A Shift in Strategy for Merrimack River Atlantic Salmon Restoration

CONCORD, N.H. -- The New Hampshire Fish and Game Department won't need as much volunteer help this year stocking millions of inch-long salmon fry (young salmon) into the Merrimack River basin because of an exciting new development. About the same number of fry will be stocked, but fewer rivers are being targeted because Fish and Game does not want to stock on top of fry that may have hatched in the wild.

Last fall, adult salmon were released into the Souhegan, Baker and upper Pemigewasset rivers, and successful spawning was confirmed by monitoring radio-tagged fish and counting redds (salmon nests). The shift in strategy was inspired by a record number of 402 returning Atlantic salmon counted at the Essex Dam fish lift downstream in Massachusetts in the spring of 2011. Similar increases were recorded on salmon rivers throughout Maine and Canada. The increase in numbers allowed Fish and Game to take some big steps toward answering questions about natural salmon reproduction.

It has been 35 years since the first salmon fry were released in the Merrimack River watershed under the current Atlantic salmon restoration program, which is funded by the federal Sport Fish Restoration Program. Before 1976, Atlantic salmon had been missing from the waters of the Merrimack since the first attempt at salmon restoration ended more than a century ago in 1895. The original salmon population had been extirpated by dams built in Lawrence and Lowell in the early 1800s.

Optimism ran high in the early days of the modern program. Targets for adult salmon returns were set in the thousands. The program became a catalyst for habitat restoration, land conservation and fish passage projects throughout the Merrimack watershed. Yet the goal of achieving a sustainable salmon run has remained elusive, with an average of 121 adult salmon returning to the Merrimack River each year.

The restoration program holds the first 300 returning Atlantic salmon at the National Fish Hatchery in Nashua, where their eggs are used to produce the millions of juvenile salmon that are stocked throughout the Merrimack River watershed each year. Until 2011, this target was only exceeded once, with 331 salmon returns counted in 1991.

Salmon returns have typically been low because populations throughout North America are in decline. Poor survival in the ocean has been a major obstacle to salmon restoration efforts throughout the region. This remains true despite the closing of an ocean fishery off the western coast of Greenland, where Atlantic salmon congregate before migrating back to their home rivers. Determining the potential cause, or causes, of declining marine survival is a major focus of current research.

"If ocean survival is cyclical, then it is reasonable to believe that salmon restoration can succeed," said Matt Carpenter, a fisheries biologist who coordinates New Hampshire's salmon restoration program. "However, if there has been a fundamental shift in the North Atlantic ecosystem because of a changing climate or other factors, then salmon restoration may not be possible."

It was with this uncertainty about the marine phase of the salmon's life cycle in mind that regional anadromous fisheries planners began, in 2010, to rethink the strategy of the Merrimack River Salmon Program. A common theme has been scaling back hatchery production and shifting focus toward evaluating the potential for natural salmon reproduction in the watershed. This looks especially promising in the Souhegan River, where a recent dam removal has made salmon spawning habitat accessible for the first time in the history of the program. Releasing adult salmon and evaluating their ability to spawn in the wild, rather than waiting until we reach a minimum target of 300 fish before breeding adults are released, will tell us whether the Souhegan River contains habitat that is capable of supporting a sustainable salmon population if marine survival improves.

"It was encouraging to see that marine survival did improve, at least for salmon returning in 2011," said Carpenter.

Fish and Game will continue to monitor the progress of salmon breeding in the wild in the Souhegan and other rivers. In two years, biologists will be able to sample for juvenile salmon, called parr, in areas where successful spawning was recorded.

Link:
A Shift in Strategy for Merrimack River Atlantic Salmon Restoration