81
Technical Report Series 32 Number 87-1 32
HARD CLAM MERCENARIA MERCENARIA (LINNE'), POPULATIONS OF COASTAL GEORGIA
Randal L. Walker
31 31 Georgia Marine Science Center University System of Georgia Skidaway Island, Georgia
81 Hard Clam, Mercenaria mercenaria (Linne'),
populations of coastal Georgia
Randal L. Walker Marine Extension Service University of Georgia P. 0. Box 13687 Savannah, Georgia 31416-0687
The Technical Report Series of the Georgia Marine Science Center i s issued by the Georgia Sea Grant College Program and the Marine Extension Service of the University of Georgia on Skidaway Island (P. 0 . Box 13687, Savannah, Georgia 31416). It was established to provide dissemination of technical information and progress reports resulting from marine studies and investigations mainly by staff and faculty of the University System of Georgia . In addition, it is intended for the presentation of techniques and methods, reduced data, and general information of interest to industry, local, regional, and state governments and the public. Information contained in these reports is in the public domain. If this pre-publication copy is cited, it should be cited as an unpublished manuscript. (Sea Grant College Program, Grant #04-7-158- 44126) . 1987. Acknowledgements
I wish to thank Mr. John Veazey, Drs . Peter Heffernan and Stuart Stevens
for their help in coll ecting clams from the Christmas Creek area and Bruce and
Cathy Paulson for their he lp in collecting c lams at the Crooked River and northern Cumberland Island Stations . I wish to thank Mr s. J eanette Haley for
typing the manuscript. I would especial l y like to thank Drs. E. Chin, J .
Crenshaw, J . Harding, P . Heffernan, and Stuart Stevens for rev iewing the
manuscript. The work was supported by the Georgia Sea Grant Program unde r
grant numbers NA80AA-D-00 091 and NA84AA-D-00072.
i Abstract
The growth rate, density, age structure, size structure and commercial size structure of 40 populations of the h ard clam, Mercenaria mercenaria
(Linne'), throughout the coastal waters of Georgia are described. The hard clam grows to a commercial size in 2 to 3 years t hroughout the coastal area of
Georgia except under extreme environmental conditions. In non-fished or unexploited clam populations, a wide range of clam sizes (up to 11 . 8 em) and ages (up to 40 years) may occur. The range of clam sizes and a ges, however , narrows in the presence of fishing pressures.
Keywords: aquaculture, bivalve, clam, coast, estuary, fishery, mollusc, recruitment, resource, saltmarsh, s tock, s urvey
ii List of Figures
Figure 1 . Map of Wassaw Sound showing collection sites of hard clam,
Hercenaria mercenaria, populations.
Figure 2. Map of St. Catherines Sound and the Crooked River area showing
collection s ites of hard clams, Hercenaria mercenaria,
populations.
Figure 3. Map of Sapelo Sound showing collection sites of hard clam,
Hercenaria mercenaria, populations .
Figure 4. Map of Christmas Creek and Cumberland Island showing
collection sites of hard clam, Hercenaria mercenaria ,
populations.
Figures 5 -17 . Growth rate (mean ± standard deviation), age structure and
size structure of populations of hard clams, Hercenaria
mercenaria, from Wassaw Sound.
Figures 18-20. Growth rate (mean± standard deviation), age structure and
size structure of populations of hard clams , Hercenaria
mercenaria, from St . Cathe rines Sound .
Figures 21-35 . Growth rate (mean± standard deviat ion) , age structure and
size structure of populations of hard c lams, Hercenaria
mercenaria, from Sapel o Sound.
Figures 36-42 . Growth rate (mean± standard deviation), age structure and
size structure of populations of hard clams, Herc enaria
mer c enaria, from Christmas Creek .
Figur e 43. Growth rate (mean± standard deviation), age s t ructure and
s i ze structure of populations of hard c lams , Hercenaria
mercenaria, from Cumberland Island.
iii Figure 44. Growth rate (mean± standard deviation), age structure and
size structure of populations of hard clams, Hercenaria
mercenaria, from Crooked River.
Figure 45. Hard clam, Hercenaria mercenaria, age structure in areas not
fished, lightly fished and heavily fished.
Figures 46-47. Commercial size grouping of hard clams, Hercenaria mercenaria,
for each c l am population sampled in Wassaw Sound.
Figure 48. Commercial size grouping of hard clams, Hercenaria mercenaria,
for each clam population sampled in St. Catherines Sound ,
Cumberland Island and Crooked River .
Figures 49-50. Commercial size grouping of hard c lams, Hercenaria mercenaria,
for each clam population sampled in Sapelo Sound.
Figure 51. Commercial size grouping of hard clams, Hercenaria mercenaria,
for each clam population sampled in Christmas Creek, Little
Cumberland and Cumberland Islands.
Figure 52. Overall percentages of commercial grouping of hard clams,
Hercenaria mercenaria, from all populations in coastal
Georgia. Percentage of c ommercial grouping of clams i n non
fished, lightly fished and heavily fished clam populations.
iv List of Tables
Table 1. Hard clam, Herc enaria mercenaria , production in pounds of meat
landed from 1882 to 1986 in Georgia.
Table 2. Habitat type, substrate type, mean density of clams, Hercenaria
mercenaria ±standard deviation per m2 , and relative commercial
harvesting pressure per station.
Table 3. Hard clam, Hercenaria mercenaria, densities reported for natural
clam populations.
v Table of Con tents
Acknowledgements ...... i
Abstract ...... ii
List of Figures ...... i ii
List of Tables ...... v
I ntroduction ...... 1
Methodology ...... 3
Res ults ...... 4
Discussion ...... 5
Conclusions ...... 1 3
References ...... 14
Figures 1-5 2 ...... 19
Appendix ...... 72
v i Introduction
The hard clam, Hercenaria mercenaria (Linne'), fishery in the State of
Georgia dates back to 1880 with peak landings of clams occurring in 1908
(Table 1). Since the 1930's, clam landings have been sporadic or virtually non-existent in Georgia. However, with the increase in consumer demand for clams and the decline in clam landings in traditional northern U.S. clamming areas due to pollution and overharvesting (National Marine Fisheries Serv ice ,
1977), there has been an increasing interest in Georgia clamming among local as well as out-of-state fishermen. This, coupled with the mariculture potential of hard clam, Hercenaria mercenaria, (Walker , 1983; Walker, 1984a;
1984b), has led to a re-emergence of the fishery in Georgia with steady landings reported since 1981.
Although the coastal waters of Georgia contain unexploited populations of hard clams (Godwin, 1967, 1968; Walker et al. , 1980; Walker and Tenore ,
1984; Walker and Rawson, 1985), most of these populations occur in small areas and are difficult to locate and harvest. They are, however, indicati ve of the existence of extensive pollution-free marshes suitable for shellfi sh production and culture. Hard clams grow year round in southeastern U. S. waters (Eldridge et al., 1979; Walker, 1984a), and clam densities above 25m-2 are common in Georgia (Walker and Tenore, 1984). Densities up to 101m-2 have been observed in intertidal regions of small creeks, headwaters of major creeks, and in shell deposits associated with oyster bars (Walker et al.,
1980; Walker and Tenore, 1984; Walke r and Rawson, 1985).
At present, the majority of Georgia clams represent natural unexploited populations. As fishing pressures increase, they wi ll undergo dramatic changes in population dynamics. Therefore, in the interest of future
1 Table l . Hard clam, Hercenaria mercenaria, production in pounds of meat landed from 1882 to 1985 in Georgia. Data from Department of Natural Resources (1979-1986) and Lyles (1964-1978).
1880 24,000 1957 0 1887 0 1958 1,000 1888 0 1959 0 1889 3,000 1960 0 1890 4 , 000 1961 0 1897 3,000 1962 0 1902 10,000 1963 0 1908 43,000 1964 0 1918 7 , 000 1965 0 1923 0 1966 0 1927 1,000 1967 0 1928 1,000 1968 0 1929 2,000 1969 1,000 1930 2,000 1970 17,000 1931 1,000 1971 0 1932 1,000 1972 0 1935 0 1973 6,000 1936 0 1974 0 1937 0 1975 0 1938 0 1976 10,885 1939 0 1977 0 1940 0 1978 0 1945 0 1979 0 1950 0 1980 0 1951 0 1981 5,855 1952 0 1982 9, 725 1953 0 1983 3,482 1954 0 1984 3,474 1955 0 1985 6,966 1956 0 1986* 2,655
*Partial Landings from January to March, 1986
2 comparisons , it is important at this time to obtain basel ine studies on the various disturbed and undisturbed clam populations in Georgia.
The purpose of this study is to assess the status of c lam populations in
the coastal waters of Georgia. It describes distribution, densities, growth
rates, populat i on age structure, population size structure and commercial size
structure for unharvested versus harvested clam populations in the coastal
waters of Georgia.
Methodology
Clams were collected from 40 populations of coastal Georgia ( 13 from
Wassaw Sound , 15 from Harris Neck, 1 from Crooked River , 1 from Cumberland
Island, 7 from Christmas Creek, and 3 from Ossabaw Island) by taking three
0.44 m2 quadrat samples per site . A 66 x 66 em square PVC frame was randomly
thrown on the creek bottom and clams were dug by hand, placed in field
sampling bags and marked as to locality. Clams were returned to t h e
laboratory, where they were counted, measured for shell length ( longest
possible measurement, i.e., anterior-posterior), and aged by shell sectioning
techniques (see Rhoads and Lutz, 1980; Rhoads and Pannella, 1970). Growth
curves for each c lam were constructed by back-plotting shell length to each
summer annual ring increment.
Clams at each station were categorized according to the following
commercial size groups: juveniles, <38 mm; pre-legal littlenecks, 38 to
44.4 mm; littlenecks, 44.4 to 67.0 mm; cherrystones, 68 to 77 mm; and chowders
>78 mm in shell lengths. This classification scheme is similar to Godwin's
( 1967) scheme except that his littleneck s ize class (38 to 68 mm) was divided
3 into legal littlenecks, those >44.4 mm and pre-legal littlenecks , those <44.4 mm (Walker 1984b).
Results
The growth rates of the various clam populations are given in Figures 5-
44. In 95% of populations sampled, the mean time for clams within a population to reach marketable size (44.4 mm in shell length or 25.4 mm in shell width) is 2 to 3 years,while individual clams obtain this size in 2 to 7 years. The exceptions to this are Sapelo Sound Station number 9 and
Cumberland Island Station number 1 in which 5 and 4 years of growth were required before commercial size was obtained (Figures 30 and 45 respectively).
Population shell size and age structure are given in Figures 5-44.
Clams were aged to 40 years with an overall mean age of 10.8 years. Overall, clams less than 10 years accounted for 60% of the harvested animals, whereas clams 11 to 20, 21 to 30 and those greater than 30 years old accounted for
25% , 13% and 2% respectively . As clam populations were fished, the percentage of older clams was reduced. Conversely, the percentage of juveniles increased as fishing pressure increased (Figure 45). Most populations appear to be healthy as exhibited by the presence of younger individuals. Christmas Creek
Station number 4 (Figure 41) is the major exception in that within this dense population, only two individual clams were less than 10 years old. In essence, there has been virtually no recruitment to this population in 12 years. Wassaw Sound Station number 3 had only 3 individuals less than ten years of age, with the majority of the clams being over 20 years of age
(Figure 7). In terms of shell lengths, clams were sized to 11.83 em with an overall mean shell length of 7.21 ± 1.12 S.D. em.
4 In terms of commercial size grouping (Figures 46-51), juveniles accounted for 3% of the overall population with pre-littlenecks, littlenecks, cherrystones, and chowders accounting for 4%, 32%, 28% and 33% respectively
(Figure 52). Chowders dominated in 40% of t h e populations with cherrystones and littlenecks dominating at 38% and 22% of the clam populations respectively
(Figure 52). In terms of effects of fishing pressure on clam populations, chowders dominated in non-fished stations (N=27) with decreasing percentages in areas lightly fished (N=ll) to lesser percentages in intensely fished areas
(N=2). The percentage of littlenecks increases with increase in fishing pressure (Figure 52).
Mean clam densities ranged from less than 1 to 151 clams per square meter (Table 2), whereas individual samples ranged from 0 to 216 clams per square meter. Overall average density of the 40 clam populations samp led was
22 clams per square meter. Large differences in clam numbers per sample per station were observed.
Discussion
The results of this study show that the growth rate of the various clam populations in coastal Georgia result in a marketable product in 2 to 3 years.
These findings agree with those growth rates observed in other naturally occurring c lam populations in Georgia (Walker, 1984b, Quitmyer et al., 1985;
Walker and Stevens, in press) . Furthermore, they agree with growth rates obtained from hatchery-reared c lam seed in Georgia (Wa lker, 1984a, b), in
South Carolina ( Eldridge et al., 1976, 1979) and in Florida (Menzel, 1964).
Of t he 40 clam populations , only Cumberland Island Station number 1 and
Sapelo Sound Station number 9 required over three years of growth to obtain a
5 Table 2. Habitat type, substrate type, mean density of clams, Hercenaria mercenaria standard deviation per m2 . and relative commercial harveting pressure per station.
Area/Station Habitat Substrate Mean Den~ity Commercial Type Type per rn Harvesting t-lassaw Sound 1 Intertidal Flat Shell/ Sand 8.8 ± 7.7 Intense 2 Intertidal Flat Shell/Sand 20.3 ± 8.9 I ntens.e 3 Creek Mud 13.5 ± 18.4 None 4 Feeder Creek Shell/Mud 3.0 ± 1.5 None 5 Feeder Creek Shell/Mud 47.3 ± 30.9 Light 6 Feeder Creek Shell/Mud St. Catherines Sound 1 Major Creek Shell/Mud 10.1 ± 5.6 Light 2 Major Creek Mud ll . 5 ± 8.3 Light 3 Sound - Intertidal Flat Shell/ Sand 2. 1 ± 1.6 Light Sapelo Sound 1 Feeder Creek Shell/Mud 4.0 ± 3.5 None 2 Creek Shell/Mud Area/ Station Habitat Substrate Me an Den ~ity Commerc i al Type Type per m Harvesting Christmas Creek 1 Feeder Creek Shell/ Mud 34.1 ± 19.6 None 2 Feeder Creek Shell/ Mud 6. 1 ± 3.9 None 3 Feeder Creek Shell 73 . 5 ± 27.2 None 4 Feeder Creek Mud/Shell 151.0 ± 10. 2 None 5 Feeder Creek Shell to Mud* 85.7 ± 92.6 None 6 Feeder Creek Shell/Mud 14.3 ± 7.7 None 7 Feeder Creek Shell/Mud 67.7 ± 52.1 None Cumberland Island 1 I ntertida l Flat Sand/Gr ass 10 to 15** None * Creek bottom had only small area of shell; most of c reek bottom was mud . High density of clams (95 per sample ) occurred i n shell bottom; whereas, 4 and 14 clams occurred per sample in mud . ** Estimated. These animals were collected while accompany ing commercial clammers. Out of the 1817 clams harvested , 66 we re juveniles, 2 pre-litt lenecks, 1741 litt1enecks, 6 cherr ystones and 1 chowde r. 7 mean marketable size. In the Sapelo Sound Station, clams occur on top of an oyster wrack well above the mean low water mark . Clams here occur in a dense substrate of dead oyster shells and are estimated to be above the mean low water within the intertidal zone for 6 hours per tidal cycle. At the Cumberland Island Station, clams occur in a substrate of sand and Spartina alterniflora short form roots. Clams here are estimated to be uncovered approximately 8 hours per tidal cycle and may be harvested by hand at a mean high tide (mean tidal amphitude in Georgia is 2.1 m, Johnson et al . , 1974). It is interesting to note that clams at Cumberland Island Station 1 required 4 years versus 5 years at the Sapelo Sound Station to obtain commercial size. One can hypothesize that substrate (i.e., clams growing in dense shell substrate) inhibits clam growth more than increased exposure time. For instance, in Sapelo Sound Stations 9 and 10, the two populations occur within 12 meters of each other. Station 10 occurs on the same oyster wrack , but clams here occur in a shelly mud substrate and are estimated to be exposed for 2 1/2 hours per tidal cycle. Ye t c lams at Station 10 grew almost twice as fast as those at Station 9 with only an l /2 hour greater exposure time. Furthermore at clam populations in Beach Creek (St. Catherines Stations 1 and 2), both populations occur within approximately 4 meters of each other . Clams at Station 1 occur in a shelly-sand substrate at the mean low water mark, whereas those at Station 2 occur in mud up on the creek b a nk and are estimated to be uncovered by the tide for approximately 6 hours per cycle. Yet c lams at Station 2 have a higher mean size per year than those at Station 1. Thus it appears that substrate in certain cases may be more inhibitory to clam growth than exposure time . 8 The life span of the hard clam, Hercenari a mercenaria, is estimated to be 40 years (Hopkins, 1930; Comfort , 1957). Clams were aged to 40 years in this study, to 34 years in c l am popul ations in t h e vicinity of Little Tybee I sland (Walker, l984b), and to 25 years at King ' s Bay, Georgia (Quitmyer et al., 1985). I n oth er studies of hard clam populati ons , c l ams were aged to 29 years at Cape Lookout, North Carolina (Peterson et al., 1983), to 32 years at Co r e Sound, North Caroli na (Peterson et al .. 1985), to 20 years in Virginia ( Haven and Loesch, 19 73), to 15 years in Fishers Isl and, Ne w York ( Ma l inowski , 1985). and t o 8 to 9 years in Barnegat Bay, New Jer sey (Kennish, 1978). The s out hern hard clam, Hercenaria campechiensis was aged to 22 years i n Boca Ciega Bay, Florida (Saloman and Tayl or, 1969). The clam populat i ons of coas t al Georgia consist mostl y of chowders. This is in agreement with the r esults of a c l a m resour ce sur vey of Wassaw Sound (Walke r et al., 1980) and the State (Godwin, 1968 ; Walker and Rawson, 1985). The results differ from a c l a m resource survey in South Carolina where litt l e n ecks were found to dominate (Anderson et al., 1978). The difference in findings between states c an he explaine d by the pr esence and absence o f a viable clam fishery. In South Carolina, a viabl e f ish ery exist s and the large r and older c l ams have probably been f i shed out over time. Reductions o f larger size and age c l asses of clams due to fishin g pressure c an be seen in t his s tudy (Figures 45 and 53). In non- fished area s , chowders dominate. In heavily-fished areas, t h e percentages of c h owders and cherrystones decrease and the percentages of smaller clams and littlenecks increase. The low percentage of juvenile clams in our study c an be attributed to sampling error. Clams were collected by h a nd , whic h is often an i neffective method of collecting smalle r individua l s. 9 Theoretically, during the incipient stages of fishing, older and larger clams are caught first . With time and according to the level of harvesting pressure, smaller, younger clams come to dominate. This has been observed in the New York area. In heavily fished areas of Great South Bay, c lams were found to be under four years of age (i.e . , age that c lams are marketable size), whereas in areas that are closed to fishing, the populations contain older and larger clams with few juveniles or littlenec ks (Greene, 1978). In Barnegat Bay, New Jersey, no clams were found under 9 years of age (Kennis h, 1980) and Peterson ec al ., (1985) attribute this absence of older clams to fishing pressure. In the clam populations of coastal Georgia, mean clam densities ranged from 0 to 151 adult clams per square meter. These densities agree with densities reported in other clam resource surveys in Georgia (Godwin 1967, 1968 ; Walker et al., 1980; Walker and Rawson, 1985) . Reported clam densitie s from other areas throughout the United States are given in Table 3. In Georgia, clams frequently occur in dense numbers, however, the overall area of the bed is u sually small. For i nstance, in Wassaw Sound, Georgia, a clam population with a mean of 50 clams per square meter covered an area of approximately 90m2 . In this population, the mean density was reduced to 20 c lams per square meter after 3 days of illegal harvesting (Walker, 1984b) . The clam populations· of coastal Georgia are representative of harveste d and unharvested populations. In unharvested populations in Georgia, chowders generally dominate (Godwin, 1968; Walker et al., 1980; Walker and Rawson, 1985) and the population is comprised of older individuals (Walker, 1984b; Walker and Stevens, in press). MacKenzie (1979) describes unharvested clam populations as those which exhibit sparse and sporadic setting, declining 10 Table 3 . Hard c l am, Mercenaria mercenaria, densities reported for natural clam popul ations . Location Reference Maquoit Bay, ME *860 Dow and Wall ace, 1951 Barnstable Harbor, MA 1 Sanders et al . , 1962 Narragansett Bay, RI 4 Russell, 1972 Greenwich Bay, RI 2 to 12 Stickney and Stringer, 1957 Greenwich Bay, RI 215 Stringer, 1955 Long Island Sound, CT 0.9 MacKenzie, 1977 Northport Bay, NY 6.5 MacKenzie, 1977 Great South Bay, NY 18.4 MacKenzie, 1977 Islip, NY Buckner, 1979 Open Areas 16 Closed Areas 30 Patchogue Bay, NY 81 Greene, 1978 East Patchogue Bay, NY 16 Greene, 1978 Patchogue Bay, NY 50 Greene, 1978 Barret Beach, NY 16 Greene, 1978 East Islip, NY 11 Greene, 1978 Goose Creek, NY 10 Kaplan et al., 1975 Raritan Bay, NJ 14 MacKenzie, 1977 Raritan Bay, NJ 5 to 11 Campbell, 1965 Little Egg Harbor, NJ 34 Carriker, 1961 Chinocoteague Bay, MD 1 Wells, 1957 Poquoson Flats, VA 5 Loesch and Haven, 1973 Johnson Creek, NC 6.4 Peterson et al . , 1983 Back Sound, .NC 2 to 10 Peterson et al., 1984 Santee River, SC 18 to 24 Rhodes et al., 1977 North Inlet, SC 6 Dame, 1979 Coastal Georgia 0 . 1 to 21 Godwin, 1968 Christmas Creek, GA 151 This Study Wassaw Sound, GA 0 to 100 Walker et al., 1980 Coastal Georgia 0 to 91 Walker and Rawson, 1985 Colorado Lagoon, CA 556 Crane et al . , 1975 Southampton Waters, 6 Great Britain to 8 Ansell, 1963 Southampton Waters, 0.3 Great Britain to 12.3 Hibbert, 1976 *This popul.1tion was undergoing heavy mortality due to overcrowding. 1 1 setting densities of spat, increased predation of juveniles, and populations comprised mostly of older clams. Malinowski (1985) concludes that even in populations with low rates of annual recruitment (due to sporadic s e tting and/or to predation) into the adult age classes, the population will ultimately result in dense assemblages of c lams. From the data pre sente d in this study, Malinowski's characteriz ation of old populations is more applicable to Georgia populations than MacKe nzie's. Sporadic and low setting densities are the rule in Georgia (personal observation) regardless of whether the population is being harvested or not. Recruitment is a gradual event in Georgia with spawning possibly occurring over most of the year (Pline, 1984). Gonadal studies in Georgia show that spawning occ urs over a 10-month period (Pline, 1984), but peaks in fall and spring. This may account for the absence of any major sets occurring in Georgia. Thus it appears that in Georgia, a relatively few individuals recruit to the population each year resulting in dense numbers of older clams over time. Beal (1983) hypothesized that dense assemblages of neighboring large clams (80 m- 2 ) may protect smaller clams from predation. Kennish (1978) observed clam populations that were without juveniles. He hypothesizes that this indicated an inverse association between adults and juveniles . He further states that adult populations may preclude successful settlement of young clams because of competition for food. Therefore successful recruitment of Hercenaria mercenaria may be regulated by a density-dependent factor, i.e. , when density of adults is high, juveniles are forced to settle unoccupied areas (Kennish, 1978). Unfortunately, Kennish (1978) gave no density estimates, and his population was comprised of individuals less that 9 years old. If one looks at the four most dense populations in the Christmas Creek 12 2 area (Stations 3, 4, 5 and 7, with 74, 151, 86 and 68 clams m- respectively), only Population 4 would support Kennish's conclusions that dense adult populations preclude successful recruitment. In Population 4, only 1.5% of the clams are less than 12 years old, which suggests that adults preclude recruitment. Yet in Populations 3, 5 and 7, there are clams in nearly all year classes, indicating there has been recruitment every year for the last 10 years into each of these populations. The majority of the populations would support Beal's hypothesis that dense assemblages of large clams protect smaller clams. Populations 3, 5 and 7 are approximately equivalent to his experimental density of 80m- 2 , whereas Population 4 is almost twice that density. It is possible that both investigators are correct, but that the density of adult clams needed to preclude successful recruitment is much greater than that envisioned by Kennish . Conclusions The hard clam grows to a commercial size in 2 to 3 years throughout the coastal area of Georgia, except under extreme environmental conditions. In non-fished or unexploited clam populations, a wide range of clam ages (up to 40 years) and c lam sizes (up to 11 . 8 em) may occur, however, in lightly fishe d to heavily fished populations, the range of sizes and ages is narrowed. The range decreases with increased fishing pressure. It is hoped that the data provided in this report will provide base line information for future comparisons to determine the impact of a viable fishery upon presently unexploited hard clam populations. 13 References Anderson, W.O ., W.J . Keith , F.H. Mills, M.E. Bailey , and J . L. Steinmeyer. 1978. A survey of South Carolina hard clam resources . S.C. Wildlife and Marine Resources Department, Marine Resources Center, Tech Rept. 21, vi + l7p + 15p. Appendix III. Ansell, A.D. 1963. Venus mercenaria (L.) in Southampton wa t er. Ecol ogy 44:396-397. Beal, B.F. 1983. Effects of environment, intraspecific density, predation by snapping shrimp and other consumers on the population in biology of Hercenaria mercenaria near Beaufort, North Carolina. Masters Thesis, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina. 177 pp . Buckner, S.C. 1979. Shellfish management in the Town of Islip. Proc. Symp. Mariculture in New York State . New York Sea Grant Inst. and Cornell Univ. NUSG -I-RP-79-01:13-18. Campbell , R. 1965. A report on the economically important shellfish resources of Raritan Bay. U.S. Depart. HEW, Pub. Health Serv. , Northeast Shellfish Research Center, Narragnasett, RI. 11 pp. Carriker, M.R. 1961. Interrelation of functional morphology, behavior, and autoecology in early stages of the bival ve, Hercenaria mercenari a. J. Elisha Mitchell Sci. Soc. 77:168-241. Comfort, A. 1957. Duration of life in molluscs. Proceed . Malacolgical Soc. 32:219-241. Crane, J.M ., Jr., L.G. Allen and C. Eisemann. 1975. Growth rate, distribution, and population density of the northern quahog, Hercenaria mercenaria in Long Beach, California. Calif. Fish and Game 61:82- 94 . Dame, R. F. 1979 . The abundance, diversity and biomass of macrobenthos on North Inlet, South Carolina intertidal oyster reefs . Proc. Natl . Shellfish. Assoc. 69:6-10 . Department of Natural Resources, 1975 through 1985. Georgia Landings Annual Summary(s) 1975 through 1985. Commercial Fisheries Statistics Number(s) 75-A through 85-A. Department of Natural Resources, Coastal Resources Division, Data Management Section, Brunswick, Georgia . Dow, R.L. and D.E. Wallace . 1951. A method of reducing winter mortalities of Venus mercenaria in Maine waters . Dept. Sea Shore Fish., Augusta, Maine , Res. Bull. 4, 3lp. 14 Eldridge, P.J., W. Waltz, R.C. Gracy and H.H. Hunt. 1976. Growth and mortality rates of hatchery seed clams, Nercenaria mercenaria, in protected trays in waters of South Carolina. Proc. Natl. Shellfish. Assoc. 66:13-20. Eldridge, P.J., A.G . Eversole and J.M. Whetstone. 1979 . Comparative survival and growth rates of hard c lams, Nercenaria mercenaria, planted in trays subtidal ly and intertidally at varying densities in a South Carolina Estuary. Proc. Natl . Shellfish. Assoc. 69:30-39. Godwin, W.F. 1967. A preliminary survey of a potential hard clam fishery. Georgia Game and Fish Comm. Contribution Series No. 1, Brunswick, Georgia. 23 pp. Godwin, W.F. 1968. The distribution and density of the hard clam, Nercenaria mercenaria, on the Georgia coast. Georgia Game and Fish Commission, Series No. 10, Brunswick, Georgia. 30 pp. Greene, G.T. 1978. Population structure, growth and mortality of hard clams at selected lcoations in Great South Bay, New York. Master Thesis, State University of New York at Stoney Brook, Stoney Brook, New York. 199 pp. Haven, D.S. and J.G. Loesch . 1973 . Summary, conclusions and recommendations based on an investigation into commercial aspects of the hard clam fishery and development of commercial gear for the harvest of molluscs. Final Report for PL 88 -309, Project 3-124- R, Va . Instit. Mar. Sci . Gloucester Point, VA. 108 pp. Hibbert, C.J . 1976. Biomass and production of a bivalve community on an intertidal mud-fl at. J. Exp . Mar . Biol . Ecol. 25:249- 261. Hopkins, H.S. 1930. Age differences and the res piration in muscle tissues of mollusks. Journ. Exper. Zool. 52:209-239. Johnson, A.S., H.O. Hillestad, S.F. Shanholtzer, and G.F. Shanholtzer. 1974. An Ecological Survey of the Coastal Region of Georgia. National Park Service Scientific Monograph Series. Number 3. 233 pp. Kaplan, E.H., J.R. Welker, M.G. Kraus and S. McCourt. 1975. Some factors affecting the colonization of a dredged channel. Mar. Biol. 32:193-204. Kennish, M.J. 1978. Effects of thermal discharges on mortality of Nercenaria mercenaria in Barnegat Bay, New Jersey . Environ. Geol. 2:223-254. Kennish, M.J. 1980. Shell microgrowth analysis. Nercenaria mercenaria as a type example for research in population dynamics . p. 255-294. In D.C. Rhoads and R.A. Lutz (editors), Skeletal growth of aquatic organisms. p2 55 - 294. Plenum Press, NY . 750 pp. 15 Loesch, J.F . and D. Haven. 1973. Estimated growth functions and size-age relationships of the hard clam, Hercenaria mercenaria, in the New York River, Virginia. The Veliger 16:76-81. Lyles, C.H. 1956 through 1976. Statistical Digest No. 50 through No. 70. Fishery statistics of the United States. Fish and Wildlife Service, Bureau of Commercial Fisheries. Washington, DC. MacKenzie, C.L., Jr. 1977. Predation on hard clam (Hercenaria mercenaria) populations. Trans. Am. Fish. Soc. 106:530-537. MacKenzie, C.L., Jr. 1979. Management for increasing clam abundance. Mar. Fish. Rev. 41:10-22. Malinowski, S. M. 1985. The population ecology of the hard clam, Hercenaria mercenaria, in Eastern Long Island Sound. Ph.D. Dissertation, University of Connecticut, Groton, Connecticut. 112 pp. Menzel, R.W . 1964. Seasonal growth of northern and southern quahog, Hercenaria mercenaria and H. ca111pechiensis, and their hybrids in Florida. Proc. Natl. Shellfish. Assoc. 53:111-119. National Marine Fisheries Service . 1977. The molluscan shellfish industries and water quality:' Problems and opportunities. U.S. Dept . of Commerce, NOAA, Natl. Mar. Fish. Ser., Off. Fish. Devel . , Supt. Docs . , Washington, DC. v + 46 pp. Peterson, C.H., P.B. Duncan, H.C. Summerson and G.W. Safrit, Jr. 1983. A mark-recapture test of annual periodicity of internal growth band deposition in shells of hard clams, Hercenaria mercenaria, from a population along the southeastern United States. Fish. Bull. 81:765- 779. Peterson, C.H., H.C. Summerson and P.B. Duncan. 1984. The influence of seagrass cover on population structure and individual growth rate of a suspension feeding bivalve, Hercenaria mercenaria. J. Mar. Res. 42:123- 138. Peterson, C.H., P.B. Duncan, H.C. Summerson and B.F. Beal. 1985. Annual band deposition within shells of the hard clam, Hercenaria mercenaria: consistency across habitat near Cape Lookout, North Carolina. Fish. Bull. 83:671-677. Pline, M.J. 1984. Reproductive cycle and low salinity stress in adult Hercenaria mercenaria L . of Wassaw Sound, Georgia. Masters Thesis, School of Applied Biology, Georgia Institute of Technology, Atlanta, Georgia. 74 pp. 16 Quitmyer, I.R., H.S. Hale and D.S. Jones. 1985. Paleoseasonality determination based on incremental shell growth in the hard clam, Hercenaria mercenaria, and its implications for the analysis of three southeast Georgia coastal shell middens. Southeastern Archaeology 4:27-40. Rhoads, D.C. and G. Panella. 1970. The use of molluscan shell growth patterns in ecology and paleoecology. Lethaia 3(3):143-161. Rhoads, D.C . and R.A. Lutz. 1980. Skeletal growth of aquatic organisms: biological records of environmental change. New York, Plenum Press. 750 pp. Rhodes, R.J., W.J. Keith, P.J. Eldridge and V.G. Burrell, Jr. 1977. An empirical evaluation of the Lesile-Delury method applied to estimating hard clam, Hercenaria mercenaria abundance in the Santee River estuary, South Carolina. Proc. Natl. Shellfish. Assoc. 67:44-52. Russell, H.J . , Jr . 1972. Use of a commercial dredge to estimate a hard shell clam population by stratified random sampling. J. Fish Res. Bd. Canada 29:1731-1735. Saloman, C.H . and J.L. Taylor. 1969. Age and growth of large southern quahogs from a Florida estuary. Proc. Natl . Shellfish . Assoc. 59:46-51. Sanders, H.L., E.M. Goudsmit, E.L. Mills and G.E. Hampson. 1962. A study of the intertidal fauna of Barnstable Harbor, Massachusetts. Limnol. Oceanogr . 7:63 - 79 . Stickney, A.P. and L.D. Stringer. 1957 . A study of the invertebrate bottom fauna of Greenwich Bay, Rhode Island. Ecology 38:111-121. Stringer, L.D. 1955. Greenwich Bay hard clam productivity studies. US Fish Wildl. Serv., Clam Invest. Conf. Clam. Res. 5:1-9. Walker, R.L. 1984a. Effects of density and sampling time on the growth of the hard clam, Hercenaria mercenaria, planted in predator-free cages in coastal Georgia. The Nautilus 98:114-119. Walker, R.L. 1984b. Population dynamics of the hard clam, Hercenaria mercenaria (Linne'), and its relation to the Georgia hard clam fishery. Masters Thesis, School of Applied Biology, Georgia Institute of Technology, Atlanta, Georgia. 121 pp. Walker, R.L. 1983. Feasibility of mariculture of the hard clam, Hercenaria mercenaria (Linne'), and clam predators in coastal Georgia. Journal Shellfish Research 3:169-174. Walker, R.L. and M.V. Rawson. 1985. Subtidal hard clam, Hercenaria me rcenaria (Linne) resources in coastal Georgia. Georgia Marine Scienc~ Center, Tech. Rept. 85 -1. 164 pp. 17 Walker, R.L. and K.R. Tenore. 1984. The distribution and production of the hard clam, Mercenaria mercenaria, in Wassaw Sound, Georgia. Estuaries 7: 19-27. Walker, R.L., M.A. Fleetwood, and K.R. Tenore . 1980. The distribution of the h a rd clam, Mercenaria mercenaria (Linne'), and clam predators in Wassaw Sound, Georgia. Georgia Marine Sci. Center, Tech. Rept . 80-8, 59 pp. Walker, R.L. and S.A. Stevens. Hard clam , Mercenaria mercenaria (Linne'), Resources of Christmas Creek, Little Cumberland and Cumberland Island . Georgia Dept. Natl. Res. Contrib. Series. No. 41. (In Press). Wells, H. W. 1957. Abundance of the hard c lam , Mercenaria mercenaria, in relation to environmental factors. Ecology 38:123-128. 18 FIGURES 1 - 52 19 N 0 _,, ,_...... ,. t! .l . .l ~:·/: ·•:' ____ .. ,, • :::o:'r-'"'~· •:I";: ,:.{ ,,·;~~~ .. . \.~_{ Wosscw Sound ;ui:~r::~f>\i :· 0 2 ...... Kilometers Ossabaw Island St. Catherines Sound v •c v c -;:• .a• e :2 u St. Catherlnee Sound Crooked River STUDY AREAS 2 1 "-- STUDY ~ AREA Sapelo Sound 22 Little C"mberland leland Station 1 ,'::·:_ __ :;--:··:)/!~C~ }~~(:\f~~l~ -: .. '::' ~-. ~- ...' . : .·. · .. ~:- . ~-. : : Cumberland leland :-·· ...... ;· ·:.·~. ·. ~ ~ . : ~ . ·. ... ~· - ;,' .' ··.; . .: - •.- 1 .'·· ·:·.- _: =··;.:;::- ' ~ . . .. ~-: ~~- :~. ':·· ,: .. ;···. : ...... --:· .· .· · .,~: : ·."' · ·.··:.. ·.: .· . ;. ' ..· . ·_: ~- .· . ·, . .: ~ · -.· : ...... ' .... . ":",: ~.. ~-~-/ .:·! ... :>·: __... - ..··. ; .•. ~...... •· ....· · ·:-· .. :.·.~·.:: ''• .'· ~. ~ •• ·-! ~·· : .: ~.: ~-:::'· .· ..... ' : ,;.· .. . . ·.·-·· . .-.- _..... ~ ·. . ., .-~· 23 Wassaw Sound Cabbage Island Clam Station 1 8 6 ...... 0> c 4 Q) I Q) 2 £ (f) 123456789 Clam age (summers) .28 .24 .20 . 16 n = 24 . 12 mean 4.0 ± 2.3yeara .08 median 4.0 years .04 1 2 3 4 5 6 7 8 9 Clam age (summers) -Q) .20 > ...... 16 ct1 n = 24 Q) . 12 mean 4 .98 ± 1.40cm a: .08 median 5.14cm .04 0.25 2.25 4.25 6 .25 8.25 10.25 Class midpoint (em) 24 Wassaw Sound Cabbage Island Clam station 2 ,--... E 8 (.) 6 4 Q.) .c. (f) 2 I 1 2 3 4 5 6 7 8 9 10 Clam age (summers) .28 .20 > (.) c n = 100 Q.) . 12 mean 3 .96 ± l.89years ::::J cr 4.0years Q.) ~ .04 Q.) > 1 2 3 4 5 6 7 8 9 10 Clam age (summers) -ro . 1 8 Q.) a: . 1 2 n = 100 mean 5.43 ± l.57cm .04 median 5 .66cm 0.25 2.25 4.25 6.25 8.25 10.25 Cla ss midpoint (em) 25 Wassaw Sound Cabbage Island Clam station 3 10 r-"'1 E (.) 1....-1 8 .c I I I I I I I 0> -c 6 (l) I I (l) 4 .c (./) 2 I 1 2 3 4 5 6 7 8 9 10 Clam age (summers) n=37 .08 mean 25.3±8.9years median 25years .06 .04 .02 4 8 12 16 20 24 28 32 36 40 (l) Clam age (summers) > .30 n:37 -ro .24 mean 9 .89± 1.09cm a:(l) . 18 median 1 0 . 18cm . 12 .06 0.25 2.25 4.25 6.25 8.25 10.2 5 12.25 Class midpoint (em) 26 Wassaw Sound Wassaw Island Clam station 4 ,...--.. 8 E u 7 I I I I I · '--' ..r:: ...... 6 CJ) I I c 5 Q) 4 I Q) 3 ..r:: (f) 2 I 1 1 2 3 4 5 6 7 8 9 10 Clam age(summers) .32 .- ,-.. .28 f- .24 f- n=l 6 mea n 12.7±4.lyears .20 r- . 16 med ian 13years . 12 .08 r- ~ I- r- .04 r 2 4 6 8 1 0 12 14 16 18 20 2 2 24 Q) Clam age(summers) > .28 ro .24 n :16 Q) a: .20 mean 8.01 ±L58cm .16 median 7 .93cm .1 2 .08 .04 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 2 7 Wassaw Sound W ass a w Island Clam station 5 ,--.. 9 E 8 (.) "--'..c 7 ...... I I I I I I 0> 6 c (l) 5 4 I I Q) ..c 3 (/) 2 I 1 n=95 mean 6. 7 ±6.2years . 16 median 4.0years . 12 > u c .08 Q) .04 :::> cr Q) 2 4 6 8101 2 14161820222426283032 Clam age (summers) Q) .1 4 > - .12 "'Q) .10 0: n=94 .08 mean 6 .12±1.57cm .06 median 6.24cm .04 .02 0.25 2.25 4 .25 6 .25 8 .25 10.2 5 Class midpoint(cm) 28 Wassaw Sound Wassaw Island Cia m station 6 ,--.. 8 E 7 (.) I • • • '--" 6 ..c...... I I 0') c: 5 I I (l) 4 I Q) 3 ..c 2 I (f) 1 1 2 3 4 5 6 7 8 9 10 Clam age(summers) ,... .20 n= 11 .16 ~ mean 9 .2±3.9yea rs median 9.0years >- . 12 ~ .-- ~ g .08 r- ~ .04 cr 29 Wassaw Sound Wassaw Island Clam station 7 8 7 6 5 4 l Q) 3 £ I (f) 2 1 l 2 3 4 5 6 7 8 9 10 Clam age(summers) .32 .28 - r-- n=7 .24 ~ mean 8.1 ±4.2year s .20 median 7.0years .16 ...... __ ...- .--- >- .12 () c .08 Q) :::J .04 cr Q) I I I 1 1 j_ I i I j_ 1 ~ 1 2 3 4 56 7 8 910111213141516 -(1) Clam age(summers) > .24 -ro .20 £ .16 n=45 .12 mean 7 .40±0.76cm .08 median 7.34cm .04 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 30 Wassaw Sound Wassaw Island Clam station 8 I I I I I I I I I Q) ...c I (f) 1 2 3 4 5 6 7 8 9 10 Clam age(summers) . 16 n=90 mean 1 0.0±3.90years . 12 median ll..Oyears 6 .08 ~ .04 ~ ~~~~~~~~~~~~~~~~~~~-- cr 1 2 3 4 5 6 7 8 9 10 11121314 15 16 Q) Clam age(summers) - .40 Q) > .36 ...... ro .32 Q) a: .28 .24 .20 . 16 n=90 . 1 2 mean 7 . 11±0.76cm .08 median 7.llcm .04 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 3 1 Wassaw Sound Skidaway Island Clam station 9 r--.. E (.) 1.....-J ...c...... CJ) c 5 Q) 4 I 3 2 I 1 1 2 3 4 5 6 7 8 9 10 Clam a.ge(summers) .24 .20 . 16 n=47 > .12 mean 14.1±5.0years (.) c .08 median l4.0years Q) :::J .04 0" Q) 2 4 6 81012141618202224262830 Q) Clam age(summers) ...... > .28 cu .24 £ .20 n=47 . 16 mean 8.24±0.83cm . 12 median 8 . 11 em .08 .04 0.25 2.25 4.25 6 .25 8.25 10.25 Class midpoint(cm) 32 Wassaw Sound Little Tybee Island Clam station 10 ,--., 8 E (.) 7 '---'...c 6 I I I I I I I -0'> 5 c I CD 4 3 I CD ...c U) I 1 1 2 3 4 5 6 7 8 9 10 Clam age(summers) n=216 .12 mean 6.5 ±4.8years >. 0 .08 c median S.Oyears CD .04 ::J cr CD I.... -Q) > +--'ro Q) .16 0: .12 n=215 mean 6.44 ±1.23cm 6.66cm 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 33 Wassaw Sound Little Tybee Island Clam station 11 9 r-"\ E 8 (.) I I I I '--'.c 7 I I I 0) 6 -c Q) 5 4 I I Q) .c 3 (/) 2 I 1 123456 78 9 10 Clam age(summers) .36 .32 .28 .24 .20 n=lOO .16 mean 4.4±2.5years > (.) . 12 median 4.0years c Q) .08 :J (]' .04 Q) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Q) > Clam age(summers) -ro .20 Q) .16 a: .12 n=lOO mean 6.35 ±1.36cm .08 median 6 .27cm .04 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 34 Wassaw Sound Little Tybee Island Clam station 12 10 r--. E 9 () 8 "--' ..c 7 Ol -c 6 Q) 5 4 I 3 2 I 1 1 2 3 4 5 6 7 8 9 10 Clam age(summers) .16 n=68 . 12 mean 11.6 ±5.9years .08 median 9 .0years .04 2 4 6 81012141618202224 Clam age(summers) -Q) .24 > n=68 ....- .2 0 mean 8.29±0.99cm Q)"' . 16 median 8 .25cm a: . 12 .08 .04 0.25 2.25 4.25 6 .25 8.25 10.25 Class midpoint(cm) 35 Wassaw Sound Little Tybee Island Clam station 13 I 1 2 3 4 5 6 7 8 9 10 Clam age(summers) n = 3 9 .16 mean 13.7±6.9years .12 median 14.0years .08 >. u c Q) ~ cr Q) ~ .32 -Q) > _.. .24 n=39 ro .20 mean 8 .54±1.05cm Q) median 8.30cm 0: .16 . 12 .08 .04 0.25 2.25 4.25 6.25 8.25 10.25 Class midpoint(cm) 36 St. Catherines Sound 10 Station 1 Q e 7 I -E (.) 8 I I I I I -~ '& 6 c I e 4 I ..J - 3 I !- UJ 2 I 2 3 ... 6 8 7 8 8 10 Clam age (summers) .30 N: 64 (,)>o. .20 c Median • years •:1cr ...• . 10 ~ ~• .. 4 6 II 10 12 14 16 18 20 "i• Clam age (summers) a: .40 N: 5 .. Mean 6.88 ~1 . 16 em .20 Median 5.e.- em 3.25 4 .25 5.25 6.25 7.25 9 .25 Class midpoint (em) 37 St. Catherines Sound JO Station 2 II 8 I -E 7 u I I l I I I e -.c '& 5 c I ...1• 4 - a I !- 0 2 I 2 3 4 6 e 1 1 • 10 Clam •ge (summers) .30 N: 63 .20 Median 7 years > u c .10 •::::. 0' ....•.. 2 3 • 5 e 7 I 8 10 11 12 13 •> Clam •ge (aummera) -~• 'i .40 a: N: 63 Mean 7 .10 t.O.II em .20 Median 7.11 em 3.25 4 .25 6.26 • . 26 7.26 1 .25 Claaa midpoint (em) 38 St. Catherines Sound 10 8 a St~tloi i J f -E 7 (,) I I -...s:.., • c 6 I CD ..J 4 -'i 3 ~ f/) I 1 2 Clam age (summers) N: 11 Mean 20 3 + 6 .9 years to- ... . 18 Median 20 years > (,) c P"" ... P"" ... ., .oe ""' :I - cr •... ,._ - hll~II •• 16 111 20 22 2• 26 28 JQ 32 ...•> Clam age (summers) II .40 'i N: 11 a: Meen 8.82 ! 0.73 em .20 Median 10.14 ~m 7.26 9.25 10.25 Class midpoint (em) 39 Sapelo Sound 10 Station 1 8 a -E u 7 e -~ I I I I J I I '&e 6 _,• .. I I - 3 ~,• I 2 1 2 3 4 15 8 7 8 g 10 Clam age (summers) N: 18 .20 ,... u c .10 •:I •..17 - 2 4 I I 10 U 14 11 11 10 22 24 II 21 30 » ..-•> Clam •a• (summers) .! .40 N: 18 g:• Mean 7.18 t0.87 c111 .20 ...dian 7.48 em 3.25 4.25 6.25 8.25 7.25 8.25 8.25 Class midpoint (em) 40 3 . 25 •. 25 6 .25 8.25 7.25 8 .25 Class midpoint (em) 41 Sapelo Sound 10 Station 3 8 • I I I E 7 -u I f I 8 ~ -~ ~ 5 I I ..J• • I -'i 3 ~ U> 2 l 8 1 e 8 10 Clam age (summers) .20 N: 32 Mean 10.2 ! 8.7 yeara >- .12 u Median 7 yeara c •;:::, 0' .04 ..•... •> Clam age (summers} -~ 'i• ,40 a: N: 32 Mean 8 .84 .t 1.60 em .20 Median 7. 18 em 3.25 4.25 6 . 25 •• 26 7.25 1.26 • . 26 Class midpoint (em} 42 Sapelo Sound Station 4 8 e E 7 -u e I I I I I I -.1: '6 ..c 6 I I ...J "' -'i 3 .1: 0 I 1 2 2 3 Clam age (summers) . 12 N: 28 .08 Mean 18.1 ~ 10.0 yeara Median 16 years ~ u •r:: •04 ~ ...cr ~• ' 2 4 I a 10 12 14 IIi 18 20 2 2 24 21 21l 30 32 34 36 ;;•> Clam age (summers) 'i• .40 m: N: 20 Mean 7.44 :!: 1.12 e m .. 20 ...dian 7.45 em 2 .25 3 . 26 4 .26 ~ .25 8 .25 7 .25 1 . 25 1 .25 Class mldpiont. (em) 43 Sapelo Sound 10 Station 5 8 • -E 7 u -....&. e g) c 6 ..I• 4 = I .! 3 fJ) 2 I 2 3 4 5 8 7 8 8 10 Clam age (summers) N: 60 .20 Mean 8.8 :!: 7.0 years Median 5 years .10 2 4 S I 10 1 2 14 111 U 20 22 24 211 211 JO • Clam age (•ummers) ~... Ill .40 - N: 50 lr• Mean 8.88 t. 1.54 01n .20 Median 7.00 em 2.25 6.26 8.26 7.25 1.25 1.215 10.215 Class midpoint (em) 44 Sapelo Sound Station 6 8 -E 7 -u - "i 3 ~ 0 2 I 2 3 4 6 8 7 8 8 10 Clam age (summers) . 12 N: 40 .08 Mean 14.8 t 8 .3 years ~ (J c .0-4 •:I 0' •... -• 4 I I 10 1 2 14 11 18 22 24 u ze 30 ..~ Clam age (summers) .. .so N: 40 u:-• Mean 7. 57 t 1. 12 em .to Median 7.85 em .10 2.25 3 .25 -4.25 6 .25 8 .25 Class midpoint (em) 45 Sapelo Sound 10 Station 7 8 8 -uE 1 8 I 1 I I I -~... I c0) 15 I I ..J• • 1 =• 3 ~ (I) 2 I 2 3 • 15 8 7 8 8 10 Clam age (summers) N: 21 ~ Mean 18.8 !. 10.8 yeara - Median 18 yeara .08 ... ~ ~ ~ ~ ~ ,.... ~ .o~ ...... _ ...~c(J a • a 12 ,. ,. 11 ao 22 a• • Clam age (summers) ..~ .40 -• N: 21 IE:• ....n 7.24 t 0 .82 em Median 7.32 em 3.215 ~.26 15.25 1 . 215 7.26 8.26 1.25 Class midpoint (em) 46 Sapelo Sound 10 Station 8 0 8 E 7 -u e I I I I I 1 -~ I I 0) 6 -c G) 4 I ..J 3 -G) ~ I tn 2 2 3 4 6 8 1 8 0 10 Clam age (summers) .30 N: 85 .2 0 Mean 4 .0 ± 4 .0 years >o Median 3 y e ars u c .10 G) ::;, e0' ~ 1/.z::::::= -e 0 2 • • • 1 0 12 1 4 27 > Clam age (summers) ~ ca ..20 -G) N: 8 5 a: Mean 5. 85 ± 1.44 em .10 Median 6. 12 em 1.25 2 .25 8 .25 4 .2 5 6 .25 8 . 25 7.25 8 .25 Class midpoint (em) 47 Sapelo Sound 10 e Station 9 8 -E u 7 -.c 8 0) -c ., 6 ..J I I I I I I - .. I I .c• 3 0 I 2 I 2 3 4 5 e 1 e e 10 Clam age (summers) .20 N: 29 Mean 18.1 !. 11.1 years no 2 4 •> - Clam age (summera) -.!!• ..a a: N: 31 .20 Mean 5.70! 0 .56 em Median 5.86 em 1.26 2.25 3 .26 4.25 5.26 8 .26 7.25 Class midpoint (em) 48 Sapelo Sound Station 10 -E -u • • 3 2 I 1 2 3 4 6 6 7 8 8 10 Clam age (summers) .so N: 43 .20 I!Aean 3.2 ! 1.2 year& ~ u Median 3 yeau; c . 10 G) :II CT G)... 2 3 6 6 7 8 8 10 -G) -...> Clam age (summers) ca .40 G) N: 43 a:- Mean 5.6 1 ! 0.71 em .20 Median 5.52 em 2.25 3.25 4.2 5 6 .25 8.25 7.25 8.25 Class midpoint (em) 49 N: 19 Mean 13.3 t. 7.0 yean Median 12 years I J 2 3 .. 6 II 8 s 10 11 ..La-.--.- 7... Q.OO ., Clam age (summers) > ..-ID .40 'i N: 19 a: Mean 7.74! 1.06 em .20 Median 8.08 em 4 .25 6.26 8.26 7.25 8.25 8.25 10.2 5 Class midpoint (em) 50 2 3 -4 6 ti 7 8 8 10 Clam age (summers) .26 N : 22 . 1 5 Mean 8 .80 ! 6.0 yean Median 7 year6 22 23 Clam age (summers) .40 N : 22 Mean 7 . 61 t. 0 . 72 em .20 Median 7 . 60 em 4. 25 5.25 6 . 25 7.25 8.25 9.25 10.25 Class midpoint (em) 51 Sapelo Sound JO Station 13 e I I -E 8 u 7 1I I s; - 6 0) -c I I G) 6 ...I I =Cl) " s; 3 0 I 2 2 3 " 6 6 7 8 8 10 Clam age (summers) .24 . 16 N: 27 Mean 4.4 1 2.2 yean u> c .08 •:J D' ...... CD Q) -.,> Clam age (summers) -.;- .20 u: N: 27 Mean 6 .49 :t 1 .65 em .12 Median 6 .34 em .04 3.25 4.26 6.25 6 .26 7 . 26 8.26 8 . 2 5 Class midpoint (em) 52 2 3 .. 5 6 7 • 8 10 Clam age (summer&) . 12 N: 38 .08 Mean 12.8 ~ 8 .7 yaara Median 11 yaara Q) e • 10 12 14 t6 •• ao z2 24 2" 211 J O ·-...> Clam age (summers) cu .40 -Q) a: N: 38 .20 Mean 7 .38 .t 0.78 em Median 7 .35 em 3 . 25 4.25 6.2 5 6 . 25 7 . 25 8 . 26 8 .25 Class midpoint (em) 53 Sapelo Sound 10 Station 15 8 8 -E I u 7 -.1: l I I I I I ..., 6 0) c ., 6 I .J -., ~ I .1: 3 0 I 2 1 2 3 • l!i 8 7 • 8 10 Clam age (summers) .12 H: 43 Mean 10.5 1 5. 7 year a .08 u> c •::l ...,cr - 2 4 • • 10 t2 14 ,. " 20 22 24 Clam age (summers) .40 N: 43 .20 Mean 7 .21 11.12 em Median 7.62 em 2.26 3 .25 4 .25 5 .25 6 . 25 7 . 25 8.26 8 . 26 Class midpoint (em) 54 Christmas Creek 10 Station 1 ...... 8 E e ...... u .c..., 7 I II II I 0) e c 1 Q) 5 I -..J .. 1 -Q) 3 .c (/) 2 I 3 • 5 ' 7 8 • 10 Clam age (summers) H : 46 . 24 .20 M e an 8.4 ± 6 .8 y ears . 1 e Medl en 6 y ear s . 1 2 .08 .04 • 8 I 10 12 ,. 16 18 2 0 2 2 2• 26 Clam •a• (aummera) 20 • H: 4 5 Mean 8 . 8 6 ± 1.04 em . 10 Me di an 8 . 8 2 em 3.25 55 Christmas Creek to Station 2 ...... 8 E I (.) ...... 1 • -G) 3 .J::. I U) 2 1 J 4 5 fi 1 . '~ Clam age (summers) .2. ~ N: 8 .20 Mean 12. t :t 3.0 yeara (.)~ .te Median 12 year• c:Q) . t2 ~ ...... - g. .01 4D .o• .t: 6 • 10 12 14 16 Clam ege (aummera) ...... •~ ... . 40 .!! N: 8 • . 30 Wean 7 .e& ~ 0.1 c:m Q:: . 20 .10 l I 4 .26 5 . 26 1 . 2 5 7.26 8.25 '&. 25 ·class midpoint (em) 56 Christmas Creek 10 Station 3 ...... 0 E a .__..CJ .c 7 e I I I I I I I ..0) c CD 6 -..J .. I I .c-CD 3 (/) 2 1 1 2 3 4 6 e 1 e o 10 Clam age (summers) N: 85 .10 Mean 17.1 ~ 8.2 yean ~ .08 () Median 18 year a c: .08 CD 5 .::CD .o2 2 • CD .....::...... 40 .!! N: 86 CD Mean 7.80 ~ 1.07 em ct: .20 Median 7 .ee em 3 .25 4 . 25 6 . 26 G.26 7.25 8 .25 • . 26 Class midpoint (em) 57 6 .26 8.215 7.26 8.26 1 .26 ·class midpoint (em) 58 Christmas Creek 10 Station 5 ..-.. 8 E 8 ...... 0 7 .1:. ...en e I I 11 I I I I c CD 6 ~ " I -CD 3 .1:. 0 2 I 2 ~ " & e 7 a • 10 \;l•m age (aummera) . 12 N: 100 .10 Mean 1 1.7 .!: 7.1 years Median 1 1 years ~------~»04 6 • 10 1 2 14 16 18 10 22 24 26 35 Clam age (summers) 40 " N : 100 .30 Mean 7 . 07 + 0 . 84 e m . 20 M edlen 7.22 em .10 4 . 2 5 6 . 2 5 6 .25 7.25 8 . 25 9 . 25 10.25 Class midpoint (em) 59 Christmas Creek 10 Station 6 .-. 8 E e (.) ...... 7 ,c ... 8 Jill Ill 0) c 6 G) -J " 11 -G) 3 -,c 0 2 I 2 3 4 6 8 7 8 8 ~ Clam age (aummersJ .30 N: 32 ~ Mean 8 .0 :!: 0 . 4 yean (,) .20 c: Median 4 .0 years •::s .10 0' .::• a i:; 4 5 I 1 I I tO 11 1 2 13 ,.1rQ •:.. lam age (aummera) ...... <40 .!! N: 32 Q:• Mean 8.4 7 ! 0.83 em .20 Median 8 .44 em 4.25 6.25 e . H 7 .26 e . 25 e.26 Class midpoint (em) 60 Christmas Creek 10 Station 7 8 ..-.. e E ...... (.) 7 1I I l I I .r:..., e I C) 6 I c Q) 4 _J I 3 -Q) .r:. 2 I 0 2 3 4 6 fl 7 8 8 }0 Clam age (summers .1 2 N: 8 9 ~ . 10 (.) Mean 18 .5! 8.2 y e ara c:: . 08 Q) Median 20 years ~ .0 6 tt Cl) .0 4 .:: .0 2 CD ~ 12 H I 1 8 20 • • 10 1. 22 z• ~ .... Clam age (summers) ·-.qJ- CD .4 0 a: N: 89 Mean 8.3 4 ! 1.03 em .20 Median 8.4 7 em 4 .25 5 . 25 6 . 26 7 .25 8 .25 8 .25 Class midpiont 6 1 Cumberland Island 10 Station 1 8 8 -E 7 (,) e -~ I I I '& 6 l c I I I -J• " I - 3 ~• U) 2 I 1 1 2 3 4 6 8 7 8 8 10 Clam age (summers) .20 H: 35 Mean 8.9 :!. 4.4 years :1111\10 Co) Median 15 yeera c •5 -•.. 2 1 2 13 14 1S 16 •,.. -...•. 20 - N: 35 a:• Mean 6.84 ! 1.22 em . 10 2.25 4.25 9 .25 Class midpoint (em) 62 Crooked River 10 8 8 St~ioi 1I I I I -E 7 (.) -.c 6 Q l5 I I -c G) -' 4 l -., 3 -.c 0 2 I 2 3 4 6 6 7 8 8 10 . 16 Clam age (summers) . 14 .12 N: 68 . 10 Mean 13. 9 ~ 4.8 years .08 Median 14 years .06 .04 .02 6 II t O 12 14 16 18 20 !2 24 26 28 -•> Clam age (summers) .!-., .40 « N: 58 .20 Mean 8.94 •. 0 .77 em Median 8.99 em 5 .25 6.25 7.25 Class midpoint (em) fi3 1.00 .eo Overall .eo ... o .20 I I 1.00 .eo Non-fished areas .eo >-u .,c ·"O .20 .,c::r~ ... 1.00 ~ Lightly-fished areas .eo •> ...-., .eo - ... o .20 a:• 1 1.00 Heavily-fished areas .eo .eo ... 0 .20 c 10 10 to 20 20 to 30 ,. 30 Age In Years 64 65 Wassaw Sound 1.00 Station 7 Station 8 .eo N:45 N: 90 .80 .40 I .20 1 Station 9 Station 10 1.00 ~ N:47 N: 215 0 .eo c: .60 Q) c:r== .40 1 Cl) .20 :: I I Q) ._:a. Station 11 Station 12 .... 1.00 .!! .80 N: 100 N: 68 Q) a: .80 .40 .20 I r Station 13 1.00 .80 N: 39 .60 ..-o . 20 I c... ~ 0 0 c ... :7 < ~ :7 • • 0 :•. - .. lE ' •:;) '<- D. ..• - •n !. •... - 0 ,.. Ill •::> • ::> •n,.. • • 66 St. Catherines Sound Beach Creek St. Catherine& Sound 1.00 Station 3 .80 N: 11 . 60 .40 .20 Cumberland Island Crooked River 1.00 Station 1 Station 2 .80 N: 35 N: 58 .60 .40 .20 l L. "l:l r C'l C'l L. r C'l C'l c ~ '::T '::T c ~ '::T '::T < CD Cll 0 < CD CD 0 Cll l ~ d) l ~ ::> m- ~ f :> m- ~ ~ ::> 0. ::> "< 0. a> Cll "" Cll m- CD Cll .. ~ .. ~ (D -m- C'l Ill -CD 0 :> 7'" -0 .. ::> 7'" -0 CD ::> CD ... ::> "' C'l "' CD n d) CD .. (D"' ..."'" 67 Sapelo Sound Julienton River 1.00 Station 1 Station 2 .80 N: 13 N: 32 .60 .40 I . 20 I 1.00 Station 3 Station 4 .80 N: 29 N: 50 .60 . 40 . 20 1.00 Station 5 Station 6 N: 18 N: 40 ..I I 1.00 Station 7 Station 8 .80 N: 21 N: 85 . ISO .40 .20 I J I c.. , r- 0 0 ~ , 0 0 c: .. ::r :7 c: .. 7 ::r c 0 c ~ 0 .. •I - • .. :I - •.. :I .. :I • • '<.. •~ :! ~ • '< •~ .. - ..n • ~ •n ..• • - 7r - 7r 0 .. • :I 0 • ~ • • :I • • • -:I • • •n .. •n .. 7r 7r • • • • 68 Sapelo Sound Sapelo Sound 1. 00 Station 9 Station 10 .80 N: 43 N: 31 .60 .40 . 20 I Barbour Island River 1.00 Station 11 Station 12 .60 N: 19 N: 22 . 60 .40 .20L.c:::!::=:=..._j 1.0 0 Station 13 Station 14 .8 0 N: 27 N: 38 .60 .40 .20 I I 1.00 Station 15 .eo N: 43 .60 . 4 0 .20 <.. "1) ,... (") (") c: .... ::r :r < It It.... 0 I .... ~ :l Cl> "' :I '< c. Cl> n "' ...... "' ,.. -0 "' "'::> ... :::> "' "'..,..n ..."' 69 Christmas Creek 1.0 0 Station 1 Station 2 .8 0 N: 45 N: 8 .eo .40 ,20 I 1.00 Station 3 Station 4 .ao N: 95 N: 133 ~ .eo ~ Q) .40 &~ .2 0 Q) I ~ Q) :a. 1.00 Station 5 Station 6 ;: .80 .....co N: 100 N: 32 a:Q) .80 .40 I .20 I J I 1. 0 0 Station 7 Station 1-7 .80 N: 89 N: 502 .60 .40 .2 0 I r ~ "CI 0 0 ... "CI 0 0 c: ... ::r ;r 1: ... ::r ::r < CD ~ <( CD CD CD 0 - 0 CD ... CD I i'- .. i'- ;) lE b t ;) .. !) .. :. '< c.. CD '< c.. i' CD i' - n CD 0 •n • ... i'- ,. • ... 0 • ::;) ,. 0 • !) - !) .. CD ::;) "' CD • n • CD n CD ..7'C .. ,... .. 70 1.00 Overall Non-fished areas .80 .60 >- u . 40 c Cl) .20 ~ tT Cl) -...... Cl) > ·-... 1.00 Lightly-fished areas Heavily-fished areas C'O .80 -Cl) a: .60 .4 0 . 20 1 l ~ "C r- 0 0 ~ ~ r- 0 0 c: ... :::T :::T c: ... :::T :T < CD 0 < CD 0 I CD CD I CD CD ... ~ CD- •... - ~ ::J - ... ::J ::J ... ::::1 - '< c. -· '< c. -· CD -· CD ., Gl- - C/1 CD -CD CD CD 0 ... (I) -CD 0 ... (I) (I) - Cl) - 0 ::J '/(' 0 ::::1 71:' CD (I) -:I Gl (I) -:I 0 CD 0 CD '/(' (I) 71:' Cl) (I) (I) 7 l APPENDIX 72 Appendix I. Mean shell lengt:h in mm of the hard clam, Hercenaria mercenaria, per year band per area. Year Band 1 2 3 4 5 6 7 8 9 10 Wassaw Sound Population l 29.7 41.8 46.3 55.3 58 . 9 62.3 62.6 65 .2 2 22.0 38.2 50.4 58. 8 64.8 70. 5 75.2 75.9 70.5 3 25.0 42.5 57.3 67.1 72.7 76 .9 80.7 83 . 8 85.7 88.2 4 25.0 42.9 56.4 65.1 70.7 73.9 74.2 76.8 82.1 79.8 5 22.8 41.1 53.9 62.0 65.6 68.2 71.6 74.1 74.3 75.6 6 25.5 36.2 46.1 50.9 56.1 61. 3 66.0 68.1 68.7 69.8 7 23.4 39.4 49.6 57. 1 61.2 64 . 4 67.2 73.3 8 24.3 39.9 53.2 60 . 0 64 .3 67.1 69.2 70.4 71.4 72.6 9 23.9 42.0 57.2 65 .7 70.5 74 . 0 76.3 77.2 79.0 79 .9 10 21.3 40.2 53.4 61.0 65.1 67.0 69.8 71.7 73.2 73. 1 ll 21.5 41.3 55.3 64.0 69.9 73.7 76.8 79.7 83.6 85.9 12 24.3 42.1 57.3 66.1 71.6 75.4 78.6 79.5 80.8 83.0 13 25.8 43.2 56.5 64 . 8 70.1 73.9 78.3 79.1 81. 7 8.16 St. . Cat.herines Sound 1 21.2 36. 1 48 .7 54.7 61.1 65.6 70.5 72.6 75.4 73 .0 2 23.9 40.0 53.0 61.6 67.0 70.7 73.6 74 .8 75.0 77.9 3 23.0 36.9 52.5 60.8 67.5 73.4 77.1 78.7 81.6 83.8 Sapelo Sound l 27.0 42.1 52 .7 60.6 65.0 65 . 1 66.9 68.4 69 .8 71. 1 2 21.1 41.7 53 . 8 62.0 69.0 72 .l 75.7 76 . 0 78.3 80.4 3 23.2 38.9 53.3 61.2 66.5 70.2 73 .7 76. 1 78.3 78 .7 4 25.5 37.2 48.6 56.8 62.5 66.2 68.1 70.8 72 . 9 74.3 5 24. 7 39.8 53.4 60.7 66 .2 66.4 68.4 70.1 71.9 74 . 7 6 25.6 41.6 54.9 61.8 66.4 69.4 72.3 73.1 74.8 76.0 7 25.5 39.6 49.1 55.3 59.6 62.8 64.7 66.2 67 . 1 68.6 8 29.0 46.9 57.8 61.7 65.0 68 . 4 69.1 70 .0 69.3 70 .6 9 16.8 26.9 35.9 42 . 1 46 . 6 50. 1 50.4 52 . 5 53.1 54.0 10 26.2 44.9 53 .0 59.1 59 .1 ll 31.6 45.6 54.8 61.5 66.4 69.6 72.1 73.6 75.8 76.8 12 28.5 47.6 59.3 65.9 69.5 73.0 74.8 75 .6 77 .5 76.8 13 30 . 5 44.3 56.7 65.6 73.9 80.7 83.4 89.9 92 .5 14 25.9 41.4 52.3 59.3 64.1 67 .7 70.9 72 . 2 73.7 74 . 9 15 33.0 4 7 . 2 56.5 62 . 8 67.2 70 . 4 72.6 74 .7 76.6 80.8 Christ:mas Creek 1 23.5 41.5 53.4 60.8 65.1 68.3 71.2 73.0 73. 9 73 . 4 2 26.5 42 . 2 54.5 62.3 67 .0 69.6 71.7 73.5 74.2 76.4 3 24.5 41.9 54 . 2 61.0 65.5 68 .5 70. 8 71.5 73 .3 74. 7 4 27. 1 44. 1 55.3 62.8 67. 3 70. 9 73.2 75.0 76.2 76 . 9 5 26.6 42.4 54.3 60.8 64.5 66.0 67.9 66.8 69. 8 70 . 9 6 24 . 7 42.9 53 .3 59.6 60. 7 64.0 67.1 69.5 71.4 72 .2 7 26.4 44.5 56.3 67.0 71.9 75 . 3 77.3 79 . 4 80.8 82 . 0 Cumberland Island 1 16. 5 26.0 38.3 4 7 . 3 53 .5 56. 8 59 .7 62 . 0 62.0 64 .8 Crooked Ri ver 1 24.9 40 . 1 53.2 64.1 70.5 76. 2 79.7 82 . 2 83.7 85.1 73 UPD 8328{10 -87