The ocean quahog, Arctica
islandica, is a bivalve mollusk distributed in temperate
and boreal waters on both sides of the North Atlantic Ocean. In
the northeast Atlantic, quahogs occur from Newfoundland to Cape
Hatteras. Ocean quahogs in US waters are managed as a single stock
35.1) although trends in abundance, recruitment and mortality
Ocean quahogs are found at depths from 8 to
400 m. Ocean quahogs further north occur closer to shore. The
US stock resource is almost entirely within the Exclusive Economic
Zone (EEZ, 3-200 mi from shore), outside of state waters and at
depths between 20 and 80 m. The notable exception is fishable
concentrations in state waters off the coast of Maine. Ocean quahogs
are rarely found where bottom water temperatures exceed 16o
C. They burrow in a variety of substrates and are often associated
with fine sand.
Ocean quahogs are among the longest lived,
slowest growing marine organisms in the world. Ocean quahogs off
Southern New England, in the Mid-Atlantic Bight and on Georges Bank
can live to at least 200 years. Ocean quahogs in the EEZ resource
are relatively large and old, with most individuals 70-110 mm (2.8-4.3
in) shell length. Growth is slow after about age 20, which is also
about the age at which many individuals become vulnerable to fishing.
Growth is faster on Georges Bank and off Maine although ocean quahogs
in Maine waters are seldom larger than 70 mm (2.8 in).
Size and age at sexual maturity
are variable and poorly known. Based on studies in Icelandic waters,
10%, 50% and 90% of female ocean quahogs were sexually mature at
40, 64 and 88 mm (1.5, 2.5 and 3.5 in) shell length or approximately
2, 19 and 61 years of age. Spawning occurs over a protracted interval
from summer through autumn. Free-floating larvae may drift far from
their spawning location because they develop slowly and are planktonic
for more than 30 days before settling. Major recruitment events
appear to be separated by periods of decades.
Based on their growth, longevity
and recruitment patterns, ocean quahogs are relatively unproductive
and able to support only low levels of fishing (removals of a few
percent per year). The current resource, which is still at a relatively
high biomass level, consists of individuals that accumulated over
The ocean quahog fishery was among
the first US fisheries managed using an individual transferable
quota (ITQ) system. ITQ management was established in 1990 by the
Mid-Atlantic Fishery Management Council under Amendment 8 to the
Surf Clam-Ocean Quahog Fishery Management Plan (FMP). Management
of the ocean quahog resource off Maine was addressed in Amendment
10, which was approved in 1999. Amendment 13, the most recent amendment,
was approved in 2002. It implemented various measures to facilitate
efficient management, including multi-year quotas and provisions
for use of automatic vessel monitoring systems (VMS) aboard fishing
The principal gear
used in the fishery is hydraulic clam dredges, which use jets of
water to dislodge ocean quahogs from sediments. A smaller “dry”
dredge (without hydraulic jets) is used in Maine waters. Recreational
and foreign fishing do not occur in the EEZ.
Ocean quahogs were first harvested
commercially during World War II off Rhode Island. Total landings
never exceeded 2,000 mt of shucked meats until 1976. Annual ocean
quahog landings increased from about 23,000 mt during 1979-1983
to about 20,000 mt of meats during 1987-1993. Landings
declined from 1994 to 2000, increased during 2001-2003, but declined
in 2005 to about 13,000 mt meats, which was the lowest level since
1980. Landings from Maine waters are minor (< 2% of EEZ landings)
(Table 35.1, Figure
[Fig 35.2 Data]).
Large ocean quahogs from the EEZ
have relatively small, dark and tough meats which prevent their
use as clam strips or in higher valued products. Landings from the
EEZ are used in processed clam products such as soups, chowder and
sauces. Landings of smaller ocean quahogs from Maine waters are
marketed as “mahogany clams” sold on the half-shell
market or for steaming.
Fishing effort for ocean quahogs
in the US EEZ increased from 21,000 to 46,000 hours fished during
1980-1991, decreased to 33,000 hours during 1996, varied without
trend until 2004, and then declined to 22,000 hours during 2005,
which was the lowest level since 1982. Number of trips per year
declined from 3,400 to 1,215 during 1991-2005. The number of active
permits during each year declined from 92 in 1991 to 47 in 2005.
Declines were due to industry consolidation, market factors and
use of larger and more efficient vessels.
A substantial ocean quahog
resource exists on Georges Bank in the EEZ, but this area has been
closed to harvesting of ocean quahogs since 1990 due to the risk
of paralytic shellfish poison (PSP).
Surveys and Commercial LPUE Indices
NEFSC clam surveys during 1982-2005
indicate that ocean quahog biomass (meat weights) has declined by
about 75% off Delmarva and 50% off New Jersey where the traditional
southern fishing grounds are located. In contrast, survey indices
indicate relatively high and stable biomass off Long Island, in
Southern New England and on Georges Bank.
Trends in LPUE (landings
per unit of fishing effort, mt meats per hour fished) at the regional
level are similar to trends in research survey trends. LPUE during
2005 was relatively low off Delmarva and New Jersey and nearshore
where the fishery had operated for many years.
Total ocean quahog biomass has been gradually
decreasing since the late 1970s (Figure
35.3 Data]). Biomass during 2005 (3.05 million mt meat weight)
was 78% of that during 1978 (3.91 million mt meat weight). Estimated
stock biomass in the exploitable portion of the stock (less Georges
Bank where fishing is not allowed) in 2005 (1.78 million mt meat
weight) was 67% of that during 1978 (2.64 million mt).
Fishing mortality (Figure
35.3 Data]) on ocean quahogs has been low (F=0.008 and F=0.010
per year) and stable since 1985. In contrast, losses due to natural
mortality are about 2% per year.
The biomass target for ocean quahogs
is specified in the FMP as one-half of the virgin (unfished) biomass
for the whole stock (Table 35.2). Virgin biomass
is assumed to be the same as the biomass in 1978 (3.91 million mt
meats). On this basis, the biomass target is 1.95 million mt meats.
The biomass threshold is one half of the target value or 977 thousand
The fishing mortality target for
the exploitable stock (less Georges Bank) is defined as F0.1=
0.028 (2.8%) per year. The fishing mortality threshold as F25%
= 0.052 (5.2%) per year.
On the basis of current
reference points (Table 35.2), ocean quahogs
were not overfished in 2005 because the estimated biomass for the
entire stock (3.05 million mt) exceeded the target of 1.95 million
mt. Overfishing did not occur because the estimated fishing mortality
F=0.0075 (0.75% per year) during 2005 for the exploited region (excluding
Georges Bank) was less than the fishing mortality target of 0.028
(2.8%) per year.
Ocean quahog biomass remains
relatively high and fishing mortality rates are relatively low.
The stock is not overfished and overfishing is not occurring.
Cargnelli, L.M., S. J. Griesbach,
D. B. Packer, and E. Weissberger. 1999. Essential fish habitat source
document: Ocean quahog, Arctica islandica, life history
and habitat characteristics. NOAA Tech. Mem. NMFS-NE-148.
Dahlgren, T., J. Weinberg, and K. Halanych. 2000. Phylogeny of the
ocean quahog (Arctica islandica): influences of paleoclimate on genetic
diversity and species range. Mar. Bio. 137: 487-495.
Lewis, C., Weinberg, J. and Davis, C. 2001. Population structure
and recruitment of Arctica islandica (Bivalvia) on Georges Bank from
1980-1999. J. Shellfish Res. 20: 1135-1144.
Leavitt, D.F., J. McDowell Capuzzo, and J.R. Weinberg. 1995. Shellfish
resources and their management, p. 185-193. In: Colgan, C.S. (ed.).
Sustaining coastal resources: economics and the natural sciences,
Univ. of S. Maine, Portland.
Mann, R. 1985. Seasonal changes in the depth-distribution of bivalve
larvae on the southern New England shelf. J. Shellfish Res. 5(2):57-64.
Mid-Atlantic Fishery Management Council. 2005. Overview of the surfclam
and ocean quahog fisheries and quota considerations for 2006 and 2007.
Mid-Atlantic Fishery Management Council, Room 2115, Federal Building,
300 South New Street, Dover, DE 19904-6790.
Murawski S.A., and F.M. Serchuk.
1989. Mechanized shellfish harvesting and its management: the offshore
clam fishery of the eastern United States, p. 479-506. In: Caddy
J.F. (ed.). Marine invertebrate fisheries: their assessment and
management. Wiley and Sons, Inc., NY.