An Interview with Professor Thomas Grothues of Rutgers University about his underwater research at the park
August 24, 2011
By: Ellen Nicholson
Visitors to Pier 6 on a recent Sunday evening were unknowing witnesses to some interesting waterfront research happening just beyond the promenade railing. A motorboat holding a small team of researchers from Rutgers University was studying the water beneath the 1914 Lehigh Barge. Barely visible in the dark, the team was recording moving images of underwater marine life using a DIDSON (Dual-Frequency Identification Sonar) as part of an ongoing project researching the effect of modified shorelines on shallow water ecology.
The project is directed by Professor Thomas Grothues, Associate Research Professor at Rutgers University Institute of Marine and Coastal Sciences, and Professor Ken Able, Distinguished Professor at Rutgers University of Marine and Coastal Sciences. They are researching the response of fish to shoreline modification by measuring the number and assemblage of fish around shoreline modifications such as bulkheads, rip rap, and barge placement.
Rutgers DIDSON research team at the park | Courtesy of Nautilus International Development Consulting, Inc.
The research team has visited twice this summer and plans to return in early September, as well as two trips next year. In between these trips I had the pleasure of interviewing Professor Grothues about his work at the park.
Why your interest in shallow water ecology?
Shallow water is disproportionately important to fisheries because of its nursery value. The great majority of fish die of natural causes within the first days to year of their lives. The difference between 98 and 96 percent mortality of young fish might seem insignificant, but on the survivorship side that translates to a doubling of fish numbers. To me, those life histories are exciting. Many of the processes that happen in shallow water, and on the east coast in particular, happen in salt marshes fringing the banks of our major estuaries. But these have been largely replaced in some areas by artificial shorelines or simply by deepening (the process by which bulkhead steepens – or deepens – the shoreline). That is not to say that these have lost their function completely. Sorting out which species respond to what change and why is key to making artificial shorelines serve us better.
Explain the timing of your visits to the park. Are they contingent on environmental conditions or life cycles?
Most of the fish of this region are migratory because of the huge temperature swing from winter to summer. We first visited in mid-summer because adult fish spawn in the spring, and by mid-summer their progeny have picked a habitat and are large enough to see. By late summer we can measure the persistence of these habitats to see if they are real and important.
What is focus of each trip to the park? Why the multiple trips?
The focus is the always the same, sampling in multiple different habitats and at different times. Multiple trips are required because of the patchy nature of fish distribution - fish do not occur consistently because of factors such as social (schooling) behavior, or conflicts between different needs, such as spawning, hiding, and eating. Confidence in an answer is developed only through the development of a pattern following repetitive sampling.
Why did you want to conduct research under the Waterfront Museum barge?
Barges are an alternative to piers and other kinds of permanent shoreline structures. Like piers, they cast shade, but unlike piers they have few or no pilings and can be moved. They can dampen wave energy along the shore and so might act as "softer" shoreline protection in some respects. They might also double to serve as oyster culture supports some day. A partnership between New York and Rotterdam is exploring the growing use of barges as land is at a premium. The Dutch have already proposed whole "floating cities."
DIDSON Image of rip-rap shoreline | Courtesy of Rutgers Marine Field Station
We have used DIDSON since late 2007 and it is one of several tools we use to address our research. DIDSON is not a camera, and so it requires no light. That is important when one of the impacts of study is light itself, either more or less of it as from pier shading or waterfront lighting. DIDSON is a sonar and uses sound to "see" like a dolphin does. It is special because it can convert those echoes into a movie-like image set that is easily interpreted.
Who initiated the research and where is funding coming from?
Funding was provided by the Hudson River Foundation. The organization specializes in funding scientific research that benefits the Hudson River. The grant allows us to continue a legacy of work that Ken Able, his graduate students and associates and I have collected on shallow water ecologies along modified shorelines.
How will the research findings be used?
Our primary product as biologists is publication of our findings in peer-reviewed professional journals. These publications are available to the public at libraries and through blogs like yours. We are not regulators and can't dictate how findings will be used, so it is up to managers such as the NYS Department of Environmental Conservation to use the data to devise a regulatory framework that balances the needs of our society and our marine habitats.
What other areas around the City are you visiting this summer?
New York has a highly modified shoreline, but in a historically productive and recovering estuary. We are visiting several types of shorelines (bulkheaded, natural sloping beaches, and rip-rap) throughout the harbor including along New Jersey, at Governor's Island, and the Bronx. Last month we spotted numerous schools of large Atlantic Menhaden on the New Jersey side; they showed as huge schools on DIDSON but were barely visible from the surface.
