The Atlantic salmon, Salmo salar, is
a highly prized game and food fish native to New England rivers
(Figure
41.1). The historic North American range of Atlantic salmon
extended from the rivers of Ungava Bay, Canada, to rivers of Long
Island Sound. As a consequence of industrial and agricultural
development, most populations native to New England were extirpated.
Remnant native populations of Atlantic salmon in the United States
now persist only in Maine. Restoration and rehabilitation efforts,
in the form of stocking and fish passage construction, are underway
in the Connecticut, Pawcatuck, Merrimack, Saco, Kennebec, Penobscot,
and eastern Maine rivers of New England.
Atlantic salmon life
history is extremely complex owing to its use of both freshwater
and marine habitats and long ocean migrations (Figure
41.2). Atlantic salmon spawnin freshwater during fall. Eggs
remain in gravel substrates and hatch during winter, and fry emerge
from the gravel in spring. Juvenile salmon, commonly called parr,
remain in freshwater one to three years in New England rivers,
depending on growth. When parr grow to sufficient size (>13cm)
they develop into smolts and migrate to the ocean in spring. Tagging
data for New England stocks indicate that US salmon migrate as
far north as Greenland.
After the first winter at sea for
US salmon (the fish are now referred to as 1 sea-winter or
1SW salmon), a small portion (~ 10%) of the cohort, typically
males, become sexually mature and return to natal rivers to
spawn. Those remaining at sea feed in the coastal waters of
West Greenland and Canada (off the Newfoundland and Labrador
coasts). Historically, it has been in these foraging areas
that commercial Northeast Atlantic gillnet fisheries for salmon
occurred. After their second winter at sea (2SW), most US
salmon return home to spawn. Three sea-winter and repeat-spawning
salmon life history patterns also occur in New England populations
but have become rare (< 5%) with declining stock size.
Figure 41.2
Significant declines in abundance
of Atlantic salmon populations in the US prompted an endangered
listing of the species under the Endangered Species Act (ESA,
65 Federal Register 69459, November 17, 2000). The ESA of 1973
was amended in 1978 to define a species as “...any subspecies
of fish or wildlife or plants, and any distinct population segment
of any species of vertebrate fish or wildlife which interbreeds
when mature”. A Distinct Population Segment (DPS) is a
subgroup of a vertebrate species that is treated as a species
for purposes of listing under the Endangered Species Act. It
is required that the subgroup be separable from the remainder
of and significant to the species to which it belongs (61 Federal
Register 4722).
The strong homing capability
of Atlantic salmon fosters the formation and maintenance of
local breeding groups resulting in intraspecific sub-structuring.
Stocks from a given area exhibit heritable adaptations to local
riverine ecosystems. The importance of maintaining these local
adaptations has been demonstrated in Atlantic salmon. Assessing
DPS structure requires broad scale consideration of geologic
and climatic features that shape population structure through
natural selection. For Atlantic salmon, factors such as climate,
soil type, and hydrology are particularly important because
these factors influence ecosystem structure and function including
transfer of energy in aquatic food chains. Numerous ecological
classification systems were examined which integrate the many
factors necessary to perform such a DPS analysis (Colligan et
al. 1999; Fay et al. 2006). Biologists have delineated US Atlantic
salmon populations into four discrete DPSs for the purpose of
management: 1)Long
Island Sound DPS; 2)Central
New England DPS; 3) Gulf of Maine DPS and the 4) Outer
Bay of Fundy SFA (Figure
41.1). Both the Long Island Sound and Central New England
DPS were extirpated in the 1800’s. Atlantic salmon stocks
from the Penobscot River in Maine were used in the restoration
programs in the Connecticut (Long Island Sound DPS) and in the
Merrimack and Saco in the (Central New England DPS). Outer Bay
of Fundy SFA populations are supplemented by St. John River
Atlantic salmon stock and the core populations of this DPS have
freshwater nursery areas in Canadian watersheds.
Gulf of Maine Distinct
Population Segment
The Gulf of Maine (GOM) DPS
comprises all anadromous Atlantic salmon whose freshwater range
occurs in the watersheds from the Androscoggin River northward
along the Maine coast to the Dennys River, including all associated
conservation hatchery populations used to supplement natural populations;
currently, such populations are maintained at Green Lake and Craig
Brook National Fish Hatcheries. Excluded are those fish raised
in commercial hatcheries for aquaculture.
Both physiographic information
and biological information from extant stocks were used to delineate
the boundaries of the GOM DPS. The biological information included
genetic and life history information that was not available for
the extirpated DPSs to the south. The geographical northern limit
of the Gulf of Maine DPS as the northern boundary of the Dennys
watershed (including the Dennys River). This conclusion is supported
by the observed life history similarities (Baum 1997) and genetic
structure among populations within the range of the GOM DPS (Spidle
et al. 2003), life history similarities and genetic structure
among salmon stocks to the north (Verspoor et al. 2002), and differences
in life history strategies and genetic structure between the GOM
DPS and salmon stocks to the north (Spidle et al. 2003, Baum 1997).
Outer Bay of Fundy Statistical
Fishing Area
These headwater streams of the
St. John River system lie in northern Maine but flow into the
Bay of Fundy in St. John New Brunswick. The St. John River is
one of a number of salmon rivers in eastern Canada that flows
into the outer Bay of Fundy region. Native populations of Atlantic
salmon still exist in a number of these systems, but these populations
as a whole have dropped to critically low levels. The Outer Bay
of Fundy salmon rivers are considered to be separate from the
GOMDPS based on life history and genetic difference (Colligan
et al. 1999; Fay et al. 2006).
US ATLANTIC SALMON
The Fishery
Homewater Fisheries
Atlantic salmon were likely targeted by Native
Americans but US Atlantic salmon commercial fisheries started
in Maine during the 1600’s with records of catch by various
means. Around the time of the American Revolution, weirs became
the gear of choice and were modified as more effective materials
and designs became available (Baum 1997). Weirs remained the primary
commercial gear with catches in Maine exceeding 90 mt in the late
1800s and 45 mt in some years during the early 1900’s (Baum
1997). Penobscot River and Bay were the primary landing areas
but when the homewater fishery was finally closed in 1948, only
40 fish were caught in the Penobscot Fishery.
Recreational angling for Atlantic
salmon had historically been important. Reportedly, the first
Atlantic salmon caught on rod and reel was captured in the Dennys
River, Maine in 1832 by an unknown angler (Baum 1997). The dynamics
of Atlantic salmon fishing are very ritualistic with fly fishing
being the most generally acceptable method of angling and the
advent of salmon clubs among many US Rivers creating an important
and unique cultural and historical record (Beland and Bielak 2002).
Recreational angling has been closed in the USA for decades with
the exception of Maine where regulations became more restrictive,
but the fishery remained open (Table 41.1).
However, in 1999 when low salmon returns threatened sustainability
of even hatchery populations, the remaining catch-and release
fishery was closed. There remain some unique fisheries for Atlantic
salmon in New Hampshire where fish retired from hatchery broodstock
are released for angling and in Maine where an experimental fall
catch-and-release fishery has been opened in 2006.
According to the Atlantic salmon
fishery plan completed in 1997 by the New England Fishery Management
council: "The management unit for the Atlantic salmon FMP
is intended to encompass the entire range of the species of U.S.
origin while recognizing the jurisdictional authority of the signatory
nations to NASCO.” Accordingly, the management unit for
this FMP is: All anadromous Atlantic salmon of U.S. origin in
the North Atlantic area through their migratory ranges except
while they are found within any foreign nation's territorial sea
or fishery conservation zone (or the equivalent), to the extent
that such sea or zone is recognized by the United States."
Presently there is a prohibition on the possession of salmon in
the EEZ. Effectively this protects the entire US population complex
in these marine waters and is complementary to management practiced
by the States in riverine and coastal waters. However, distant
water fisheries must be managed as well to conserve and restore
US salmon populations. Additionally, after the GOMDPS was listed
as endangered the Services and State of Maine developed a recovery
plan for these populations that is also influencing salmon management
(Anonymous 2005).
Commercial fisheries for
Atlantic salmon in Canada and Greenland are managed under the
auspices of the North Atlantic Salmon Conservation Organization
(NASCO), of which the United States is a member. The mixed-stock
fisheries in Canada were managed by time-area closures and quotas,
however all commercial fisheries for Atlantic salmon in Canada
have been closed since 2000. The Greenland fishery has been managed
by a quota system since 1972. In 1993, a modified quota system
was agreed to that provided a framework for quotas based on a
forecast model of salmon abundance. From 1993-1994, quotas were
bought out through a private initiative, but the fishery resumed
in 1995, still under forecast modeling-based quotas. In 1997,
the NASCO agreement was modified to allow for a local use fishery
and to provide for data collection when stock abundance is particularly
low. Since 2002, scientific advice from ICES recommended no commercial
harvest due to continued low spawner abundance. Salmon conservationists
have acted on this advice and in August 2002, an annual agreement
renewable for up to five years was signed by conservation organizations
and the commercial fishermen's organization in Greenland. This
agreement suspended all commercial salmon fishing and allows only
a limited annual local-use harvest. This agreement is set to terminate
after the 2006 fishing season.
Figure 41.3
Aquaculture
Despite declining natural populations, the
Atlantic salmon mariculture industry continues to develop
worldwide. In eastern Maine and Maritime Canada, companies
typically rear fish to smolt stage in private freshwater facilities,
transfer them into anchored net pens or sea cages, feed them,
and harvest the fish once they reach market size. In the Northwest
Atlantic, 66% of production is based in Canada with 99.4%
of Canadian production in the Maritimes and 0.6% in Newfoundland.
The balance (44%) of Northwest Atlantic production is in eastern
Maine. US production trends for Maine facilities and areas
occupied by marine cages have grown exponentially for two
decades. By 1998, there were at least 35 freshwater smolt-rearing
facilities and 124 marine production facilities in eastern
North America. Since the first experimental harvest of Atlantic
salmon in 1979 of 6 mt, the mariculture industry in eastern
North America has grown to produce greater than 32,000 mt
annually since 1997. In Maine, production increased rapidly
and peaked at about 16,500 mt in 2000 but abruptly declined
to below 6,000 mt in 2005 (Figure
41.3[Fig
41.3 Data]). Current management efforts focus on the recovery
of natural populations and support of sustainable aquaculture
to ensure both resource components are managed in a sustainable
fashion.
Atlantic salmon in the ocean
are pelagic, highly surface oriented and of relatively limited
abundance within a large expansive area and therefore are not
typically caught in standard NEFSCbottom trawlsurveys or midwater
trawls used to calibrate hydroacoustic surveys. However, researchers
in Canada and Norway have successfully sampled Atlantic salmon
postsmolts using surface trawls. The NEFSC has been experimenting
with these techniques to test them in US waters while learning
more of the distribution and ecology of Atlantic salmon in the
marine environment. Since 2001, a total of 4,000 postsmolts
have been collected and sampled (Figure
41.4). All postsmolts were counted, weighted and measured.
The presence of any marks and clips were also recorded as well
as their external appearance in terms of fin condition and deformities,
which can aid in origin determination, and the degree of smoltification.
These assessments are providing novel information on salmon
ecology and status at sea.
US Atlantic salmon populations
are assessed by the US Atlantic Salmon Assessment Committee,
a team of state and federal biologists tasked with compiling
data on the species throughout New England and reporting population
status. Population status of salmon can be determined by counting
returning adults either directly, at traps and weirs, or indirectly
using redd surveys. Total returns also include retained fish
from angling where allowed. Some mortality can and does occur
between counts returns and actual spawners – the actual
number of spawners is termed spawning escapement and is not
estimated for US populations, though redd counts provide a
reasonable proxy for some rivers. A unique element of Atlantic
salmon populations in New England is the dependence on hatcheries.
Since most US salmon are products of stocking, it is important
to understand the magnitude of these inputs to understand
salmon assessment results.
All US Atlantic salmon hatcheries
are run by the US Fish and Wildlife Service. Hatchery programs
in the US take two forms; 1) conservation hatcheries that
produce fish from remnant local stocks within a DPS and stock
them into that DPS or 2) restoration hatcheries that produce
salmon from broodstock established from donor populations
outside their native DPS. Hatchery programs for the Gulf of
Maine DPS are conservation hatcheries. All other New England
hatcheries are restoration hatcheries. These restoration hatcheries
developed broodstock primarily from donor stocks of Penobscot
River origin. However, because these programs have been ongoing
for more that 25 years, the majority of fish reared for Long
Island Sound and Central New England DPS units are progeny
of fish that completed their life cycle in these waters for
3 or more generations. The number of juvenile salmon stocked
in New England waters totaled 13.8 million in 2005, a number
typical of the decade. Fry stocking dominates numerically
overall with 12.7 million fry and fry are used in all systems
stocked. Six river systems are stocked with parr and seven
river systems stocked with smolts. Almost 700,000 smolts are
stocked annually in US waters with about 530,000 of them comprised
of age-1 smolts stocked in the Penobscot River. Penobscot
River smolts consistently produce over 70% of the adult salmon
returns to the US. Cost and logistical issues prevent more
extensive use of smolts. However, fry stocking is an important
tool because it minimizes selection for hatchery traits and
naturally reared-smolts have a higher per capita marine survival
rate than hatchery smolts. Building sustainable Atlantic salmon
populations in the US will require increasing natural production
of smolts in US river systems and using hatchery production
to optimally maintain population diversity and effective population
sizes.
The
modern time series of salmon returns to US rivers starts in
1969. Average annual Atlantic salmon returns to US rivers
from 1969 to present is 2,156 and the median is 1,645. The
time series of data clearly shows the rebuilding of US populations
from critically low levels of abundance in the early part
of the 20th century (Figure 41.3[Fig
41.3 Data]). Because many of these populations in southern
New England were extirpated, the salmon returns graph (Figure
41.5[Fig
41.5 Data]) illustrates the sequential
rebuilding of the populations through restoration efforts
in the 1970s – with success first in the Penobscot River
then the Merrimack and Connecticut Rivers. The remnant populations
of the smaller rivers in the Gulf of Maine DPS and the Penobscot
River were the donor material for all rebuilding programs
during this time. Unfortunately, the trajectory of this recovery
did not continue in the late 1980s and early 1990s. Starting
in the early 1990s there was a phase shift in marine survival
and an overall reduction in marine survival occurred in all
US and most Canadian populations (ICES 2003).
Figure 41.5
There has been a downward
trend in production of salmon on both side of the Atlantic
(particularly populations dominated by 2SW fish) that have
affected US populations. In addition, recovery from historical
impacts was never sufficient so US populations were at low
absolute abundance when the period of lower marine survival
began.
Returns to US waters were
1,320 fish – this ranks 25 out of the 39 year time series
and is over 300 fish below the median. However, relative to
the average during the last 5 years (1999-2004) of 1,208 -
returns in 2005 demonstrated a slight improvement. To gain
a better sense of the relative status of the stocks, it is
best to examine target spawning escapements. Because juvenile
rearing habitat can be measured or estimated efficiently,
these data can be used to calculate target spawning requirements
from required egg deposition. The number of returning Atlantic
salmon needed to fully utilize all juvenile rearing habitats
is termed Conservation Spawning Escapement (CSE). These values
have been calculated for US populations and total just over
29,000 spawners (Table 41.2). In the
last decade, total returns have accounted for less than 2
percent of these target values in Long Island Sound and Central
New England DPS. However, salmon returns to the Penobscot
River have been as high as 10% of CSE during this period and
the Gulf of Maine DPS ranged from 3-4 percent for other populations.
These CSE levels are minimal recovery targets since they are
based on spawning escapement that could fully seed juvenile
habitat. In self-sustaining populations, the number of returns
would frequently exceed this amount by 50 to 100 percent allowing
for sustainable harvests and buffers against losses between
return and spawning. As such, the status of US Atlantic salmon
populations is critically low for all stocks, with the remnant
populations of the Gulf of Maine DPS listed as endangered.
Over the past 5 years, the
contributions of each stock group to total US returns averaged:
Penobscot stock (75%), Central New England (12.5%), Gulf of
Maine DPS (6.6%), and Long Island Sound (4.6%), with other
regions making up less than 2%. Returns in 2005 were typical
in that the Penobscot River population accounted for 75% of
the total return. Overall, 24% of the adult returns to the
USA were 1SW salmon and 76% were multi sea winter (MSW) salmon.
From 1967–1985, the ratio of three-seawinter (3SW) salmon
to 2SW fish averaged 2% and was as high as 7%. However, from
1986 to 2005 this average declined to 0.6% and the highest
ratio was only 1.2%. Most (78%) returns have been hatchery
smolt origin and the balance (22%) originated from fry or
parr stocking and natural reproduction.
Return rates also
provide an indicator of marine survival. The adult return
rate (1SW plus 2SW) of hatchery smolts released in the Penobscot
River in 2005 was 0.17%, with the 2SW fish return rate 0.12%.
Smolt survival on the Penobscot River correlates well with
other large restoration programs in the Connecticut and Merrimack
rivers. Return rates for wild and naturally reared smolts
on the Narraguagus River in recent years have mirrored those
trends as well but in general are between five and ten fold
higher.
Biological Reference
Points
Biological reference points
for Atlantic salmon vary from most other species assessed
because they are managed in numbers not biomass and also because
they are a protected species with limited fisheries targets.
Fisheries targets (MSY, BMSY, FMSY,
FTarget) have not been developed because current
populations are so low relative even to sustainable conservation
levels. A proxy for minimum biomass threshold for US Atlantic
salmon would be Conservation Spawning Escapement since this
provides the minimum population number needed to fully utilize
available freshwater nursery habitat. This number is based
on a single spawning cohort not the standing stock of all
age groups. As such, a number for comparison to CSE would
be estimated returns. Natural survival of Atlantic salmon
in the marine environment is estimated to be 0.03/month resulting
in an annul M of 0.36/year.
Summary
Historic Atlantic salmon abundance in New England probably
exceeded 30,000 returns annually. Overfishing and habitat
destruction resulted in a severely depressed US population
restricted to Maine and by 1950 with adult returns of just
a few hundred fish in a handful of rivers. Hatchery-based
stockrebuilding occurred from 1970-1990 reaching a peak
of 5,624 fish in 1986. A widespread collapse in Atlantic
salmon abundance started around 1990. In the past decade,
US salmon returns have averaged 1,600 fish and returns in
2005 were 1,320 fish. All stocks are at very low levels,
only the Penobscot River population is at 10% or greater
of its conservation spawning escapement. Most populations
are still dependent on hatchery production and current marine
survival regimes are compromising the long-term prospects
of even these hatchery-supplemented populations.
Table
41.1.Recreational (reported
in numbers), aquaculture production (thousand metric tons)
and commercial (no fishery) landings of Atlantic salmon from
Maine.
Table 41.2.Conservation spawning escapement requirements
for US River populations and reported returns (with % of CSE)
as determined by US Atlantic Salmon Assessment Committee (2006)
and consolidated by DPS where possible. (* - composite of some
GOM and CNE rivers).
Allan, D. J. 1995. Stream Ecology:
Structure and function of running waters. Chapman and Hall. New
York, NY. 388 pp.
Anonymous 2005. Final Recovery
Plan for the Gulf of Maine Distinct Population Segment of Atlantic
salmon (Salmo salar). National Marine Fisheries Service/
U.S. Fish and Wildlife Service Joint Publication. Gloucester,
MA 325 pp. http://www.nero.noaa.gov/nero/hotnews/salmon/FinalATSRPlan.pdf
Baum, E. T. 1997. Maine Atlantic
Salmon: A National Treasure. Atlantic Salmon Unlimited. Hermon,
ME.
Beland K. F., A. T. Bielak.
2002.. Atlantic salmon fisheries in eastern North America: the
prince and the pauper. Pages 61–76 in K. L. Dawson and M.
L. Jones, editors. North American salmon fisheries: binational
perspectives. American Fisheries Society, Bethesda, Maryland.
Colligan, M. A.; Kocik, J. F.;
Kimball, D. C.; Marancik, G.; McKeon, J. F.; Nickerson, P. R.
Status Review for Anadromous Atlantic Salmon in the United States.
National Marine Fisheries Service/ U.S. Fish and Wildlife Service
Joint Publication. Gloucester, MA 232 pp. http://library.fws.gov/salmon/
CRASC (Connecticut River Atlantic
Salmon Commission). 1998. Strategic plan for the restoration of
Atlantic salmon to the Connecticut River. Connecticut River Atlantic
Salmon Commission. Sunderland, MA. 106 pp.
Fay, C. A., Bartron, M, Craig, S., Hecht, A.,
Pruden, J., Saunders, R., Sheehan, T. and Trial, J. 2006. Status
Review for Anadromous Atlantic Salmon (Salmo salar) in the United
States. National Marine Fisheries Service/ U.S. Fish and Wildlife
Service Joint Publication. Gloucester, MA 294 pp. http://www.nmfs.noaa.gov/pr/pdfs/statusreviews/atlanticsalmon.pdf
ICES (International Council
for the Exploration of the Sea). 2003. Report of the Working Group
of North Atlantic Salmon. Copenhagen, Denmark, 31 March - 10 April
2003. ICES, Doc. CM 2003/ACFM:19, 310 pp.
ICES (International Council for
the Exploration of the Sea). 2006. Report of the Working Group
on North Atlantic Salmon, 4-13 April, 2006, ICES Headquarters.
ICES CM 2006/ACFM:23. 254 pp. http://www.ices.dk/iceswork/wgdetailacfm.asp?wg=WGNAS
Meisner, J. D., J. S. Rosenfeld,
and H. A. Regier. 1988. The role of groundwater in the impact
of climate warming on stream salmonines. Fisheries 13(3): 2-8.
National Research Council. 2002.
Genetic Status of Atlantic Salmon in Maine. National Academy Press.
Washington, DC 62 pp. http://www.nap.edu/books/0309083117/html/
Spidle, A. P., S. T. Kalinowski,
B. A. Lubinski, D. L. Perkins, K. F. Beland, J. F. Kocik, and
T. L. King. 2003. Population Structure of Atlantic Salmon in Maine
with Reference to Populations from Atlantic Canada. Transactions
of the American Fisheries Society 132(2): 196-209.
Stolte, L. 1981. The forgotten
salmon of the Merrimack. Department of the Interior, Northeast
Region. Washington, D.C. 214 pp.
USASAC (United States Atlantic
Salmon Assessment Committee). (2006) Annual Report of the U.S.
Atlantic Salmon Assessment Committee Report No. 18 – 2005
Activities. Gloucester, MA. 106 pp. http://www.nefsc.noaa.gov/USASAC/
Verspoor, E., M. O'Sullivan,
A. L. Arnold, D. Knox, and P. G. P.G. Amiro. 2002. Restricted
matrilineal gene flow and regional differentiation among Atlantic
salmon (Salmo salar L.) populations within the Bay of
Fundy, Eastern Canada. Heredity 89: 465-742.