Study Finds Block Island Salt Pond an ‘Oasis’ for Fish
August 27, 2020
While the coastal ponds in Rhode Island’s Washington County — Winnipaug, Quonochontaug, Ninigret, and Green Hill — have received a great deal of research and conservation attention through the years, their cousin on Block Island, the Great Salt Pond, has only recently begun to be studied and monitored.
Early results of a monthly fish survey suggest it’s a unique and important ecosystem deserving of restoration and additional protection.
The 673-acre waterbody was a freshwater pond as late as the mid-1800s, which would occasionally breach during storms, according to Scott Comings, associate director of the Rhode Island office of The Nature Conservancy (TNC). A channel opening to Block Island Sound was dug by hand in the 1870s, and it has been a tidal salt pond ever since.
“It’s very clear that the Great Salt Pond is one of the jewels of Block Island,” Comings said. “It’s about as pristine a coastal pond as you can find in Rhode Island. We’ve done a lot of land acquisition around it, but about six years ago we became engaged in the marine environment throughout Rhode Island, and we decided to figure out what we could do to get an idea of what’s happening on the pond and gather a long-term data set to inform future decisions.”
TNC started with a fish survey, following the same protocols that the Rhode Island Department of Environmental Management has followed at the state’s coastal salt ponds for decades. Once each month from May through October, TNC scientists deploy a 130-foot seine net at eight sites around the pond. They count and identify every species of fish they capture and then release them back into the pond.
The quantity and diversity of fish they capture is impressive. Nearly 120,000 fish of 78 different species were tallied during the first six years of the survey, and the research team often catches thousands of fish each time they pull in the net. Most are common baitfish such as silversides, mummichogs, and killifish, but they also catch good numbers of species of commercial and recreational importance, like winter flounder, tautog, black sea bass, scup, and squid.
“It’s a highly productive site that serves as a nursery for a lot of fish species,” said Dee Verbeyst, TNC’s Great Salt Pond scientist who coordinates the surveys and other monitoring efforts in the pond. “The pond is a refuge for resident and migratory species, and for an increasing number of tropical species as well. Compared to the coastal ponds, the Great Salt Pond is smaller in size but our fish numbers and diversity are similar.”
The number of tropical species that find their way to the pond is especially impressive. They include butterflyfish, mojarra, longhorn cowfish, lizardfish, chain pipefish, seahorses, and even blue-spotted cornetfish, a pencil-thin reef-dwelling species native to the Indian and Pacific oceans that has only recently spread into the Mediterranean Sea and the Atlantic Ocean.
“My first summer doing the survey in 2015 we caught something that we couldn’t identify at first,” Verbeyst recalled. “I had done a semester of fisheries research in the Turks and Caicos, where bonefishing is popular, so as I looked at this torpedo-shaped fish I thought it might be a bonefish. We sent them to some researchers at the University of South Florida, who confirmed that’s what they were and said it was the farthest north that juvenile bonefish had ever been documented.”
The fish survey of Great Salt Pond, along with water-quality monitoring, bay scallop surveys, and salt marsh monitoring, are providing a picture of a healthy ecosystem that is facing increasing demands from human users.
“It’s an oasis in the middle of the ocean and a really important offshore refuge for juvenile fish,” Comings said. “For the amount of use it gets, it’s in good shape, though we definitely want to focus on getting it in better shape.”
He noted that the pond was healthier before the climate crisis began impacting the area and before the effects of development and boating were as noticeable.
“Block Island is often an afterthought when it comes to resource management in the state, but this fish survey is one of those things we can work together on to base some conservation work on in the future,” said Comings, noting that TNC plans to continue the survey for at least 20 years to identify trends in fish diversity and abundance.
“We’ve been very good at conservation of the watershed around the pond,” he said. “Working in the pond itself is much more dynamic and there’s a lot more to it. We need to be careful about the next steps we take, but I’d like to see us move into some sort of restoration or conservation action, to take some of the data we’re collecting and use it to improve the pond and its natural resources.”
Rhode Island resident and author Todd McLeish runs a wildlife blog.