Oyster growth analysis: a comparison of methods.
Kraeuter, John N.
|Publication:||Name: Journal of Shellfish Research Publisher: National Shellfisheries Association, Inc. Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Zoology and wildlife conservation Copyright: COPYRIGHT 2007 National Shellfisheries Association, Inc. ISSN: 0730-8000|
|Issue:||Date: August, 2007 Source Volume: 26 Source Issue: 2|
|Topic:||Event Code: 310 Science & research Computer Subject: Company growth|
|Product:||Product Code: 0913050 Oysters NAICS Code: 114112 Shellfish Fishing SIC Code: 0913 Shellfish|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
ABSTRACT The increase in disease related mortality has made
managing oyster resources increasingly difficult. In Delaware Bay
sustaining harvest requires specific information on growth rates of
adult oysters on the different beds. We reviewed the literature and
found such information, particularly that depicting oyster growth
directly on subtidal oyster beds, lacking. We used three methods to
determine growth of oysters on Delaware Bay seed beds: measuring the new
growth at the lip of oysters retrieved from the bottom, tethering
individually identifiable oysters on specially designed frames, and
size-at-age information based on ages developed from check marks in
growth lines in the oyster hinge. Measuring new growth on the lip of the
oyster was not accurate. Use of the frames was exact but very labor
intensive and only provided data for the one season. Use of the check
marks in the hinge to estimate age provided a growth history, and was
relatively accurate. Intensive harvesting of oysters appeared to
significantly reduce the accuracy of all techniques. Based on literature
values, it is difficult to determine latitudinal gradients in oyster
growth, but these data indicate more rapid growth in the northern Gulf
of Mexico than in other locals. In general, oysters in higher salinity
portions of the Delaware Bay seed beds grew faster than those in the
lower salinity regions.
KEY WORDS: oyster, Crassostrea virginica, growth, salinity, methods
A large number of studies have provided data on the growth of spat, yearling, and small adult size classes of Eastern oysters (Crassostrea virginica [Gmelin 1791]) (Table 1, Table 2). These efforts often follow the oysters to nearly market (~75 mm) size, and have typically been conducted in trays. There are limited data when oysters are not grown from set, but most studies of these larger oysters (>50 mm) are also often done in trays. It is well known that the use of a tray raises the oyster off the bottom and increases the growth rate. In addition, many earlier studies examined oyster growth in differing terms including weight, volume or meat yield (Butler 1953, Andrews & McHugh 1957, Menzel & Hopkins 1951, Hopkins & Menzel 1952) as well as shell size. Analysis of the growth rate of oysters >50 mm is essential for determining the rate at which submarket oysters grow into market classes at various salinities, and for estimating the potential additional growth that might accrue from transplanting oysters to higher salinity beds. Growth is particularly important in years in which Perkinsus marinus (Mackin et al. 1950) (Dermo) or Haplosporidium nelsoni (Haskin et al. 1966) (MSX) infects a high percentage of oysters in the transplant area, because the number of oysters lost to the disease increases with the salinity (Andrews & Ray 1988, Ford & Haskin 1988). Large numbers of oysters can be lost to the disease, or not reach market quality, if they remain in lower salinity areas, but even larger numbers can be lost when infected individuals are transplanted to higher salinity for additional growth.
Because growth increments of larger oysters can be small relative to the existing shell size, growth can be difficult to measure. We examined growth of large oysters in three ways: (1) growth increment; (2) repeated measurement of known individuals; and (3) measurement of historic growth using lines in the hinge plate. The first two methods provide data only for the particular year in which the measurements are taken. Growth at any location can vary greatly from year to year, and if the historical method can be calibrated it may provide a means of estimating growth over a number of years.
Monthly collections of 100 oysters haphazardly selected from dredge hauls were measured at each of 5 sites (Arnolds, Middle, Cohansey, Shell Rock, and New Beds) along the Delaware Bay salinity gradient each month from April to November 2001 (Fig. 1). Each oyster was measured with an electronic caliper for total height, width, and thickness, and the maximum amount of new growth on the lip of the oyster. Because this latter method relies on the ability to recognize "new growth" two individuals independently measured the same groups of oysters each month. The animals were classified into 10 mm size categories starting at 20 mm, and the growth increment for that size category was estimated by the new growth.
To establish a means of comparison between the "growth increment" and "known individuals" we randomly selected groups of 60 oysters of each size (20 of each size from each location) of the "known individuals" on the frames and measured their size increment.
Four replicate groups of 20 oysters of each size (3 size groups) were collected from three Delaware Bay natural beds (Fig. 1). They were attached to a frame using a fishing leader tether. The center of the frame was a piece of concrete that held the edges of the frame approximately 5 cm off the substrate. The tethers were long enough to allow the oysters to rest on the bottom thus reducing the potential for growth artifacts caused by raising oysters in the water column, but still allowed their retrieval. We used this method of "tethering" oysters in other transplant studies (Kraeuter et al. 2003). Initial measurements were made on each oyster in April, the frames were deployed on the bed from which the oysters were collected and these individual oysters were followed until November when oyster growth ceases in Delaware Bay. Data on growth and mortality were recorded monthly at each site. The initial size groups, 50.8-56.9: 57-63.2; and 63.5-69.6 mm shell height, were selected to reflect those most likely to reach market size in one to two years. Oysters larger than 70 mm were assumed to be of marketable size and no growth information was required. The frames were deployed in April, but oysters on the Shell Rock site had to be replaced in June because the frames from the earlier planting were lost because of intense fishing on the bed. The last measurement provides a cumulative record of that oyster's growth and the data from individual months provide a means to estimate month-to-month growth.
This method utilizes microgrowth lines laid down in the ligostracum (hinge plate) by the oyster during periods of high and low growth to estimate the age (Kent 1988, Palmer & Carriker 1979). We used the methods outlined by Kent (1988) by staining with hematoxylin and then counterstaining with eosin to enhance the contrast between the lines on the hinge.
[FIGURE 1 OMITTED]
To calibrate the growth bands we sampled oysters grown in Delaware Bay at our oyster aquaculture facility (Cape Shore, Fig. 1). Animals of known age were collected from the trays, shells dried, measured and the hinge area was stained. The annual growth lines on the hinges were then counted and these data were compared with the known age of the oysters. Once this was accomplished we selected 25 oysters each month from June to November from each of 5 beds along the salinity gradient for size and age analysis.
Each sampling period on each site bottom water temperature, salinity, dissolved oxygen, pH, and total suspended solids were recorded. Electronic meters were used for temperature, DO and pH. Salinity was evaluated with a refractometer, and suspended solids were collected from 500 mL of water filtered through preweighed glass fiber filters, dried in a 50[degrees]C oven and weighed. In addition, at the each site a temperature probe was attached to the frames with the tethered oysters and set to record every 15 min.
Temperature, pH, dissolved oxygen and total suspended solids, varied only slightly between sites (Table 3). Salinity, as expected, exhibited a gradient. Highest salinity was at New Beds and lowest was at Arnolds. In general, salinity increased from April to November at all stations, and when all data are considered, there was overlap in the salinity range along the entire gradient. Dissolved oxygen ranged from 5.4-9.7 [mg.sup.-1] L and was lowest during the warmest part of the year. The percent oxygen saturation was >80% except for 6 readings (none <70%) which were mostly focused up bay during late August. Total suspended solids for all sites ranged from 20-80 [mg.sup.-1] L except for one sample period at the most up bay station, when it reached 192 [mg.sup.-1] L. Such values are typical for the Delaware Bay oyster bed areas.
There were no significant differences between the increment measurements made on the same 100 oysters by two individuals by month within a bed ("t" test). With the exception of Shell Rock bed, by July most size categories of oysters had growth increments that were equal to the entire growth for the year (Fig. 2). At Shell Rock, maximum growth in the larger size category was not recorded until October (Fig. 2). Within bed there was month to month variation by size category, but by November growth in all size categories was similar (Fig. 2). Between beds, except for the bed in the lowest salinity (Arnolds), growth was similar (Fig. 2). In general, when sufficient numbers of oysters were present within a size category, 95% confidence limits were in the range of [+ or 2] mm, but when fewer than 10 oysters were present in a category, error bars could be very large. Total growth on Arnolds was in the range of 6-10 mm for all sizes and the upper range of the 95% confidence limits was about 13 mm. On all other beds total growth was in the range of 11-16 mm and the upper range of the 95% confidence limits was about 17 mm (Fig. 2). Combining all size categories within a month to yield average growth for the year (Fig. 3) emphasizes two aspects of this method: first, after July (August in the case of New Beds) the measurers were unable to distinguish new growth and second, growth at Shell Rock was significantly lower that would be expected based on its location in the salinity gradient.
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Growth increments were also measured on 20 randomly selected oysters of each size group from the rack experiment (Fig. 4). By November the average oyster growth measured by the "growth increment" method on frames always showed greater growth than was indicated by the change in average height of individuals in the same size group measured at the beginning and end of the experimental period (Table 4). For the largest size group, measuring by growth increment produced significantly greater estimates of oyster growth in all cases (Table 4). Smaller oysters showed the same trend with the increment method indicating greater growth, but these were not significantly different because of the high variability in growth among individual oysters (Table 4).
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Known Individuals (Tethered to Frames)
Mean sizes at initiation (small, medium, large respectively) for each of the beds were Cohansey: 56.0, 60.8, 67.9; Shell Rock: 18.104.22.168, 66.8; New Beds: 54.9, 61.7, 68.8 mm. There were no significant differences between any of the similar size groups from the different beds, but the average of the small, medium and large size groups were significantly different within a bed. Initial analysis indicated that there were no significant differences in growth between the replicates of a size group at a bed so all data for each size group were combined.
Small oysters added significantly more shell length than the large size group on all three beds, but did not differ from the medium sized individuals except for New Beds. Growth was the same for large and medium size individuals within all beds (Fig. 5, Table 4).
Oysters of all size groups showed significantly less growth at the most up bay site (Cohansey) and significantly greater growth at the most down bay site (New Beds) (Table 4, Fig. 5). Growth on Shell Rock was only for the period June through October and thus might have overlapped with that on New Beds if the entire season had been available for estimating growth. If the data are normalized for growth from June to November for Cohansey and New Beds, growth on Cohansey remained significantly lower for all size groups than on the other two beds. The middle size group showed no statistically significant growth difference between Shell Rock and New Beds, but both small and large oysters exhibited significantly greater growth on New Beds.
Mortality was not computed at Shell Rock because of the late deployment of the second group of oysters. Cumulative mortality of oysters on the frames on Cohansey was 20% or less for all size groups, whereas on New Beds mortality exceeded 50% for all sizes groups (Fig. 6). At this higher salinity site, mortality for small and medium oysters was greater than for larger individuals. Although disease level was not evaluated for this study, regular sampling of oysters in October 2001 showed dermo (Perkinsus marinus) prevalence levels of 40, 33, 80, 100, and 95 percent at Arnolds, Middle, Cohansey, Shell Rock and New Beds, respectively. Based on these levels a significant part of the mortality was probably because of dermo disease.
Growth was not uniform throughout the summer months or on individual beds (Fig. 7). The majority of the yearly growth on Cohansey took place in the June to July period. On New Beds the growth was more protracted but peaked in the May to June period, then gradually tapered off through the remainder of the summer and into fall. The May to June growth at Shell Rock may have been affected by the redeployment of frames in early June, but, after that period, the pattern of growth mirrors that of New Beds.
Evaluation of this method used known-age hatchery-reared stocks. All oysters were collected in August 2001. These oysters were produced by our hatchery on Delaware Bay, and they were reared in a rack and bag system on an intertidal flat (spring, summer, and fall) and placed in trays that were attached to floating docks (always submerged) in Cape May harbor for the winter. As such, they experience a greater range in temperature on the intertidal flats than typically experienced by Delaware Bay oysters on natural beds. These conditions made interpreting check marks more difficult than is typical for oysters that remained in one place. The hinge area of the lower valve of the oyster shell was stained and the growth lines in the hinge were counted under a dissecting microscope. In spite of these disadvantages, average age estimates for 5 oysters of each age from 2.5 to age 5.5 y, correctly predicted the year of production (Fig. 8), and the 95% confidence limits ranged from 0.4-0.9 y. Because the shells were measured, the size of the oyster as well as the age are known, the method provides a direct estimate of the size at a particular age.
[FIGURE 5 OMITTED]
The calibrations, mentioned earlier, indicated that the method provided reasonable estimates of age, and we used it to evaluate growth along the salinity gradient. Estimates of the size-at-age were made on individuals collected in conjunction with the dredge-sampled growth-increment studies. These data (Fig. 9) show maximal growth at all sites in the first two years of life. Growth is greatest at the bed with the highest salinity (New Beds) and least at the bed with the lowest salinity (Arnolds). Oysters reach market size (about 70 mm) in 3 y on New Beds and about 5 y on Middle and Cohansey. The data suggest that it would take 5-6 y to reach market size on Shell Rock, but this bed has been intensely harvested for the past 3 y, and it is likely that most fast growing oysters have been removed. This leaves older oysters that have not grown rapidly and may have skewed the results toward smaller size-at-age. New Beds have also been intensely harvested, but heavy mortality from dermo in the past has made oysters scarce and harvest intensity is currently much less than on Shell Rock. Annual growth increments (Fig. 10) based on estimated ages indicate rapid growth during the first two years at all locations on the gradient. Growth after the first two years appears to be 5-10 mm per year, except at the most up bay bed (Arnolds) where oysters continue to grow at about 15 mm per year for 3 y before slowing down. The 95% confidence limits on the growth rate (Fig. 9) generally increase in year 6 and we have not included points beyond that age. The increase in the confidence limits particularly at Cohansey, suggests that the negative growth for that bed in years 5-6 (Fig. 10) is within the confidence limits of the technique.
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It is remarkable that an organism so thoroughly studied as the oyster has such sparse information on growth rates after the first few years of its life, and that most of the available information was collected in tray studies where oysters were raised off the bottom. In addition, there is little data that has been collected along salinity gradients. Shaw (1966) compared growth in high and low salinity water (Chincoteague Bay and the Tred Avon River, MD, respectively, and Paynter & Burreson (1991) compared growth at sites from 8-10, 12-15, and 16-20 ppt, but both were for oysters in trays or racks. There is surprisingly little information on growth rates of oysters on the bottom along a salinity gradient. Shaw (1966) found no differences in growth but higher mortality at the high salinity site. Paynter and Burreson (1991) found greater growth at the high salinity site, but later growth at the high and intermediate sites was retarded by dermo infections. The primary difficulty in obtaining accurate growth information for this species on natural beds is the need to recapture the same individuals for repetitive measurements, particularly when most beds are subtidal. After the first few years, growth rates decrease and oysters cannot reliably be separated into "year classes." We had hoped that the "increment" method would be useful
for the older individuals, but the measurement of "growth increment" by two different individuals did not prove to be reliable. Both individuals measured "growth" in the same manner, and their results were statistically the same, but as the season progressed they were unable to distinguish where the growth interval began. This inability caused a distinct and major over estimate of shell growth. The anomalous data from Shell Rock oysters (Fig. 3) may reflect the heavy harvest pressure on the bed. This pressure may affect the increment method in two ways: larger, faster growing oysters could be removed and/or the constant harvest handling could remove the newly developing shell edge and thus make it difficult to discern recent growth. Because the Shell Rock oyster size anomaly also appears in the size-at-age method, the most reasonable interpretation is that the intense harvest is reducing the estimated growth rate of the oysters remaining on this bed in some fashion.
[FIGURE 10 OMITTED]
Growth of tethered oysters offered the most direct way of evaluating growth of large oysters without the potential effects of placing them in trays, but the method is labor intensive and provides data only for the year in which the measurements are made. Even direct measurements of individual growth such as tethering may be biased in areas with size-selective harvest. If oysters are selected from the bed to establish the experimental population, as we did, and they are residual "slow growers," they may continue slow growth or, conversely, they may exhibit compensatory growth.
In the early 1900s, individuals noticed that some oysters had various bands of shell deposition that appeared to reflect growth events, but Massy (1914) concluded these were not a reliable means to age an oyster. Lutz (1976) and Palmer and Carriker (1979) did not find growth lines in oyster shell, but the latter were able to age oysters by using the lines in the hinge plate (ligostracum). We have attempted to reevaluate this technique. Our data suggest it would allow size-at-age information to be collected if the investigation is conducted cautiously. Establishing that the hinge contains the first year growth line can be difficult because the early stages of oyster growth can become eroded and age can be underestimated. Our data from Shell Rock suggest that intense harvest may cause faster growing oysters to be selectively removed and thus growth rates could be underestimated. Harvest of fast growing individuals would affect size-at-age estimates once oysters reach market size. It would also affect interpretation of any other method that does not isolate oysters from the harvest pressure. Further work on ageing techniques are desirable, and sectioning the shell, though more labor intensive may yield significant improvement in age determination (J. Harding, VIMS, pers. comm.).
Earlier studies, conducted from oysters growing directly on-bottom, and in trays of various kinds often reported very rapid growth rates. We have attempted to extract growth data from published studies and present them based on the size of the oysters at the beginning of the study, and whether they were deployed for <10 mo. (Table 1) or >10 mo. (Table 2) in the field. The 10 mo. break point was somewhat arbitrary, but most studies were either well below the 10-mo period, and encompassed all or a portion of one growing season, or greatly exceeded it. A wide variety of techniques, starting sizes, lengths of time in the field and other variables are present in these data. In spite of all the differences, and with the exception of the first year of growth in the Northern Gulf of Mexico, examination of the data indicates relatively little latitudinal difference in growth rate of oysters. An obvious observation, is that when oysters are retained in the field for >10 mo, monthly growth rate estimates are substantially less than when they are retained for <10 mo. This is primarily because the former data encompass periods when oyster growth is minimal or, in the north, stops entirely.
Data from these Tables 1 and 2 were then separated based on the size of the oysters when the studies were initiated. The resulting summary (Table 5) should be interpreted with caution because there are relatively few studies represented, and some studies dominate some of the size classes. In spite of these caveats, it is clear that monthly rates of oyster growth of any size class derived from data collected for less than 10 mo should not be used to estimate total annual growth because it will result in an overestimate. These short-term data would require some correction term to accommodate for the periods when growth is either greatly reduced or ceases. It would be difficult to derive some simple metric that could be used to correct the short-term data throughout the latitudinal and salinity range of this species. Studies that retained oysters for >10 mo show relatively consistent results, even across the latitudinal gradient (Table 1, Table 5), and clearly represent growth commonly achieved by oysters of varying sizes. It is relatively clear that once oyster reach about 50-60 mm shell length, the growth rate declines substantially.
Our initial purpose for this study was to develop a series of growth curves for larger oysters in Delaware Bay. Dittman, et al. (1998) evaluated the effects of oyster strain origin, year class and age of selected strains of oysters grown in intertidal trays in lower Delaware Bay (Cape Shore) and found highly significant interactions between all three variables. These data indicate that changing conditions can favor one strain for a period of time and then, under alternate conditions, another strain. The cumulative effects of such interactions can provide substantial growth differences through time. We combined data from Dittman et al. (1998) with additional growth data, collected over the years at the same location using the same techniques. These are hatchery reared, tray-raised, selected strains of oysters and thus not directly comparable to the on bottom data from the current study, but they provide a means of bounding the growth rates in Delaware Bay. Based on the size-at-age data (Fig. 11) growth at the most upbay low salinity area (Arnolds) is much lower that that of the down bay intertidal area, and the rate at Arnolds is also lower than that for oysters from the lower area of the natural beds (New Beds). Growth in the higher salinity area is greater even though dermo infection (prevalence and intensity) is much greater. There appears to be intermediate growth at the midportion of the natural beds (Cohansey, Middle, and Shell Rock), but the age-specific data from Shell Rock may have been strongly affected by heavy harvest pressure (2001 landings from this bed were 23,000 bu, whereas only 7,600 bu were landed from the larger New Beds.). As important as the overall growth information, is the rapid growth in the first two years at all locations (Fig. 11), and the rapid drop in growth rate in most sites once the animals reach approximately 50 mm in size.
[FIGURE 11 OMITTED]
Comparison of the data from the intertidal hatchery-produced oysters with studies from other locations (Fig. 12) also show relatively fast growth for the first few years. These data suggest that the initial post set growth rate of oysters from the Gulf of Mexico is higher than for similar age oysters from Chesapeake Bay north. Given the longer growing season in the south this is not unexpected, but we have been unable to find data on oyster growth in the Gulf region beyond the first few years.
To further evaluate the growth of oysters along this gradient we computed Von Bertalanffy growth plots (Fig. 13) for all beds from which we computed growth by the historical method, the two selected hatchery lines grown on the Cape Shore flats and a growth series from Horsehead reef in the James River tributary to Chesapeake Bay (Mann & Evans 2004). For these latter data we averaged the two sets of data presented by Mann and Evans (2004) for growth at the end of each of the years so their curves would match the annual growth from our estimates. We used the maximum size recorded on each bed to provide Linf, set the to (age at which L = 0) at 0.2 mm, and then varied K (the growth constant) until the sum of squares for height was minimized (Table 6). We have retained the usual nomenclature for the Von Bertalanffy calculations, but in all cases have substituted oyster shell height for the Von Bertalanffy length (L) parameter.
Most of the Von Bertalanffy plots (Fig. 13) show a reasonably good fit to the data. The exceptions are the Cohansey and Shell Rock beds. The best Von Bertalanffy plot does not approximate the Cohansey data. We have no explanation for this. The other exception, Shell Rock bed, clearly shows a drop in the observed growth rate relative to the Von Bertalanffy plot beyond year 3. We attribute this to the effects of the intense fishing removing the larger oysters as they near 70 mm. Growth at the James River site is similar to that of the Arnolds-Middle area of Delaware Bay, and given that the salinity in that part of the James is similar to that of the Arnolds--Middle area of Delaware Bay this is not particularly surprising. What is striking is that the growth constant (K) from Middle to New Beds is within the range of 0.2-0.26 and only Arnolds a low salinity end member, and the two hatchery derived rack and bag grown stocks appear to be different. We clearly need more on bottom growth data for oysters along the salinity gradient before we can assess differences across estuaries or latitudinally.
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[FIGURE 13 OMITTED]
Estimating oyster growth by examining the "new" growth at the edge of the shell did not prove to be a reliable technique. Measuring known individuals deployed on the bottom is clearly the best method to obtain accurate data, but this is very labor intensive in subtidal areas and provides data only for the year in question. Use of lines in the hinge can provide growth information across broad areas and over a number of years, but there are a number of caveats that must be applied: the technique requires a means of calibration; not all oysters provide clear growth lines, and thus some cannot be used; and care must be taken in areas of heavy harvest so that the removal of fast growing individuals does not compromise the size-at-age estimates.
Oysters, across their range, have rapid growth rates for the first two to three years and then the rate drops appreciably, but there is remarkably little data on growth of oysters older than 3 y for a variety of reasons. In most locations studies have focused on producing a market oyster and this is about a 3 y-old-individual. It has proven to be difficult to age oysters much older than about 5 y. Extrapolation of annual growth rates derived from studies conducted for less than one year require correction based on local conditions or growth can be greatly overestimated. Growth during the first year or two of life appears to be the largest variable affecting size-at-age. Lastly most studies have focused on areas where oyster growth is relatively rapid rather than examine growth throughout the salinity gradient. In Delaware Bay, there is a clear growth gradient with oysters in higher (mesohaline) salinities growing at a faster rate than those in the lower salinity parts of the system. Whereas the growth clearly correlates with salinity in our system, this should not be interpreted to indicate that salinity is the only variable along this gradient. In Delaware Bay, turbidity and density of oysters on the bed increase as salinity decreases, and there is evidence that food supply may decrease in an up bay direction. Lastly, as compared with our nearest neighbor, Chesapeake Bay, we have higher tidal amplitudes and in the upper part of the bay greater changes caused by freshwater and tidal pulses.
As with any study of this nature a significant number of individuals assisted and Bob Barber, Jess Gandy and Royce Reed deserve special recognition. The study was funded, in part, by funds from the State of New Jersey and the Agriculture Experiment Station of Cook College, Rutgers University.
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JOHN N. KRAEUTER, (1) * SUSAN FORD (1) AND MEAGAN CUMMINGS (2)
(1) Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349; (2) Aqua Survey, Inc., 469 Point Breeze Rd., Flemington, NJ 08822
* Corresponding author. E-mail: Kraeuter@hsrl.rutgers.edu
TABLE 1. Published reports on oyster shell growth. Data are for studies of oysters deployed in the field during the growing season and for periods <10 mo. Data are generally arrayed from smallest to largest initial size and, within an initial size group, from North to South. Initial Size Time Deployed Study Location Container (mm) (Months) Beaufort, NC BT set 2 North Carolina set 2.5 North Carolina set 6 South Carolina set 6.5 Louisiana set 1.5 Terrebonne, LA T set 2.24 Long Island, NY 1.4 1.5 Apalachicola Bay, FL T 3.9 4 Apalachicola Bay, FL T 4.5 7.75 Broadkill River, DE 5 3.8 Chesapeake Bay, VA R 22.5 7 Chesapeake Bay, MD R 22.5 7 Chesapeake Bay, MD B 27.6 6 Terrebonne, LA T 29.45 6 Terrebonne, LA T 30.85 7.4 Long Island, NY R 33 6 Newport River, NC ST 33.5 2.06 Newport River, NC ST 33.6 1.6 Long Island, NY R 34 6 Long Island, NY 34.9 2 Long Island, NY 34.9 6 Chesapeake Bay, MD R 36.5 7 Terrebonne, LA T 40.89 6.3 Newport River, NC ST 53.3 2.03 Apalachicola Bay, FL B 60.6 2.8 Apalachicola Bay, FL B 60.6 2.8 Long Island, NY L 66.9 6 Long Island, NY L 67.5 6 Apalachicola Bay, FL B 67.8 2.93 Delaware Bay, NJ B 68.5 5 Delaware Bay, NJ B 68.6 9 Long Island, NY L 69 6 Milford, CT ST 69.5 4.75 Long Island, NY L 70.2 6 Delaware Bay, NJ B 74.5 9 Delaware Bay, NJ B 74.6 5 Newport River, NC ST 75.7 2.03 Apalachicola Bay, FL B 79 2.93 Milford, CT ST 88 7.75 Milford, CT T 88.2 8 Delaware Bay, NJ B 89.4 9 Delaware Bay, NJ B 89.5 5 Barnegat Bay, NJ 93.2 4.4 Great Bay, NJ 97.8 4.1 Total Growth Monthly Growth Study Location (mm) (mm/mo) Beaufort, NC 25.4 12.7 North Carolina 38.1 15.24 North Carolina 76.2 12.7 South Carolina 50.8 7.82 Louisiana 25.4 16.93 Terrebonne, LA 16.2 7.29 Long Island, NY 74.8 49.87 Apalachicola Bay, FL 62.3 15.58 Apalachicola Bay, FL 99.5 12.84 Broadkill River, DE 42.4 11.16 Chesapeake Bay, VA 70.5 10.07 Chesapeake Bay, MD 37.5 5.36 Chesapeake Bay, MD 17.2 2.87 Terrebonne, LA 28.4 4.73 Terrebonne, LA 30 4.04 Long Island, NY 26 4.33 Newport River, NC 9.5 4.68 Newport River, NC 44.2 27.63 Long Island, NY 36 6 Long Island, NY 41.3 20.65 Long Island, NY 41.3 6.88 Chesapeake Bay, MD 26.5 3.79 Terrebonne, LA 8.1 1.28 Newport River, NC 6 2.96 Apalachicola Bay, FL 17.4 6.21 Apalachicola Bay, FL 4.9 1.75 Long Island, NY 7.5 1.25 Long Island, NY 9.7 1.62 Apalachicola Bay, FL 8.2 2.8 Delaware Bay, NJ 3.9 0.78 Delaware Bay, NJ 4.7 0.52 Long Island, NY 9.9 1.65 Milford, CT 22.2 4.67 Long Island, NY 10.9 1.82 Delaware Bay, NJ 7.1 0.79 Delaware Bay, NJ 4.8 0.96 Newport River, NC 1 0.49 Apalachicola Bay, FL 8.6 2.94 Milford, CT 26.6 3.43 Milford, CT 22.6 2.83 Delaware Bay, NJ 8.1 0.9 Delaware Bay, NJ 5.7 1.14 Barnegat Bay, NJ 1.8 0.4 Great Bay, NJ 1.8 0.44 Study Location Reference Beaufort, NC Osborn, 1883 North Carolina Moore, 1905 North Carolina Higgins, 1940 South Carolina Moore, 1905 Louisiana Moore, 1899 Terrebonne, LA Menzel and Hopkins, 1951 Long Island, NY Moore, 1905 Apalachicola Bay, FL Ingle and Dawson, 1950 Apalachicola Bay, FL Ingle, 1950 Broadkill River, DE Palmer and Carriker, 1979 Chesapeake Bay, VA Paynter and Burreson, 1991 Chesapeake Bay, MD Paynter and Burreson, 1991 Chesapeake Bay, MD Shaw, 1966 Terrebonne, LA Menzel and Hopkins, 1951 Terrebonne, LA Menzel and Hopkins, 1951 Long Island, NY Matthiessen, 1989 Newport River, NC Glaser, 1905 Newport River, NC Glaser, 1905 Long Island, NY Matthiessen, 1989 Long Island, NY Moore, 1905 Long Island, NY Moore, 1905 Chesapeake Bay, MD Paynter and Burreson, 1991 Terrebonne, LA Menzel and Hopkins, 1951 Newport River, NC Glaser, 1905 Apalachicola Bay, FL Ingle and Dawson, 1950 Apalachicola Bay, FL Ingle and Dawson, 1950 Long Island, NY Matthiessen, 1989 Long Island, NY Matthiessen, 1989 Apalachicola Bay, FL Ingle and Dawson, 1950 Delaware Bay, NJ Kraeuter et al., 2003 Delaware Bay, NJ Kraeuter et al., 2003 Long Island, NY Matthiessen, 1989 Milford, CT Loosanoff and Nomejko, 1955 Long Island, NY Matthiessen, 1989 Delaware Bay, NJ Kraeuter et al., 2003 Delaware Bay, NJ Kraeuter et al., 2003 Newport River, NC Glaser, 1905 Apalachicola Bay, FL Ingle and Dawson, 1950 Milford, CT Loosanoff and Nomejko, 1955 Milford, CT Loosanoff and Nomejko, 1949 Delaware Bay, NJ Kraeuter et al., 2003 Delaware Bay, NJ Kraeuter et al., 2003 Barnegat Bay, NJ Nelson, 1921 Great Bay, NJ Nelson, 1921 B, oysters on bottom; BT, tray on the bottom; L, Line hung from surface; R, rafts or floating trays; ST, Suspended trays; T, Trays mounted on the bottom. Blank spaces indicate the information was not reported in sufficient detail to determine the means of deployment. TABLE 2. Published reports on oyster shell growth. Data are for studies of oysters deployed in the field for > 10 mo. Data are generally arrayed from smallest to largest initial size and, then within an initial size group, from North to South. Container codes are in Table 1. Initial Size Time Deployed Study Location Container (mm) (Months) Chatham, MA R set 14 Chatham, MA R set 25 Chatham, MA R set 25 Chatham, MA B set 25 Chatham, MA L set 29 Milford, CT set 25? St. Jerome Creek, MD set 23 Chesapeake Bay set 24 James River, VA BT set 36 Louisiana set 10.3 Terrebonne, LA T set 23.1 Louisiana set 18 Terrebonne, LA ST set 24 Aransas Pass, TX set 11 Texas set 12 Galveston Bay, TX BT set 18 Galveston Bay, TX B set 12 Galveston Bay, TX B set 24 Galveston Bay, TX B set 36 Long Island, NY 2 48 Pensacola, FL 5 18 Pensacola, FL 5 30 Pensacola, FL 5 48 Charleston Area, SC 5 18 Charleston Area, SC 5 30 Charleston Area, SC 5 48 Chesapeake Bay, MD B 5 26 Chesapeake Bay, MD B 5 76 Chesapeake Bay, MD 5 60 Chesapeake Bay, MD B 5 39 Chesapeake Bay, MD B 5 39 Chesapeake Bay, MD 5 30 Chesapeake Bay, MD B 5 30 Chesapeake Bay, MD B 5 24 Chesapeake Bay, MD B 5 21 Chesapeake Bay, MD B 5 21 Chesapeake Bay, MD 5 18 Chesapeake Bay, MD B 5 18 Chesapeake Bay, MD B 5 17 Long Island, NY 5 80 Long Island, NY 5 52 Long Island, NY 5 42 Canada, PEI 5 84 Canada, PEI 5 66 Canada, PEI 5 48 Canada 5 24 Canada, NB R 7.8 40 Canada, NB R 8.5 40 Chesapeake Bay, MD R 9 16 Chesapeake Bay, MD R 9 16 Pensacola, FL 16 36 Pensacola, FL 16 12 Chesapeake Bay, VA ST 19 12 Chesapeake Bay, MD ST 25 19 Terrebonne, LA T 26.8 20 Chincoteague Bay, MD ST 28.6 19 Chesapeake Bay, VA ST 39 12 Terrebonne, LA T 42.45 12 Chesapeake Bay, MD ST 46 60 Chesapeake Bay, MD T 46 24 Terrebonne, LA ST 47 14.5 Chesapeake Bay, MD ST 48 60 Chesapeake Bay, MD T 48 24 Terrebonne, LA ST 49 16 Terrebonne, LA ST 53 14.5 Chesapeake Bay, VA ST 54 12 Terrebonne, LA T 54.14 12 Pensacola, FL 57 12 Terrebonne, LA T 58.89 12 Chesapeake Bay, MD ST 67 60 Chesapeake Bay, MD ST 67 60 Chesapeake Bay, MD T 67 24 Chesapeake Bay, MD T 67 24 Pensacola, FL 68 12 Chesapeake Bay, VA ST 70 12 Chincoteague Bay, MD T 73 12 Chesapeake Bay, VA ST 84 12 Terrebonne, LA T 84.5 12 Barnegat Bay, NJ 85 12 Chesapeake Bay, VA ST 91 12 Chesapeake Bay, VA ST 91 12 Great Bay, NJ 93.30 12 Total Growth Monthly Growth Study Location (mm) (mm/mo) Chatham, MA 67 4.79 Chatham, MA 72 2.88 Chatham, MA 88 3.52 Chatham, MA 50 2 Chatham, MA 91.4 3.15 Milford, CT 78 3.12 St. Jerome Creek, MD 69.85 3.03 Chesapeake Bay 79.4 3.31 James River, VA 55.6 1.54 Louisiana 78.7 7.64 Terrebonne, LA 80.8 3.5 Louisiana 88.9 4.94 Terrebonne, LA 95 3.96 Aransas Pass, TX 65 5.91 Texas 94 7.83 Galveston Bay, TX 87 4.83 Galveston Bay, TX 32.3 2.69 Galveston Bay, TX 61.8 2.58 Galveston Bay, TX 78.6 2.18 Long Island, NY 112.3 2.34 Pensacola, FL 71.2 3.96 Pensacola, FL 71.2 2.37 Pensacola, FL 71.2 1.48 Charleston Area, SC 71.2 3.96 Charleston Area, SC 71.2 2.37 Charleston Area, SC 71.2 1.48 Chesapeake Bay, MD 78 3 Chesapeake Bay, MD 36 1.97 Chesapeake Bay, MD 71.2 1.19 Chesapeake Bay, MD 79 2.03 Chesapeake Bay, MD 73 1.87 Chesapeake Bay, MD 71.2 2.37 Chesapeake Bay, MD 55.5 1.85 Chesapeake Bay, MD 64 2.67 Chesapeake Bay, MD 44 2.1 Chesapeake Bay, MD 43 2.05 Chesapeake Bay, MD 71.2 3.96 Chesapeake Bay, MD 55 3.06 Chesapeake Bay, MD 33 1.91 Long Island, NY 71.2 0.89 Long Island, NY 71.2 1.37 Long Island, NY 71.2 1.7 Canada, PEI 71.2 0.85 Canada, PEI 71.2 1.08 Canada, PEI 71.2 1.48 Canada 45.8 1.91 Canada, NB 49.9 1.25 Canada, NB 58.3 1.46 Chesapeake Bay, MD 89 5.56 Chesapeake Bay, MD 78 4.88 Pensacola, FL 72 2 Pensacola, FL 18 1.5 Chesapeake Bay, VA 48 4 Chesapeake Bay, MD 55 3.06 Terrebonne, LA 63.3 3.17 Chincoteague Bay, MD 49.3 2.6 Chesapeake Bay, VA 39 3.25 Terrebonne, LA 24.7 2.06 Chesapeake Bay, MD 46 0.77 Chesapeake Bay, MD 39 1.63 Terrebonne, LA 42 2.9 Chesapeake Bay, MD 30 0.5 Chesapeake Bay, MD 25 1.04 Terrebonne, LA 46 2.88 Terrebonne, LA 21 1.45 Chesapeake Bay, VA 35 2.92 Terrebonne, LA 26.7 2.22 Pensacola, FL 2 0.17 Terrebonne, LA 19 1.59 Chesapeake Bay, MD 23 0.38 Chesapeake Bay, MD 12 0.2 Chesapeake Bay, MD 25 1.04 Chesapeake Bay, MD 16 0.67 Pensacola, FL 0 0 Chesapeake Bay, VA 26 2.17 Chincoteague Bay, MD 45 3.75 Chesapeake Bay, VA 12 1 Terrebonne, LA 12 1 Barnegat Bay, NJ 2.1 0.17 Chesapeake Bay, VA 12 1 Chesapeake Bay, VA 6 0.5 Great Bay, NJ 2 0.17 Study Location Reference Chatham, MA Shaw, 1962 Chatham, MA Shaw, 1962 Chatham, MA Shaw, 1962 Chatham, MA Shaw, 1962 Chatham, MA Shaw, 1963 *** Milford, CT Loosanoff, 1946 from Shaw, 1962 St. Jerome Creek, MD Ryder, 1884 Chesapeake Bay Moore, 1905 James River, VA Mann and Evans, 2004 Louisiana Gunther, 1951 Terrebonne, LA Moore, 1899 Louisiana Menzel and Hopkins, 1951 Terrebonne, LA Menzel and Hopkins, 1955 Aransas Pass, TX Menzel, 1955 Texas Gunther, 1951 Galveston Bay, TX Moore and Trent, 1971 Galveston Bay, TX Hofstetter, 1963 Galveston Bay, TX Hofstetter, 1963 Galveston Bay, TX Hofstetter, 1963 Long Island, NY Churchill, 1921 Pensacola, FL Butler, 1953 * Pensacola, FL Butler, 1953 * Pensacola, FL Butler, 1953 * Charleston Area, SC Butler, 1953 * Charleston Area, SC Butler, 1953 * Charleston Area, SC Butler, 1953 * Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Butler, 1953 * Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Butler, 1953 * Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Butler, 1953 * Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Long Island, NY Butler, 1953 * Long Island, NY Butler, 1953 * Long Island, NY Butler, 1953 * Canada, PEI Butler, 1953 * Canada, PEI Butler, 1953 * Canada, PEI Butler, 1953 * Canada Stafford, 1913 Canada, NB Mallet and Haley, 1983 Canada, NB Mallet and Haley, 1983 Chesapeake Bay, MD Paynter and DeMichele, 1990 Chesapeake Bay, MD Paynter and DeMichele, 1990 Pensacola, FL Butler, 1952 * Pensacola, FL Butler, 1952 * Chesapeake Bay, VA McHugh and Andrews, 1955 Chesapeake Bay, MD Shaw, 1966 Terrebonne, LA Menzel and Hopkins, 1951 Chincoteague Bay, MD Shaw, 1966 Chesapeake Bay, VA McHugh and Andrews, 1955 Terrebonne, LA Menzel and Hopkins, 1951 Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1949 Terrebonne, LA Menzel and Hopkins, 1955 Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1949 Terrebonne, LA Menzel and Hopkins, 1955 Terrebonne, LA Menzel and Hopkins, 1955 Chesapeake Bay, VA McHugh and Andrews, 1955 Terrebonne, LA Menzel and Hopkins, 1951 Pensacola, FL Butler, 1952 * Terrebonne, LA Menzel and Hopkins, 1951 Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1952 ** Chesapeake Bay, MD Beaven, 1949 Chesapeake Bay, MD Beaven_1949 Pensacola, FL Butler, 1952 * Chesapeake Bay, VA McHugh and Andrews, 1955 Chincoteague Bay, MD Beaven, 1949 Chesapeake Bay, VA Andrews and McHugh, 1956 Terrebonne, LA Menzel and Hopkins, 1951 Barnegat Bay, NJ Nelson, 1922 Chesapeake Bay, VA Andrews and McHugh, 1956 Chesapeake Bay, VA McHugh and Andrews, 1955 Great Bay, NJ Nelson, 1922 * Butler (1953) gives poor, average and good conditions, and no methods are provided. So these can only be considered to be estimates. ** Beaven (1952) data from suspended trays was for 5 y, but growth was nearly static after the first 15 mo. *** Shaw (1963) compared oysters from 4 different areas all grown at the same site, and the data used is the mean of these four groups (range = 82.9-99.5 mm). Data from Hofstetter (1963) were picked off the size frequency figures and averaged for the entire bay. TABLE 3. Temperature, salinity, pH, dissolved oxygen (DO, mg/1) and total suspended solids (TSS, mg/L) for 5 Delaware Bay oyster beds. Beds arranged from up bay (Arnolds) to down bay (New Beds). Shell New Arnolds Middle Cohansey Rock Beds Temp ([degrees]C) High 26.8 26.4 26.7 26.2 26.2 Low 11.7 11.5 11.5 11.2 11.2 Salinity High 15 21 21 22 23 Low 5 7.5 10 12 14 pH High 8.1 8.2 8.1 8.6 8.6 Low 7.3 7.5 7.6 7.6 7.7 DO ([mg.sup.-1]L) High 9.7 9.6 9.7 9.6 9.4 Low 5.4 5.8 5.7 7.4 5.6 TSS ([mg.sup.-1]L) High 192 65 65.2 84.8 65.8 Low 17.6 28.8 18.4 13.5 23.4 TABLE 4. Mean growth (mm) of 3 size groups of tethered oysters (known) from April to November (Cohansey and New Beds) and June to November (Shell Rock) compared with "growth increment" estimates of a random selection of the same oysters. Similar letters indicate means that are not significantly different within a column (One way ANOVA, Tukey HSD test). In all cases, including those that were not significantly different within a column, the "increment" method produced a larger growth estimate than indicated by "measure" of known individual oysters. Cohansey Shell Rock Initial size Measured Increment Measured Increment 50.8-56.9 4.3 (a) 6.4 (a) 9.6 (a) 12.1 (a) 57.0-63.2 2.8 (a b) 5.7 (a) 7.3 (a b) 9.1 (a) 63.5-69.6 1.8 (b) 5.1 (a) 6.3 (b) 9.3 (a) New Beds Initial size Measured Increment 50.8-56.9 15.1 (a) 18.1 (a) 57.0-63.2 10.9 (b) 13.4 (b) 63.5-69.6 10.9 (b) 14.9 (a b) TABLE 5. Mean monthly growth for oysters from Tables 1 and 2 grouped by initial size and length of deployment. Top data are the computed monthly growth (mm), bottom data are the same growth x12 to provide annual rates. The 95% confidence limits for the data are provided in () with the monthly growth data. Initial Size (mm) Set to 10 11-30 31-50 Monthly Growth Out < 10 Months 10.74 (2.59) 5.41 (3.43) 6.97 (7.15) Out > 10 Months 2.78 (0.46) 2.73 (0.63) 2.02 (1.08) Annual Growth Out < 10 Months 128.88 64.97 83.64 Out > 10 Months 33.36 32.71 24.26 Initial Size (mm) 51-70 >70 Monthly Growth Out < 10 Months 1.99 (0.71) 1.73 (0.89) Out > 10 Months 1.30 (0.57) 0.84 (0.5) Annual Growth Out < 10 Months 23.83 20.81 Out > 10 Months 15.62 10.07 TABLE 6. Von Bertalanffy growth parameters for oysters collected from Delaware Bay seed beds and analyzed by the historical growth method (see text). Additional groups are selected lines of hatchery reared stocks from Delaware Bay (DB) and Long Island Sound (LI) reared in Delaware Bay for many generations and data provided by Mann and Evans (2004) (M&E) from the James River, VA. Linf = Field observed asymptotic height, to = age at which height (L) = 0, K = computed growth constant, and y = estimated years to reach 70 mm. Arn = Arnolds, Mid = Middle, Coh = Cohansey, Shr = Shellrock, New = New Beds. Arn Mid Coh Shr New M&E DB LI [L.sub.inf] 110 125 125 125 140 120 140 140 [t.sub.0] 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 K 0.175 0.20 0.26 0.25 0.23 0.20 0.275 0.346 y 6.0 4.5 4.5 3.5 3.0 5.5 2.5 2.5
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