While Acadia’s terrestrial wildlife is utterly majestic, there are no less fascinating stories playing out just underneath the surface of the park’s streams and ponds. Every spring a species of herring known as an alewife migrates in droves from the ocean, up streams along the New England coast to breed and lay eggs. Unlike pacific salmon species, which die after spawning, adult alewives will brave the journey back to the ocean, hoping to survive yet another year to breed the following spring. Alewives make this adventurous breeding journey as many as four times. Those that don’t survive feed a plethora of other species: mink, eagles, vultures, raccoons, even bears.
Every summer, the newest generation of alewives hatches in several ponds in Acadia National Park. Over the course of several weeks, they will begin to feel the pull of the ocean and migrate en masse, and with great fervor towards the Atlantic. The entire migration is over almost as soon as it begins; those that survive will spend a few years in the ocean before beginning the cycle again and returning to lakes and ponds. Scientists call this style of migration anadromous.
Some anadromous fishes (fishes that spend part of their lives in the ocean, and part in freshwater) have been struggling in New England for a long time. Alewives, smelt, and Atlantic salmon runs have been interrupted, and in some cases blocked completely, by humans damming streams and rivers for power, flood control, and property management. At Acadia, we have been monitoring the alewife populations that migrate to our waterways. We sample them at fish ladders. These structures assist fish at dams - we take length measurements and scale samples to determine age classes throughout the run and release them into the ponds they’ve been working so hard to reach. This allows researchers to determine if newer generations are making it back to streams to spawn, and what proportion of older generations have returned. Through research and science-based management, we hope alewives will continue to visit our park alongside our human visitors for generations to come.
Last updated: November 23, 2018