Reasons for Listing
In determining whether to list, delist, or reclassify a taxon under the ESA, five threat factors are evaluated, including:
- Factor A. the present or threatened destruction, modification, or curtailment of its habitat or range;
- Factor B. overutilization for commercial, recreational, scientific, or educational purposes;
- Factor C. disease or predation;
- Factor D. the inadequacy of existing regulatory mechanisms; and
- Factor E. other natural or manmade factors affecting its continued existence.
Threats, categorized into the above factors, and the subsequent reasons for listing Atlantic salmon in Maine have been identified and extensively analyzed in a number of documents (NOAA and USFWS 1999, NRC 2004, NOAA and USFWS 2005, Fay et al. 2006, 74 FR 29344). New information and increased knowledge led to the expansion of the DPS and a better understanding of the threats and relative importance to the recovery of Atlantic salmon. The 1999 Review of the Status of Atlantic salmon in Maine (NOAA and USFWS 1999) identified dams and overfishing as the major threats contributing to the precipitous decline and current low abundance of adult Atlantic salmon in the United States. The original 2000 GOM DPS listing and 2005 Recovery Plan concentrated on Atlantic salmon in central and eastern Maine; dams and road stream crossings were not identified as significant threats affecting Atlantic salmon in this much smaller geographic region.
The expanded listing of the GOM DPS in 2009 continued this broader geographic perspective. The 2009 listing rule (74 FR 29344) highlighted the following three threats and identified each as being a significant factor in the decline of Atlantic salmon in Maine:
- Dams (Factor A)
- Inadequacy of existing regulatory mechanisms for dams (Factor D)
- Continued low marine survival rates for U.S. stocks of Atlantic salmon (Factor E)
The 2009 listing document further detailed these threats.
Dams significantly impede migration pathways and increase direct and indirect mortality of Atlantic salmon by:
- Limiting access to otherwise suitable habitat
- Directly and indirectly killing adults and smolts going through or around the structure, i.e., entrainment and impingement
- Creating impoundments that degrade the productive capacity of habitats upstream by inundating formerly free-flowing rivers, reducing water quality (e.g., increasing water temperature), and changing fish communities
- Delaying outmigration of smolts
- Delaying upstream migration of adults
- Altering natural flow regimes
- Affecting in similar ways other co-evolutionary diadromous fish upon which salmon depend
Regulatory mechanisms for hydroelectric dams regulated by the Federal Energy Regulatory Agency (FERC) were determined to be insufficient (i.e., many recommendations proved to be ineffective or were not adopted) in providing appropriate fish passage (access) necessary for Atlantic salmon survival. Currently, within the historical range of the GOM DPS, there are 19 FERC-licensed dams in the Androscoggin River, 18 in the Kennebec River, and 23 in the Penobscot River. Many of these do not provide for adequate fish passage.
Regulatory mechanisms for non-FERC dams are also insufficient to provide for fish passage. Because most non-FERC dams predate the Clean Water Act (CWA), section 404 of which regulates the discharge of dredged or fill material into waters of the United States, State law 12 M.R.S.A section 12760 is the only statute other than the ESA dealing with fish passage at these structures. However, this law requires an administrative process and hearing only if requested by the dam owner. For the State to require fish passage under this statute, a finding that fish can be restored “in substantial numbers” and the habitat above the dam “is sufficient or suitable to support a substantial, commercial or recreational fishery” must occur. This statute has been used to require fish passage at only one dam in Maine and remains untested in the courts and at the administrative level (74 FR 29344). It should be noted that construction of any new barriers would be subject to CWA section 404 guidelines regarding water degradation if they significantly impair aquatic life movement.
Natural mortality in the marine environment can be attributed to four general sources: predation, starvation, diseases and parasites, and abiotic factors like changing ocean conditions. However, we are currently unable to partition total natural mortality into these categories. Consequently, investigations of natural mortality are currently based upon an examination of return rates or total marine survival estimated by relating either hatchery smolt stocking rates or estimates of wild smolt production to the return or adult spawners. This method integrates all natural mortality factors and, if applicable, fishing mortality. If smolts are counted near the marine environment, the return rate likely indexes marine survival, although some freshwater experiences (outmigration delays at dams, sublethal harm at dams, poor freshwater rearing leading to lowered fitness) can cause delayed mortality that is actually attributable to freshwater sources. If the smolts are counted as they are stocked into upstream reaches, then assessment of return rate will include outmigration mortality caused by dam, predation, environment, and fitness in the freshwater system.
The 2009 final listing rule also mentioned a number of secondary threats (“lesser stressors”) that collectively contributed to the listing determination:
Reduced habitat complexity, reduced water quantity, and degraded water quality (Factor A); overutilization (Factor B); disease and predation (Factor C); inadequacy of existing regulatory mechanisms for water withdrawals and water quality (Factor D); and aquaculture, depleted diadromous fish communities, and competition (Factor E). With regard to climate change, the Services concluded in the 2009 rule that, “At this time, we do not have enough information to determine whether the GOM DPS is threatened or endangered because of the effects of climate change.” However, climate change has since been identified as a priority area of research for the DPS.
Dams, inadequate regulatory mechanisms related to dams, and marine survival,as well as numerous secondary threats, continue to affect the survival and recovery of the GOM DPS. These threats are covered in detail in the following section.