Northeast Fisheries Science Center Reference Document 06-12
Report from the Atlantic Surfclam
(Spisula solidissima)
Aging Workshop,
Northeast Fisheries Science Center,
Woods Hole, MA, 7-9 November 2005
by by Larry Jacobson1, Sandra
Sutherland1, Jay Burnett1, Maureen Davidson2, Juliana Harding3, Jeff
Normant4, Adriana Picariello3, and Eric
Powell5
1National Marine Fisheries Service, Woods Hole Lab., 166 Water St.,
Woods Hole, MA 02543
2New York State Department of Environmental Conservation,
Bureau of Marine Resources, 205 North Belle Mead Road, Suite 1, East
Setauket, NY 11733
3The College of William and Mary, Virginia Institute of Marine
Science, P.O. Box 1346, Gloucester Point, VA 23062-1346
4New Jersey Department of Environmental Protection, New Jersey Division
of Fish and Wildlife, Bureau of Shellfisheries, Nacote Creek Shellfish Office, P.O. Box 418, Port Republic,
NJ 08241
5Rutgers University, Haskin Shellfish Research Laboratory, 6595 Miller
Avenue, Port Norris, NJ 08349-3167
Print
publication date July 2006;
web version posted July 10, 2006
Citation: Jacobson L, Sutherland S,
Burnett J, Davidson M, Harding J, Normant J, Picariello A, Powell
E. 2006. Report from the Atlantic Surfclam (Spisula solidissima)
Aging Workshop,
Northeast Fisheries Science Center, Woods Hole, MA, 7-9 November 2005. Northeast Fish. Sci. Cent. Ref. Doc. 06-12; 24 p.
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Section
1. INTRODUCTION
A workshop was held at the Northeast Fisheries Science
Center (NEFSC) in Woods Hole, Massachusetts during November 7-9, 2005,
to facilitate communication among scientists involved in aging Atlantic
surfclam (Spisula solidissima) and to lay the groundwork for future
collaboration. The workshop included (a) scientists from the NEFSC,
the New York State Department of Environmental Conservation (NYSDEC),
the Virginia Institute of Marine Science (VIMS), and Rutgers University,
and (b) industry representatives.
This workshop was important and timely because age data from state and
federal surfclam surveys are expected to be used more extensively in
future surfclam stock assessments. Age data are important in fishery
stock assessment analyses for surfclam and other species because age
data contain information about growth, recruitment, and mortality. The
fishing industry is interested in age data because information about
the geographic location and timing of recruitment events is important
in making business plans and managing the stock.
The objectives of the workshop were to:
- describe sampling, processing, aging, and QA/QC protocols/methods
for surfclam aging programs at each laboratory;
- discuss aging terminology, birthdate conventions, and annulus identification;
and
- develop the framework for periodic aging exchanges between aging
programs and the establishment of a surfclam reference collection.
A significant portion of the workshop was spent with the three professional
age readers and other participants gathered around a TV screen that displayed
images of magnified specimens. This arrangement allowed all participants
to view samples from various areas, to gain experience with aging procedures,
and to discuss how closely they agreed on age determinations for each
specimen.
Although a number of issues and uncertainties were discussed during
the workshop, experienced age readers at the meeting indicated that Atlantic
surfclam are easier to age than many fish species that are aged on a
routine basis. Informal analysis of age composition data from the
NEFSC clam surveys in the most recent stock assessment (NEFSC 2003) indicates
that the age data for Atlantic surfclam are likely to be useful in stock
assessment work. In particular, two strong cohorts were evident
in survey age data for the New Jersey and Delmarva regions (Figure 1). The
mode in survey age data at 5 y during 1997 shows up again as a mode at
6-7 y during 1999 and as a mode at 9-11 y in 2002. A relatively
strong cohort at 3-4 y is evident in both areas during 2002.
This section of the report describes the dates, venue, and objectives
of the workshop. Section 2 gives relevant biological information
and describes past aging studies, current programs and ongoing research. Section
3 lays out general issues involved in processing and aging surfclam. Section
4 provides recommendations for future work. Appendix
1 is the workshop
agenda. Participants (with a group photo) are listed in Appendix
2.
Section
2. SURFCLAM BIOLOGY
Biological characteristics are important because they affect timing
and development of annual marks used to age Atlantic surfclam. Biological
information about Atlantic surfclam in the rest of this report is from
Cargnelli et al. (1999) or Ropes and Shepherd (1988), unless otherwise
noted. The former is a thorough review of biological and habitat
characteristics. The latter emphasizes aging techniques for Atlantic
surfclam.
In United States waters, major concentrations of Atlantic surfclam are
found on Georges Bank, south of Cape Cod, and off Long Island, southern
New Jersey, and the Delmarva Peninsula (Cargnelli et al. 1999). Atlantic
surfclam inhabit waters from the surf zone to a depth of 128 m but are
found most often at depths of less than 73 m in well-sorted, medium sand
in turbulent areas beyond the breaker zone. Along Long Island and New
Jersey, the highest concentrations occur in waters shallower than 18
m. In contrast, off the Delmarva Peninsula, the greatest concentrations
occur from 18 to 36 m. Atlantic surfclam are typically found in
areas where bottom temperatures rarely exceed 25°C and where salinities
are higher than 28 ppt.
Surfclam have separate sexes, although some individuals are hermaphroditic
(Cargnelli et al. 1999). In the Middle Atlantic Bight, spawning
occurs primarily during summer, although some activity has also been
documented in autumn. Full sexual maturity is attained in the second
year of life at a shell length of 45 to 85 mm.
Atlantic surfclam spawn in the summer and early fall at temperatures
above 15°C. In New Jersey, spawning occurs from late June to
early August, although spawning may begin as early as late May or early
June closer inshore (Cargnelli et al. 1999). Spawning begins and
ends earlier in the south. In Virginia, for example, it may begin
in May and end in July. There may be a second, minor spawning in
October, caused by breakdown of the thermocline. In cold years,
the second spawning may not occur.
A southern subspecies, S. solidissima similis, occurs primarily
south of Cape Hatteras (Cargnelli et al. 1999). Based on unconfirmed
but probably reliable reports, S. solidissima similis has become
more common during recent years in northern coastal areas such as Long
Island Sound (M. Davidson, New York State Department of Environmental
Conservation, pers. comm.). S. solidissima similis is shorter-lived,
grows to a smaller maximum size, and spawns in the spring to early summer. The
two subspecies can be distinguished based on shell morphology and habitat
but may be confused occasionally in samples from warm coastal areas. Distinguishing
between the two species may become more important in the future because
coastal waters will probably continue to warm (Nixon et al. 2004) and
the distribution of S. solidissima similis is
likely to shift northward. Under warm water conditions, S. solidissima
similis is more likely to be found in areas originally occupied by
Atlantic surfclam (Weinberg 2005).
Growth of Atlantic surfclam is fairly rapid to about age 7 (Figure 2),
but diminishes thereafter (Cargnelli et al. 1999). Maximum shell length is about 23 cm (9 in) and longevity may be as high as 37 years.
Growth of Atlantic surfclam varies by region (Weinberg and Helser 1996)
and may be slower in regions where density is highest (Weinberg 1998).
Growth is not uniform throughout the year (Cargnelli et al. 1999). Growth
of Atlantic surfclam in the Middle Atlantic Bight was positively correlated
with temperature and negatively correlated with variation in temperature. For
example, growth in the coastal Gulf of Maine was higher at warmer temperatures
and at higher chlorophyll concentrations. Shell growth in New Jersey
waters reflects seawater temperature; growth is most rapid in spring
and early summer, slow in late-summer and fall, and extremely slow or
non-existent in winter.
Previous age reading
methodology studies
Annual marks (“annuli”) that are counted and used to age
surfclam are clearly visible in surfclam shells and shell sections (Ropes
and Shepherd 1988). Annual growth comprises alternating bands of
relatively broad opaque (more calcified) zones formed during periods
of fast growth and relatively narrow translucent (less calcified or “hyaline” zones
formed during periods of slow growth. These hyaline zones are considered
to be annuli.
Using transmitted light, annuli appear light, owing to the passage
of light through the less-calcified shell material. Under reflected light,
annuli appear dark for the same reason. Surfclam are usually aged under
reflected light, as this approach requires less time and expense for
sample preparation.
Environmental conditions may influence the timing of annulus formation. Surfclam
from inshore and offshore regions along the Middle Atlantic coast grow
at different rates and consequently have different annuli patterns. In
some dynamic environments, conditions are not suitable for consistent
deposition of annular material.
In 1975, procedures were developed for sectioning whole valves from
the umbo to valve margin using a diamond-impregnated saw blade (Ropes
and Shepherd 1988). The cut edges were then polished to remove saw marks
and enhance the growth structures. Distinctive dark lines seen in the
cut edges of the valves terminated at external rings on the surface of
the shell. The annual periodicity of these lines was validated by marking
experiments (Ropes and Merrill 1976, Jones et al. 1978). Although the
method was reliable, age determinations required careful microscopic
examination of the cut surface, which, together with the cutting and
polishing procedures, proved to be excessively time-consuming.
The method used currently (described below) is more efficient and based
on annuli in the chondrophore (Ropes and Shepherd 1988). According
to reports (no longer available) cited by Ropes and Shepherd (1988),
the number of annual marks in valves corresponded with the number of
annual marks in chondrophore sections. Ropes and O’Brien (1979)
report a 97% linear correlation between valve length and chondrophore
length. These
results suggest that chondrophores may work as well as shell sections
in aging Atlantic surfclam. It is important to note, however, that
age estimates from chondrophores have not been validated directly.
Geographic differences in the timing of annulus formation create confusion
in age interpretation (Ropes and Shepherd 1988). Ages are usually
assigned assuming 1 January as the birthdate. Annuli formed in
early fall may show substantial growth that occurred prior to the assumed
1 January birthdate. Therefore, caution must be exercised in assigning
an additional year of age due to a specimen with a hyaline zone at the
distal edge of samples collected between the time of annulus formation
and the beginning of January. Two studies found developing annual
marks during late summer-early fall for specimens collected off New Jersey
with annulus formation later in the fall (October-November) for surfclam
off Delmarva (Ropes and Shepherd 1988).
The first annulus is usually a single, relatively narrow hyaline zone
(Ropes and Shepherd 1988). Distance from the umbo to the distal edge
of the first hyaline zone is variable. Typically, this variation results
from an annual variation in the timing of larval production and settlement
due to protracted spawning activity, or to differences in growing conditions
at the place of settlement.
The second to tenth annuli appear relatively clear in Atlantic surfclam
(Ropes and Shepherd 1988). Double hyaline zones with a split annulus
are separated from preceding and subsequent annuli by wide opaque bands.
Widths of annuli are compressed as surfclam age and growth slows. Hyaline
zones and opaque bands of subsequent annuli are somewhat compressed.
Existing programs
and current research
Age data are collected on a routine basis from samples taken on research
surveys carried out by the New York State Department of Environmental
Conservation (NYSDEC) and by the NEFSC. The New Jersey Department
of Fish and Wildlife (NJDFW) also conducts clam surveys but samples
are not collected for aging. The Virginia Institute of Marine Science
(VIMS) and the Haskin Shellfish Laboratory at Rutgers University conduct
research on surfclam aging. All of the existing programs and research
are accomplished in close collaboration with the fishing industry, which
provides financial support and makes extensive use of the resulting information. Each
of the existing programs and current research projects are described
below.
With the exception of a single aspect (when a hyaline zone is found
at the edge of a chondrophore, see Issues and Recommendation sections),
participants at the workshop concluded that differences in procedures
used by VIMS, NYSDEC and NEFSC to section and age surfclam were superficial. Participants
hypothesized that similar age estimates would be obtained using either
method.
New York State Department of Environmental Conservation
Surfclam surveys were carried out by the NYSDEC (Davidson et al. 2005)
aboard commercial fishing vessels during August-September of 1993, 1994,
1996, 1999, 2002 and 2005. NY state waters (less than 3 nautical
miles from shore) were surveyed along the south shore of Long Island
between Rockaway Inlet and Montauk Point (Figure
3). Aging of these
samples commenced in 2002. The sampling and aging procedures described
below were used to determine ages of surfclam collected during the 1999 – 2005
NYSDEC surveys (Davidson et al. 2005). Age reader training is provided
to seasonal staff by the biologist in charge (M. Davidson), who was trained
by R. Cerrato at the Marine Sciences Research Center, SUNY, Stony Brook.
NYSDEC surfclam surveys since 1992 were carried out on the F/V Ocean
Girl, an 80-foot stern-rigged commercial surfclam fishing vessel,
equipped with a hydraulic clam dredge (90-in blade) operated at approximately
80 psi. The dredge was lined with 1.5 inch square wire mesh to
insure that small surfclam were retained during survey operations.
At each survey station, five randomly selected surfclam were measured
(shell length to the nearest millimeter) and shucked. The right
valve was retained in a labeled bag for aging. In the laboratory,
the shells were washed, dried and labeled with the station and shell
numbers. After labeling, the shells were trimmed, leaving the chondrophore
and sufficient shell for further processing. Each trimmed shell
was placed in a labeled plastic bag. All shells from the same station
were kept together in a larger labeled bag. About 1,200 clams are
aged per survey.
A Buehler Isomet 1000 precision saw was used to cut shells for aging. The
load on the saw was approximately 80 g and the blade speed was 600 rpm. Blade
speed was decreased further to avoid breaking very small or thin shells. Prior
to cutting, pencil marks were made at the center of the bottom edge of
the chondrophore and at the center of the umbo (Figure 4). These
pencil marks were aligned with the saw blade and used to help place the
trimmed shell on the saw chuck and guide the direction of cutting. The
cutting process was monitored carefully to ensure that the cut was in
the correct position (Figure 5). If the alignment was wrong, the
saw was stopped and the shell was repositioned on the chuck of the saw. Shells
were cut once through the center of the chondrophore. Once cut,
both halves of the shell were labeled and kept in the same sandwich bag. The
shell was discarded if an appropriate cut could not be made.
Cut shell halves were held in sand while an image of the chondrophore
was projected onto a TV screen for viewing (Figure 6). Light and
dark rings are readily visible in the cross-section of the cut chondrophore. The
dark rings were assumed to be annual marks and counted to determine the
age of the shell. One year was added to the age if the edge of
the chondrophore was hyaline. Each shell was aged individually
by two persons. If the ages differed, a third person aged the shell,
and the best estimate of age was determined by discussion. If agreement
on the age could not be reached, the shell was discarded. Maximum
age in NYSDEC samples has been about 26 y for samples outside of Long
Island Sound, and about 11 y for samples from within Long Island Sound.
Surfclam age and survey data collected by NYSDEC are stored in Excel
files. The data from this survey are an important source of information
about year-class strength and stock size in NY state waters.
Northeast Fisheries Science Center
Northeast Fisheries Science Center clam surveys in federal waters were
conducted during May-July approximately every three years since 1982. The
survey is carried out in continental shelf waters between Georges Bank
on the US-Canada border and Southern Virginia/North Carolina, at depths
of 10-200 m (Figure 7). The NEFSC survey also targets ocean quahogs
(Arctica islandica), which occur on the continental shelf in deeper
waters than Atlantic surfclam.
The NEFSC clam surveys are conducted by the R/V Delaware II using
a hydraulic dredge that differs from commercial dredges in having a submersible
pump mounted on the dredge. The NEFSC clam survey dredge has a
60-inch blade, a 2-inch mesh liner in the cage to retain small clams,
and is operated at about 40 psi. Station locations are randomly selected
except for special studies.
Surfclam taken in the survey (one clam from each 10-mm size group at
each station) are aged routinely following each survey. Roughly
1000 clam shells have been aged per survey during recent years.
Each sample saved for aging is measured again at the lab to verify length,
width, and height of shells. The more complete shell (right or
left) is chosen for further processing, and trimmed to fit into the saw. Chondrophore
sections are cut along a line from the umbo to the valve margin (Figure 8) using a Buehler Isomet low-speed saw mounted with two diamond-impregnated
blades (Figure 9).
Age is determined by counting the dark rings (assumed to be annual marks;
Figure 10) on the cut sides of the chondrophore section (Ropes and O’Brien
1977). Rings are counted under reflected light using a dissecting
microscope at 50-100x magnification. Each sample is aged twice, and if
the two ages disagree, the sample is viewed once again to establish a
consensus age before inclusion in the database. Aging and processing
methods are modified from Ropes and Shepherd (1998).
Age data for surfclam taken in NEFSC surveys are ring counts per
se. When the age data are recorded, no adjustment is made
to the number of rings counted to account for the age reader’s
beliefs about visibility of the first annulus, timing of annulus formation,
date of sampling or other factors that complicate age assignment for
surfclam (see below). This policy is advantageous because the
data stored in the database are not affected by assumptions that may
prove incorrect. If future research shows that adjustments are
required, then the adjustments can be made after the data are extracted
based, for example, on location and date of capture, latitude and other
variables.
Formal experiments to measure age reader precision are now conducted
as part of standard aging procedures. This allows one measurement of ‘aging
error’ which can then be reported in stock assessments, or even
incorporated into population models. In addition, an aging warm-up,
using samples from a previous year, is conducted prior to aging any new
samples.
Data from NEFSC clam surveys are stored in an Oracle database, which
also includes information about where and when the specimen was collected,
shell dimensions, weight, and age. Meat weight data are collected
from a subsample of the clams aged from some surveys. For surveys since
2001, it is possible to link shells with specimen-specific
data such as meat weights.
New Jersey Department
of Fish and Wildlife
Surfclam surveys were carried out in New Jersey state waters on a generally
annual basis during 1988-2004 by NJDFW Bureau of Shellfisheries (Normant
2005) using commercial fishing vessels. However, surfclam samples
for aging were not collected.
Surveys during 2000-2004 included extensive Peterson grab samples that
captured many small (1-46 mm) juvenile surfclam. These juvenile
surfclam taken in grab samples may be very useful in detecting new recruitment,
in estimating the growth rate of young animals, and in identifying the
position of the first annulus.
Virginia Institute
of Marine Science and Rutgers
Three studies by academic collaborators at VIMS and Rutgers are significant
in the context of aging Atlantic surfclam. The first study relates
latitudinal and bathymetric patterns in growth to environmental conditions
and, in particular, to recent coastal warming that has shifted the geographic
distribution of Atlantic surfclam northward and into deeper water. Collections
include surfclam 32-180 mm shell length from southern, northern, inshore
and offshore areas along the coast. Ages are determined using methods
used at the NEFSC. Growth curves for clams from different areas
will be developed and compared statistically. It is likely that
this project may also be useful in validating chondrophores used in aging
Atlantic surfclam.
The goal of the second study is to develop predictive relationships
between the location of annual marks in the chondrophore and shell length
in Atlantic surfclam. This type of predictive relationship can
be used to “back-calculate” growth curves for individual
surfclam from annuli in chondrophores. Similar approaches are widely
used to back-calculate growth of individual finfish based on the position
of annual marks in scales and otoliths (Le Cren 1947, Casselman 1983). The
principal impediment to back-calculating growth curves for Atlantic surfclam
is uncertainty about the exact relationship between annual marks in the
chondrophore and shell length.
The third study involves using new optical and digital technologies
that can be used to characterize molluscan growth patterns at annual
and sub-annual time intervals. The main goal is to interpret sub-annual
growth patterns in relation to environmental conditions and the annual
spawning cycle. These methods are currently not suited for routine
aging because large amounts of data are generated from relatively small
numbers of individuals. However, the technology does show promise
as an alternate and objective means to estimate age in difficult or unusual
specimens, and as a means to provide quality control in routine aging
work. In this context, the new optical and digital methods are
promising because age estimates are objective and repeatable once parameters
used to interpret the data are specified.
Section
3. PROCESSING/AGING ISSUES
Key issues and problems identified at the workshop are described below. The
list is organized in approximate priority order.
- There is uncertainty about the position and nature of the first annulus
in surfclam. This is an important consideration because identification
of the first annulus affects all age data for surfclam.
- Several
studies support the use of chondrophores for aging surfclam but this
approach has not yet been validated.
- No birthdate has been
established for aging surfclam, as all samples have been taken on
surveys during the same season. The season during
which annuli form is not known. The group discussed factors which
may be related to growth and physiology of ring formation, including
temperature, spawning season, depth, seasonality, water temperature and
feeding behavior. These factors may vary latitudinally, as well,
making it possible for clams in some areas to form two marks in one year
or none at all. Due to the lack of knowledge about what causes
these marks to form, it is not possible to agree on a single birthdate
until further research has been conducted.
- The cause and timing of
band formation in surfclam is not known. Spawning
may trigger the formation of hyaline zones. In hard clams, non-optimal
temperatures may cause growth bands to form, as both high and low temperatures
cause suspension of feeding activity and efficient respiration. It
would be advantageous to investigate the causes of ring formation,
particularly at the most northern and southern extent of the species
range where environmental conditions are presumably suboptimal.
- One
potentially important difference exists between procedures used to
age surfclam. Ring counts are recorded at the NEFSC without
adjustment whereas the NYSDEC records the ring count plus one if the
edge of the chondrophore is in a hyaline zone. The importance of
this difference in procedure should be investigated to more accurately
characterize potential differences in age data due to this procedural
difference.
- Growth curves, as estimated from surfclam age data, are
likely to change over time, depth, and latitude. Growth rates
increased off Delmarva, for example, after the die-off caused a hypoxia
event in 1976 and growth slowed later as densities became very high
(Weinberg 1998). In
recent years, coastal waters have warmed (Nixon et al. 2004), and the
southern boundary of the surfclam stock appears to have shifted northward
(Weinberg 2005). These considerations seem to indicate that growth
equations should be updated with new data at regular intervals.
- Routine
QA/QC testing to measure aging error is necessary to ensure use of
consistent protocols and criteria in collecting age data for surfclam. Some
of these measures are already in place at the NEFSC. These measures
will likely become more important as surfclam age data are used in stock
assessment models that incorporate variance in age data.
- Establishing
a reference collection would be very useful, both to increase the accuracy
of age readings and as a tool to train new age readers. The Fishery
Biology Program at the NEFSC (responsible for aging a variety of fish
and shellfish species) has recently been assembling a series of reference
collections for other species.
- Image analysis is a promising
approach that may allow automation of aging for various species. Promising
work is currently underway at VIMS to use image analysis to age ocean
quahogs. This research
program may soon be expanded to include surfclam aging.
- Age data are
not available for commercial fishery catches from either state or federal
waters. Age data are available only from annual
or triennial research surveys. This limits use of survey age data
(e.g. age-length keys) to calculate the age composition of commercial
landings because the fishery operates year-round while surveys occur
mostly during May-June. In particular, commercial fishery age composition
data derived from survey age-length keys may be inaccurate for relatively
fast growing young surfclam caught early and late in the year. Additional
sampling and age data collection from the commercial fishery may become
necessary to accommodate future stock assessment work.
Section
4. WORKSHOP RECOMMENDATIONS
The research recommended in this section (particularly research
involving the first annulus and timing of annulus formation) should
be addressed prior to the 2008 NEFSC clam survey, so that high
quality age data are ready for the 2009 stock assessment cycle. It
is hoped that the assessment model to be used during 2009 will
incorporate age data from all geographic areas along the coast. In
the meantime, stock assessment work during 2006 will focus on development
and testing of stock assessment models that fully utilize age data
for Atlantic surfclam.
- Studies to determine the timing
of annual mark formation are a top research priority. The
group agreed to put together a cooperative research plan that
would, ideally, include monthly sampling at a number of ports
along the coast and at a range of depths. Sample collection
for this project would require industry cooperation, as many
of the required samples could be obtained opportunistically during
normal fishery operations. This study should elucidate
what birthdate convention should be used for surfclam, or at
least help to create an aging algorithm, which would convert
the number of marks into an age. If
the timing of annual mark formation differs along the coast,
then region-specific criteria for determining age may be required.
- New
optical and digital approaches for aging Atlantic surfclam
appear promising and should be pursued.
- Henceforth, edge type should
be characterized (opaque or hyaline, and relative width of the
edge) and recorded for all surfclam shells that are aged. This
information, along with information about the time of annulus
formation, could be used to obtain better age data. This
recommendation has already been incorporated into the standard
NEFSC surfclam datasheet for use in the future.
- In addition to edge type, it
would be useful to record some measure of the quality of each
specimen, and the level of difficulty in determining its age.
- Conduct routine inter-calibration
studies based on periodic exchanges of chondrophores between
laboratories (NEFSC, NYSDEP, VIMS and others) to insure consistency
of aging criteria and consistency of age data for surfclam. Exchanges
should be initiated as soon as possible and will facilitate establishment
of reference collections (see below).
- A surfclam reference collection
should be established, consisting of at least 300 shells. Reference
collections ideally contain samples of known age. However, this
does not appear possible in the near future, so a collection of
shells for which consensus ages have been established will suffice. The
NEFSC volunteered to host the collection, but it was emphasized
that the collection would be a group product established and available
to all users. It is not possible for the NEFSC to provide
all samples because NEFSC surveys do not visit shallow nearshore
areas. Sampling should include a range of depths, all four
seasons, and both sexes. Chondrophores and digital images
should be included in the reference collection.
ACKNOWLEDGMENTS
Workshop participants enjoyed and appreciated a social hosted by the
surfclam fishing industry as well as support for travel and research
provided by their employers. F. Serchuk and F. Almeida (NEFSC)
provided helpful editorial suggestions.
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