Sea scallops Placopecten magellanicus
are distributed in the northwest Atlantic Ocean from Newfoundland
to North Carolina, mainly on sand and gravel sediments where bottom
temperatures remain below 20oC (68oF). North
of Cape Cod, concentrations generally occur in shallow water less
than 40 m (22 fathoms) deep. South of Cape Cod and on Georges
Bank, sea scallops typically occur at depths between 25 and 200
m (14 to 110 fathoms), with commercial concentrations generally
between 35 and 100 m (19 to 55 fathoms) (Figure
Sea scallops are filter feeders,
feeding primarily on phytoplankton, but also on microzooplankton
and detritus (Hart and Chute 2004). Sea scallops grow rapidly during
the first several years of life. Between ages 3 and 5, they commonly
increase 50 to 80% in shell height and quadruple their meat weight.
During this time span, the number of meats per pound is reduced
from greater than 100 to about 23.The largest observed size is about
23 cm (9 in.) shell height, but sea scallops rarely grow larger
than 17 cm (6.7 in.) shell height. Sea scallops have been known
to live more than 20 years.They usually become sexually mature at
age 2, but individuals younger than age 4 probably contribute little
to total egg production. Sexes are separate and fertilization is
external. Spawning usually occurs in late summer and early autumn;
spring spawning may also occur, especially in the Mid-Atlantic Bight.
Sea scallops are highly fecund; a single large female can release
hundreds of millions of eggs annually. Larvae remain in the water
column for four to seven weeks before settling to the bottom. Sea
scallops attain commercial size at about four to five years old,
though historically, three year olds were often exploited.
The commercial fishery for sea scallops is conducted year round,
primarily using offshore New Bedford style scallop dredges.
A small percentage of the fishery employs otter trawls, mostly
in the Mid-Atlantic, and divers and Digby dredges are sometimes
used in near-shore areas in the Gulf of Maine. The principal
U.S. commercial fisheries are in the Mid-Atlantic (from Virginia
to Long Island, New York) and on Georges Bank and neighboring
areas, such as the Great South Channel and Nantucket Shoals.
There is also a small, primarily inshore fishery for sea scallops
in the Gulf of Maine. Recreational fishing is insignificant.
Most of the sea scallop landings in the federal E.E.Z. (>
3 miles from shore) are harvested by vessels with limited-access
permits that typically undertake fishing trips of one to two
week duration. Each of these vessels has an annual days-at-sea
allocation for the open areas, and is allotted a number of trips,
each under a trip limit, to former closed areas that have been
reopened. There is also an increasing amount of landings from
vessels operating with open access general category permits
that allow landings of up to 400 lbs. of meats per trip. Other
measures under the current management plan (Amendment 10) include
gear restrictions (4” rings and 10” twine top for
dredges), crew limits (no more than a 7 man crew on open area
trips), and rotational and long-term closed areas. The Gulf
of Maine sea scallop fishery occurs primarily in state waters
managed by the state of Maine using gear and seasonal restrictions.
The Canadian Georges Bank sea scallop fishery is managed using
enterprise allocations, a form of individual transferable quotas
landings of Atlantic sea scallops from NAFO areas 5 and 6 (all U.S.
landings together with those from the Canadian portion of Georges
Bank) averaged 30,800 mt meats during 2003-2005, more than triple
the 1996-1998 average (Table 36.1, Figure
36.2 Data]). The highest recorded U.S. landings occurred in
2004, when 29,321 mt meats were taken. Historically, a majority
of the landed meats were in the smaller market categories (>30
meats per pound), but improved management has caused most recent
landings to be in larger market categories (Figure
36.3 Data]), so that the mean weight of a landed scallop meat
in 2005 was about twice that which occurred in the 1990s. The recent
high landings can be attributed to the increase in landed meat weight
together with favorable environmental conditions in the Mid-Atlantic.
The U.S. Atlantic sea scallop fishery is one of the most valuable
fisheries in the United States and the most valuable wild scallop
fishery in the world; its ex-vessel value exceeded $430 million
GULF OF MAINE SEA SCALLOPS
The Gulf of Maine sea scallop
fishery occurs primarily in Maine waters, within three miles of
shore. The vessels in this fishery are relatively small (typically
around 40’), and fish for scallops during the state sea
scallop season, December 1 through April 15. During the remainder
of the year, many of these vessels fish for other species (e.g.,
lobsters). A few vessels also harvest scallops in Gulf of Maine
federal waters throughout the year, but in recent years, the landings
from these waters have been minimal.
Gulf of Maine scallop landings
have averaged about 500 mt meats per year, and peaked at 1614
mt meats in 1980 (Figure
36.4 Data]). During the most recent period (2000-2005), landings
have been low, averaging about 290 mt meats per year.
GEORGES BANK SEA SCALLOPS
During the past 50 years, annual Georges Bank
sea scallop landings (U.S. and Canada combined) have ranged
between 3,000 and 15,000 mt meats. U.S. landings averaged about
5,000 mt meats during 1999-2004, but rose to about 9,900 mt
in 2005 (Figure
36.5 Data]). The fishery has been strongly affected in recent
years by the closure of three large areas on Georges Bank to
groundfish and scallop gear in December 1994, and limited reopenings
of portions of these areas since June 1999.
Research Vessel Survey Indices
The Georges Bank NEFSC sea scallop survey
biomass index remained low from 1982 through 1994 (Figure
36.6 Data]). Subsequently, the index increased markedly,
and has remained at a high, roughly stable level since 2000.
The percentage of Georges Bank sea scallops in the larger size
categories has also increased considerably since 1994 (Figure
Between 1982 and 1993, fishing mortality on
sea scallops in the U.S. portion of Georges Bank averaged around
1.1, with a low of about 0.6 in 1985 and a high of about 1.7
in 1991 (Figure
[Fig 36.5 Data]). Fishing mortality declined
markedly between 1993 and 1998, first due to a shift in effort
to the Mid-Atlantic, and later to effort reduction measures
and the closure of three areas to scallop fishing. Fishing mortality
on sea scallops averaged about 0.1 during 1998-2005, and was
about 0.15 in 2005. The slight increase in 2005 was largely
due to limited reopenings of portions of the closed areas.
Recruitment has been highly variable,
with periods of strong recruitment during 1988-1990 and 1996-1999
36.8 Data]). Egg production increased considerably
after the 1994 closures, but recent year classes (2000-2003)
have all been below average, suggesting that the increased egg
production has had little effect on recruitment.
Prior to 1987, annual landings
of sea scallops from the Mid-Atlantic ranged from less than 1000
mt meats to a maximum of about 4000 mt meats (Figure
36.9 Data]). Landings increased in subsequent years,
ranging between 2000 and 9000 mt meats from 1987 and 2000, and between
15,000 and 25,000 mt meats since 2001. About 94% of these landings
were taken with scallop dredges, with nearly all of the remainder
taken with otter trawls.
Research Vessel Survey
The Mid-Atlantic NEFSC sea
scallop survey biomass index remained low from 1979 through 1998
36.6 Data]), and then increased about ten-fold between
1998 and 2003. The increase was due to strong recruitment combined
with conservation measures such as reduced fishing mortality, increased
dredge ring requirements, and the implementation of rotational closures
that allowed many scallops to grow to larger sizes. Prior to 1999,
most scallops were captured during the first few years after they
recruited to the fishery (at about 75 mm shell height), so that
very few survived to grow beyond 100 mm (Figure
36.10 Data]). Since then, reduced fishing mortality together
with a shift in fishery selectivity toward larger scallops has resulted
in substantial numbers of larger scallops in the landings (Figure
36.3 Data]) and in the population as a whole.
Fishing mortality increased during
the 1980s and early 1990s, reaching a peak of over 1.6 in 1992 (Figure
36.9 Data]). Fishing mortality subsequently declined,
averaging around 0.5 during 1999-2004. It declined further to about
0.3 in 2005, mostly due to the rotational closure of an area off
of southern New Jersey and Delaware (the Elephant Trunk closed area).
Prior to the mid-1980s,
sea scallop productivity was low in the Mid-Atlantic, as evidenced
by the relatively low landings and recruitment (Figure
recruitment and landings in the Mid-Atlantic have been increasing.
Since 1998, biomass has more than doubled due to a combination of
strong recruitment and reduced fishing mortality. As a result, egg
production has increased more than an order of magnitude from 1998-2005.
ASSESSMENT AND BIOLOGICAL REFERENCE POINTS
Fishing mortality for the combined
Mid-Atlantic and U.S. Georges Bank sea scallop resource averaged
about 1.1 during 1982-1994, and peaked at about 1.6 in 1991 (Figure
36.12 Data]). Fishing mortality decreased considerably
during 1994-1998 due to effort reduction measures and the implementation
of closed areas. Fishing mortality averaged about 0.3 during 1998-2004,
and was about 0.2 in 2005.
Yield and spawning stock biomass
per recruit curves for Mid-Atlantic and Georges Bank sea scallops
are fairly similar (Figure
36.13 Data]). Maximum yield per recruit occurs at Fmax
= 0.24 for Georges Bank sea scallops, and Fmax = 0.25
for Mid-Atlantic sea scallops (Table 36.2).
The overfishing threshold, based on using Fmax as a proxy
for Fmsy, is specified at F = 0.24, with a target fishing
mortality of 80% of the threshold (Ftarget = 0.20). Similarly,
the biomass target of Btarget = 5.6 kg/tow, computed
as Bmax times median recruitment, is used as a proxy
for Bmsy. The threshold for being in an overfished condition
is specified as one half the target, or 2.8 kg/tow.
Closed Areas and Spatial
Sea scallops have a somewhat uncommon
combination of life-history attributes: low mobility, rapid growth,
and low natural mortality. These attributes enable sea scallop populations
to respond rapidly after areas have been closed to fishing. This
has been observed in the Georges Bank closed areas, where sea scallop
biomass increased almost 25-fold between 1994 and 2000 (Figure
36.14 Data]), and in the Hudson Canyon South rotational
closed area in the Mid-Atlantic, where sea scallop biomass increased
about five times during its three year (1998-2001) closure. Significant
increases have also occurred in the Elephant Trunk rotational area
since it was closed in 2004. These observations are consistent with
rotational theory which predicts that rotational closed areas can
increase sea scallop yield and biomass (Hart 2003).
Biomass survey indices for
both Georges Bank and Mid-Atlantic sea scallops were at or near
their historical maximums in 2005. The combined survey index for
2005 was 7.7 kg/tow, well above the biomass target of 5.6 kg/tow.
Sea scallops were therefore not overfished in 2005. Fishing mortality
has declined considerably from its peak in 1991. Fishing mortality
in 2005 was 0.22, slightly above the target fishing mortality rate
of 0.2, but below the overfishing threshold of 0.24. Therefore,
overfishing was not occurring in the sea scallop fishery in 2005.
Hart D.R. and A.S. Chute. 2004.
Essential Fish Habitat Source Document: Sea Scallop, Placopecten
magellanicus, Life History and Habitat Characteristics (2nd
edition) NOAA Tech Memo NMFS NE-189, Woods Hole, MA.
Hart, D.R. and P.J. Rago. 2006.
Long-term dynamics of U.S. sea scallop (Placopecten magellanicus)
populations. North American Journal of Fishery Management 26:490-501.
Naidu, K.S., and G. Robert. 2006.
Fisheries sea scallop, Placopecten magellanicus. Pgs. 869-905
in S. Shumway and J. Parsons (eds.), Scallops: Biology, Ecology
and Aquaculture, 2nd ed. Elsevier.
NEFMC [New England Fishery Management
Council]. 2003. Final Amendment 10 to the Atlantic sea scallop fishery
management plan with a supplemental environmental impact statement,
regulatory impact review, and regulatory flexibility analysis. New
England Fishery Management Council, Newburyport MA.
Orensanz, J.M., A. M. Parma,
T. Turk and J. Valero. 2006. Dynamics, assessment and management
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