Semester 52 just completed their Human Ecology Projects, an opportunity to explore something that relates to human’s relationships with the natural world, and also a chance for students to go more in depth on a project of their own choosing. This project culminated with three required elements: a piece of reflective writing, the product itself and some interactive sharing. At the end of the project period, there was a Human Ecology Celebration, during which students presented and observed each others’ projects. This is an example of a research project by Dale Lattanzio from Phillips Academy about alewife populations.
How have dams and dam removal projects impacted alewife populations and what impact does this species have on its ecosystem?
Dams have many uses in modern society. They provide much needed water to arid places, others protect against flooding, whiles some have even been designed to provide electricity through hydro turbines. However, in Maine and the greater New England area there are many dams that are no longer playing a functional role. The old logging industry and mill companies built many of these dams for their businesses in the mid eighteen hundreds and early nineteen hundreds. They provided them with an efficient means of mechanical work, yet they are now controversial because they radically alter stream ecology and their presences in river systems negatively affect many organisms. According to John Catena, the Northeast Regional Supervisor for the NOAA restoration center, “dams have been a critical factor in the reduction of the natural species that are inhabiting these streams.” For example, the 782 dams in the state have massively depleted the Alewife run in Maine.
Alewife (Alosa pseudoharengus), may not be the most glamorous fish, but its significance as a member of both marine and aquatic ecosystems is astonishing. Alewives are an anadromous fish species, meaning that they are primarily sea going fish that migrate into freshwater aquatic ecosystems to spawn. They can be found in the coastal waters of North Carolina all the way to Newfoundland. Unfortunately due to a variety of reasons, alewives, an important keystone species, have seen drastic stock declines.
To understand the importance of the alewives’ existence in marine and aquatic ecosystems one must look at their life cycle. Alewives start their lives as eggs and larvae far into the upper reaches of river systems most commonly in ponds and lakes. As young juvenile fish they begin their seaward migration in response to the declining temperatures of late summer and early fall, many of the young of the year alewives migrate offshore. Some juveniles will winter in the inshore waters and can be found in estuaries until the next major offshore migration. The developed alewives join a seasonal ocean migration up and down the north Atlantic coast. Sexually mature fish then venture up freshwater river systems to find adequate spawning grounds. Alewives are believed to be multiple breeders, which means that an individual alewife has the capability to make this freshwater migration to spawn multiple time throughout its life. They also have sight fidelity, meaning that alewife return to the same freshwater ecosystem to spawn that they were born in, and continue to do so throughout their life.
Alewives are a crucial fish species because of their role in many ecosystems. They are a seagoing fish and as prey they support just about every predator fish species in the northeast. For example, the highly stressed stripped bass (Morone saxatilis) and bluefin tuna (Thunnus thynnus) stocks are among some of the fish species that rely on alewives as a food source. These predator species are also extremely economically important for many fisheries. For example, striped bass support recreational, game, and commercial fisheries from Nova Scotia to south of the Chesapeake Bay. Similarly, the Atlantic bluefin tuna is one of the most majestic species in the ocean and it supports a massive component of the rod and reel fishery in the United States. With current stocks at 36% of levels from the 1970’s (when bluefin was already being depleted, these tuna stocks are truly struggling. If we do not make an effort to regain the amazing alewife run that once existed in New England’s waters, we could lose significant components of multiple other fisheries that many communities rely upon for economic and recreational activity.
Alewives impact on ecosystems does not end in the marine world. They are also a key source of food for many birds of prey such as ospreys and eagles, among others. There are even terrestrial animals that prey on alewife during their freshwater migration, such as weasels and foxes. Alewives provide food for many animals and birds during spring and summer months, which are crucial breeding times for many organisms. Without the nutrients that alewife provide their predators stocks could collapse as they would be unable to support themselves through such strenuous periods.
As aforementioned, alewives are an extremely multifaceted component in many ecosystems. The thought of losing such an important species is unimaginable to me. It would be like taing soil away from plants; there would be no room for growth. The dams that where made during the logging industry and mill boom prevent alewife from being able to reach suitable spawning conditions in order to procreate. We are essentially passively diminishing alewife populations by leaving these old dams in river systems to decay.
Even if communiites decide they don’t want to remove old or functioning dams, there is still work we could do to protect alewives. For example, fish ladders and lifts are some of the most common methods implemented in river systems blocked by dams. Fish ladders are essentially stairlike structure with increasingly raised pools that fish can use to make their way past unsurpassable humanmade structures and on to spawning grounds. The fish lifts basically mechanically lift fish over the dams so that they are able to continue their journey upstream, similiar to ferry locks on canals. These methods use an alternate source of water flow to attract the fish to them but these solution are not always effective. However, while ladders do provide fish with some means of theoretically reaching their desired spawning location, a fish ladder is not as good as completely open river.
The removal of old unused dams is essential in the resurgence of alewife populations. Other fish species like Atlantic salmon (Salmo salar), and the American eel (Anguilla rostrata) would also benefit greatly as they follow similar upstream migrations. According to NOAA, “[t]here is no single better way to restore habitat quicker and more effectively than removing a dam.” Removing dams is the first step, and a necessary one, in bringing back historical alewife populations in a river system.
The Montsweag Brook Restoration Project is an excellent example of a dam removal project executed on a local level that opened up a river system for fish passage. The Lower Montsweag Dam in Wiscasset, Maine was built by Maine Yankee Atomic Power Company, a now decommissioned nuclear power plant. The dam and land was given to he Chewonki Foundation as part of a natural resources damages settlement. The foundation decided to take down the dam. Once dam removal permits were granted to Chewonki, the process began. Today, the Chewonki Foundation has restored the area, creating three miles of free flowing river to native diadromous fish species. Private and local projects like this one are the key to the resurgence of fish stocks that the region used to know.
Dams like The Lower Montsweag are all over Maine and New England. Many of these dams longer serve their original purpose and yet are harming the natural ecosystem directly and indirectly. As a member of the commons, we have the right to act upon the dams that scatter our local rivers and streams. Although, many of the dams are privately owned and removal can be costly, the ecological benefit makes it worthwhile. If projects like these were to take storm across the New England area, we would most certainly see massive booms in alewife, river run herring, Atlantic salmon, striped bass, sea run trout, and other diadromous fish species in the Northast. Small-scale actions like removing old, unused dams could be what secure the stocks of these fish species for future years. Thus, it is important that we act as soon as possible.
-Dale Lattanzio, Phillips Academy
Dale, on the left, during a recent work program. To see more photos of Semester 52 Human Ecology Projects go to the Chewonki Semester School Flickr Page.