The Great Fish Migration Story – PT I



Imagine hundreds, even thousands, of grayish-green fish filling a river from one bank to the other, fighting their way upstream in the brisk waters swollen by the spring melt. Their silver sides and bellies flash. Occasionally one will propel itself out of the water, avoiding some obstacle that threatens its forward progress. This is the annual run of Alewives at Bride Brook in East Lyme, CT. This spring, nearly 300,000 of them made the journey back to their birthplace along Bride Brook or in Bride Lake in order to spawn.

In spite of this seeming abundance, you may have never seen an Alewife – and if you have there’s a good chance that you didn’t give it a second thought. Lacking the  striking physical characteristics of other native species like Brook Trout, and topping out around 15 inches fully grown – far from the size of trophy fish like Brown Trout, Striped Bass, and Bluefish – Alewives are in many ways the epitome of unassuming. However, like so many things in nature, there is much more to this journeyman species than meets the eye.

Like other native species, such as Blueback Herring, American Shad, and Gizzard Shad, Alewives are anadromous fish. This means that they are born in rivers or lakes but live most of their lives in the ocean, returning to freshwater ecosystems only to spawn (reproduce). This migration is a harrowing one, fraught with predators and obstacles, and yet it is precisely this journey that makes Alewives indispensable members of the marine and freshwater ecosystems they frequent, as well as the estuaries in between.

Alewives are what is known as a “keystone species” – a species that has a critical impact on many others within an ecosystem, whose removal or dwindling could spell disaster for the overall health of that ecosystem. Their importance is primarily as a “forage fish” – a source of food for many different species, including Bluefish, Osprey, and Harbor Seals – and as a transporter of nutrients between marine and freshwater ecosystems. Their range is extensive, with native habitat covering every state on the eastern seaboard of the United States and into Canada, as well as some landlocked locations where they are considered invasive species (the Great Lakes, in particular).

Alewives were once incredibly abundant here in the Northeast. A firsthand account from 1616 described their run upstream:

“experience hath taught them at New Plymouth that in April there is a fish much like a herring that comes up into the small brooks to spawn, and when the water is not knee deep they will presse up through your hands, yea, thow you beat at them with cudgels, and in such abundance as is incredible.” 
– Capt. Charles Whitborne, in “The True Travels of Capt. John Smith,” 1616

Over the ensuing centuries, however, several factors have contributed to the significant decline and then fluctuation of the Alewife population in this area.

During the 17th and 18th centuries, the biggest impact on Alewife populations was fishing for food and bait. Their popularity waned a bit as refrigeration and canning made other, more prized species available for capture, storage, and sale. Beginning in the late 18th and throughout the 19th century, thousands of dams were installed throughout the region to provide power to burgeoning industrial activity (there are still more than 4,000 in Connecticut alone). These dams rendered many rivers and streams impassable for fish, cutting off access to spawning grounds for Alewives, Shad, and other migratory species. This industrial activity also produced a large amount of pollution, which was most often dumped into the nearest body of water. Human waste from growing cities and fertilizer runoff from industrial farming dramatically raised nitrogen levels in Long Island Sound, leading to low oxygen zones that render the waters less hospitable. All of these factors critically disrupted the ability of Alewives to reproduce, and populations in many areas were decimated.

Today we have a much clearer understanding of the link between these factors and the population of anadromous fish, and are working to reverse the damage through legal advocacy, dam deconstruction, and habitat restoration. Through this work, Save the Sound and our scientific partners have learned a great deal about just how important these fish are, and the ways we can help them thrive in their native habitat around CT and NY. In this short series of blog posts, we invite you to journey alongside the Alewives – from birth in freshwater, to life in the ocean by way of Long Island Sound, and back again—and learn about the challenges they’re facing – and beginning to overcome – at Bride Brook and so many other critical waterways that feed into the Sound.


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