Comments: Native U.S. populations south of Maine are essentially extirpated due primarily to the effects of dams and water pollution; excessive harvest of adults by humans, stream acidification, sedimentation of spawning and holding habitat, and possibly changes in water temperature regimes contributed to the decline in some areas. Evidence from New England indicates that landlocked populations of Atlantic salmon may be negatively influenced as abundance of northern pike and/or Esox hybrids increases. In the U.S., some of these threats have been alleviated; water quality has improved in recent decades, and fish ladders have been constructed at many dams; reintroduction programs are in progress. Poor marine survival continues to result in reduced returns to U.S. rivers (USFWS 1995, Anderson et al. 2000); depletion of forage species by commercial fisheries and freshwater exposure of juveniles to an endocrine disrupter (leads to mortality in marine phase) are suggested possible causes. Escaped farmed salmon may pose a threat to native populations in coastal Maine rivers (USFWS 1995). See USFWS (1995), NMFS (Federal Register, 29 September 1995), Colligan and Nickerson (1996), and Anderson et al. (2000) for further information on threats to North American populations.
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