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Atlantic salmon

Salmo salar


Rev. 1.1 - 9/2011

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Species Summary

The Atlantic salmon (Salmo salar) is native to drainages flowing into the North Atlantic Ocean. There are three generally recognized groups: European, Baltic, and North American. Historically, North American Atlantic salmon reproduced in nearly every major river north of the Hudson River in Long Island Sound to northern Quebec. Historical runs in the United States have been estimated between 300,000 and 500,000 fish, with the Connecticut, Merrimack, Androscoggin, Kennebec, and Penobscot rivers having the largest runs.

Context Map
(click to enlarge) Context Map

While there are still Canadian populations that are self-sustaining and strong, by the early 19th century many Canadian and all United States populations had become severely depleted. Salmon runs disappeared from southern New England by the 1860’s, and by the end of the century had been extirpated from three of the five rivers with the largest populations: Androscoggin, Merrimack, and Connecticut. Current populations of Atlantic salmon are divided into three Distinct Population Segments (DPS): Long Island Sound, Central New England, and Gulf of Maine. Stocks native to Long Island Sound and Central New England are considered extinct, and current populations are a result of stocking with fish from the Gulf of Maine DPS. In 2000, the Gulf of Maine DPS – from the Kennebec to the Dennys - was listed as Endangered under the Endangered Species Act. The 2006 Status Review has much background information on the current state of Atlantic salmon.

Many factors have been implicated in the demise of salmon populations and their endangered status. Land use change, water quality degradation, and poaching have all been cited. However, dams constructed for hydropower, mills, and other water uses have played a major role in declines because they prohibit adult fish from ascending rivers to spawn in tributary streams and can delay out-migration. Commercial fishing in Greenland and low marine survival, non-native predators, and aquaculture are seen as continual threats to Atlantic salmon persistence and recovery.

Restoration has a long history in New England. Atlantic salmon restoration began with limited success in the late 1800’s due to impassible dams and inefficient fishways. Dam removal and use of fish ladders and fish lifts to pass fish over dams continue to be important restoration and recovery actions. Restoration of freshwater and marine habitats is also ongoing, as is protection of key freshwater habitats. Most New England populations are supplemented with hatchery salmon. Some returning adults are collected at dams for hatchery propagation, while others are released for natural spawning. Widespread stocking sustains most of the current distribution of Atlantic salmon across New England. Populations in the Gulf of Maine DPS are considered representative of historical stocks. The Connecticut and Merrimack populations were restored with fish from the Penobscot or Canadian rivers. Restoration and recovery actions follow recovery plans, especially for the Gulf of Maine DPS, developed by NOAA and US Fish and Wildlife Service.

Atlantic Salmon photo
Atlantic Salmon. Photo: William Hartley, USFWS

Our CSI analysis was based on information from multiple sources, including: the states of Maine, Massachusetts, New Hampshire, Rhode Island, and Connecticut; The Nature Conservancy; U.S. Atlantic Salmon Assessment Committee; U.S. Fish and Wildlife Service; and NOAA. A complete list of data sources can be found under the Rule Sets and Data Sources link.

Key CSI Findings

  • Atlantic salmon occupy a small fraction of historical subbasins
  • The fraction of historical subwatersheds currently occupied varies widely by river basin
  • Adult returns are low; the Penobscot River has the largest runs numbering over 1,000
  • Existing habitat for most populations is highly fragmented by dams
  • Hatchery fish consistently represent a high number of adult returns.
  • Despite low returns, returning wild fish often represent a good life history diversity in terms of sea-winter ages and repeat spawners
  • Roads along streams and converted lands adjacent to streams threaten existing stream habitat, especially in southern New England
  • Over 1/3 of subwatersheds scored 1 for connectivity due to high numbers of dams and road-stream crossings
  • Watershed conditions are generally good owing to large amounts of forested land cover
  • Large tracts of productive forests pose risks to the future security of populations and habitat
  • Increased summer temperature and changes in precipitation due to climate change pose high risks to stream temperatures and flow regimes along the coast, especially in southern New England

Prepared by Dan Dauwalter, September 2011

Table 1. CSI scoring result summary for Atlantic salmon

    Number of Subwatersheds
Receiving Scores
Total
Subwatersheds
Scored
  CSI Indicator 1 2 3 4 5  
 
Range-wide Conditions



Percent historic stream habitat occupied 141 396 0 0 686 1223
Percent subbasins (4th) occupied 1223 0 0 0 0 1223
Percent subwatersheds (6th) occupied 510 21 42 186 464 1223
Percent of historic rivers occupied 0 1223 0 0 0 1223
Dam density in occupied habitat 1223 0 0 0 0 1223

Population Integrity



Population size 943 280 0 0 0 1223
Habitat extent 291 475 183 12 262 1223
Hatchery influence 507 400 4 312 0 1223
Disease vulnerability 447 395 271 26 84 1223
Life history diversity 33 0 285 551 354 1223

Habitat Integrity



Riparian condition 65 114 624 506 481 1790
Watershed connectivity 562 353 317 281 277 1790
Watershed conditions 73 50 141 246 1280 1790
Water quality 560 58 75 220 877 1790
Flow regime 345 238 181 235 791 1790

Future Security



Land conversion 338 488 506 309 149 1790
Resource extraction 1357 307 75 28 23 1790
Energy development 907 166 158 363 196 1790
Climate change 112 330 203 563 582 1790
Introduced species 0 219 810 761 0 1790

Conservation Strategies Map

(click to enlarge)
Conservation Strategies Map