Mechanized shellfish harvesting and its management: the offshore clam fishery of the eastern United States

Full text

OFFPRINTS FROM MARINE INVERTEBRATE FISHERIE9I THEIR
ASSESSMENT AND MANAGEMENT
Edited bv lohn F, caddv
Copynght (c) f989 by Ibbn Wttlt'& 8onr, Ins
21 MEcHANI zED sHELLFIsH
HARVESTING AND ITS
MANAGEMENT:
THE OFFSHORE CLAM
FISHERY OF ThIE
EASTERN UNITED STATES
Steven A. Murawski and Fredric M. Serchuk
National Marine Fisheries Service
Woods Hole Laboratory
Woods Hole, Massachusetts
1. Introduction
2. History and Development of Ocean Clam Fisheries
3. Population Dynamics of the Surf Clam and Ocean Quahog
3.1. Surf Clam
3.2. Ocean Quahog
4. Management of Ocean Clam Resources in the EEZ
5. Bioeconomic Overview of Bivalve Fishery Management
References
1. INTRODUCTION
oceanic clam fisheries off the eastem united States currently produce landings of
56,000 tonnes of meats with an ex-vessel (first sale) value of U.S. $58 million
(Table 1). These figures alone are impressive, but they are even more so when one
considers that the entire catch is processed into products worth many times their
dockside value (value-added products). Landings and value derived from these
479

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481

482 STEVEN A. MURAWSKI AND FREDRIC M. SERCHUK
mechanized clam fisheries have increased steadily since the late 1970s when stocks
of surf clam (Spisula solidissima) were at historically low levels and large-scale
fisheries for the deeper-water-dwelling ocean quahog (Aruica islandica) had not
yet been initiated. The current prognosis for the long-term economic viability of
these fisheries is good. Both species are relatively long-lived, and exploitation rates
are low in comparison to standing stocks. Based on known resources, current
production levels ofboth species can be sustained well into the 1990s. In the case
of ocean quahog resources, exploitation rates are so low (an estimated 2% of
standing stock per year) that the fishery can be maintained for several decades
without significant new recruitment. A rigorous management program adopted
initially in 1977 has resulted in sustainable landings remaining at or near histori-
cally high levels and considerable economic benefits accruing to a relatively small
number of individuals and vertically integrated companies (i.e., companies
involved in catching, processing, and marketing these products). The surf clam-
ocean quahog fisheries currently are the object of a level of management control
unprecedented for U.S. marine fisheries. The fisheries have been described as the
most stringently regulated in waters under the jurisdiction of the U.S. federal
government.
This chapter examines the historical development of the mechanized clam
fisheries and the population dynamics of surf clams and ocean quahogs in relation
to exploitation. Biological and economic justifications are reviewed for various
restrictive management measures implemented initially to conserve and rebuild
declining surf clam stocks and to promote orderly development of the ocean quahog
industry. Subsequent management decisions have focused on stabilizing product
flow over time from a substantially rebuilt surf clam resource, and equitable alloca-
tion to a significanfly overcapitalized harvesting sector. We also consider the unique
biological characteristics of these and similar bivalve resources with respect to
issues of resource productivity, recruitment variability, and density-dependent
processes, particularly as they relate to long-term management stratagems.
2. HISTORY AND DEVELOPMENT OF OCEAN CLAM
FISHERIES
Yancey and Welch (1) divided the history of the surf clam fishery into three
relatively distinct phases: The early period (1870-1942), the developmental period
(1943-1949), and the recent period (1950-1965). Subsequent to these we wpuld
add: full development and overcapitalization period (1966-t976), and intensive
management period (1977-present). Each period is characterized in terms of the
status of surf clam utilization, the development of harvesting and processing equip-
ment and methods, and the state of knowledge of the magnitude and distribution
bf the resource base (Fig. 1).
Although surf clams had been utilized by aboriginal Americans along the
Atlantic seaboard for several centuries (Yancey and Welch 1; Parker 2), a formal
industry for the species was not initiated until the 1870s. This early fishery was

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484 STEVEN A. MTJRAWSK: AND FREDRII M. IERaHUK
conducted off southeastem Massachusetts (Fig. 2) and employed rakes and tongs
in addition to hand gathering of clams. The earliest use of surf clams was as bait
for the hand-line cod fishery, and thus clams were generally not used for human
consumption during the early period. Maximum annual production during 1870-
1928 was 120 tonnes of salted clam meats (1908). Power dredging techniques were
first introduced into the fishery during 1929, in nearshore waters off Long Island,
New York (Fig. 2). These early scrape dredges were L - 1^ wide with the blade
set to dig to about 2O cm (Westman 3). These early dredges relied solely on
mechanical factors for substrate penetration, and thus could not be used in hard-
packed substrata. Although landings increased during 1929-1942, to an average
of 385 tonnes of meat per year (Lyles 4), most of the landings continued to be
used as bait.
The period from 1943 to 1949 was important in the development of the modem
surf clam fishery because of the advent of the significant utilization of surf clams
as food. Early attempts to use the clam meats for human consumption failed, in
part owing to the inability to remove the considerable quantities of sand that
permeate the meat. Most of the sand was "blasted" into the mantle cavity and
viscera during the dredging process (Westman 3). The technological development
of mechanical washers, combined with increased wartime protein demands, stimu-
lated a fishery for surf clam human consumption. At the same time, similar circum-
stances contributed to the initial interest in harvesting of ocean quahog resources,
primarily off Rhode Island (Neville 5).
A second major technological development, introduced during 1945, was the
use ofhydraulic dredges incorporating waterjets at the cutting edge ofthe dredge,
instead of the dry or scrape dredges (Yancey and Welch 1). By employing water
pressure to loosen the clams from the substrate, harvesting efficiency (CPUE) was
increased with a corresponding decrease in the breakage rate of clams, and a
reduced incidence of "cut feet" (Westman 3). The latter condition occurs when
the clam clamps its valves together without first retracting the large foot muscle,
thereby lacerating the foot and potentially reducing yields from the most valuable
portion of the clam.
Landings statistics (Table 1) document the substantial development of surf clam
and ocean quahog fisheries during the late 1940s. Although interest in the ocean
quahog waned after 1948, the surfclam fishery (which had expanded to cover New
York and northern New Jersey waters) increased greatly. Improved meat yields
per bushel and higher-density (bushels per hour) beds were sought along the New
Jersey, Delaware, and Maryland coasts during 1950-1965 (Yancey and Welch l;
Ruggiero 6). During this period landings from New York waters declined as the
fishery developed fully in more southerly areas. In 1957, the fleet had expanded
to approximately 100 small vessels, primarily owner-operated, but by 1965 the
fleet had been reduced by nearly half, with a corresponding increase in vessel size
and the advent of vessel ownership by the major clam processing companies
(Yancey and Welch 1).
Technological innovation in clam harvesting, shucking, and processing methods
was most rapid during 196-1976. The introduction of large stern-rigged vessels

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Figure 3. A modern stern-rigged surf clam-ocean quahog lishing vessel. Note hydraulic
dredge on stern ramp. Vessel length is 29 m; 190 gross registered tons.
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1.1 kL) and weighs 4000 lb (1 .8 tonnes) when full.
486

MECHANIZED HARVESTING IN THE EASTERN U.S, OFFSHORE CLAM FISHERY 487
(Fig. 3), and less labor-intensive methods for landing and transporting the catch
to the processing plants (Fig. a) were among the most important developments
during this phase. Also significant were the introduction of mechanized shucking
techniques to replace laborious hand opening and shucking and improved methods
for eviscerating and washing the clam meats. The advent of automatic shucking
was a critical development, because prior to this innovation, only the largest clams
(>14-cm shell length) were landed, for hand-shucking smaller clams is not
efficient. Further improvements were made in the design of dredging and dredge
handling systems (Fig. 5). Dredge width also increased markedly in response to
less labor-intensive catch handling methods and the need to increase fishery
productivity to meet market demands. Biological research was also identified at
the time as an important element for the continued viability of the expanding surf
clam fishery. Intensive research, initially sponsored by industry, was undertaken
to (1) survey forpossible new concentrations ofharvestable clams, (2) characteize
the size composition, growth rate, and recruitment of surf clams, and (3) monitor
the production and relative productivity (CPUE) of various clam fishing areas along
the Mid-Atlantic coast (Fig. 2). Much of this initial research is summarized by
Ropes (7, 8).
The period from 1966 to 1976 was one of substantial flux in the surf clam
fishery. The areal distribution of landings shifted from a concentration offthe New
Jersey coast to Maryland-Delaware waters, and later and most importantly, to a
Figure 5. Schematic diagram of a surface-supplied hydraulic dredging system. From
Smolowitz and Nulk (25).
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488 srEyEN A. MURAuSKI AND FREDRI? M. sER:HUK
large aggregation of clams of a single-year class, off the mouth of Chesapeake
Bay, during the early 1970s. Landings stabilized at about 20 thousand tonnes during
L965-1969, in spite ofthe significant areal shifts by the fishery to virgin resources.
The discovery ofthe large concentration off chesapeake Bay (1971-1972) resulted
in a dramatic increase in landings, CPUE, and fleet size (Table t, Figs. 6 and 7).
By 1974 the fleet had again increased to about 100 vessels, with a large increase
in the proportion of vessels in the 100-GRT and greater range (Fig. 7: Ropes, 8).
Processing capacity was also increased during the mid-1970s to accommodate
increased fleet capacity and landings, particularly from the area off Chesapeake
Bay.
Landings of surf clams peaked in 1974 at 44 thousand tonnes (Table 1). The
extensive beds of a single year class of clams that contributed to the rapid expan-
sion of the fishery were quickly depleted, and rapid reductions in landings and
CPUE ensued (Fig. 6). By 1976 total landings had declined 49% from the peak
in 1974. Processing capacity and the combined fishing power of the fleet had
increased dramatically however, in response to the stimulus of unconstrained
fishing on the local resource off the Chesapeake. Overcapacity in harvesting and
processing sectors manifested itself in several ways during the late 1970s. Consid-
erable interest was renewed in ocean quahogs as a market substitute for surf clams.
Surf clams had been the preferred species because they occur at shallower depths
(Menill and Ropes 9), produce significantly greater usable meat yields per bushel
lYb4 1969 1974 1979 l9B4
YEAR
Figure 6. Landings (thousands of tonnes of meats), and CPUE (bushels per hour fishing) for
ihe Mid-Atlantic surf clam fishery conducted in waters more than 3 nautical miles from the
coast (the Exclusive Economic Zone, EEZ, under federal government control).
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MECHANIZED HARVESTING IN THE EASIERN U.S. OFFSHORE CLAM FISHERY 489
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1-25 26-50 51-75 76-100 >100
GROSS REGISTERED TONNAGE
Figurc 7. Size distributions of fleet ol vessels used to catch surf clams, 1965, 1974, and
1985. Data in parentheses are the numbers of vessels landing surt clams from EEZ waters
during the three time periods.
of shell stock, and are more desirable as a finished product. Ocean quahog landings
increased slightly during the late 1960s, exceeding wartime production for the first
time in 1970 (Table 1). Prior to 1976 virtually all quahog landings were from
nearshore Rhode lsland waten. It was not until 1976 that a fishery for ocean quahog
was developed in the offshore Mid-Atlantic area (off New Jersey and Maryland).
Developments in food processing methods rendered the ocean quahog an effective
substitute for the increasingly scarce surf clam during the late 1970s (Bakal et al.
10, 11). Ocean quahogs were noto however, a complete substitute in all product
forms owing to some significant anatomical differences between the two clams.
Traditionally, surf clams had been processed into several product forms including
minced clams for chowders and soups, and the large foot muscle was sliced into
thin strips for frying. The ocean quahog has a significantly smaller foot muscle
than the surf clam, precluding quahogs from being processed for clam strips. The
scarcity of the surf clam resource, combined with the lack of a suitable analog for
certain products, combined to increase significantly the ex-vessel unit value of surf
clams. Average price per kilogram of surf clam meat increased from U.S. $0.28
in 1974 to $1.05 in 1976 (a275% increase). In spite of declining surf clam landings
during the late 1970s, the total ex-vessel value of the fishery more than doubled
(Table 1), thereby stimulating the construction of even more large and efficient
vessels.
Clearly the surf clam industry was in a crisis mode during the late 1970s.
Landings had decreased greatly; harvesting and processing sectors were signifi-
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490 STEyEN A. MURAWSKI AND FREDRII M. SERIHUK
cantly overcapitalized. New virgin surf clam resources could not be located and
prospects for substantial recruitment to areas previously fished were unknown. A
widespread and virtually complete natural kill of surf clams of the northern New
Jersey coast during the summer of 1976 (Ropes et al. 12) further diminished a
tenuous resource base.
Initial attempts at developing a comprehensive management program for surf
clams were begun in 1972. At the time, several of the large vertically integrated
companies were becoming concerned at the rapid increases in fleet size and
landings, particularly with respect to the long-term viability of the resource.
Discussions of the necessity for management efforts, and their desirability, were
initiated under the auspices of the Atlantic states Marine Fishery commission
(ASMFC). It was not until the passage of federal extended fisheries jurisdiction
legislation in 1976 (the Magnuson Fishery conservation and Management Act),
however, that a clear authority and mandate for conservation and management of
fisheries resources in offshore waters was established. The development of a
comprehensive management plan for surf clam and ocean quahog fisheries in waters
under federal jurisdiction [the Exclusive Economic zone (EEZ),3-200 nautical
miles from the coast] was one of the first tasks of the management councils estab-
lished under the Magnuson Act. The development of explicit management objec-
tives and strategies for the offshore clam fisheries, and measures used to attain
them are discussed in Section 4.
Subsequent to the imposition of restrictive management measures for offshore
clam fisheries, the industry carried out substantial development activity exploring
fishing areas not traditionally fished. Thus, for example, harvestable surf clam
resources have been identified on Georges Bank (Murawski and Serchuk 13), in
southern New England (Murawski and Serchuk 14), and in Long Island Sound,
New York. Since the adoption of the management program for offshore clams, the
surf clam resource has been substantially rebuilt, ocean quahog landings have
increased steadily, and new surfclam resources in both offshore and inshore areas
have been explored and are now contributing to production.
3. POPULATION DYNAMICS OF THE SURF CLAM AND
OCEAN QUAHOG
3.1. Surf Clam
Systematic prcgrams to collect data on the population dynamics of surf clams (and
to some extent ocean quahogs) were initiated in the early 1960s (Ropes 8; Merrill
and webster 15). Two major focuses of these activities were: (l) the collection
and compilation of fishery statistics (catch, effort by area fished, fleet size and
composition) and biological sampling of the catch, and (2) the initiation of compre-
hensive regionwide surveying to document the distribution and abundance of
harvestable sized clams (an industry objective) and prefishery recruits (serchuk et
al. 16). These programs have retained their essential elements for more than two

MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 491
decades, although data collection procedures and sampling design have changed
markedly (Murawski and Serchuk 17). Extensive dockside interviews by personnel
assigned to the major landing ports have been conducted since 1965. Beginning in
1978, mandatory logbooks have been submitted on a trip basis by all participants
in the EEZ fishery. Other specific studies have been undertaken to assess growth
rates (Ropes and O'Brien 18; Serchuk and Murawski 19; Murawski and Serchuk
20), length-weight relationships (Murawski and Serchuk 20), and aspects of
densitydependent growth and implications for harvest strategies (Murawski and
Fogarty 21; Fogarty and Murawski 22).
Ropes (7, 8) and others have extensively documented annual changes in the
areal distribution patterns of landings, their size composition, and trends in CPUE
for various subareas of the Mid-Atlantic region (Fig. 2). We have combined the
estimates of CPUE by subareas, weighting by landings, to derive a single index
of vessel performance for the EEZ surf clam fishery, 1965-1985 (Fig. 6). Vessel
interviews were not conducted in t975, and thus data for that year were interpo-
lated. CPUE data from 1978 to 1985 are based on logbook submissions and thus
represent a census ratherthan a subsample of vessel catches (Murawski and Serchuk
t7').
Synoptic research vessel surveys of surf clam (and later ocean quahog) resources
began in 1965 (Parker and Fahlen 23). Between 1965 and 1986, a series of 17
surveys have been conducted to evaluate the distribution, relative abundance, and
size structure of the oceanic clam and quahog populations (Murawski and Serchuk
17; MurawskiZtl). Pior to t976, surveys were conducted intermittently, but have
since been performed on an annual basis (1976-1984). Earliest surveys (1965-
1977) were based on a grid-type design, with stations generally spaced at 10-
nautical mile intervals along either LORAN or latitude-longitude lines. Beginning
in 1978 the survey was changed to a stratified-random design (Fig. 8), with selec-
tion of strata based primarily on depth, and to a limited extent on bottom type.
Earlier survey results (pre-1978) have been post-stratified to conform to the strat-
ified-random scheme, and abundance indexes in numbers and weight developed
for a number of subareas corresponding to those from which the CPUE data were
acquired.
Surveys are performed by allocating a predetermined number of stations (tows)
to each stratum. Initially, the number of stations allocated is proportional to stratum
area. However, in strata known to contain significant clam resources (as deter-
mined from previous surveys and commercial catch data), additional stations are
added in order to reduce overall variance of abundance estimates. At each station
a 5-min tow is now made with a hydraulic clam dredge 1.5 m (60 in.) wide
(Smolowitz and Nulk 25). Surveys prior to 1978 employed smaller dredges and
different tow times, and earlier data have been standardizedby ratios of current
tow time and dredge width to those employed in earlier years (Murawski and
Serchuk 20). Survey catches are enumerated and a subsample is measured to record
the size distribution of the catch at each station. The total meat weight of clams
caught at each station is then computed from length-weight equations (Murawski
and Serchuk 20). Mean number and weight per tow (Fig. 9), and number per tow

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MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 493
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Figurc 9. Stratified mean meat weight (kg) per tow research vessel survey indexes for surf
clams in two Mid-Atlantic subareas. Indexes are presented for combined New Jersey (NJ)
and Delmarva (DMV, off the states of Delaware, Maryland, and Virginia) areas. Indexes for
southern Virginia-North Carolina (SVA-NC) are presented separately (open squares)
because the region was not surveyed consistently in all years.
at each l-cm shell length interval (Fig. 10) are computed for each set of survey
strata corresponding to assessment subareas.
Both commercial catch rates (CPUE) and research vessel survey data for 1965-
1986 document significant changes in the abundance and age structure of surf clam
resources in the Mid-Atlantic assessment areas (Figs. 6, 9, l0). During 1965-1970
the resource primarily consisted of large ( > 14-cm shell length) clams at moderate
to low levels of abundance. Average CPUE during this period was about 30
bushels/hr fishing (Fig. 6), with the fleet primarily comprised of vessels from26
to 75 GRT (Fig. 7). Resource abundance was relatively stable during 1965-1970,
with a low proportion of clam biomass in the southern Virginia-North Carolina
region (SVA-NC, Figs. 8 and 9). Total landings declined during 1965-1970 as
the fishery searched for clam concentrations in both inshore ((3 nautical miles
from shore) and offshore waters.
The discovery of a large concentration of a single year class of clams off the
entrance to Chesapeake Bay (Fig. 2) during the early 1970s had a dramatic effect
O NJ-DMV

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MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 495
on surf blam CPUE, landings, and fleet composition. This resource was primarily
situated in the SVA-NC region (Fig. 9) and landings were dominated by relatively
small clams (the mean shell length in the SVA-NC fishery during 1972-1974 was
13 cm; Ropes 8). CPUE increased rapidly from 28 bushels/hr in 197I to more
than 120 bushels/hr in t974 (Fig. 6). Research vessel survey indexes for the SVA-
NC region peaked in 1974, coincident with the year of maximum landings and
highest CPUE (Table 1; Figs. 6 and 9). The fleet size increased and its composi-
tion exhibited a shift to larger, more modern vessels during the early and mid-
1970s. These shifts were primarily stimulated by the larger vessel hold capacities
needed because CPUE had increased greatly, and processing capacity had expanded
to accommodate the elevated landings levels. Total fleet size increased 8l% from
54 vessels in 1965 to 98 in 1974 (Ropes 8). Vessels in the 76* GRT range made
up about 4O% of the fleet in1974, whereas in earlieryears they formed a much
smaller proportion of the fleet (Fig. 7). Resource abundance in the SVA-NC area
declined rapidly after 1974 as evidenced by reductions in both CPUE and research
vessel survey indexes. Landings from the entire Mid-Aflantic surf clam fishery
declined from a peak of 44,000 tonnes of meats in 197 4 to 22,OOO tonnes by I97 6.
As the resource in the SVA-NC area dwindled, the fishery began to concentrate
on the residual stock of relatively large-sized clams in the Delmarva assessment
area (Figs. 9 and 10). Average fleet CPUE retumed to levels exhibited during
1965-1971; the fleet now, however, significantly expanded in numbers, and was
represented by larger, more efficient vessels. The research vessel survey conducted
in 1976 indicated a predominance of large, relatively old clams in the major fishing
areas off northern New Jersey (NNJ) and Delmarva (DMV, Fig. 10).
During the summer of 1976 a large hypoxic water mass killed a considerable
fraction of the extant surf clam resource off NNJ (Ropes et a1., l2). The "clam
kill" resulted in an historic low in stock abundance in that area, and led to a further
concentration of the fleet in the Delmarva assessment region. The entire fishable
resource of surf clams in the Mid-Atlantic BEZ thus reached its lowest levels
during 1976-1978 after the demise of the SVA-NC fishery, the kill of surf clams
off NNJ, and the concentration of fishing on the limited Delmarva resource (Fig.
9). It was in this period that management plans for the EEZ surf clam fishery were
first implemented.
Recovery of the Mid-Atlantic surf clam resource in the NNJ and DMV subareas
is documented in research vessel and commercial catch statistics (Figs. 6,9, and
10). Larger than usual 1976 (NNJ) and, 1977 (DMV) year classes resulted in the
total biomass of the Mid-AtlanticEEZ resource recovering to those levels observed
during the mid-1960s (Fig. 9).
It is clear that, apart from the catastrophic mortality occurring in 1976, the
instantaneous rate of natural mortality (M) is generally low ( < 0.1) for surf clams
greater than 1 yr of age. Substantial predation mortality (due to crabs and snails)
is common for post-settlement juvenile clams (C. McKenzie, personal communi-
cation). However, crabs are generally not capable of killing clams greater than - 2
cm. Thus M is thought to be initially very high, but reduced substantially after
about 1 yr. The observation of low post-juvenile M is supported by aging studies

496 srEyErv A. MURAWSK: AND FREDRI: M. IERCHUK
ihdicating a maximum life-span of about 30 yr (Ropes and O'Brien 18) and by the
persistence of strong year classes in resource surveys when fishing mortality is low
(Fig. 10). Number-per-tow indexes for the 1976 and 1977 cohorts did not decline
significantly in 9 yr of consecutive surveys (1978-1986, Fig. 10). Considering
that fishing occurred during a portion of the 9-yr period on these two year classes,
their persistence in surveys strongly indicates a very low total instantaneous
mortality rate (z). Year classes after 1977 have been relatively poor and thus the
1976 and,1977 cohorts will support the bulk of the EEZ fishery through the early
1990s. Given continued presumed low fishing mortality rates, there should be
adequate resources to support current landings levels for some years to come based
on these known concentrations and the absence of any catastrophic mortality in
the area occupied by the stock.
Surf clams are fully capable of spawning at the end of their second year of life
(Ropes 26). The production of large year classes (i.e., 1976 and 1977) when
spawning stock biomass was low (Fig. 9) and the lack of significant new year
classes generated after recovery of the stocks suggests no apparent positive
relationship between parental biomass and subsequent recruitment. There may well
be an inhibitory effect of the current high stock size on recruitment, but the neces-
sary microscale studies of stock-recruitment dynamics have not been conducted.
It has been postulated that the hypoxic event off NNJ during 1976 acted to reduce
the abundance of clam predators such as crabs and Limulus (Botton and Haskin
27), as well as of clams. The hypoxic conditions subsided during the late surnmer
months, when surf clam larvae setfled. Owing to the dearth of predators, small
post-settlement clams off NNJ were probably not subjected to normal high preda-
tion mortality, and thus a large 1976 year class resulted. However, this mechanism
does not apparently explain the appearance of an outstanding 1977 year class of
DMV. Although factors influencing year class strength are at this point conjec-
tural, it is clear that outstanding cohorts are indeed rare: we have observed but
three strong year classes in two decades of surveying.
The large 1976 cohort off NNJ has exhibited reduced growth in comparison to
rates determined from previous aging studies in that area (Serchuk and Murawski
19; Murawski and Fogarty 21), Density-dependent growth rates have obvious
implications for management, particularly since biological reference points from
yield-per-recruit studies have been used to analyze alternative minimum size
options for the fishery (Murawski and Fogarty 2l). Minimum size regulations had
to be adjusted downward in 1985 because the growth rate of the cohort did not
meet expectations. Adjustments to the minimum size were required owing to high
levels of at-sea discarding of undenized clams, because only a portion of this
cohort had reached minimum legal size (Murawski and Serchuk 17; see Section
4).
CPUE indexes for the Mid-Atlantic FCZ surf clam fishery show an increasing
trend between 1981 and 1985, indicative of the two large year classes supporting
the fishery. The CPUE index for 1985 (160 bushels/hr fishing) exceeded that for
1974, and, is likely to remain high during the next several years, owing to the

MECHANTZED HARVESTTN9 lN THE EASTERN U.S. OFFSHORE CLAy FISHERr 497
continued high resource abundance and the restrictive management regime being
used to husband the known resource.
3.2. Ocean Quahog
whereas surf clam populations have exhibited pronounced fluctuations in both
abundance and corresponding landings, ocean quahog stocks remained extremely
stable during 1965-1986. Analyses of trends in research survey indexes indicated
extremely poor recruitment throughout the period, but high and stable standing
stocks of a very long-lived resource (Murawski and Serchuk 28). Research on the
age, growth, mortality, and biomass of ocean quahog (Murawski and Serchuk 28,
29; serchuk and Murawski 30; Murawski et al. 31) has established that ocean
quahogs are among the slowest growing and longest lived of exploited animals on
the continental shelf. Mid-Atlantic populations are dominated by animals from 40
to 80 yr of age, with a substantial proportion of individuals in excess of 100 yr.
The age composition of the ocean quahog resource has received close scrutiny
from scientists and fishermen alike owing to the implications of the extreme age
and slow growth rate on fishery management policies. Thus a variety of techniques
have been employed to validate aging studies (Murawski et al. 31; Ropes et al.
32), including mark-recapture, length-frequency analysis, and intra-annual vari-
ability in external banding patterns of small individuals.
Because of the relative stability in survey abundance indexes (in numbers) for
ocean quahogs over time (Murawski and Serchuk 28), the survey data were grouped
into four periods spanning 1965-1982. Estimates of ocean quahog standing stock
in the Georges Bank-Cape Hatteras area for 1980-1982, the most recent period,
are based on stratified mean weight per tow indexes expanded by the ratio of the
area "swept" by a standard tow to the total area surveyed (Table 2). Area-swept
population estimates (in meat weight) assume complete retention of animals in the
path of the survey gear and thus are minimum calculations of the total stock avail-
able for harvest. Based on the pooled 1980-1982 data (three surveys), the total
standing stock of quahogs in the Georges Bank-cape Hatteras region was estimated
to be 1.2 million tonnes of meats (Table 2). Of that total, approximately 557o
occurred in southern New England-Georges Bank waters, 38% otr Long Island
and New Jersey, andT% from Delmarva south to Cape Hatteras.
A series of yield-per-recruit (Y/R) analyses were conducted to determine
optimum exploitation rates for maximizing the yield potential of ocean quahog
cohorts. These calculations assumed very slow growth rates (Murawski et al. 31)
and instantaneous natural mortality rates of 0.01-0.03, consistent with a popula-
tion in which a substantial proportion of individuals survive to ) 100 years
(Murawski and Serchuk 28). The Y/R analyses indicated that exploitation rates
gr€ater than2-Svolyr (depending on the assumed age at first capture) would result
in growth overfishing of the stock. These analyses assumed constant annual
recruitment to the stock. Survey data indicate, however, that recruitment during
the past two decades has been extremely poor. Thus optimal exploitation rates

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MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 499
indicated by YIR analyses would not be expected to result in stable ocean quahog
stock sizes. It has been suggested (Murawski and Serchuk 28; Murawski et al. 31)
that because theEEZ ocean quahog tesource was essentially virgin until 1976, the
extremely slow growth rate and poor recruitment reflect a resource at the carrying
capacity of the ecosystem. If density-dependent population regulatory mechanisms
are contributing to the low productivity of the ocean quahog stock, then areas
subjected to intense fishing prcssure should exhibit increased growth and recruit-
ment rates as quahog density is reduced. Current surveying procedures for ocean
quahogs are intended to sample heavily exploited areas intensively to determine
the response ofthe populations to harvesting.
The current harvest quota for ocean quahogs (27,000 tonnes) is approximately
2% of the overall standing stock. This harvest rate is consistent with the lower
values calculated from Y/R analyses. However, virnrally all of the FCZ landings
are being derived from the New Jersey and Delmarva subareas, where orly 17%
of the regionwide resource exists. If the areal pattern of landings persists for the
next several years, the ocean quahog resource in these areas will decline substan-
tially. As CPUE declines, the fishery is expected to expand to other more produc-
tive areas off Long Island and New England.
4. MANAGEMENT OF OCEAN CLAM RESOURCES IN THE
EEZ
Management plans for the EEZ surf clam and ocean quahog fisheries were fully
implemented beginning inlate 1977 (Mid-Atlantic Fishery Management Council
33). Major elements of the management program during 1977-1985 are given in
Figure I l. Explicit objectives of the initial fishery management plan (FMP) were
to:
1. Rebuild declining surf clam populations to allow eventual harvesting to
approach 23,000 tonnes, which was the average annual catch during 1960-
1976.
2. Minimize short-term economic dislocations to the extent possible with (1),
and promote economic efficiency.
3. Prevent the harvest of ocean quahogs from exceeding biologically sound
levels, and direct the fishery toward maintaining optimum yield (Mid-
Atlantic Fishery Management Council 33).
These objectives were adopted in response to several prevailing factors extant
during the mid-1970s. The depletion of the surf clam resource off SVA-NC and
the hypoxic water event off NNJ both led to a general consensus among industry
and government representatives (as well as within the scientific community) that
tresource abundance had drastically declined. Although clam landings fellby 49%
between 1974 and, 1976, value of the catch increased 9l% due to the higher

500 STEVEN A. MURAWSKI AND FREDRIC M. SERCHUK
SURF CLAM ANNUAL OUOTA
OUARTERLY OUOTA
VESSEL MORATORIUM
LOGBOOK REPORTING
EFFORT LIMITATION
FISHERY CLOSURES
CLOSED AREAS
-DISCARDTARGET
OCEAN OUAHOG ANNUAL CUOTA
LOGBOOK REPORTING
r EFFORT CONTROL
1977 1978 1979 1980 '1981 1982 1983 1984 1985 1986
YEAR
Figure 11. Time lines of the implementation of major fishery management measures for the
Surf Clam-Ocean Quahog Fishery Management Plan, 't977-1986. Management authority for
these resources in federal waters was initiated in 1977 under the extended jurisdiction laws
of the United States.
dockside prices paid by processors for an increasingly scarce resource (Table 1).
This prompted further increases in fleet size (Fig. 7), particularly of larger, more
powerful vessels. The management objectives established by the Regional
Management Council were, and continue to be, the basis of a very restrictive
program aimed at constraining catch and fishing effort in order to rebuild the surf
clam stocks, and to distribute economic benefits among the participants in the
fishery fairly.
Initial management tactics included annual quotas on surf clams and ocean
quahogs, with quarterly subquotas on surf clams to spread catch throughout the
year. Spreading catch throughout the year was intended to avoid long fishery
closures and the attendant unemployment of vessel crews and particularly of skilled
processing plant workers. A moratorium on the entry of new vessels into the surf
clam fishery was established, as well as mandatory logbook reporting requirements
forvessels and processing plants (Fig. 11). A limitation on the amount of time
each vessel could fish weekly was also implemented in order to spread catches
throughout each quarter. Initially, an annual surfclam quota of 13,600 tonnes was
established; well below the maximum catch levels exhibited during the mid-1970s.
Nonetheless, the fishery was (and currently remains) significantly overcapitalized
with respect to the harvesting capacity necessary to take the available quota. As a
result, short-duration fishery closures became necessary when, despite the weekly
effort limits imposed on each vessel, quarterly quotas were still being significantly
exceeded (Fig. 11).
Surf clam quotas have increased since 1977 in response to improved resource
conditions. The annual surf clam quota for the Mid-Atlantic management area for

MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 501
1985-1987 was 20,400 tonnes. Separate quotas have also been established for the
southern New England and Georges Bank resources. These regions have recently
become more extensively utilized by industry and are now included in the research
vessel survey program.
Additional management regulations for surf clams were implemented during
1978-1986 in response to changes in the resource itself. When the large 1976 afi,
1977 cohorts were first identified in the surveys, concern was expressed that signif-
icant quantities of very small clams would inevitably be caught. This led to areas
of high densities of small clams being closed to fishing until the average shell
length of clams in these areas exceeded explicit target sizes. A minimum size limit
(initially, tr4-cm shell length) was likewise established to restrict the catch of small
individuals outside the closed areas. Nevertheless, fishery catch rates (CPUE)
increased steadily during 1981-1985, as did the catch of undersized clams.
Although some small clams were landed, large quantities were discarded at sea
(Murawski and Serchuk 17). Dockside interview sampling for scientific purposes
documented increasing numbers of sublegal-sized clams being landed, and vessel
captain estimates of fraction discarded increased markedly during this period.
Because discard mortality can be high (Haskin and Starypan 34; H. H. Haskin,
personal communication), fishery managers became concerned that production was
being wasted by excessive discarding to meet the minimum size requirement.
Accordingly, in 1983, a"target" discard rate of not more than 3O% of the landed
portion of the catch was established. Subsequently, minimum size requirements
have been adjusted downward to achieve this target (during late 1985 the minimum
size was set at 12.7 cm). Because surf clam Y/R is maximized at shell sizes of
12-13 cm (with small declines in Y/R for a given fishing mortality at LI or 14
cm), the effect of lowering the minimum size on surf clam Y/R has been negligible
(Murawski and Serchuk 20). The original minimum size of 14 cm resulted in about
a 5 % loss in Y/R at Fmax relative to size limits of 12-13 cm. This is because the
14-cm size was originally established to promote harvesting of large clams ( > 14
cm), which economically are higher valued because of the large foot muscle that
can be sliced for frying. Smaller clams are used primarily for lower-valued
products, such as soups, which require only minced clam meat.
With the recovery of the Mid-Atlantic EEZ surf clam stocks, quotas have
increased and CPUE has escalated (Fig. 6). Although quotas increased 50%
between 1977 and 1985, CPUE values have risen by several hundred percent. As
a result, fishing time per week has been shortened in order to prevent the quarterly
quota allocations from being exceeded. For most of 1985 and all of 1986 each
EEZ vessel was allowed 6 hr of fishing time every 2 weeks; this limited fishing
time has been sufficient to catch the quotas.
Although quotas could clearly be increased in the short term without detrimental
effects on the stock, the managers have elected to husband the known resources of
1976 and 1977 year classes because more recent cohorts are relatively weak. Given
that known resources will have to support the fishery at least until the mid-1990s
(clams are not recruited until 6-7 yr of age and the 1986 survey indicates poor
prerecruit abundance), managers have sought to maintain moderate catch levels

5O2 srEyEN A. MURAwsKt AND FREDRII M. IERaHUK
with the expectation that the 1976-1977 cohorts will necessarily be the major
contributors to landings well into the next decade.
Compared to surf clams, ocean quahog fishing has proceeded relatively
unimpeded. Calculations of MSY have been based on "area-swept" population
estimates with biological reference points derived from Y/R studies. Recognizing
the limited productivity of the resource, managers have chosen to maintain
relatively low exploitation rates (-2%lyr) and closely monitor the effects of
fishing. Effort regulations have only been required in late 1985; in prioi years,
annual quotas were generally not attained by the fishery.
5. BIOECONOMIC OVERVIEW OF BIVALVE FISHERY
MANAGEMENT
what have we learned from the historical development of the surf clam and ocean
quahog fisheries and from the intensive programs instituted to manage bioecon-
omic aspects of these and similar fisheries? Clearly, our knowledge of the popula-
tion biology of these resources has expanded. Equally, new and more complete
data have become available on these fisheries as a result of mandated reporting
requirements. Because of the economic importance of both species, considerable
scientific resources have been directed at answering key questions relating to
population dynamics (i.e., growth, recruitment, and abundance). The management
scheme initially implemented for these resources utilized MSY concepts derived
from finfish management, tempered with the desire to (1) freeze the number of
vessels in the surf clam fishery to limit further overcapitalization; (2) preserve
anticipated long-term economic benefits gained from restrictive management of
the surf clam fishery for those who would suffer short-term losses; and (3) not to
repeat the boom and bust cycle ofoverfishing on the still undeveloped ocean quahog
fishery. Unbeknownst to the fishery managers who were developing the initial
FMP during 1977 , very strong year classes would quickly rebuild the depleted surf
clam resource. Thus the task of managers would shift from preserving a low-level
fishery on small stocks to managing an increasing surf clam resource to preclude
repeating the 1970s scenario of resource collapse and fishery overcapitalization.
As can be seen from the timing of adoption of various management measures (Fig.
11), the regulation of the surf clam resource has adapted to changing resource
conditions, particularly as related to recruitment of large year classes. Protection
of small clams to maximize economic Y/R was initiated through closed areas and
minimum size regulations. However, owing to increased utilization and discard of
undersized clams and an apparent compensatory change in surf clam growth rate,
the minimum size limit was reduced to achieve higher aggregate resource yields.
Both surf clams and ocean quahogs are relatively long-lived, have a low natural
mortality rate for animals surviving their first year of life, and infrequently exhibit
strong recruitment. For surf clams, instantaneous natural mortality rate (M) on
clams ) -20 cm is <0.1; for ocean quahogs M : 0.01-0.03. Given these low
M values, it is possible to "stockpile" biomass to sustain the fisheries on these

MECHANIZED HARVESTING IN THE EASTERN U.S. OFFSHORE CLAM FISHERY 503
bivalves through extended periods of poor recruitment. In both fisheries, large
financial investments in harvesting and particularly processing facilities are
required; equally, specialized equipment is necessary to catch and prepare clam
products for market. Thus in the long term it may be economically more advan-
tageous to forego mncimum yield potential of particularly stmng year classes if
annual yields are likely to become highly oscillatory. Traditional biological refer-
ence points for fishery management (i.e., F-u", F6.1) may not be appropriate for
stocks such as these in which M is low, strong year classes are infrequent, recruit-
ment strength seems independent of spawning stock size, and the long-term capital
invested in the fishery is great. From an investment perspective, there is a financial
advantage in knowing that catch rates and landings can be maintained at moderate
levels for an extended time interval (several years). This is particularly important
given a multi-year debt amortization schedule necessary for the substantial invest-
ment in processing/harvesting technology. Baning catastrophic natural mortality
on surfclam and ocean quahog, harvestable biomass ofboth stocks is adequate to
sustain current landings levels well into the 1990s.
The historical development of the surf clam fishery illustrates the fundamental
vulnerability of fisheries on sessile organisms to extreme overcapitalization. This
is due to the high unit value of shellfish, and the fact that dense concentrations,
once located, can be systematically explored and fished utilizing modern harvesting
and navigation equipment. The rapid technological development of such gear has
resulted in a continued increase in the effective fishing power of the surf clam fleet
despite a moratorium on new vessel entrants. Thus established annual quotas for
surf clams are caught with a very short allocation of fishing time per vessel. In the
absence of absolute individual property rights to a fixed portion of the resource,
each vessel competes for a larger fraction of the available total quota. Many vessels
are rigged with larger dredges, or tow two dredges simultaneously, to increase the
relative catchability of their individual vessels. This naturally leads to lower avail-
able fishing time for the fleet as a whole if the quota is not to be exceeded. Thus
even though the EEZ surf clam fleet was capped in t977 , effective effort continues
to increase owing to vessel replacement and gear modifications to increase catch-
ability. The fishery remains significantly overcapitalized with respect to the
harvesting sector. Several altemative schemes to assign individual, transferable
quota allocations to each vessel, based on prior productivity or other measures,
have been explored and continue to be debated by fishery participants and
manageni. Such a scheme could allow for a more efficient use of participating
vessels, with a lower aggregate overhead cost in vessels and harvest equipment.
Finally, given the high level and considerable expense of management control
exerted in the BBZ surf clam-ocean quahog fisheries, one might ask, "Has the
management progmm been a 'success'?" The initial objectives of the FMP were
primarily related to the rapid decline in surf clam abundance and the ensuing
overcapitalization of the fishery in the 1970s. Clearly, the surf clam resource has
been rebuilt and the management progfitm has allowed the economic benefits of
the fishery to accrue to those initially impacted by low annual quotas. The aggre-
gate value of the catch from these fisheries increased 134% between 1976 and

504 SIEVEN A, MURAWSKI AND FREDRI' M. 9ERC,HUK
1986 (an avemge of r2%lyr, well above the average annual inflation rate for the
period). Total landings of both species was a record 56,300 tonnes in 1986, r2j %
above the 1976 total. Employment in the surf clam harvesting sector has declined,
however, with the advent of effort control strategies. For vertically integrated .-
companies one vessel crew may be used for several different vessels, because
current fishing time per boat is 6 hr every 2 weeks. Employment in the processing
sector has increased in recent years, particularly with the large increases in ocean
quahog landings. opportunities for fishing for ocean quahogs have also increased,
thereby replacing some jobs lost in the surf clam harvesting sector. Although the
number of surf clam vessels remains well in excess of the numbers required to
harvest the annual quota, total effort exerted in the fishery has been reduced
dramatically since the mid-1970s, and industry and government continue to seek
equitable methods to reduce fleet size. By these standards, the management program
has successfully met its initial stated objectives. continued "success" of this
management prcgram will require the establishment and attainment of long-term
bioeconomic objectives consistent with the demands of the markeplace for ocean
clam products, and the unique population dynamics ofthese bivalve resources.
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