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Maine Department of Marine Resources Concludes Annual Assessment of Atlantic Salmon Smolt Population

Piscataquis Smolt Smolt Assessment

Above left DMR seasonal contract worker Andrew Gibbs shows off an Atlantic Salmon smolt trapped on the Piscataquis River as part of the department's annual assessment work. Above right seasonal contract workrer Derik Lee marks and measures smolts before returning them to the river.

The Maine Department of Marine Resources Division of Sea-run Fisheries and Habitat staff recently concluded annual assessments of Atlantic salmon smolt populations in the Narraguagus River, the East Machias River, the Piscataquis River, and the Sheepscot River. The work will help the Department and its partners at the state and federal level understand the status of Atlantic Salmon and the quality of habitat in Maine waters.

The four rivers are chosen because their geographic range provides an indicator of Atlantic Salmon and habitat health along the coast. A smolt is the life stage of Atlantic salmon that transitions from freshwater river and stream habitats to saltwater coastal and open ocean areas.

Listed as an Endangered Species since 2000, the Atlantic salmon is one of Maine’s iconic fish species, long the favorite of recreational anglers. However factors including overexploitation, degradation of water quality, and damming of rivers have been associated with the decline in abundance. The populations of Atlantic salmon present in the Gulf of Maine represent the last wild populations of U.S. Atlantic salmon.

“Our efforts to preserve and protect the Atlantic salmon population in Maine include the spring trapping and evaluation of both wild and hatchery grown smolts to assess their abundance and related management actions, as well as adult returns,” said Oliver Cox, Director of DMR’s Division of Sea-run Fisheries and Habitat. “Our objective is to increase the population of smolts through management actions including stocking and habitat restoration. Data from these assessments, which will be reviewed over the next year, will help us determine future management actions.”

On their way to the sea, migrating smolts were captured for DMR assessments in rotary screw traps which were suspended from a cable and float on pontoons. A “cone” portion of the traps has vanes inside that prevent fish from swimming out. The fish were directed to the back of the trap where they end up in a container called a live car.

During May and June DMR scientists tended the traps on the four rivers daily, counting trapped fish, recording biological data such as length, weight, age, and origin before releasing the smolt to continue their migration.

The scientists estimated the total number of smolts passing by the traps since all the smolts leaving the river cannot be captured. “Use of smolt traps gives the best estimate of smolt production in salmon habitat located above trapping sites,” said Cox. Data obtained during the smolt trapping season is used by DMR scientists to estimate freshwater and marine survival when used in conjunction with the juvenile or adult abundance of the same year class.

Since 1996, Atlantic salmon smolts have been monitored on the Narraguagus River in Cherryfield. “This is the longest series of smolt data Maine currently has,” said Cox. “This project is part of a long term program of monitoring Atlantic salmon in the Narraguagus River. The data collected from the smolt trapping activities combined with juvenile assessments and adult trap data form a complete picture of salmon biology in the Narraguagus River and can be used to indicate the health of Atlantic salmon across Maine.”

For a second year, assessment on the East Machias River was done in partnership with the Downeast Salmon Federation as part of a larger project that uses juvenile salmon known as fingerling parr which are raised at the East Machias Aquatic Resource Center. The project, an effort to increase juvenile salmon production in the drainage, uses two rotary screw traps located downstream of the Route 191 bridge in Jacksonville.

The population in the East Machias River is comprised of 2 and 3 year old wild smolts resulting from natural reproduction, as well as hatchery smolts resulting from fall fingerling parr stocking.

Since 2008, Atlantic salmon smolt production has also been evaluated in the Upper Piscataquis River to understand how smolt produced from direct adult releases compared to previous fry stocking efforts. In 2009, adult Atlantic salmon were trapped at the Veazie Dam and transported to the U.S. Fish and Wildlife Service Craig Brook National Fish Hatchery. The fish were held at the hatchery until October when they were released in to the Upper Piscataquis to spawn on their own. “Since 2012, smolts handled at this site have been the result of adults spawning in the wild. Preliminary results indicate that this management action can successfully produce smolts at densities equal to what we would expect for a healthy Atlantic salmon run,” said Cox.

The Sheepscot River Atlantic salmon smolt trapping project has been operated annually since 2001 to document smolt migration timing and run size. “Since 2009, population estimates for smolts have been used to assess management changes,” said Cox. “In 2004, we started stocking parr in the fall instead of fry in the spring. The population estimates from parr releases indicated that smolt production double due to this change.”

“More recently, smolt population estimates have been used to evaluate a watershed wide egg planting project,” said Cox. “Most of the juvenile habitat is now being supplemented by Atlantic salmon egg planting. Starting in 2014 the majority of the naturally reared smolts, in the Sheepscot River, will have been a result of this egg planting effort.”

Funding and equipment for smolt assessments is provided by NOAA Fisheries through a Cooperative Agreement with Maine Department of Marine Resources.

Atlantic salmon return as adults during the spring and summer and spawn in the fall. Their eggs typically hatch in April and fry emerge in May. The juveniles then spend one to three years in the stream before smolting and leaving for the ocean. There they spend an additional one to three years gaining size before returning to their natal streams to spawn and start the life cycle over. Atlantic salmon can spawn repeatedly if they survive the migrations.

“Atlantic Salmon are the king of fish and the DMR is working hard on many fronts, from partnering with other agencies on dam removal efforts to stocking and trapping projects like these to protect this once abundant and still remarkable fish species,” said Cox.

The Maine Department of Marine Resources Division of Sea-run Fisheries works in partnership with other state and federal agencies to protect, conserve, restore, manage and enhance diadromous fish populations, including Atlantic salmon, and their habitat in all waters of the State. For more information on the Maine DMR Division of Sea-run Fisheries visit