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Anadromous Atlantic salmon (Salmo salar) migrate from the mouths of U.S. rivers to the Northwest Atlantic Ocean, overwintering in the southern Labrador Sea and the Bay of Fundy. Atlantic salmon begin their lives in rivers where they stay for two to three years before beginning the process of smoltification to prepare for migration to the ocean. During smoltification, biochemical and physiological changes prepare the Atlantic salmon for the transition from fresh to salt water. The ocean portion of the species life history typically lasts from one to three years (adults that return after only one year at sea are called grilse), during which they undertake feeding migrations over thousands of miles. Atlantic salmon feed on capelin, herring, sand eels and large zooplankton (Reddin 1988), and appear to be opportunistic feeders as their numbers are not correlated with the availability of a particular prey species. After returning to spawn, kelts (spawned-out salmon) either return to the ocean or overwinter in the river.
Mature adults show a strong affinity for their native river (a straying rate of 2% for hatchery fish over 22 years according to Baum and Spencer 1990), and appear to use olfactory stimuli to return to their native streams (Stasko et al. 1973) between April and November. This strong homing ability has resulted in the evolution of unique characteristics for each river population, for example in the timing of smolt migration. Historically, there were significant differences in the timing of outmigrating smolts. Each river population appeared to be timing its outmigration during the period when the river and estuary were the most suitable in terms of water flow and temperature. However, many of these differences have been lost or at least reduced as genetic diversity has been affected by decreasing run size.
Insight into the marine life stage of U.S. Atlantic salmon has been gained from marking and tagging studies of fish stocked in the Connecticut, Merrimack, and Penobscot Rivers. Over the history of the U.S. program, marking has progressed from fin clipping (1942-1962) to Carlin tags (1962-1992) and, finally, to coded-wire tags (CWT) in use since 1985 (Meister 1984; NASCO 1993). A diagram of the life cycle of an anadromous Atlantic salmon is presented in Figure 1.
As depicted in Figure 2, the original range of Atlantic salmon in the U.S. was from the Housatonic River (Connecticut) to the St. Croix River (Maine) (Kendall 1935; Scott and Crossman 1973). Historic runs have been estimated at 500,000 fish annually. Atlantic salmon populations were present in at least 34 rivers in Maine alone (Rounsefell and Bond, 1948). By the early 1800's the Atlantic salmon runs in the U.S. were severely depleted due to sport fishing, water quality degradation, excessive commercial netting, and barriers to migration caused by development accompanying the Industrial Revolution.
The presence and abundance of Atlantic salmon in a river has traditionally been viewed as a gauge of a river's health. In the late 1960's and early 1970's there was a great deal of energy and effort directed at improving the water quality and habitat in the rivers to a condition that could support Atlantic salmon. Improvements in water quality, installation of fish passage facilities, movement from harvest to catch and release, and increased public awareness all contributed to an atmosphere of hope for successful Atlantic salmon restoration throughout New England, thereby encouraging more partners to join the effort. During the 1970's and early 1980's, returns increased and recreational fishing success in Maine was high. However, Atlantic salmon were being heavily fished at sea by Canadian and West Greenland commercial fisheries. This reduced the number of adults that returned to spawn in rivers of the eastern U.S. In addition, the recreational fishery harvested 15-25% of the returning spawners. Those factors, coupled with worsening natural conditions at sea, have drastically reduced Atlantic salmon abundance in many U.S. rivers during the past decade.
Currently the Atlantic salmon populations in New England consist primarily of river runs restored or enhanced by fish of hatchery origin. Adult fish are captured upon returning to the river, spawned in hatcheries, and their offspring are used to maintain the runs. In addition, juvenile offspring of sea-run stock are reared in captivity to sexual maturity and their offspring are then released into the wild as fry. Major populations, notably the Penobscot, Connecticut, and Merrimack River populations, have been partially restored during the past 10 to 25 years after virtually disappearing, and in 1994 a total of 1,634 Atlantic salmon were documented to have returned to a total of 19 rivers in New England.
For the purposes of review under the Endangered Species Act (ESA), it is important to analyze the status of the Atlantic salmon populations in those rivers that have had persistent returns of naturally spawning Atlantic salmon and thus qualify as species under the ESA. Currently the National Marine Fisheries Service and Fish and Wildlife Service (collectively "the Services") believe that the only remaining populations that consist at least in part of native fish in the U.S. occur in seven Maine Rivers: the Dennys, Machias, East Machias, Narraguagus, Pleasant, Ducktrap and Sheepscot Rivers. In 1991 the FWS listed 5 of those populations as category 2 candidate species under the ESA. In 1994, only an estimated 79 Atlantic salmon returned to these rivers. Recent downward trends in abundance have put most of these rivers at less than 10 percent of escapement goal (the number of adults needed to produce enough eggs to fully seed the river). The combination of low adult returns and low numbers relative to spawning requirements indicates that these river populations are in peril.
In October and November of 1993, the Services received petitions from Restore: The North Woods; Biodiversity Legal Foundation; and Jeffrey Elliot, to list the Atlantic salmon throughout its historic range in the contiguous United States under the ESA. The Services decided to respond to the petition jointly as they had worked cooperatively for the conservation, rehabilitation and restoration of the species in the Northeast Region for years. The Services published a notice on January 20, 1994, that the petition presented substantial scientific information indicating that a listing may be warranted and requested input from the public.
The Services had been working individually and cooperatively for decades to further the scientific knowledge of Atlantic salmon, to manage the species throughout its migratory route, to restore the species to its historic range, and to address threats to the species. In March of 1994 the FWS and NMFS signed a Regional Memorandum of Agreement to pledge greater coordination and cooperation between the FWS and NMFS, as well as with the states and the international community, to avoid duplication of effort and concentrate efforts on priority issues with the greatest potential to benefit anadromous Atlantic salmon. The Regional Directors of the NMFS and FWS appointed a team to conduct a status review pursuant to Section 4 of the ESA.
The ESA defines species as "any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife that interbreeds when mature" (emphasis added). Distinct population segments (DPS) are particularly important to anadromous salmonines because their strong homing capability fosters the formation of discrete populations exhibiting important adaptations to local riverine ecosystems (Utter et al. 1993). Guidance on defining species under the ESA has been provided by the NMFS in the context of listing decisions involving Pacific salmon (Waples 1991). This guidance introduces a more precise definition called the Evolutionarily Significant Unit (ESU). Because the structure of Atlantic salmon populations is similar to Pacific salmonines, the ESU approach provides a practical framework for delineating DPSs of Atlantic salmon under the ESA. To qualify as a DPS a population (or group of populations) 1) must be reproductively isolated from conspecific populations and 2) must be evolutionarily significant (i.e. contribute substantially to the ecological/genetic diversity of the species).
Regarding the first of the necessary DPS criteria, tagging studies indicate that U.S. Atlantic salmon stocks do not stray far from their natal streams. In addition, there has been a lack of recolonization by Atlantic salmon in U.S. rivers where they have been extirpated. Given available information, the Atlantic Salmon Biological Review Team (Team) concluded that wild river-specific populations of Atlantic salmon in the U.S. are substantially reproductively isolated from Canadian stocks.
In examining the second criteria for a DPS, evolutionary significance, the Team considered the following three factors: phenotypic traits, life history traits, and habitat characteristics. Historic records indicate that distinct, locally-adapted Atlantic salmon stocks existed in river systems in the U.S. Genetic analyses and life history traits demonstrate that U.S. stocks of Atlantic salmon are distinct from stocks in Canada and Europe. Historically, adult spawners in U.S. rivers have been predominately those that spend two winters at sea, whereas many Canadian and European stocks return after one year at sea. The riverine habitat occupied by U.S. Atlantic salmon is distinctive in that it is located at the southern extent of the range of the species in North America. The continuous presence of U.S. Atlantic salmon in indigenous habitat provides evidence that important local adaptations have persisted, although at present differences are subtle and difficult to assess due to low abundance. The populations of anadromous Atlantic salmon present in the Sheepscot, Ducktrap, Narraguagus, Pleasant, Machias, East Machias and Dennys Rivers represent the last wild remnant of U.S. Atlantic salmon. All of these factors indicate that the DPS is evolutionarily significant.
Candidate status is recommended for Atlantic salmon in the Kennebec River, Penobscot River, Tunk Stream and St. Croix River, rivers where the link to native stocks and degree of persistence is not well understood. Atlantic salmon populations have been extirpated from many other rivers in the United States. Some of these rivers are currently the focus of restoration efforts using nonindigenous stocks. Restoration of Atlantic salmon in these watersheds will contribute to the biodiversity of these ecosystems.
The Team evaluated the status of the seven river stocks that comprise the DPS of Atlantic salmon by analyzing trends in historic and current relative abundance and spawner escapement goal. The status of these populations was then examined in relation to the ESA which defines an endangered species as one in danger of extinction throughout all or a significant portion of its range, and a threatened species as one likely to become endangered in the foreseeable future. Species may be determined to be threatened or endangered due to any one or more of the following factors: (1) the present or threatened destruction, modification, or curtailment of its habitat or range; (2) overutilization for commercial, recreational, scientific, or educational purposes; (3) disease or predation; (4) the inadequacy of existing regulatory mechanisms; and (5) other natural or manmade factors affecting its continued existence (Section 4(a)(a)(1)).
The construction of dams with either inefficient or non-existent fishways was a major cause of the decline of U.S. Atlantic salmon. In the late 1800's Atkins stated: "The disappearance of salmon from so many rivers appears to have been entirely the result of artificial causes, chief among which is the obstruction of the way to the breeding grounds by impassable dams (1874)."
In the Strategic Plan for Management of Atlantic Salmon in the State of Maine (1984), Beland reported that: "As colonization and development accelerated during the 17th and 18th centuries, the salmon habitat was degraded, destroyed, and/or made inaccessible. By 1947, less than 10% of the original habitat remained accessible to Atlantic salmon." The substrate and water quality of a river or stream must meet certain criteria in order for it to be suitable as Atlantic salmon spawning and nursery habitat. The egg, alevin, fry and parr stages of Atlantic salmon are especially sensitive to impacts associated with watershed development. Potential impacts to habitat quality include alterations in water temperature, reductions in dissolved oxygen, the introduction of pollutants and sediment, and other factors that may alter substrate or river discharge. Water temperature can be impacted by introductions of heated effluent, reductions in riparian vegetation, or by impounding water. Water quality can also be affected by the introduction of chemicals such as chlorine added during sewage treatment, metals discharged with industrial effluent, herbicides and pesticides used in agriculture, and nutrients in treated wastewater which increase the level of biological activity, decreasing the level of dissolved oxygen in the water.
Atlantic salmon are vulnerable to exploitation throughout their entire range, in both marine and freshwater and in both recreational and commercial fisheries. Many countries are moving toward eliminating commercial fisheries to preserve sports fisheries. This is based in part on an economic evaluation of commercial versus recreational fishing. The issue is made complex in that it is a mixed stock fishery where nations can intercept fish originating from another country even if they have no anadramous stocks themselves.
Historically, the marine exploitation of U.S.-origin Atlantic salmon occurred primarily in foreign fisheries. U.S.-origin Atlantic salmon have been documented in the harvests of West Greenland, New Brunswick, Nova Scotia, Newfoundland, and Labrador fisheries, with the Newfoundland and Labrador fisheries constituting the majority of the harvest. In the absence of West Greenland and Canadian interception fisheries, returns of U.S. Atlantic salmon could potentially increase two-fold. In Canada, a 5-year moratorium is in place in Newfoundland and licenses are being purchased by the government. The Labrador fishery is now managed by quotas, and the 1993 quota represents a reduction of 92 percent from that of the 1990 quota level. In 1982, the North Atlantic Salmon Conservation Organization was formed for the purpose of managing salmon through a cooperative program of conservation, restoration and enhancement of North Atlantic stocks. NASCO accepted an agreement in 1993 that set quotas on the harvest off West Greenland with the goal of reaching target spawning escapements for North American stocks. During the next three years of the management plan, the number of spawners needed to sustain North American stocks of Atlantic salmon (194,000) will be protected by adjusting the West Greenland quota.
In 1987 the New England Fishery Management Council prepared a Fishery Management Plan (FMP) to establish explicit U.S. management authority over all Atlantic salmon of U.S. origin in Federal waters. The FMP prohibits the possession of Atlantic salmon in the exclusive economic zone, the area between 3 and 200 miles off the U.S. coastline. During the 1970s, recreational fishermen were harvesting as much as 15 to 25 percent of the Atlantic salmon returning annually to home waters. Currently state law allows only a catch and release fishery for Atlantic salmon, and no salmon fishing is authorized on the Pleasant River. Multi-sea-winter salmon could incur some mortality from catch-and-release fishing and parr are vulnerable to incidental hooking mortality or illegal harvest by trout anglers. Poaching may also pose a serious threat to depressed populations of Atlantic salmon in New England rivers.
During their various life stages, Atlantic salmon are preyed upon by numerous species of fish, birds, and mammals and also compete with other species of fish. Major freshwater predators on Atlantic salmon include brook trout, brown trout, eel, burbot, northern pike, chain pickerel, smallmouth bass, belted kingfisher, heron, common and red-breasted merganser, osprey, herring and greater black-backed gull, otter and mink. Documented predators in the estuarine and marine environments include striped bass, shark, skate, ling and Atlantic cod, pollock, whiting, garfish, double-crested cormorant, European cormorant, harbor seal, gray seal, harp seal, and ringed seal.
The Atlantic salmon compete with other fish species for food and habitat and are a source of prey for some predators. Those interactions become more complex as new species are introduced, naturally or artificially, to rivers where they were not historically present and did not co-evolve with Atlantic salmon. Introduced species such as smallmouth bass, chain pickerel and brown trout have been documented to prey upon juvenile Atlantic salmon (Baum et al. 1995). Species assemblages and abundances have also changed in estuaries utilized by Atlantic salmon with the recent increase in populations of striped bass, seals and birds.
Atlantic salmon are susceptible to a number of diseases and parasites that can result in high mortality. Parasites of Atlantic salmon are the gill maggot, freshwater louse, leach, flukes, tapeworms, spiny-headed worms, roundworms, the skin parasite Gyrodactylus salaris, sea louse, and sea lamprey. Atlantic salmon are susceptible to numerous bacterial, viral and fungal diseases, including furunculosis, bacterial kidney disease and vibriosis. Disease-related mortality is primarily documented for hatcheries and aquaculture facilities. Disease epizootics in wild salmon are uncommon. In New England, furunculosis is the only known source of disease-related mortality in wild Atlantic salmon.
Management of anadromous fish, such as Atlantic salmon, is a complex issue. There are a variety of demands being placed on the riverine, estuarine and marine habitats utilized by the Atlantic salmon. The challenge is to manage these multiple uses in a way that allows the various needs to be met without compromising the health and natural resources of the river.
Management of Atlantic salmon in the State of Maine is conducted by the Maine Atlantic Sea Run Salmon Commission (ASRSC) which was created in 1947 to focus efforts on recovering stocks of Atlantic salmon in Maine. Over the years the ASRSC has monitored river population studies, evaluated the relative success of stocking methods, and participated in tagging studies. The Atlantic salmon restoration program focuses on sixteen river systems in the state ranging from the Aroostook River in the north to the Saco River in the south. The goals of the ASRSC are to restore river specific stocks of Atlantic salmon through the following means: preserving existing populations and habitat; restocking of fry; reducing removals; and eliminating or minimizing threats. Recently the state of Maine replaced the ASRSC with a new management entity called the Maine Salmon Authority.
In 1990 the Atlantic Sea Run Salmon Commission and the U.S. Fish and Wildlife Service signed a Cooperative Agreement and established a Technical Advisory Committee (TAC). The purpose of the TAC is to advise the ASRSC and the FWS on technical matters related to the Atlantic salmon restoration program in Maine, to review and comment on proposals for cooperative research, and to provide assistance in developing and updating restoration plans.
Many federal and state laws and programs have affected the abundance, health and survival of anadromous Atlantic salmon populations in the United States. However, they have not prevented the decline of the species. The effectiveness of certain existing laws and regulations could be strengthened by more stringent implementation and enforcement. Aquaculture facilities are located within 20 kilometers (km) (12 miles) of the mouths of five of the rivers within the DPS. Atlantic salmon that have been released or that have escaped from aquaculture pens are known to have entered some of these rivers. Released aquaculture Atlantic salmon can impact wild populations through competition, genetic dilution or the introduction of diseases (Kapuscinski and Jacobson 1987; Utter et al. 1993).
Scientific evidence suggests that low natural survival in the marine environment is a major factor contributing to the decline of Atlantic salmon throughout North America. Recent research indicates that major seasonal events influence post-smolt survival of Atlantic salmon. It appears that survival of the North American stock complex of Atlantic salmon is at least partly explained by sea surface water temperature, during the period when Atlantic salmon concentrate in winter months in habitat at the mouth of the Labrador Sea and east of Greenland. Until more direct observation can be made on the marine ecology of post-smolts during the winter, the exact mode of mortality will be unknown. Currently, researchers speculate that a combination of factors related to slow growth and increased predation contribute to marine mortality.
Potential genetic impacts of hatchery practices include inbreeding depression, outbreeding depression and domestication. Potential ecological impacts of hatchery practices include competition and predation, displacement of wild fish, altered migratory and spawning behavior, and disease transfer. The practice of stocking fry transferred from other rivers may have exacerbated the decline of the wild population by possibly displacing wild fish. For six of the seven rivers, the average percentage of the run that was of natural origin (wild) was higher during years not influenced by the stocking of fry transferred from other rivers. However, the Services do not believe that stock transfers in the DPS rivers have eliminated all historic characteristics of wild Atlantic salmon. Although past stocking practices may have contributed to the decline of Atlantic salmon in the DPS rivers, the Services are committed to ensuring that future hatchery practices contribute to recovery of each river population. Use of river-specific fry stocking on the Penobscot River has boosted the percentage of natural origin fish and is a tool for recovery of the DPS rivers.
The product of the Team's efforts, a Status Review for Anadromous Atlantic Salmon in the United States, was distributed in draft form in January of 1995. The notification that the Services would be recommending a listing for these seven river populations elicited a response from the state of Maine and other potentially affected parties. There are numerous measures underway to prevent the loss of any of the river populations of Atlantic salmon within the DPS. Collectively, these measures have the potential to reduce the likelihood of extinction and enabled the Services to propose listing the DPS for threatened rather than endangered status, as was recommended by the Team. The proposed rule was published in the Federal Register on September 29, 1995. The Services have up to one year to publish a final rule as proposed or modified, or withdraw their proposal.
The threatened designation provides the Services with more flexibility in implementation of the ESA, should the proposal be finalized. The Services proposed to adopt joint regulations for the protection of the DPS which apply all the standard prohibitions of the ESA and allow exceptions for incidental take under sections 4(d) and 10 of the ESA. Section 4(d) of the ESA allows the Services to define the conditions under which the incidental "take" (take, as defined in the ESA, includes the following: harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or collect, or to attempt any of these) of Atlantic salmon resulting from activities regulated by State and local governments would not violate section 9 of the ESA. Under the special rule, incidental take of Atlantic salmon when conducting otherwise lawful activities addressed in an Atlantic salmon conservation plan prepared by the State of Maine and approved by the Services, would not be considered a violation of section 9 of the ESA. The intent of the special rule is to provide the State of Maine an opportunity to maintain the lead role in the management of activities that could impact Atlantic salmon in the DPS. The State has convened a task force with subgroups addressing recreational fishing, aquaculture and habitat alteration to begin the development of a conservation plan. The Services believe that a state plan provides a more comprehensive, less bureaucratic procedure for addressing the potential incidental take of Atlantic salmon than the traditional Section 10 permitting route.
In addition to the state-led effort to develop a conservation plan, a number of federal and private initiatives have been launched in recent years. The Maine Wild Atlantic Salmon Stewardship Program was initiated by the FWS in 1994. Program activities include angler and habitat surveys and weir and trap installation and maintenance. Project S.H.A.R.E (Salmon Habitat and River Enhancement) formed in 1994 to "conserve and enhance Atlantic salmon habitat in the Downeast region of Maine through voluntary and mutual cooperation of area landowners and businesses; local, state and federal agencies; academia; and conservation organizations." Projects conducted to date include replacement of a dam gate on the Dennys River, removal of a major obstruction on the Machias River, provision of material support for the Pleasant River Hatchery, and fabrication of parts for a floating weir.
The restoration and rehabilitation of Atlantic salmon to their native habitat in New England has challenged federal and state resource agencies and private conservation groups for decades. Recently there has been interest in critically evaluating past efforts to refine those management practices that have had success and to try to evaluate new strategies. The introduction of a potential listing of some Atlantic salmon populations under the ESA has introduced a new variable into the equation. The key challenge has been, and will continue to be, to bring together interested and affected parties in a cooperative rather than a confrontational manner.
Portions of the text are taken from: Status Review for Anadromous Atlantic Salmon, FWS and NMFS, draft published January 1995.
Atkins, C.G. 1874. On the salmon of Eastern North America and its artificial culture. Report of the Commissioner for 1872 and 1873, part II. United States Commission of Fish and Fisheries, Washington, D.C.
Baum, E. T. , R. Owen, R. Alden, W. Nichols, P. Wass, and J. Dimond. 1995. Maine Atlantic Salmon Restoration and Management Plan, 1995-2000.
Beland, K. F. 1984. Strategic plan for management of Atlantic salmon in the State of Maine. Atlantic Sea-Run Commission, Bangor, Maine.
Kapuscinski, A., and L. Jacobson. 1987. Genetic Guidelines for Fisheries Management. Minnesota Sea Grant, University of Minnesota.
Kendall, W.C. 1935. The fisheries of New England: the salmon family, part 2-the salmons. Boston Society of Natural History. 9(1).
Meister, A.L. 1984. The marine migrations of tagged Atlantic salmon (Salmo salar L.) of USA origin. ICES C.M. 1984/M: 27.
NASCO. 1993. Report of the tenth annual meeting of the North American Commission, North-East Atlantic and West Greenland Commission. Edinburgh, UK. North Atlantic Salmon Conservation Organization.
Reddin, D. G. 1988. Ocean life of Atlantic salmon (Salmo salar L.) in the Northwest Atlantic. Pages 483-511. In D. Mills and D. Piggins [eds]. Atlantic Salmon: Planning for the Future. Timber Press, Portland, Oregon.
Rounsefell, G. A., and L.H. Bond. 1949. Salmon restoration in Maine. Research Report 1. Atlantic Sea-Run Salmon Commission, Bangor, Maine.
Scott, W. B., and E. J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research Board of Canada, Bulletin 184. 966 pp.
Stasko, A. B., A. M. Sutterlin, S. A. Rommell, Jr., and P. F. Elson. 1973. Migration-orientation of Atlantic Salmon (Salmo salar). Int. Atl. Salmon Found. Spec. Publ. Series 4(1): 119-138.
Utter, F., K. Hindar and N. Ryman. 1993. Genetic effects of aquaculture on natural salmonid populations. Pages 144-165 In K. Heen, R. L. Monahan and F. Utter [eds.] Salmon aquaculture. Fishing News Books. Oxford, England.
Waples, R. 1991. Definition of 'species' under the Endangered Species Act: Application to Pacific salmon. U.S. Dept. Commerce, NOAA Tech. Memo. NMFS F/NWC-194.
Mary Colligan is a fishery biologist with the Habitat and Protected Resources Division of the Northeast Region of the National Marine Fisheries Service. Paul Nickerson is the Chief of the Endangered Species Division, Region 5, U.S. Fish and Wildlife Service.