop and grow until they reach a point where they transition into juveniles recognizable as a fish.
The distribution of larvae in the sea is determined by where adult fish reproduce and by currents that move these early-life stages around. In the study published last September, researchers used long-term survey data to compare the distributions of larvae between two decades, 1977-87 and 1999-2008. They also used long-term survey data for the entire Northeast shelf, from Cape Hatteras to Cape Sable, Nova Scotia, to compare distributions of adult fish over the same time periods.
“The distribution and timing of the life cycle of many fish species are changing,” said the study’s lead author, Harvey Walsh, a fisheries biologist at NOAA’s Narragansett Laboratory and a colleague of Hare’s. “The consequences of these changes for fisheries management need to be considered, but an important first step is documenting that change is occurring.”
Walsh and his colleagues found that larval stages of 43 percent of the species studied changed distribution, while adult stages of 50 percent of the species shifted distribution over the same time period. Shifts were predominantly northward or along the shelf for both life stages, which they said is expected given the warming ocean in the region.
But not all the shifts were northward, or along the shelf. Butterfish and Atlantic mackerel, for example, shifted inshore, while red hake and silver hake moved into deeper but more inshore waters in the Gulf of Maine. Adult spiny dogfish, little skate and offshore hake shifted southward, perhaps because of differences in fishing pressures and changes in habitat, according to Walsh.
“It is clear significant changes are underway,” he said. “It is apparent that fish stocks in the Northeast shelf have changed over decades for both larvae and adults. These changes will impact the productivity and distribution of these stocks, and that will have significant implications for their assessment and management.”
Editor’s note: John Torgan is an ecoRI News board member. Also, the article's author is an Eating with the Ecosystem board member.