Living on the edge

            As regions grow in human population, forests become more and more fragmented when trees are cut down to make way for roads, housing developments and shopping centers.  Most of the previous research on forest fragmentation has examined its negative effects on wildlife and biodiversity. But two Boston University researchers recently investigated the effect of fragmentation on carbon storage and found some surprisingly positive news.

            Associate Professor Lucy Hutyra and former BU post-doctoral researcher Andrew Reinmann, now an assistant professor at the City University of New York, discovered that trees at the edge of a forest in southern New England grow faster and absorb more carbon than those

Lucy Hutra and Andrew Reinman

in the interior. “When you create that edge, you essentially are reducing competition and freeing up more resources like light, water and nutrients for trees,” he said, noting that the effect extends about 20 meters in from the forest edge. (Curiously, researchers have found the opposite to be true in the Amazon rain forest.)

            This finding was the result of studying 21 fragmented forest plots dominated by red oaks in greater Boston. The researchers mapped every tree over 5 centimeters in diameter and collected cores from 210 trees at least 10 centimeters in diameter to get an estimate of the biomass of the forest and how it changes from the edge to the interior.

            Reinmann said this result is not a justification for further fragmenting the forested landscape. “When you fragment a forest, the remaining forest can offset a little bit of what was lost, but not completely,” he said. “So fragmentation may not be as terrible from a carbon perspective as we thought, but it is still bad.”

            The results of his research weren’t all positive, however. The cores he collected also revealed that trees on the edge of a forest grow more slowly when they are stressed by heat – and as the climate changes and temperatures rise, heat stress is likely to increase as well.

            The researchers defined heat stress as the number of days the forest was exposed to temperatures above 27 degrees Celsius in June and July, the months when most wood is produced. “That’s the average high temperature in July in the Boston area, so that’s the temperature the trees are used to growing in,” Reinmann said. “Any higher than that and we saw a decline in growth.”

            That decline was most pronounced at the edge of the forest, where growth declined from heat stress three times faster than in the interior. “The forest edge is typically hotter than the interior,” he added, “so you would expect heat stress to be magnified at the edge because the trees aren’t buffered as the interior trees are.”

            Based on the results of this study, Reinmann believes that climate models that calculate carbon storage in southern New England are likely underestimating how much carbon is being removed from the atmosphere, because they are not including the positive edge effect. But as temperatures increase, that positive carbon benefit may decline significantly.

This article first appeared in the summer 2017 issue of Northern Woodlands magazine.

Backyard bee bonanza

            Lawns cover 163,000 square kilometers of the United States, making grass the largest irrigated crop in the country. As much as ecologists consider them biological deserts that Americans should be encouraged to eliminate from their properties, it is unlikely lawn cover will decline any time soon.

            So urban ecologist Susannah Lerman at the U.S. Forest Service’s Northern Research Station in Amherst, Mass., decided to figure out how to make lawns “less bad” by examining how lawns could serve to provide habitat to declining populations of bees.

            “While not everybody uses herbicides on their lawn, the thing almost everybody does is mow,” Lerman said. “We wondered if there were ways we can tweak this behavior to make it less bad for bees. You see a lot of dandelions and clovers growing spontaneously. Do these plants have ecological value as bee habitat?”

            In an assessment of the natural history of 16 suburban lawns in Springfield, Mass., she found that lawns that were not treated with herbicides or pesticides yielded an unexpectedly rich abundance of bee species and an equally impressive variety of what Lerman calls “spontaneous flowers” – those that are not intentionally planted but which provide nectar and pollen to bees and other pollinators.

            After visiting each yard 12 times over two years, she was surprised to discover 64 flowering plant species spontaneously growing in the lawns, including violets, creeping Charlie, hairy rockcress, purple smartweed and dwarf cinquefoil. “You go into these yards and at first glance it looks like there’s nothing there,” she said. “But then you start looking and there’s a lot more in there than you think.”

            Even more surprising, Lerman and colleague Joan Milan identified 111 different species of bees on the properties. “It was astonishing!” she said. “We recorded a quarter of all the bee species ever found in Massachusetts on these 16 suburban lawns. One yard had 53 species of bee.” Strangely enough, the most abundant species was a type of sweat bee not recorded in the state since the 1920s.

            Lerman’s study also found that bees were most abundant on lawns mowed every two weeks, compared to those mowed weekly or every three weeks.

            “Clearly there is value in these landscapes for habitat conservation,” Lerman said. “Private yards shouldn’t be ignored when thinking about conservation.”

            To improve habitat for bees and other pollinators, she said that homeowners should consider reducing or eliminating the use of pesticides and herbicides on their lawns, plant a meadow or pollinator garden if possible, and encourage the growth of spontaneous plants in their lawn.

            The latter suggestion may be difficult for some people to follow, Lerman said. “Most people look at dandelions and clovers and see them as weeds. We need to change their perceptions and show that those plants are really providing wildlife habitat.

            “And if you mow less often, you’ll have more lawn flowers and more bees,” she added. “It’s a way to do less but feel like you’re making a difference even though you didn’t spend any extra time or money.”

This article first appeared in the summer 2017 issue of Northern Woodlands magazine.

Birds moving up and down slope

            Many scientists have predicted that as the climate warms, most bird species in the Northern Hemisphere will shift their range northward or up the slopes of mountains in order to remain in their preferred climate environment. To learn whether that has already begun to occur in the mountains of New England, a team of University of Massachusetts researchers

William Deluca

analyzed bird census data collected in the White Mountain National Forest as far back as 1993. The scientists found that the data – from 768 sites visited twice each year – did not always follow the expected pattern.

            “We were looking at a relatively short period of time, so we figured we would see the species moving upslope or not at all,” said William Deluca, a research fellow at the Northeast Climate Science Center at UMass. “We actually thought maybe we wouldn’t find anything.”

            He was wrong. He found that 9 of 16 low-elevation species like ovenbirds, black-and-white warblers and hermit thrushes, which breed primarily in deciduous and northern hardwood forests, showed evidence of shifting their upper-elevation boundary upslope an average of 99 meters over the 17-year period of the study. That aligns with the results of similar studies in the Sierra Nevada Mountains and the Andes Mountains.

            But when he analyzed the data for the upper elevation species, those like white-throated sparrow, yellow-bellied flycatcher and Swainson’s thrush that prefer to breed in the montane spruce-fir forest, 9 of 11 species shifted their lower-elevation boundary downslope an average of 19 meters. Among upper-elevation species, only the magnolia warbler shifted its upper boundary further upslope.

            “The opposing elevational shifts of two distinct and adjacent bird communities is, to our knowledge, unprecedented and highlights the need for caution when applying conventional expectations to species responses to climate change,” wrote Deluca and co-author David King in the Journal of Ornithology last November.

            The surprising and contrary results also appear to have different explanations. As predicted, the researchers believe the upslope movement of the low-elevation species is a result of the warming climate, which corresponds with climate data from the Mount Washington Observatory indicating that little warming has occurred at high-elevations but significant warming has occurred at mid- and lower-elevations.

            The downward shifting of upper-elevation species appears to be the result of a downslope shift in habitat. Deluca said that recent die-offs of red spruce may have created a void in the habitat of upper-elevation species, causing them to shift downslope. An increase in the abundance of balsam firs near the lower boundaries of the birds’ distribution may also be a contributing factor.

            “Our results aren’t something that a land manager can do much about at any reasonable scale,” Deluca said. “But it helps us understand how these species are responding to the changing environment. We’re now working to understand the mechanism that’s leading to these shifts in distribution. If they’re responding to habitat, maybe there is a management solution.” 

This article first appeared in the summer 2017 issue of Northern Woodlands magazine.

Dead seabirds washing ashore on New England beaches

            Walking on the beach at the north end of Block Island last month, Matt Schenck stumbled upon two dead and decomposing seabirds, which the avid birdwatcher identified as great shearwaters. While gulls of various species are commonly found dead on local beaches, shearwaters are an extreme rarity.

            Except this year.

            Hundreds of great shearwaters have turned up dead on beaches on Long Island and southern New England this summer, and no one seems to know why. In addition to the birds on

Dead great shearwater on Block Island (Matt Schenck)

Block Island, birders and biologists have reported dead shearwaters on Rhode Island beaches in Tiverton and Charlestown.

            Shearwaters spend most of their lives far out to sea, where they soar just above the waves as they forage on small fish and other marine creatures near the surface of the water. Four species of shearwater – great, sooty, Cory’s and Manx – are typically seen in Rhode Island waters, though they seldom travel within sight of land. Most breed on remote islands in the South Atlantic.

            According to Josh Beuth, a biologist for the Rhode Island Department of Environmental Management, shearwaters have been observed in large numbers from the shore this year, including from Jamestown, Newport and Point Judith. They have also been seen regularly from the Block Island ferry.

            “There has been an abundance of sand eels in our local waters, which are a forage fish for shearwaters,” said Beuth. “As a result of them being closer to shore than usual, it would be more likely that they’d wash up on shore if they died.”

            While prey may be abundant, some biologists – including Linda Welch, a U.S. Fish and Wildlife Service biologist who studies great shearwaters off Cape Cod – have noted that many of the dead birds are juveniles that have been thin or emaciated, suggesting that the birds have starved.

            The dead birds began to show up on beaches in late June, which is about when they should have arrived along the East Coast after their long migration from their breeding grounds in the South Atlantic. By then they were likely stressed and tired and hungry, which may have made them susceptible to any number of potential sources of mortality.

Wildlife pathologist Joe Okoniewski examined some of the dead shearwaters found on Long Island beaches, and he told the New York Times that the birds were not only thin but anemic. “The big mystery is: Why are they thin? On the surface, it looks like you know what happened – they starved,” he said. “But when you ask why, it becomes much more of a mystery.”

It is especially mysterious if prey is seemingly abundant, as it has been this summer in Rhode Island waters.

Robert Kenney, an oceanographer at the University of Rhode Island’s Graduate School of Oceanography, speculates that toxic algae from red tides may be playing a role in the bird deaths. He said that a number of northern gannets, another species of seabird, have been found dead on Cape Cod beaches this summer. The only difference, he said, is that they are “in good condition, except for being dead.” He thinks that toxic algae may have also contributed to the deaths of some of the numerous whales that have been found dead along the East Coast and in the Gulf of St. Lawrence this year.

Among those trying to find an answer is Julie Ellis, director of the Seabird Ecological Assessment Network at the Tufts University Veterinary Medical Center, which uses volunteers throughout the Northeast to regularly walk beaches to collect dead birds for study. She is reaching out to a number of animal diagnosticians throughout the region in hopes that together they can come up with a consensus of what is causing the shearwater deaths. She hopes they will have an answer next month.

This article first appeared on EcoRI.org on August 10, 2017.

Mako sharks killed at far higher rate than officials estimate

Brad Wetherbee and his research team have been capturing and tracking the movements of mako sharks since 2004, and more than 25 percent of those affixed with satellite transmitters have been caught and killed by commercial or recreational fishermen.

            That mortality rate is more than 10 times the rate estimated by the international body responsible for managing the world’s mako shark fishery and far higher than is sustainable.

            Wetherbee, a shark researcher at the University of Rhode Island, along with Mike Byrne

Tagged mako shark (Photo by George Schellenger)

and other colleagues at the Guy Harvey Research Institute at Nova Southeastern University, published a paper in last week’s edition of the journal Proceedings of the Royal Society B documenting the mortality of the sharks they have been monitoring. They hope it will influence the fishery managers to take steps to reduce the catch of mako sharks.

            ““Makos are caught in all kinds of fisheries all around the world – gill netters, long liners, commercial, recreational,” he said. “They’re the shark everyone wants to catch because they’re good to eat – like a shark version of swordfish. But if our results are anything close to the true mortality rate, then they’re in trouble.”

            Wetherbee admits that his results may not be reflective of the mortality the sharks face everywhere, and he said that there are some people who think that makos are being fished sustainably. But he also believes it would be irresponsible not to report the mortality rate of his study specimens.

            “The fishery managers are faced with a lack of data about mako mortality,” Wetherbee said. “But based on our experience, the sharks are being killed at a much higher rate than they’re estimating, which means overfishing is probably occurring.”

            Wetherbee and his colleagues tag as many as 20 mako sharks each year – though some years they catch far fewer – off the coast of the mid-Atlantic states, the Yucatan Peninsula of Mexico, and Rhode Island. Each one is affixed with an electronic tag that provides data for approximately one year about the daily movements of the sharks.

            “So we know where they are in near-real time,” he said. “When they’re caught, we can follow them right to shore to someone’s dock or their house.  We were surprised how often that was happening.”

            His tagged sharks have been caught and killed by fishermen in the waters off Canada, Cuba, Mexico, Portugal, New Zealand and throughout the East Coast of the United States.

            Last summer, Wetherbee made a public plea to fishermen in southern New England when one of his tagged sharks was tracked to local waters just as a number of shark fishing tournaments were scheduled. He asked anyone catching a mako shark with a satellite tag to release the animal unharmed. The shark survived the tournament season but was killed by fishermen off North Carolina a few months later.

            Wetherbee said that those responsible for managing the mako shark fishery are expected to issue an updated stock assessment this fall, and he expects they will take into consideration the results of his research. He also hopes that new policies will be proposed to reduce the number of mako sharks caught in the commercial and recreational fisheries.

            “I’m not sure what they’ll do, but I hope they at least recognize that however they’re currently keeping track of mako shark mortality doesn’t appear to be very accurate,” he said. “Our data should help them get a better idea of what’s going on and give them more information to manage the population.”

            Wetherbee and his colleagues also believe that the use of satellite tracking data for estimating shark mortality is a novel methodology that may be useful in other fisheries.

            “Using electronic tags to learn the fate of individuals in a fishery is a pretty new way of estimating mortality,” said Mahmood Shivji, director of the Guy Harvey Research Institute. “But there’s no mistaking when a tag is reporting from shore that the shark is dead. It’s a known fate, as opposed to the estimates currently used. There’s promise for researchers to use the same technology on other species for estimating mortality.”

Commercial trawling damages fragile seafloor habitat

Commercial fishing gear that is dragged along the seafloor to capture species that live on, in or near the ocean bottom has long been criticized for damaging sensitive habitats and catching innumerable non-target species. It disturbs sediments, destroys corals, and removes many of the organisms that commercial species feed upon.

            But a new study of the predominant bottom trawling methods used in the North Atlantic found that some gear is more damaging than others.

Scallop dredges at a pier in The Netherlands (Jeremy Collie)

            Jeremy Collie, an oceanography professor at the University of Rhode Island and a member of the international team of scientists that conducted the study, said that trawling is controversial because it can affect entire ecosystems.

            “It’s a serious problem, but we’re finding that it’s a very localized problem,” he said. “The distribution of where bottom fishing takes place is patchy, and the habitat we care about is patchy. Where those two things intersect is where the problem is.”

            The researchers examined 70 previous studies on the effects of bottom trawling to determine which methods were most harmful.

            Otter trawling, which is used to catch cod, haddock, flounder and other fish near the bottom and is the most common fishing method in New England, uses two large metal doors to hold open the net as it drags along the seafloor. It was found to be the least harmful of the methods assessed. Otter trawls killed six percent of the marine organisms in its way each time the net passed, according to the study published July 17 in the Proceedings of the National Academy of Science.

            The researchers also studied beam trawling, a method that uses a metal beam to hold open the net; towed dredges that drag a toothed metal bar along the seafloor, used in New England’s scallop fishery; and hydraulic dredges, which use a jet of water to loosen the seabed to capture surf clams and ocean quahogs living in the sediment.

            Hydraulic dredges caused the most damage, killing 41 percent of animal and plant life on the seabed.

            “The degree of damage caused by each gear type can be characterized by how far the gear penetrates the seafloor,” Collie said. “The further it penetrates, the more damage it causes.”

            While some critics have argued that the most damaging gear should be banned, Collie said that approach could close entire fisheries, since each gear type is designed to harvest a targeted species.
            "Rather than banning a particular type of gear, spatial management can be used to restrict them to particular areas or to prohibit their use in closed areas," Collie said. "The information from our studies should help to inform spatial management."

            In addition to calculating the mortality caused by each bottom trawling method, the study also estimated how long it would take for various habitats to recover from trawling.

The study found that sandy habitats that are typical of large areas of the continental shelf are likely to recover from trawling in just a few months, especially if they are only trawled once or twice each year. But habitats with gravel or cobblestones could take a decade or more to recover.

“And in areas that might have biogenic epifauna, like cold water corals or glass sponges, recovery times could stretch from decades to centuries,” Collie said. “Those species grow slowly, or once you wipe them out, it’s harder for their larvae or juveniles to re-establish themselves.”

This study is part of the Trawling Best Practices Project, which is examining the impact of trawling worldwide and plans to publish trawling guidelines for the fishing industry that focus on preserving the marine ecosystem.

“From my perspective, we want to identify the vulnerable habitats and protect them, recognizing that they are a small fraction of the total area,” Collie said. “For the New England shelf, there are large areas that we don’t need to be concerned about and large areas of sandy sediment where trawling effects are not a concern. Small areas like gravel and complex habitats, and those that are fished by scallop gear, are the areas we need to focus in on.”

The next step in the project is to complete a global analysis of what Collie called “the footprint of fishing” that will identify the areas where trawling effort is greatest. The researchers will also examine the indirect effects of bottom trawling – how trawling affects the ability of certain habitats to produce fish. The project will conclude with the creation of a methodology that fishery agencies around the world can adopt to better manage their fisheries.

This story first appeared on EcoRI.org on August 4, 2017.

Fish haven

            At the public boat ramp to Quonochontaug Pond in Charlestown, a dozen volunteers wearing rubber boots and work gloves loaded thousands of pounds of clam and oyster shells into black plastic fish totes, then rolled them along a 50-foot conveyor and onto a small maroon barge. From there, the empty shells were transported to the eastern and western edges of the pond and carefully dropped over the side.

After a week of work in mid-May to ensure that the proper quantity of shell was placed in the proper locations, construction was complete on nine oyster reefs to provide habitat for juvenile fish. It will take a year or more to determine if the effort is a success, but biologists from The Nature Conservancy and the Rhode Island Department of Environmental Management are

Oyster shells are delivered to site of new reef. Photo by Mike Derr

confident that the new reefs will soon be home to juvenile striped bass, tautog, black sea bass, scup, and summer and winter flounder.

“Shellfish reefs are an important habitat for juvenile fish, but the amount of shellfish reef in Rhode Island is greatly reduced compared to what we historically had,” said Eric Schneider, DEM’s principal marine fisheries biologist.

“The idea is that there are certain areas in the ponds that don’t have good structure – reefs, rocks, something that gives fish somewhere to hide – but if we build some structure, the fish will come,” added The Nature Conservancy’s Scott Comings.

The biologists said that about 95 percent of the state’s oyster population has disappeared since the mid-1900s, largely due to over-harvesting, poor water quality and diseases. In the mid-Atlantic states, researchers found that juvenile fish move right in to man-made reef habitat in areas where it no longer exists. So the Conservancy and DEM decided to give it a try.

The project got started at Ninigret Pond, where 130 tons of shell were used to construct eight reefs in 2015. Each began with a base layer of clam shells that was then covered with a thick layer of oyster shells piled up to about two feet below the waterline at low tide.

“After it’s spent some time in the water, you start to get a host of species like crabs and snails and starfish colonizing the area,” Comings explained. “It becomes a little hub of life, a mound of shell that moves and changes just as nature would intend.”

Monthly surveys of each reef using fish traps, video cameras and other techniques found that many of the expected marine species have moved in and taken up residence, including several of the targeted fish.

Where do all those empty shells come from? Local restaurants, of course. Most originate with diners at Matunuck Oyster Bar, but other restaurants occasionally participate as well. The 20,000 oysters consumed at last year’s Newport Oyster Festival are also being used in the reefs.

“This project offers me something to do with the byproduct of our oysters without sending it to the landfill,” said Perry Raso, owner of Matunuck Oyster Bar. “It’s important that we incorporate sustainability into our business model, and while it might not be easy to see the benefits of going through all this effort, we’re happy to do something that’s good for the environment.”

After the shells are collected from the restaurants, they are stored in massive piles for “seasoning” at the Great Swamp Management Area in South Kingstown, where they are turned over several times during a six-month period, just as one would turn a compost pile for better decomposition. The turning ensures that all of the shells are exposed to the air so any leftover flesh decomposes. The shells are certified by the Coastal Resources Management Council as restoration material before they are deployed in the ponds.

After the reefs are constructed, they are “seeded” with year-old live oysters – wild strains from Green Hill Pond and the Narrow River, as well as the variety used at aquaculture farms – in hopes that the empty shells will eventually be covered with living oysters. The biologists also hope that larval oysters drifting with the currents from nearby oyster farms will settle on the new reefs.

“Oysters need something to set on, so without the reef they have nowhere to go,” Comings said. “But while we hope the oysters thrive, this project is really about benefiting juvenile fish.”

Next year, DEM and the Conservancy will build one more series of reefs in another coastal pond before shifting to sites in Narragansett Bay.

This article first appeared in South County Life magazine on August 1, 2017.