Movements of coastal brook trout after dam removals
Brook trout (Salvelinus fontinalis; Figure 1) are a species of char native to the eastern half of North America. Though commonly associated with headwater streams in the mountains, populations of brook trout have historically been found in small coastal streams from Long Island, New York to the Canadian Maritimes. These brook trout, known as “salters”, have migratory tendencies. They enter saltwater to feed and grow larger than brook trout that remain in freshwater. Unlike other anadromous fish, salters usually do not venture far from their natal streams and they typically only remain in saltwater for up to several months before returning to freshwater.
Salters were once a popular sportfish in New England waters. Prized for their fighting ability and table fare, exclusive fishing clubs targeting salters were established along a number of coastal streams in the 1800s. By the turn of the century, salter populations had declined due to overfishing, water pollution and habitat degradation caused by increased development and agriculture along the coast. The construction of dams also blocked migratory routes, isolating salters in the streams. Over time, the remaining brook trout became freshwater residents.
As dam removals became widespread in the late 20th Century, some salter populations regained access to the marine environment, though it is not known how many resumed their migratory behavior. Erin Snook and Dr. Andy Danylchuk from the University of Massachusetts-Amherst led an investigation of the movement patterns of salters in Red Brook, a small coastal stream in southeastern Massachusetts. Red Brook extends 7.25 km from White Island Pond to Buttermilk Bay, a small tidal embayment at the north end of Buzzards Bay. Just downstream of White Island Pond, the brook has been altered and flows through commercial cranberry bogs. Since 1990, a series of restoration projects took place to stabilize the shoreline along sections of Red Brook. Native plants were planted along the streambanks that provide shade to keep the water cool. Large wood, including logs and root wads, was added to improve trout habitat. By 2009, seven dams were removed from Red Brook, including two concrete flumes at the head-of-tide, improving aquatic connectivity throughout the stream.
Between 2010 and 2012, 84 brook trout were captured using a backpack electrofisher and surgically implanted with acoustic transmitters. An array of acoustic receivers was deployed throughout Red Brook, the adjacent estuary, and Buttermilk Bay to track their movements between habitats (Figure 2). Data loggers were used to measure water temperature in hourly intervals.
The results indicate that the movements of individual brook trout varied greatly. Of the tagged brook trout, 50% migrated into the estuary while the others remained in the stream. This may have been due to larger and more abundant prey in the estuary. They generally began migrating downstream after spawning in November while upstream movements peaked during the spring as water temperatures were warming. About 10% of the migratory salters ventured into Buttermilk Bay though only for short periods of time – likely due to stresses caused by temperature and salinity at different points throughout the year. These movements into the bay may have been influenced by the larger tidal ranges caused by the new and full moons.
The removal of dams has restored the migratory routes of salters in several coastal streams. In Red Brook, the last dam was removed in 2009 and salters were documented migrating into the estuary the following year. Though salters in Red Brook exhibit less anadromy than populations in the northern part of their range, the estuary is an important feeding area for this population. Removing barriers to fish movement can help restore unique populations of fish such as anadromous brook trout in New England. The return of salters in these coastal streams indicates that the aquatic habitat is returning to a healthy and balanced state, benefiting native species throughout the region.
Snook, E.L., B.H. Letcher, T.L. Dubreuil, J. Zydlewski, M.J. O’Donnell, A.R. Whiteley, S.T. Hurley, and A.J. Danylchuk. 2016. Movement patterns of brook trout in a restored coastal stream system in southern Massachusetts. Ecology of Freshwater Fish 25(3): 360-375.