NYC's Fishy Commuters - From Sea to River and BackLatest update April 9, 2019 Started on September 1, 2018
The Wildlife Conservation Society’s New York Seascape program is monitoring and restoring diadromous fishes in New York’s tidal rivers. What does diadromous mean? This term refers to fish that spend part of their lives in salt water and part in fresh water. Along with our partners, we are exploring the effects that dams and other barriers have on the access by American eels and alewife fish to freshwater habitats and we are working to promote river connectivity, restoration, and fish passage.
For centuries, New York's waters turned silver in spring time with the arrival of millions of river herring, also known as alewives. This diadromous fish (i.e., a species that splits its lifetime between fresh and salt water) spends most of its adult life at sea, filter-feeding in the cool, plankton-rich waters of the Northwest Atlantic. When spring arrives, adult alewives navigate back to the rivers in which they were born three or so years earlier to spawn in the relatively safe fresh water environments.
Unfortunately, most of those spawning runs have been blocked by dams, which were built decades or even centuries ago to provide power for human use. Many of these dams no longer serve that or any purpose, but remain in place all the same.
The Bronx River - the only freshwater river in New York City - is no exception. Its first dam, currently sitting at 182nd Street (first photo), has been there in some form for nearly four centuries! Without access to upstream spawning habitat, the alewife has long been absent from the Bronx River ecosystem. That began to change in 2015, when a coalition of Bronx River enthusiasts won a great victory for fish restoration in the Bronx River: the construction of a fish pass on the 182nd Street Dam (second photo). This "ladder" allows diadromous fish like alewives to bypass the dam and continue their upstream migrations to their spawning habitat. But another problem remained. Without any alewives born in the Bronx River for centuries, there were none left to return to the river to spawn.
Which brings us to April 9, 2019. Since 2017, the New York City Parks Department and the Wildlife Conservation Society, in partnership with the Connecticut Department of Energy and Environmental Protection and Bronx River Alliance, have been stocking the Bronx River with alewives "borrowed" from up the coast in Connecticut. These fish are caught in Connecticut rivers flush with alewives and released into the Bronx River, just as they are ready to spawn, in an effort to re-establish a spawning population.
Today, about 400 alewives were transported from Connecticut to the Bronx in a Tank-er truck specifically designed to move fish (third photo). Using our Trident ROV, we were able to catch up with the school of alewives after their release. Hopefully, these fish will spawn in the next few weeks and their offspring will return to the Bronx River in 3-5 years, utilizing the fish passage, to form the basis of a self-sustaining alewife population here for the first time in nearly 400 years!
The average New Yorker spends almost 36 minutes in a one-way commute. That’s nothing compared to the alewife (river herring) that spawn in the New York’s rivers. These fish have spent three years maturing in the open ocean and traveled hundreds miles to get to the coastal rivers where they spawn. But even that commute pales when compared to the American eel. Scientists believe that all American eels are born in the Sargasso Sea, a relatively calm area in the middle of the Atlantic Ocean, then drift as larvae on ocean currents for more than a year until they reach the coast. There they transform into “glass” eels (tiny, transparent eels) and move into freshwater rivers and streams, like the Bronx River in New York City, where they grow to adulthood over the next 20-30 years! Once mature (now a “silver” eel), they say farewell to the river and migrate – as much as 1000 miles – back to the Sargasso Sea where they were born to spawn once and die. Quite the commute for such a small fish!
Using OpenROV’s Trident Underwater Drone we will work with our partners to characterize eel habitat and monitor alewife that have been re-introduced to the Bronx River. For alewife, our ROV surveys will help determine post-restocking mortality, monitor for evidence of spawning activity and in-stream movements, and look for the presence of juvenile alewife in summer months. Other survey methods, such as fyke nets, cast nets, traps or electrofishing, can be stressful to this particularly sensitive fish. The Trident ROV offers a less invasive tool to collect data on this depleted species. Join the Wildlife Conservation Society’s New York Seascape Program as we study the lives of diadromous fishes, like eels and alewife, in southern New York rivers.
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