As we celebrate the 20th anniversary of Stellwagen Bank National Marine Sanctuary, some of the scientists and experts there are introducing us to the fascinating research and activities they are involved with. Here Leila Hatch, the Sanctuary’s Marine Ecologist, talks about her research on underwater sound in Stellwagen Bank. – Ed.
More than 2,000 years ago Aristotle told us that he was listening underwater. Leonardo Da Vinci followed up during the 1400s with the knowledge that ships could be heard underwater from far away. In the 1900s, some of the earliest applications of that knowledge were dedicated to navigation purposes in Boston Harbor. We have been able to record underwater sounds for decades. And yet, even today, we cannot identify all of the sounds recorded in Massachusetts Bay, despite knowing that some of them are biological in origin.
As a marine ecologist at Stellwagen Bank National Marine Sanctuary I specialize in the underwater acoustic habitat of this federally designated protected area at the mouth of Massachusetts Bay. I work with a team of collaborators from NOAA, universities and companies. We monitor the sound field of the sanctuary in order to better understand contributions made to it by a variety of marine animals, natural processes, and by humans.
Sound, and particularly low frequency or “low keys on the piano” sound, is transmitted extremely efficiently underwater. For this reason, animals rely on their hearing underwater as a primary means for interacting with their environment and with each other. Light degrades quickly underwater, but not sound. Some sounds can travel without losing significant energy for tens of thousands of kilometers, and, under some conditions, from pole to pole. During the course of two World Wars and beyond, humans invested large amounts of time and money to develop systems that attempted to match the abilities of marine mammals. Some products closely resemble the animals’ natural capabilities, such as long distance ship to ship communication and detection of objects of interest over large distances.
Like many other species, we want to be able to navigate the ocean or locate areas of high prey abundance. In addition to these purposeful uses of sounds, many of the sounds we make in the ocean are incidental by-products. The construction of offshore platforms and the laying of pipelines produce loud sounds. We also move more than 98% of all retail products by ship. And we are moving more and more of those products every day. Ship propellers create bubbles that produce sounds when they cavitate or burst. The low frequency sounds from large container ships and tankers travel far and wide and add to an increasing hum in the world’s oceans. This growing background noise is highest in the same frequencies used for communication by many marine species, including some of our most endangered baleen whales.
There are some places in the world that are particularly important to both baleen whales and human commerce. Stellwagen Bank National Marine Sanctuary is one of those places. Several baleen whale populations, all of which are vocally active, use these waters to feed and nurse their young every year. But the sanctuary is also bisected by the Boston Traffic Separation Scheme—the in and outbound lanes of commercial shipping to the Port of Boston. In addition, this ocean-going traffic is supplemented by active tug-tow and barge transits, fishing and whale-watching trips, recreational boating excursions, research cruises and more. It’s a busy place.
Since 2006, sanctuary researchers have been working with our partners at NOAA’s Northeast Fisheries Science Center, Cornell University’s Bioacoustics Research Program, and Marine Acoustics, Inc. to develop methods to characterize the contributions of vessels to the sanctuary’s sound field and further determine how these noises are influencing the “acoustic habitats” of baleen whales. From this work we can begin to understand how shipping noise impacts whales’ ability to communicate with each other. In particular, we can estimate the loss of communication opportunities for calling whales as shipping traffic and noise increases over time.
Many questions still remain, including how these lost opportunities to communicate affect the longevity of these species. Baleen whales evolved to exploit a very particular niche. These largest of animals eat some of the smallest of prey, so their ability to survive is based on finding and gorging on huge amounts of that small stuff. As patches of high quality food become less predictable or move due to climate change, whales’ communication systems become all the more imperative. If those systems are compromised, we can assume consequences. But much more science is needed from places like Stellwagen Bank sanctuary to fill in these answers.
Photo above: Whales and ships share space in Stellwagen Bank
National Marine Sanctuary. SBNMS file photo by WCNE. Photo
taken under NOAA permit #981-1707.