Intertidal: stories of the return of local migratory fish

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The weather is getting warmer and the fish are swimming – some of them longer and further than they have in nearly two centuries. World Fish Migration Day was May 21, a day when people around the world celebrate fish that travel long distances through a variety of waterways. This year, the day included 450 events in 75 countries.

More locally, groups in Maine have come together to celebrate the restoration of some of the state’s alewife populations. Gaspereau (Alosa pseudoharengus) is the more common of the two species called river herring. The other is the blue-backed herring (Alosa aestivalis). Both species are small, silvery fish and they are very difficult to tell apart. Alewife have a slightly larger eye and a bronze-colored head, while blue-backed herring have a smaller eye and a silver head.

Although both are called river herring, alewife and blueback herring only spend part of their lives in rivers. The reason they are celebrated on World Fish Migration Day is because they spend the other part of their lives in the ocean. These small fish form large schools in the spring and travel from their saltwater adult homes to the fresher waters of tributaries, streams, and rivers, and eventually to lakes and ponds where they spawn. Then, the “exhausted” adults return to the sea, as eventually does the new generation of fish.

Populations of river herring were once abundant and supported fisheries along the coast. People were using drift nets, hand nets and building dams to catch them. Then they were smoked and eaten or used as bait to catch larger, more valuable species. But their abundance depended both on water health and also on the connectivity between their spawning and “maturing” areas. Without the ability to go upstream to spawn, there can be no next generation of river herring.

Pollution of waterways due to industrialization, including the construction of factories along rivers that used harmful chemicals in their production of paper or textiles, threatened these and other fish populations. Additionally, the use of river power for electricity and to run those same mills has led to the construction of dams to harness power from many of Maine’s major rivers. These two major factors have caused the herring population to decline to near threatened levels.

Alewife swim in an enclosure atop a fish ladder at Webber Pond Dam in Vassalboro on May 20, 2019. Portland Press Herald photo by Gregory Rec

Fortunately, since then, efforts have been made both to clean the water and to allow the fish to follow the path necessary to complete their life cycle and rebuild their populations. The Clean Water Act of 1972, which recently celebrated its 50th anniversary, helped fund treatment facilities to improve water quality. And the removal of dams or the construction of fish ladders have restored passages for these migratory fish.

We have a fishway in Brunswick on the Androscoggin which was built in 1980 to facilitate the passage of migrating fish. It’s not designed for herring, however, but works to help endangered Atlantic salmon, another migratory species, travel upstream. It’s a good reminder that when crossing from Brunswick to Topsham you may feel like you are far from the ocean, but the river system connects through Merrymeeting Bay into the sea.

There is another place much further from the coast, however, where a big party was held this year to welcome back the historic run of river herring. In the inland town of Vassalboro, people gathered at China Lake, which is part of the Kennebec River estuary, to see crowds of alewife coming all the way to the lake to spawn.

Thanks to the efforts of Maine Rivers, a non-profit organization dedicated to restoring historic fish runs, the final seven miles between China Lake and the Kennebec River have been cleared for these incoming fish. The multi-year effort included the removal of three dams and the construction of three fish ladders. When these fish arrived this spring, it was the first time since just after the Revolutionary War. Almost a million alewife returned.

Environmental restoration work can be frustrating and full of disappointment, because trying to reverse what has happened in nature is never easy. But there are examples like this that are encouraging. The restoration process has not been quick, but for those who celebrated the abundance of herring arriving at China Lake, it was an encouraging sign that it is possible to make a difference by bringing an important species back to shore. and Maine waterways.

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