ML20033A178
| ML20033A178 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/31/1981 |
| From: | NORMANDEAU ASSOCIATES, INC. |
| To: | |
| Shared Package | |
| ML20033A174 | List:
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| References | |
| R-366, XII-1, NUDOCS 8111240825 | |
| Download: ML20033A178 (66) | |
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{{#Wiki_filter:-- I I I I SEABROOK ENVIRONMENTAL STUDIES 1980 SOFT-SHELL CLAM, MYA ARE3 ARIA STUDY TECHNICAL REPORT XII-1 lI l Pror'osed for I PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE Manchester, New Hampshire I I by NORMANDEAU ASSOCIATES, INC. Bedford, New Hampshire I R-366 I March 1981 8111240825 811118 I PDR ADOCK 05000443
I t f TABLE OF CONTENTS il 1 PAGE i 1 l
1.0 INTRODUCTION
j 2 2.0 METHODS AND MATERIALS. i 2.1 LARVAE TOWS 2 2.2 SPAT SURVEYS. 4 i 7 i 2.3 ADULT SURVEYS 2.4 GREEN CPAB (CARCINUS MAENAS) TRAPPING. 9 2.5 HISTOLOGICAL STUDY OF GONADAL CONDITION 9 I I l 3.0 RESULTS. 11 i 3.1 PLANKTONIC LARVAE 11 j 3.1.1 Temporal Distribation. 11 3.1.2 Spatial Distribution. 11 15 3.1.3 Species Composition. 3.2 AREAWIDE SPAT AND JUVENILE CLAM SURVEYS 15 3.3 HAMPTON HARBOR SOFT-SHELL SURVEYS 15 3.3.1 Population Density Trends by Shell 15 Size Categories................ 20 3.3.2 Standing Crop. 26 3.4 GREEN CRAB, CARCINUS MAENAS, TRAP CATCHES...... 3.5 SOFT-SHELL CLAM REPRODUCTIVE CYCLE. 30 I 32 4.0 DISCUSSION........................ 32 4.1 PLANKTCNIC LARVAE SPATIAL DISTRIBUTION. 4.2 TEMPORAL RELATIONSHIPS: LARVAL SWARMING AND 32 REPRODUCTIVE CYCLE. 33 4.3 LARVAL ABUNDANCE AND SPATFALL. 33 4.4 BIVALVE MOLLUSCS SPECIES COMPOSITION. I 4.5 GREEN CRAB CATCHES IN HAMPTON HARBOR AND SOFT-SHELL 35 STANDING CROP I ii 1
~... _. k -i PAGE 5.0 S UPS.ARY. 39 4 6.0 LITERATURE CITED 41 APPENDICES 44 .I 1 l l j l 4 I I l i t I. I E h iii I
LIST OF FIGURES PAGE 1. Soft-shell clam, Mya Arenaria, and green crab, Carcinus maenus sampling stations. 3 2. Spat study sites. 5 4 3. 1-mm size class Jength-frequency distribution of Mya arenaria collected October 1980. 16 4. 5-mm class length-density distribution of Mya arenaria juveniles and adults, comparing November 1978 through 1980 survevs in Hampton Harbor. 21 5. Size-frequency distribution of Carcinus maenas catch at Flat #2 in Hampton Harbor. 22 6. Means of daily minimum winter (February and March) water temperatures off Hampton Beach, New Hampshire. 37 l I e I I I I iv f
I i LIST CF TABLES PAGE 1. Clam spat sampling effort. 6 2. Clam gonad sampling effort 10 3. Densities (per m ) of unboned M. arenaria veligers collected at the cooling water intake site (I4) 1980 12 4. Densities (per m ) of umboned M. arenaria veligers collected on selected dates and at selected stations in the vicinity of Hampton-Seabrook estuary. 13 5. Percent composition and total abundance of bivalve umboned veligers in oblique net tows at I (Intake Site) 17 4 6. Young-of-the-year (1-13 mm) and juvenile (13 to 42 mm) soft-clam densities (per f t') in potentially productive areas of three northern New England estuaries 19 7. Summary of Mya arenaria population densities, annual November survey. 23 8. Annual survey standing crop estimates. 25 9. Estimates of " harvestable" standing crop 27 10. Estimates of clam flat productive area (1) in Hampton-Seabrook estuary..................... 28 11. Selected C:. maenas catch statistics 1977-1980. 29 ( 12. Results of histological study of gonadal condition.... 31 13. Comparison of M. arenaria umboned larval abundance off Hampton Beach with young-of-the-year spat densities in Hampton Harbor. 34 14. Recent history of the standing crop of adult Mya arenaria in Hampton Harbor. 36 ll. v
1.0 INTRODL' TION Soft-shell clams, Mya arenaria, in Hampton-Seabrook Estuary have been the subjec* of extensive inve.stigation for the past ten years or more (NAI 1971 1972a, I', no, 1972c, 1973, 1974, 1975a, 1975b, 1976a, 1976b, 1977, 197d, 1979, 1981). Temporal changes in population densities and standing crop have been monitored, as have trends in spatial and temporal distribution of the pelagic larvae during the summer months. Catch records of the green crab, Carcinus maenas, a major predator of soft-shell clams in New Hampshire have been maintained since the summer of 1977; in 1978, a study of the reproductive cycle in Hampton-Seabrook clams was reinstated almost eight years after the first reproduction investigation (NAI, 1971). All of these data have bean accumulated to provide a baseline for assessing impact of Seabrook Station's once-through cooling water system which, when operating, will draw from and return seawater to nearshore waters off Hampton Beach, New Hampshire. Direct impact on soft-shell clam resources may occur through entrainment of the pelagic larvae. However, since populations of both soft-shell clams and green crabs have been shown to respond to climatic temperature change (Welsh, 196 9, Dow 1977), the full ran9e of the soft-shell clams' life history is l being studied, including: gonad development, larval abundance, spat l l settlement, recruitment of harvestable stocks, and relative abundance of green crabs (a principal non-human predator; Dow and Wallace, 1961; j Welch, 1969, 1975). I
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2 I 2.0 ME"rHODS AND MATERIALS f 2.1 LARVAE TOWS To monitor temporal distribution of Mya arenaria larvae in the vicinity of the Seabrook Station cooling water intake (Figure 1), duplicate two minute, volique net tows were made approximately twice weekly from 17 June to 16 October; weekly tows were takea from 16 April through 9 June and from 20 October through 3 November when larvae were found to be scarce or absent. A O.5 m diameter No. 20 (73 um) mesh net, with a 10 lb. depressor attached, was towed at approximately 1/2 knot. The net was lowered to a depth of approximately 13 m (43 feet), in the first minute and returned to the surface after a second minute had elapsed ending the tow. A General Oceanics flow meter was used to record the = volume of water passing through the net; in practice, this volume ranged from 4 to 11 m per tow, typically averaging 7 m per tow. Upon recovery, net contents were thoroughly rinsed into a 1/2 gallon glass jar. I To separate the live bivalve larvae from the bulk of the plankton, in the laboratory the sample was transferred to 1000 ml dispensing burettes and the contents allowed to settle for 5-12 minutes. The relatively high density of the shells allowed the bivalves to rapidly accumulate at the bottom of the burette column, and to be withdrawn for um identification and enumeration. Tne entire sample concentrate containing the bivalves was enumerated for umboned (length 145-320 um) Mya arenaria larvae except when this species was particularly abundant. In this event, the bivalve larvae were concentrated by a swirling motion, into the center of a round, 100 mm diameter, plastic culture dish. The resulting concentration of larvae was carefully divided into visually equal quadrants using a camel's hair probe, viewing the operation through a dissecting nicroscope at approximately 30x; two diagonally opposed quadrants were than enumerated. The same splitting technique was also used to reduce the amount of larvae, representing other bivalve species, to sample fractions containing a total of 200 to 600 individuals. Depending on original
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.G is so s'c 90 t 4t'52'- 3 l l l 48' 70* 46' 70*5 0' A Larvae tow ctations O Clam flats x Green crab trap stations Figure 1. Soft-shell clam, Myc crencric, and green crab, Carcinus rcenns' sampling stations. Seabrook !@c crencric Study,1980.
4 (i.e., field) population densities, this required from one to four successive operations consisting of concentrating the larvae into the center of the dish and then separating and extracting a quadrant. In all cases, two sample fractions were enumerated from each sample, each fraction having originated as one of two diagonally opposite quadrants in the initial (whole) sample. Princ.1 pal references used as aids in identifying larvae to species were: Sullivan (1948), Culliney (1974), de Schweinitz and Lutz (1976) and Savage and Goldberg (1976). With few exceptions, only um-boned veligers were identified and enumerated. Abundances of M_. arenaria straight hinge veligers were noted only when their identity was reason-E ably obvious because of the large numbers involved and the paucity of straight hinge veligers of other species. On those dates when the M. arenaria umbone veliger population density was found to exceed 50 per m, a special towing program was carried out to: 1) define the onshore / offshore distribution of M_. arenaria larvae in the intake vicinity and 2) compare open coastal and Hampton Harbor larval population densities. Oblique tows were made at 1/2-nautical mile intervals along a transect running east to west through the intake site, at the entrance to Hampton Harbor, and at a station to th ' south of the Harbor entrance; in Hampton Harbor inlet, and outside the entrance, oblique tows were made on both high and low slack tides (Figure 1). Sample analysis procedures were as described above. A series of distribution free median tests (Conover 1971) were computed to investigate spatial distribution patterns. 2.2 SPAT SURVEYS To compare population densities of spat and seed clams, periodic surveys were conducted on Hampton Harbor Flats (Figure 1 and Table 1) and on flats in two adjacent estuaries, in northern Massa-chusetts anc' southern Maine (Figure 2 and Table 1). In the April, July and early October surveys, the stations were fixed; once established (on
5 I 4 OGUNOUIT 30.ACH I I JJ YORK RIVER N ( i I '4 l w _RTSMOUTH LITTLE HAR50P l HAMPTON-SEABROOK ISLES OF.g d ESTUARY SHOALS \\,'T I \\ l -.) .M:)~ ' .O l / y p./'~ \\ l [ AggA STUDY MERRIMACK l _ O'8 y,g. -u. .l [& PLUM ISLAND O f SouNo _/ Q NAUTICAL MILES JQ? i .,....? i Figure 2. Spat study sites. Seabrcok lrga crere:c Study,1980. I ~
6 TABLE 1. CLAM SPAT SAMPLING EFFORT. SEABROOK MYA ARENARIA STUDY,1980. a. FIXED STATIONS NO. OF LOCATION STATIONS DATES Plum Island Sound, MA 5 6 Apr, 2 Jul, 1 Oct Middle Ground 3 Lufkin's Flat 2 Nut Shoal I Hampton H3.rbor, NH Flat 2 5 3 Apr, 1 Jul, 2 Oct Flat 4 5 Southern Maine Ogunquit Beach 10 7 Apr, 3 Jul, 3 Oct b. RAND 0M STATIONS NO. OF LOCATION STATIONS DATES SPAT ADULT Hampton Harbor, NH F'st 1 19 30 25, 28 Oct c'lat 2 25 40 24 Oct Flat 3 25 40 23 Oct Flat 4 25 32 27 Oct Flat 5 20 42 20 Oct I I
7 the basis of prei.minary evidence of high productivity), the same general locality was resampled with each survey. Using a section of PVC plastic pipe, three sediment cores four inches in diameter, and four inches deep, were extracted at each collection site. Sediments from these core samples were washed through a 1 mm mesh screen and the M_. arenaria spat picked from the screen with forceps. After transfer to small fingerbowls, the spat from each core sample were enumerated and I measured to the nearest 1 mm. Spat samples were also obtained as described above, during the annual Hampton-Seabrook clam flat survey in late October; however, the stations (Table 1) were chosen at rc.ndom from stations designated for sampling adult clam populations. While the fixed station program, with I emphasis on high yield locations, gave relative estimates of temporal and geographical distribution, the annual sampling program in late October provided better estimates of spat densities for the five major I Hampton-Seabrook flats, including areas less favorable for spat settle-ment. 2.3 ADULT SURVEYS As in past years, the five largest harbor flats were each surveyed in the autumn (late October) for adult clams (Figure 1). Aerial photographs, taken in August 1980 at mean low water, were used to construct sampling charts as in the three previous surveys. Acreage measurements were provided by the aerial survey contractor, em-ploying the "stereotemplate laydown" procedure which is standard for the preparation of tax base maps. The maximum error in computed flat acre-age has been estimated by the contractor to be approximstely 2-3%. Statistical evaluation of previous survey data indicated that the sampling protocol instituted in 1976 to reduce unproductive sampling (the "no-holes" protocol) produced potentially biased estimates of M. arenaria abundance. Accordingly, a total random sampling protocol was I I
I 8 instituted in 1980. Results of a "wcrst case" comparison between the two methods (utilizing 1980 data) indicate that the "no-holes" protocol consistently overestimated soft-shell clam abundance in the 1980 data (Appendix 7.1). To determine' the nu-ter of (totally random) sampling stations needed on each flat to adequately characterize soft-shell clam popula-tions, statistical power analysis (Sokal and Rohlf, 1969) was performed on the previous years (1979) data (NAI, 1981). Adequacy was defined as the ability to detect a real 50% change in mean clam density per flat with 30% confidence ( 5 0 % $c, a=0.10). Flats 2, 3, 5 were shown to g require a nurter of sampling statiors well beyond the scope of these 5l studies in order to meet this criterion for adequacy; alternatively, a judgement was made to sample at least 40 stations on each of these flats. For Flats 1 and 4, a range of 25 to 30 stations was determined to provide statistically adequate data. l To select the sampling stations, rectangular (x, y) coordin-ates were plotted on charts of each flat and nodes, or intersecting points, chosen at random (using a table of random numbers) until the final quota of stations was attained. In t* e field, stations were located by compass bearing and distan.:e from a predetermined central reference point. Seven of the randcmly generated stations for F'at 4 i and two for Flat 5 fell in areas occupied by dense mussel beds; because the sunstrate around mussel beds tends to be very silty (i.e. unsuitable for sand-dwelling molluscs) these were not approached, but were assumed to be devoid of soft-shell clams. l To delineate the sample area, a frame, two feet by one foot, was placed on the substrate, with the left-hand corner of the frame at t the investigator's right foot. The substrate surface, outlined by the I inner edges of the frame, was carefully inspected for evidence of siphon holes, and then dug to a depth of about 16 inches. Juvenile and adult soft-shell clams (shell length > 25 mm) found during excavation, or in the spoil, were picked out and placed in a plastic bag along with a tag identifying the station and flat number. In the laboratory, class were tallied and measured for shell length to the nearest 1 5 i l
9 Individual sample counts and shell measurements were converted to biomass estimates (bushels per acre) using a table of clam volumes provided in Belding (1930). To express results in terms of standing crop (bushels of harvestable clams on the entire flat), the biomass I estimate was multiplied by flat surface area (acres). I 2.4 GREEN CRAB (CARCINUS MAENAS) TRAPPING I Carcinas maenas were trapped twice a month, in January and I from April through December, at four stations around the perimeter of Flat 42 (Figure 1). Two 13 mm mesh, baited traps were set at each station so that they were awash at MLW. After fishing for 24 hours they were pulled in and the catch enumerated, sized and sexed. Total weight of Carcinas maenas from cach trap was also recorded. 2.5 HISTOLOGICAL STUDY CF GONADAL CONDITION On the dates shown in Table 2 approximately 25 11. arenaria, with a minimum shell length of 51 mm, were collected by clam fork from Hampton Harbor flats. The visceral mass (gonad, liver, gastrointestinal tract, ets.) was taken out and fixed in 10% buffered formalin. Blocks cf gonadal tissue were dissected from each specimen and sent to Path Laboratories, Portsmouth, New Hampshire, where the blocks were: 1) dehydrated in alcohol and infiltrated (Armed Forces Institute of Pathology, 1949), 2) embedded in paraplast, 3) sectioned at 7 um and 4) stained in hematoxylin and eosin. Slide preparations were then returned to Normandeau Associates for evaluation of reproductive development. Recognition of the phases of genadal condition: indifferent, developing, ripe, spawning and spent, was based on the same characteristics as those used by other investi-gators (Ropes and Stickney, 1965; Porter, 1974; Brousseau, 1978). Sections analyzed were from the dorsal, posterior quadrant below the heart, where Coe and Turner (1938) have claimed that maturation begins. I L_
I 10 TABLE 2. CLAM GONAD SAMPLING EFFORT. SEABROOK NYA AREl/ ARIA STUDY,1980. NO. SPECIMENS COLLECTION DATES EXAMINED 25 March 17 9 April 25 23 April 25 7 May 25 22 May 25 4 Jun 25 19 Jun 25 2 Jul 25 21 Jul 25 6 Aug 25 19 Aug 25 3 Sep 25 I l I i l l
11 3.0 RESULTS 3.1 PLANKTONIC LARVAE 3.1.1 Temporal Distribution Mya arenaria umboned veligers first appeared in plankton samples taken on 20 June; although a few straight-hinge larvae appeared as early as 3 June; a larvae swarm occurring on 17 June consisted of late straight-hinge individuals (Table 3). In sample collections after 20 June, umboned larval densities first declined and then peaked at approximately 173 larvae per m on 3 July. Midsummer density levels generally fluctuated between 1 and 30 larvae per n. Larval densities were generally in the range of 50 to 900 larvae per m throughout September. Larvae swarms were particularly intense fram 2 to 4 September,~ from 15 to 22 September and on 29 September. October densities were intermediate between midsu=mer and September levels (Table 3). 3.1.2 Spatial Distribution onshore-offshore distribution trends were different on each date of the intensive. tows (Table 4). Offshore stations had more larvae on 2 Septembet; while, inshore stations had more larvae on 18 September. Differences between inshore stations were more consistent with stations I4 and M3 being equivalent and having less larvae than M1 or M2 on both 2 and 18 September. The inshore spatial distribution pattern may have had a significant tidal component, as I4 was found to be equivalent to M2 and greater than M1 under conditions approaching slack low water on 15 September.
12 1 3 TABLE 3. DENSITIES (PER m ) 0F UMBONED M. ARENARIA VELIGERS COLLECTED AT THE COOLING WATER INTAKE SITE (14) 1980. SEABROJK NTA ARENARIA STUDY,1980. DATE REPLIO1TE 1 REPLICATE 2 MEAN REMARKS 16 Apr 0.0 0.0 0.0 22 Apr 0.0 0.0 0.0 1 May 0.0 0.0 0.0 5 May 0.0 0.0 0.0 12 May 0.0 0.0 0.0 19 May 0.0 0.0 0.0 28 May 0.0 0.0 0.0 g 3 Jun 0.0 0.0 0.0 a few straight-hinge g larvae present 9 Jun 0.0 0.0 0.0 17 Jun (54) (83) (62) all late straight-hinge 23 Jun 36. 13. 22. 24 Jun 9.0 14. 11. 27 Jun 8.0 2.6 5.0 g 30 Jun 35. 68. 52. g 3 Jul 158. 188. 173. 7 Jul 14. 21. 18. 10 Jul 1.8 1.8 1.5 14 Jul 19. 23. 21. 17 Jul 25. 32. 28 l 21 Jul 0.0 1.2 0.7 25 Jul 1.2 3.4 2.3 5 28 Jul 2.9 1.4 2.2 1 Aug 3.3 5.2 4.2 4 Aug 3.3 4.0 3.6 7 Aug 16. 14. 15. 11 Aug 6.7 8.8 7.7 14 Aug 5.7 4.4 5.0 18 Aug 11. 10. 11. 25 Aug 16. 19. 17. 28 Aug 9.6 7.2 8.2 2 Sep 720. 620. 670. see also: Table 4 4 Sep 900 800 850 8 Sep 80 110 94. 11 Sep 56 46 51 15 Sep 600 458 525. see also. Table 4 22 Sep 290 345. 320. 25 Sep 15. 8.8 12. 29 Sep 188. 183. 186. 2 Oct 12. 10. 11. 6 Oct 8.2 7.1 7.7 9 Oct 35. 39. 37. 13 Oct 5.7 5.4 5.5 16 Oct 1.2 1.3 1.3 20 Oct 2.1 2.1 2.1 27 Oct 72. 80. 76. 3 Nov 3.0 3.1 3.1
13 3 TABLE 4. DENSITIES (PER m ) 0F UMBONED M. AREuARIA VELIGERS COLLECTED ON SELECTED DATES AND AT SELECTED STATIONS IN THE VICINITY OF HAMPTON-SEABROOK ESTUARY. SEABROOK NYA AREuARIA STUDY,1980. C TOW A TOW B EVENT DESCRIPTION STATION SPLIT 1 SPLIT 2 SPLIT 1 SPLIT 2 2 Sep. Mooring, ebbing, tide I-4 722 665 345 892 2 Sep. Afternoon, flooding tide I-2 983 538 783 496 I-4 330 155 113 140 I-6 1230 1640 1090 1040 I-8 1150 986 1220 1440 M-1 2690 1760 2600 2330 M-2 5140 5260 3080 3730 M-3 943 893 1230 1260 3 Sep. late morning, ebbing tide (nearing slack low water) M-1 628 686 1100 980 M-2 1570 1400 1140 802 4 Sep. ebbing tide I-4 1150 640 751' 842 15 Sep. Mooring, ebbing tide (nearing slack low water) I-4 512 687 492 423 I M-1 166 161 124 137 M-2 453 595 604 502 15 Sep. Afternoon, flooding tide I-4 280 344 289 252 M-2 1220 1660 1310 2190 l (Continued) l t
14 TABLE 4. (Continued) l 18 Sep. Morning, flooding tide I-2 349 394 410 567 I-4 413 278 326 259 I-6 258 194 146 271 I-8 85 117 135 79 M-1 4910 2590 1710 3390 M-2 415 513 557 454 M-3 210 157 219 274 18 Sep. Afternoon, ebbing tide (nearing slack low water) M-1 493 285 352 266 M-2 4130 5000 3230 2940 I I I I I
15 I 3.1.3 Species comoosition Mya arenaria umboned veligers comprised more than 5% of the total bivalve assemblage on only one occasion in 1980. That was during the earliest September swarming (Table 5). Mussels were the usual dominants with Mytilus edulis predominating in early summer and late fall, and Modiolus mediolus predcminating during mid to late su=mer. From the beginning of the monitoring program in mid April, until late May, Hiatella sp. was practically the only bivalve species present. I Other bivalve mollusc species exhibiting prominent seasonality of occurrence included: Anomia sp. - mid August, Ensis directus - late October, and Macoma balthica, also late October. 3.2 AREAWIDE SPAT AND JUVENILE CIAM SURVEYS Compared to Ipswich, Massachusetts, and Ogunquit Beach, Maine, flats, Hampton Harbor flats retained a relatively dense population of juvenile clams (shell size: 13 to 42 mm) throughout 1980 (Table 6). Juvenile clams were especially scarce on the Ogunquit Beach flat, a condition to which green crab predation may have contributed (B. Sterl, Maine Dept. of Marine Resources, personal communication). In all three study areas, the 1980 spat set appeared to be moderate compared to previous years c ndix 7.2). I l 3.3 HAMPTON HARBOR SOFT-SHELL SURVEYS 3.3.1 Population Density Trends by Shell Size Categories Figure 3 compares clam densities by 1-m size class for all five principal flats combined. The smallest clams measured (shell lum length: 1 to 4 m ) were by far the most abundant. Least represented among size classes below 50 m was the 9 mm class. From 10 mm upwards, the length-density distribution had a generally bell-shaped appearance, lI
,e AU o =, c uo ..ae .2 O au ..o o ~ m Q o a ~ v O o U ~ ~.g ? ~e ~ = oo n ~m M o 4 o c. 4. o O n = 0 a ~ -.a o u a w e 5 -m a, = o >, = W U c1 N. g-o a ~ w z. e >, or o u3 N %. a i w =a e o na i = t a~e c m s, w e m e o u s. c i 4 i s a N.M __o- -c ec --= u g =m ~ =t Q w -m N c O C Q ^ C C o o e N N a ,13 'd3d SWW 5 c cn I
i M M y t iss ne) e v3 Dl ma evr gi e aBp r 0 0 1 0 5 0 0 0 0 0 0 0 0 0 T el o 7 2 9 5 7 3 5 8 0 0 2 0 4 0 E vl n 5 2 2 2 9 3 4 7 4 9 3 N AA( 5 8 2 2 0 2 2 7 9 1 1 1 6 E UQ I L 0 0 0 0 1 0 5 1 8 9 8 9 5 1 B O mLE.$ E 0 0 0 0 0 2 0 0 1 4 8 0 1 0 N I S M 0 0 0 0 0 0 0 0 0 0 0 2 1 1 R G 3,3%* W E 0 0 0 0 0 0 0 0 0 0 0 < 0 < I L E V M 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 D8 s S 9* W e E9 0 0 0 0 0 0 0 0 0 0 0 < 0 0 N1 0 B, MY M UD 0 0 0 0 0 0 6 5 9 8 1 0 0 0 ET o%&E < U $3 m 0 0 0 0 0 0 0 1 1 0 0 0 0 0 VS r L e AA p VI s R 0 0 0 0 0 0 1 2 1 1 1 1 3 1 I r BA u h" e N 0 0 0 0 0 0 0 0 0 < < < 0 < e FE g OR i l A e "0 E v CA 0 0 0 0 0 0 0 0 0 4 4 2 1 AN "k8g 4 NY 0 0 0 0 0 0 0 0 0 0 0 0 0 < d D e NK g UO n M BO i AR 0 0 0 0 5 1 2 0 6 3 6 3 4 5 h B u85* e LA 0 0 0 0 0 < 0 0 0 3 1 4 1 0 t AE h TS g O i T a 1 3 r D) a* "fx 8 0 3 3 0 0 0 4 7 6 9 0 t 0 0 0 0 0 0 0 < 1 2 0 3 3 1 s NE AT e I NS t M 7 7 4 9 8 7 6 7 0 7 9 2 a O 2 l I E TK M 3.TisE 9 0 9 9 9 7 8 0 5 1 1 8 5 1 IA 9 0 9 9 9 9 8 9 8 2 2 1 0 ST 1 8 ON PI o M 1 1 t M( 0 0 0 0 0 6 5 0 1 6 7 1 O t Ml* W o i C 4 0 0 0 0 0 < 8 7 8 6 7 1 4 3 0 1 6 6 8 6 1 5 T N0 E s M 0 0 0 0 0 0 3 0 0 3 2 4 9 0 e CS t RW o38E W 0 0 0 0 0 0 0 0 0 0 0 0 1 4 o EO PT 1 8 N M 5 r r y y y y y n n n n n l l E p p a a a a a u u u u u u u L A A M M M M M J J J J J J J B A 6 2 1 5 2 9 8 3 9 7 4 0 7 4 T 1 2 1 1 2 1 2 3 1 M M
TABLE 5. (Continued) 9 a 3 3 2 2 3 R S U a h m '8 3-a t 8 El
- e R$
b e R$ 1$ E$ E 5 $2 AI di 13 Average Density e e E ls 3 'll R$ D b E ls S All Bivalves g g j j g g g g j g {-- (no per m ) 3 21 Jul 65.0 20.8 8.3 2.4 0.6 <.1 0.2 0.0 <.1 0.2 2.4 34,300 28 Jul 66.0 20.4 6.1 6.0 0.3 <.1 <.1 0.0 0.1 0.1 0.9 71,000 4 Aug 27.4 48.1 8.6 13.8 0.3 <.1 <.1 0.2 <.1 <.1 1.5 18,600 11 Aug 32.7 11.7 5.1 43.8 0.1 0.1 <.1 <.1 0.1 0.5 5.8 9,940 18 Aug 16.3 49.4 1.3 27.3 0.1 0.5 <.1 <.1 0.2 3.6 1.2 1,960 25 Aug 39.5 32.7 2.6 14.2 0.2 2.1 0.0 0.3 0.4 5.2 2.8 804 2 Sep 34.4 0.7 7.9 30.0 1.4 15.0 0.0 0.0 0.0 0.3 1.3 4,460 8 Sep 91.2 4.0 0.8 2.6 0.2 0.1 0.0 0.0 <.1 0.7 0.3 145,000 15 Sep 82.2 7.9 1.5 2.1 0.4 1.8 0.0 <.1 0.2 3.2 0.6 29,900 l 22 Sep 53.9 19.2 0.5 17.9 0.1 1.9 <.1 0.0 0.6 4.8 1.1 16,600 29 Sep 59.8 30.8 0.4 4.1 (.4 1.0 <.1 0.0 1.9 0.8 0.8 18,400 6 Oct 64.8 11.6 1.3 9.2 3.8 1.5 <.1 0.2 2.5 1.9 3.2 519 13 Oct 57.1 21.2 2.4 12.3 <.1 0.5 0.0 0.4 0.7 0.4 4.9 1,210 20 Oct 13.3 11.1 3.7 26.0 9.3 0.3 0.0 4.5 22.3 1.8 7.6 790 27 Oct 2.5 45.8 0.4 2.6 35.6 4.6 0.0 0.1 4.9 1.8 1.7 1,660 3 Nov 4.4 59.6 0.8 13.5 8.4 1.5 0.0 0.1 0.3 1.5 9.8 211 M M M M M M M M M M M M M M
2 TABLE 6. YOUNG-0F-Tile-YEAR (1-12 m) AND JUVENILE (13 to 42 m) SOFT-SilELL CLAfi DENSITIES (PER FT ) IN POTENTIALLY PRODUCTIVE AREAS OF TilREE NORTilERN NEW ENGLAND ESTUARIES. SEABROOK MYA ARENARTA STUDY,1980. APRIL JULY OCTOBER YOUNG-0F-YOUNG-0F-YOUNG-0F ESTUARY Tite-YEAR JUVENILES THE-YEAR JUVENILES Tile-YEAR JUVENILES Plum Island Sound (Ipswich, MA) 28 27 8 30 136 10 !Iampton liarbor (llampton & Seabrook, NII) 124 84 50 98 82 84 Ogunquit River (Ogunquit Beach, ME) 44 4 8 11 26 2 [
20 tapering markedly toward the larger-sized clans. The median shell size of all clams, over 8 mm, was 26 mm. By October 1980, an average of 7.4 clams per ft had attained a shell size of 43 mm or more on all flats, while an average of 1.9 per ft had attained a shell size of 51 mm or more (Appendix 7.3). Since the previous annual survey, in November 1979, clam densities in each of the 5 mm size categories, 30 mm through 70 mm, have increased substantially (Figure 4; Appendix 7.4). On all flats, population densities of juvenile and adult clams (shell length >25 mm) were restored to levels comparable with or higher than densities shown for the years prior to 1976 (Table 7). In certain g ways, however, each of the five principal flats demonstrated consider-E able individuality, in 1980. On Flat 4, the mean density of clams larger than 50 mm matched the highest previously recorded mean density. On Flat 1, mean densities of juvenile and young adult clams (shell length 26 to 50 mm) established a new record. Flat 2 experienced a spatfall second in intensity only to the great spatfall of 1976; while Flats 1, 3 and 5 showed increases in spatfall only over 1979 levels. Flat 4 exhibited a decline in meTn spat density to the lowest level since 1975. Over all flats there were considerably more clams in the 26 to 50 mm Jize class in 1979 and 1980 compared to any previous year of study, due primarily to higher numbers at Flats 1 and 4. I 3.3.2 Standing Crop Estimates of standing crop (Table 8) show that clams over 50 1 mm in shell length comprised approximately 15% by volume of the total standing stocks in Hampton Harbor, in October 1980. Clams 43 to 50 mm in length (young adults) represented approximately an additional 26%. More than 58% of the total volume consisted of juvenile clams, 25 to 43 7 mm long, 92% of which was found on Flats 1 and 4 (Table 8). On Flat 2 I the majority of the standing crop consisted of clams over 50 mm; Flat 2 ranked second, only slightly behind Flat 4, in potential yield per acre of clams over 50 mm (Table 8). i I
12-21 I 11-I 10 I 9-I 8-I M 1980 7' M 1979 filHI 1978 ~. 6- ,g u ig g o. 5-lI l 4-I I i E E = I E N E 1-E E E E I E E d d . I ..m = = = -= 30 35 40 45 50 55 60 ft 70 (SIZE CLASS (mm)) Figure 4. 5 mm class length-density aistribution of 14fa arenaria juveniles and adults, comparing November 1978 through 1980 I surveys in Hampton Harbor. Seabrook Mya arenaria Study, 1980.
l l l l. s 30-1 Eg M 1980 E 25-E h:WI 1979 E g g 181111 1 9 7 8 O E l 0 E 20-E E i = = 4 m = = = E E E o" E E E = = = 15-E E E 21 E E E = = = x = = = o = = = w 5 E E E E 5 10-E E E E = w = = = = = a: = = = = = E E E E E E E E E E E E E E E s-E E E E E E E E E E = = = = = = = E E E E E E E = E E E E E E E E i "I ~ EfB 5 5 5 5 5 5 Y 0 ~^* I I I I I I I <3 3-3 /2 3 /2-4 4-4 /2 4 /2-5 5-5 /2 S /2-6 6-6 /2 6 /2-7 >7 i Figure 5. Size-frequency distribution of Carcinus maenas catch at Flat #2 in llampton liarbor. Seabrook Nya arenaria Study, 1980. 1 2
i i 11 22 TABLE 7.
SUMMARY
OF NYA ARENARIA POPULATION DENS' TIES, ANNUAL NOVEMBER SURVEY. SEABROOK NYA ARENARIA STUDY,1980. I NUMBER OF SAMPLES POPULATION DENSITY (#/Sq. FT.) COLLECTED SPAT JUVENILES ADULTS LOCATION YEAR ADULTS SPAT (>l TO 25 mm) (26 TO 50 mm) (>50 mm) Flat 1 1971 18 18 48 6.8 2.1 1972 18 18 110 8.1 3.3 1973 36 18 44 2.5 1.3 I 1974 40 18 2.6 2.8 3.0 1975 35 18 56 0.4 1.2 1976 63 18 1084 0.12 0.53 1977 66 14 819 0.04 0.15 1978 66 14 372 0.62 0.15 1979 72 20 72 31.0 0.24 1980 30 19 103 72. 1.7 Flat 2 1971 9 9 91 4.8 3.8 1972 9 9 152 2.2 1.4 1973 9 9 316 3.8 1.1 1974 21 9 0.0 2.1 1.9 1975 21 9 9.1 0.0 0.5 I 1976 24 9 351 0.0 0.21 1977 33 7 86 0.0 0.08 1978 33 15 2.1 0.16 ~' 1979 33 9 57 3.6 0.29 I 1980 40 25 254 4.1 2.2 Flat 3 1971 6 6 74 4.7 4.6 I 1972 6 6 39 1.6 0.4 1973 12 6 8 3.6 2.2 1974 12 6 0.6 0.7 1.7 1975 12 6 1.1 0.0 0.6 1976 24 5 560 0.07 0.23 1977 24 6 75 0.12 0.04 1978 24 6 50 1.2 0.14 1979 14 4 10 1.0 0.15 1980 40 25 56 0.47 0.36 I Flat 4 1971 12 12 106 17.6 2.8 1972 12 12 138 10.6 2.3 1973 24 12 18 3.8 0.6 1974 29 12 1.1 2.8 1.8 1975 29 12 68 0.3 0.7 1976 81 18 843 0.04 0.16 1977 51 11 436 0.09 0.01 I 1978 51 11 309 12.4 0.05 1979 67 17 175 39 0.52 1980 32 25 99 36 2.8 (Continued)
24 TABLE 7. (Continued) l l Il NUMBER OF SAMPLES POPULATION DENSITY (#/SQ. FT.) COLLECTED SPAT JUVENILES ADULTS (>l TO 25 mm) l (26 TO 50 nm) (>50 m) LOCATION YEAR ADULTS SPAT Flat 5 1971 9 9 176 1.3 1.6 g 1972 9 9 196 3.8 2.3 3 1973 21 11 23 1.0 0.4 1974 17 11 2.4 0.0 0.1 1975 9 11 7.5 0.9 0.01 1976 24 12 549 0.0 0.14 1977 38 9 114 0.08 0.03 1978 38 7 56 4.1 0.07 1979 32 8 14 1.8 0.03 1980 42 20 68 2.1 0.9 All Flats 1971 54 54 92 7.7 2.7 1972 54 54 130 6.2 2.2 1973 111 56 47 2.8 1.0 l 1974 119 56 2.1 2.1 2.0 W 1975 106 56 37 0.2 0.8 1976 216 62 762 0.06 0.2 g 1977 212 47 388 0.05 0.07 g 1978 212 45 208 4.4 0.09 1979 218 58 86 24 0.3 1980 184 114 116 36 1.9 I I I I I I I
M M M M M M M M M M M m TABLE 8. ANNUAL SURVEY STANDING CR0P ESTIMATES. SEABROOK NYA ARENARIA STUDY,1980. CLAfiS 750 nm CLAMS 43-50 nm CLAMS 25-42 nm l' FLAT SURFACE : LEA BUSilELS/ ACRE BUSHELS BUSilELS/ ACRE BUSilELS BUSilELS/ ACRE BUSHELS AVERAGE AVERAGE AVERAGE a 1 53.95 47.5 2565
- 156, 8396 416.
22,450 2 24.74 72.3 1789 31.0 768 18.1 448 3 10.83 17.1 185 4.4 48 1.5 16 4 50.83 75.4 3832 113. 5762 212. 10,760 5 23.98 21.7 521 17.4 418 9.7 230 All 164.33 54.1 8892 93.7 15,390 206. 33,900 "from aerial survey, August 1980
I 26 Gains in standing crop of adult clams (shell length >42 mm) were achieved on all flats from November 1979 to late October 1980, with the highest absolute gain occurring on Flat 1 (Table 9). Although possessing a relatively modest standing crop, Flats 2 and 5 both showed comparatively large proportional gains. The smallest gain, in both proportional and absolute terms, was realised on Flat 3, where clams have in general been sparsely distributed in recent times. On all = flats, except Flat 3, clam populations were sufficiently dense in some places as to potentially yield from 230 to more than 1000 bushels per acre. A yield of 250 bushels per acre is equivalent to approximately ? E ten two-inch clams per ft' and is comparable to some of the best commer-E ':ial clamming grounds in New England. Sample yields equivalent to 40 bushels per acre (slightly less than two two-inch clams per ft ) approxi-mate the threshold between a marginal fishery and one with a healthy potential for recreational digging. As of October 1980, almost half of the 164 1/3 acres surveyed in Hampton Harbor had exceeded the 40 bushels-per-acre threshold. Over all flats, approximately the same proportion of samples yielded adult clams (Table 9) as produced clams over 25 mm is shell length (Table 10). I 3.4 GREEN CRAB, CARCINUS MAENAS, TRAP CATCHES For comparison, data from surveys in 1977 through 1979 are presented in Table 11, along with 1980 catch data; size-frequency distri-bution data for 1977 through 1980 catches are presented in Figure 5. As in 1979, the largest trap catches of C,. maenas occurred in the fall of 1980. Catches in 1980 exceeded all previous records except during spring when catches were at about the same level as in 1978 and 1979 (Table 11). The 1979 record catch of 58 crabs per trap was surpassed on three occasions in 1980, 17 October, 7 November and 21 November (Appendix 7.5). A new record of 108 crabs per trap was established on 21 November 1980. I
TABLE 9. ESTIMATES OF " HARVESTABLE"I STANDING CR0P. SEABROOK NYA ARENARIA STUDY,1980. % OF SAMPLING % OF SAMPLES TOTAL ESTIMATED % OF SAMPLES YIELDING EQUIVALENT Y!ELDING EQUIVALENT HARVESTABLE CR0P YIELDING OF >40 BUSHELS OF >250 BUSilELS (BUSHELS) IIARVESTABLE CLAMS PER ACRE PER ACRE FLAT 1980 1979 1980 1979 1980 1979 1980 1979 1 10,960 1890 83 44 60 21 33 1 2 2,560 350 68 44 42 18 10 0 U 3 230 126 38 29 25 14 0 0 4 9,600 3160 59 52 56 40 28 3 5 940 143 50 22 21 6 5 0 All 24,300 5670 66 43 48 24 22 1 Defined as clams with shells >43 mm long
28 TABLE 10. ESTIMATES OF CLAM FLAT PRODUCTIVE AREAI (%) IN HAMPTON-SEABROOK ESTUARY. SEABROOK MYA ARE' ARIA STUDY,1980. I I LOCATION 1980 1979 1978 1977 1976 1975 1974 Flat 1 83 72 60 17 35 53 80 Flat 2 72 62 36 15 17 44 63 Flat 3 50 29 42 32 48 39 67 Flat 4 59 76 62 20 19 57 88 Flat 5 55 22 43 22 27 4 20 All Flats 68 62 52 19 26 45 66 I I I l l l l 1 of total number of samples taken, proportion in which at least one clam, 5 >25 mm, was found I I I
23 I TABLE 11. SELECTED C. MAENAS CATCH STATISTICS 1977-1980. SEABROOK MYA ARENARIA STUDY,1980. I AVERAGE FECUNDITY CATCH PER SEX RATIO (% GRAVID a SAMPLE PERIOD UNIT EFFORT (M:P) FEMALES) I Summer 1977 July 24.6 1:4.9 6.2 I August 10.3 1:3.5 9.4 September 21.6 1:2.2 0.9 Oct-Dec 1977 17.5 1:0.9 0.3 I Jan-Mar 1978 0.1 Females only 0.0 Apr-Jun 1978 7.5 1:3.3 7.0 Jul-Sep 1978 8.6 1:1.5 3.2 Oct-Dec 1978 7.2 1:1.3 0.5 Jan-Mar 1979 2.7 1:1.7 0.0 Apr-Jun 1979 6.4 1:1.0 6.0 Jul-Sep 1979 6.0 1:1.5 0.6 Oct-Dec 1979 22.1 1:1.5 0.0 Apr-Jun 1980 6.7 1:1.1 8.4 Jul-Sep 1980 15.8 1:1.0 2.3 Oct-Dec 1980 53.1 1:2.0 0.0 I ^Numlaer of C_. maenas per trap per day; summer 1977, I two " prism" traps, fishing for 2 to 5 days at a time; after September 1977, eight " box" traps, fishing for 24 hours twice per month.
) Tha largest green crab captured in 1980 was 8.1 cm at the widest part of the carapace. Approximately 98% of the crabc caught had carapaces between 3.0 and 7.0 cm at the widest point. Crabs with cara-paces wider than 7.0 cm were almost exclusively males (Appendix 7. 5). Sex ratios were close to parity except in October and Novenber when there were more than two female crabs for every male (Appendix 7.4). Egg bearing females were captured on 18 April, 8 May, and from 20 June to 7 August. Fecundity peaked, at 13.7% of females bearing eggs, on 20 June 1980. I 3.5 SOFT-SHELL CLAM REPRODUCTIVE CYCLE In 1980, histological examination of gonadal development (Table 12) showed one spawning female occurring in early April and a ripe female in early May, while males showed no evidence of ripeness g until late in May. First indications of sperm releases occurred in 5 early June. The greater proportion of both sexes appeared to participate in the main reproductive sequence, in which spawning activity began in earnest in early August, culminating in early September. I I I I I I
31 I TABLE 12. RESULTS OF HISTOLOGICAL STUDY OF GONADAL CONDITION. NUMBERS OF SPECIMENS IN EACH GONADAL CONDITION CATEGORY. SEABROOK MYA ARENARIA STUDY,1980. SAMPLE DATES I GONAD 25 9 23 7 22 4 19 2 21 6 19 3 17 CONDITION MAR APR APR MAY MAY JUN JUN JUL JUL AUG AUG SEP SEP Males Indifferent 4 2 1 1 3 1 1 1 3 Developing 5 8 8 5 8 12 4 5 2 4 3 1 Ripe 1 1 3 6 9 7 6 3 I Spawning 1 2 2 1 Spent 3 Females I Indifferent 2 3 1 2 2 1 1 1 Developing 6 11 15 18 7 3 5 1 1 Ripe 1 3 1 9 10 7 6 10 4 Spawning 1 1 2 1 3 3 3 5 Spent 2 1 1 1 4 Hermaphrodites Ovary developing / testes indifferent 1 I Ovary ripe / testes developing 1 1 Testes ripe / ovary developing 1 Ovary spawning / testes developing 1 Ovary and tes.tes both ripe 1 I I I I
I 32 4.0 DISCUSSION 4.1 PLANKTCNIC LAR"AE SPATIAL DISTRIBUTION Results of the two 1980 intensive surveys were mixed, with clear support on only one of the dates for the conventional view that larval densities decrease with distanc i from shore. Exceptions to the general pattern of seaward decreasing larval density have occurred on the same spatial scale in the past, notably in 1976 and 1979 (NAI, 1977, 1981). In 1980, larvae tows were conducted for the first time at a point (Station M2) immediately seaward of Hampton Harbor Inlet. On the afternoons of 2 September (flooding tide) and 18 September (ebbing tide), M_. arenaria umboned veliger densities exceeded 3000 larvae per m at Station M2, while densities of only a few hundred larvae per m were found elsewhere including the intake site (I4). Given the limited data so far available, any speculation as to the environmental significance of these spatial distribution patterns would be premature. 4.2 TEMPORAL RELATIONSHIPS: LARVAL SWAPl4ING AND PIPRODUCTIVE CYCLE Temporal occurrencas of M. arenaria veligers in 1980 suggest the continuance of a gradual shift in peak abundance towards autumn. This trend appears to affect both the early and late summer modes of larval abundance. In 1978, for example, the early su::cer mode occurred us around the second week of June; while, in 1979, a comparable mode occurred towards the end of June and into early July. In 1980, a relatively minor mode was briefly observed on or about 3 July. Simi-larly, the late summer (principal) mode has progressed from commencement in early August, in the years prior to 1976, to commencement no earlier than 2 September, in 1980. Major swarms (defined as abundances ex-ceeding 50 larvae per m ) have, over the years, occurred later. I
4 33 In apparent departure from 1978, and to a lesser extent, 1979, breeding activity (coincidence of sperm and egg release) in Hampton Harbor soft-shell clams was in close synchrony with the timing of larval swarming in 1980. Also, ripening of testes and release of sperm appears to have shifted from essentially a single-mid summer episoi h 1978, toward two periods of activity in 1980, slightly suggestive of bimodal reproductive periodicity (cf. Table 12). In all three years of recent gonad study, 1978 through 1980, females have ripened beginning in early spring. The 1980 data, produced scant evidence of a spring egg release, the function of which is un-I known;with none of the 28 male specimens collectad in early spring 1980 showing the slightest sign of ripeness, few eggs released at that time are likely to have been fertilized. I 4.3 LARVAL ABUNDANCE AND SPATFALL I In general, M. arenaria umboned veligers were approximately as abundant ir 1980 as in 1978, and slightly less abundant than in 1979 I (Table 13). In contrast, young-of-the-year spat densities were more than twice as high in 1980 as in 1979. Present and previous data, taken together, support the conclusion that the quantity of larvae available in the vicinity of the cooling water intake has little relation to spat-fall intensity in the Hampton-Seabrook Estuary. Possible explanations for the lack of correspondence include: 1) geographic and hydrographic isolation of the intake sita from Hampton Harbor and 2) the majority of 'I larvae enumerated did not represent potential spat (i.e. were not ready to set). 4.4 BIVALVE MOLLUSCS SPECIES COMPOSITION Surveys from 1977 through 1980 have established a reasonably consistent general pattern of bivalve mollusc species composition for New Hampshire coastal waters. Even during major larval swarms, M. I l
TABLE 13 COMPARIS0N OF n. ARENARIA UMB0NED LARVAL ABUNDANCE OFF HAMPTON BEACH WITH YOUNG-0F-THE-YEAR SPAT DENSITIES IN llAMPTON HARBOR. SEABROOK NYA ARENARIA STUDY,1980. DAILY MEAN x DENSITY OF PERIOD OVER WHICH MEAN SEASON LENGTH YOUNG-0F-THE-YEAR YEAR LARVAE WERE l0LLECTED (per m / day) (per m ) (Spat per ft ) 3 3 2 1974 16 Jul to 5 Sep (51 days) 69 3,500 2 1975 16 Aug to 14 Oct (59 days) 532 31,400 37 1976 28 Jun to 17 Oct (113 days) 158 17,800 762 1977 27 Jun to 6 Oct (102 days) 7 714 179 1978 22 May to 31 Oct (163 days) 83 13,600 56 1973 21 May to 29 Oct (162 days) 136 22,000 30 1980 20 Jun to 3 Nov (137 days) 90 12,400 79 m M M M M M M M M y
35 arenaria is rarely dominant. By the time the larvae investigated here have developed to the umboned stage, they have probably aaen in the water column at least a week; neverthaless, abundance patterns at the intake site retlect the presence of bivalves which are common to the local coastal learshore environment such as Mytilus edulis, Modiolus modiolus and to a lesser extent, Hiatella sp. Mya truncata is occasionally found nestled among populations of M. Modiolus and Hiatella sp. which is probably why larvae of this species are present at detectable levels in our collections. Larvae of other species, known to inhabit patches of sandy substrate, (namely, Anomia sp., E. directus, S. solidissima and M_. balthica), are well represented during what appears to be their breed-ing season. Of the bivalve larvae routinely identified in these studies, those of the sea scallop, P_. magellanicus, likely originate from the most remote source (nea rest known pc71ations are off Rye Beach) ; cor-respondingly, the larvae are among the least abundant in our samples. 4.5 GREEN CRAB CATCHES IN HAMPTON HARBOR AND SOFT-SHELL STANDING CROP Crab trap data suggest a trend toward increasing catchability from 1978 through 1980. Coincidentally, winter water temperature minima off Hampton Beach have also increased over the same period (Figure 6) Welsh (1969) and Dow (1977) have proposed a mathematical relationship between green crab catchability and winter water temperature minima at Boothbay Harbor, Maine. Their model also implies an inverse relation-ship between soft-shell clam harvests and winter water temperature minima, given a two to three-year time lag; the Dow (1977) model seems not to pertain to Hampton Harbor, however, as standing crop estimates declined to their lowest point in 1978 (Table 14) the same year that the lowest winter temperature minima were recorded (Figure 6). Probable reasons for the failure of Hampton Harbor soft-shell clam stocks to correlate inversely with winter water temperature trends are:
- 1) that the fate of Hampton Harbor clam stocks rests primarily on the strength of occasional superabundant year classes like those of 1976 and 1977,
36 I a TABLE 14. RECENT HISTORY OF THE STANDING CR0P 0F ADULT MYA ARENARIA IN HAMPTON HARBOR. SEABROOK NYA ARENARIA STUDY,1980. ESTIMATED NUMBER TOTAL OF BUSHELS ESTIMATED NUMBER DATE PER ACRE OF BUSHELS November 1967 152 23,400 July 1969 103 15,840 November 1971 94 13,020 November 1972 58 8,920 November 1973 41 6,310 November 1974 56 8,690 November 1975 29 4,945 November 1976 11 1,350 November 1977 6.4 1,060 November 1978 5.7 940 November 1979 8.5 1,400 November 1980 54 8,890 l
- shell length >50 mm
) from Ayer (1968)
37 I I I 38 - lI 37- 'I 36-I e s h 35-lI 34-I l 33 I 1973 1974 1975 1976 1977 1978 1979 1980 YEAR OF RECORD I I I Figure 6. Means of caily minimum winter (February and March) water temperatures off Hampton Beach, New Hampshire. Seabrook I Nya arcr. aria Study, 1980. l
l 1 i 38 I i and 2) human predation, which responds more to the availability of clams 1 than to climatic shifts and is believed to be the primar* factor in-fluencing future clam stocks in Hampton t' arbor. i i I I I, I I I I I
7 39 5.0
SUMMARY
Mya arenaria umboned ve Ligers were present in plankton samples from 20 June until sampling ended on 3 Novcmber, having exhibited a brief abundance peak (173 larvae per m ) on 3 July and a sustained abundance of 50 to 900 larvae per m throughout September 1980. Sampled I intensively on two dates in September (when larval abundance was particularly high), more larvae were collected within one mile of shore than 1-1/2 to 2 miles from shore on one date, while on the other date the reverse was true. Differences between inshore stations were more consistent, with fewer larvae collected at the cooling water intake site and a point south of the entrance channel to Hampton Harbor than at the Harbor entrance channel and inlet. Mussels were the dominant bivalve larval taxa, with M_. arenaria comprising more than 5% of the total bivalve assemblage on only one occasion (15% on 2 September). In 1980, the cycle of reproductive development and activity in Hampton Harbor soft-shell clams appeared to agree well with seasonal larval abundarce. Female clams began to ripen in early spring; while males showed little evidence of ripening until late May. Some sperm and egg releases apparently occurred in early June; however, the majori ty of clams sampled showed evidence of breeding activity beginning in early August and culminating in early September. As measured in late October 1980, young-cf-the-ycar spat dencities were low compared to the dense sets of 1976 and 1977, but were more than twice as dense as in 1979, when spat set was light. On Hampton Harbor flats, clams one year or older (up to a shell length of approximately 72 mm) were numerous compared to populations in Ogunquit Beach, Maine I and Ipswich, Massachusetts. Total standing crop on Hampton Harbor flats was estimated in October 1980 to be approximately 58 thousand bushels with approximately 41% consisting of clams over 42 mm 1cng (i.e. adults and pctentially he.rvest.ablei. 'I L
40 .i Notwithstanding continued increases in soft-shell clam stand-ing stocks, from a 14-year low in 1978, in 1980 trap catches of green crabs (an important natural predator) surpassed previous records going back to 1977. As in 1979, the largest trap catches occurred in autumn. Egg bearing females, usually repr3senting less than 5% of the trap popu-lation, were captured mainly in spring, as in previous years. I I' I' I l I I. 1 I
41 6.0 LITERATURE CITED I Armed Forces Institute of Pathology. 1949. Manual of histo]ogic and special staining techniques. McGraw Hill. 2nd editior.. pp. 7-14, 25-30. Ayer, W. C. 1968. Soft-shell clam population study in Hampton-Seabrook Harbor, New Hampshire. New Hampshire Fish and Game Dept. 39 pp. Belding, D. L. 1930. The soft-shelled clam fishery of Massachusetts. Commonw. Mass. Dep. Conserv. Div. Fish Game, Mar. Fish. Ser. 1,65 p. Brousseau, D. J. 1978. Spawning cycle, fecundity and recruitment in a population of soft-shell clam, Mya arenaria, from Cape Ann, Massachusetts. Fishery Bulletin. 76(1):155-166. I Coe, W. R. and H. J. Turner, Jr. 1938. Development of the gonads and gametes in the soft-shell clam (Mya arenaria). J. Morphol. 62:91-111. Cenover, W. J. 1971. Practical nonparametric statistics. John Wiley & Sons, Inc. 462 pp. Culliney, J.L. 1974. Larval development of the giant scallop, Placopecten magellanicus (Gmelin). Biol Bull. 147: 321-332.
- Dow, R.
L. 1977. Effects of climatic cycles on the relative abundance and availability of commercial marine and estuarine species. J. Cons. Int. Explor. Mer. 37(3):274-280. Dow, R.L. and D.E. Wallace. 1961. The soft-shell clan industry of Maine. U.S. Fish & Wildlife Service Circular, 110. 36 pp. I Normandeau Associates, Inc. 1971. Seabrook Ecological Study: Phase I 1969-1970, Hampton-Seabrook Estuary, New Hampshire. Prepared for Public Service Company of New Hampshire. 313 pp. 1972a. Seabrook Ecological Study 1971. Soft-shelled clam spat density. Technical Report III-1. 1972b. Seabrook Ecological Study 1971. Soft-shelled clam spat density. Technical Report III-3. 1972c. Seabrook Ecological Study 1971. Soft-shelled clam (Mya arenaria) larvae studies. Technical Report III-8. 1973. Seabrook Ecological Study 1972. Studies on the soft-I shelled clam, Mya arenaria, in the Hampton-Seabrook estuary, New Hampshire. Technical Report IV-2. I 1974. Seabrook Ecological Study 1973. Studies on the soft-shelled clam, Mya arenaria, in the Hampton-Seabrook estuary, New Hampshire. Technical Report V-2. lI
42 I 1974. Seabrook Ecological Study 1973. The impact of entrainment by the Seabrook Station. Technical Report V-4. 1975a. Seabrook Ecological Study 1974. Spatial and temporal distribution of the larvae of the soft-shelled clam, Mya arenaria, in the Hampton-Seabrook estuary and nearby offshore waters. Technical Report VI-1. 1975b. Seabrook Ecological Study 1974. Studies on the soft-shelled clam, Mya arenaria, in the Hampton-Seabrook estuary, New Hampshire. Technical Report VI-3. 1976a. Seabrook Ecological Studies 1975. Studies on the soft-shelled clam, Mya arenaria, in the Hampton-Seabrook Estuary, NewHampshire. Technical Report VII-1. 1976b. Spatial and temporal distribution of the larvae of the soft-shelled clam, Mya arenaria, in the New Hampshire coastal waters, 1975. Technical Report VI-10. 1977. Seabrook Ecological Studies 1975-1976. Studies on the soft-shelled clam, Mya arenaria in the vicinity of Hampton-Seabrook estuary, New Hampshire. Technical Report VII-3. 1978. Seabrook Ecological Studies 1976-1977. Studies on the soft-shelled clam, Mya arenaria, in the vicinity of Hampton-Seabrook estuary, New Hampshire, New Hampshire. Technical Report VIII-2. 1979. Seabrook Ecological Studies 1978. Soft-shell clam, 5 Mya arenaria, Technical Report X-3. 3 1981. Seabrook Ecological Studies 1979. Soft-shell clam, Mya arenaria studies. Technical Report XI-1.
- Porter, R. G.
1974. Reproductive cycle of the soft-shell clam, Mya arenaria, at Skagit Bay, Washington. Fish. Bull. 72:648-656. Ropes, J. W. and A. P. Stickney. 1965. Reproductive cycle of Mya arenaria in New England Biol. Bull. 128:315-327. Savage, M. B. and R. Goldberg. 1977. Investigation of practical means of distinguishing Mya arenaria and Hiatella sp. larvae in plankton samples. Proc. Nat. Shellfish Assoc. 66:42-53, de Schweinitz, E. H. and R. A. Lutz. 1976. Larval development of the northern horse mussel, Modiolus mediolus (L.), including a compari-E son with the larvae of Mytilus edulis (L.) as an aid in planktonic 5 identification. Biol. Bull. 150(3):348-360.
- Sokal, R.
F. and F. J. Rohlf. 1969. Biometry. W. H. Freeman Co., San Francisco. 776 pp. I
f i j 43 4 j Sullivan, Charlotte M. 1948. Bivalve larvae of Malpeque Bay, PEI. Fish. Res. Bd. Can. Bull. 77. 36 pp. 1 l Welch, W. R. 1975. Report on the relative abundance of green crabs l along the Maine coast, Fall 1975. Maine Dept. of Marine Resources. !l l5 Welch, W. R. 1969. Changes in abundance of the green crab, Carcinus { maenas (L.) in relation to recent temperature changes. U.S. Fish j Wildl. Serv. Fish. Bull. 67(337-345). + t lI I i lI !,I f 'I !I 1!I I I I I
44 APPENDIX 7.1. ANALYSIS OF COMPARABILITY BETWEEN SAMPLING DESIGNS. To ecmpare the random sampling design, presently used, with the ("no-holes") sampling method, used from 1976 through 1979, a " worst W case" situation for maximum and minimum sampling results differences was simulated using 1980 survey data (adult and juvenile clams, shell lengths greater than 25 =m). This comparison allowed a flat by flat estimate to be made of the greatest potential disparity between the two sampling designs in population mean estimates. Substantial potential differences between the population estimates made by the current random sampling method and the previous "no-hole" sampling method, are indicated by the results of this enalysis (Table 7.1-1). The random sample mean fell within the range of the worst case "no-hole" method mean estimates only for Flats 2 and 5. For Flats 1 and 4, the "no-hole" method generally overestimated the mean by 10-20% (Table 7.1-2). For Flat 3, the overestimate could be as high as 70%. Variability was so great on' Flats 2 and 5 that no consistent comparability trend could be ascertained from this analysis. I I I I I I
I 45 TABLE 7.1-1. MEAN (x), STANDARD DEVIATION (S), COEFFICIENT OF VARIATION (CV), AND 90% CONFIDENCE INTERVALS FOR MINIMUM AND MAXIMUM WORST CASE ESTIf1ATES AND RAND 0M SAMPLING ESTIMATES OF SOFT-I SHELL CLAM POPULATION DENSITIES (no. per 2 ft2 plot) BY FLAT. CONFIDENCE LIMITS i S CV LOWER UPPER FLAT 1 I minimum 163.2 111.2 68.1 159.7 166.7 maximum 184.8 103.6 56.1 181.4 188.2 random sample 149.2 113.9 76.4 145.9 152.9 FLAT 2 minimum 9.0 30.0 333.5 7.3 10.7 maximum 15.5 30. 198.9 13.8 17.1 I random sample 13.4 27.7 206.5 12.0 14.8 FLAT 3 minimum 2.0 8.0 141.4 1.4 2.6 maximum 2.9 8.0 98.6 2.3 3.5 random sample 1.7 6.7 150.3 1.3 2.2 FLAT 4 minimum 93.1 105.3 113.1 89.8 96.3 I random sample 84.3 103.8 123.0 83.3 87.4 FLAT 5 minimum 4.5 12.1 267.4 3.4 5.6 naximum 7. 15.0 190.6 6.6 9.1 random sample 5.4 12.9 237.9 4.5 6.4 Maximum worst case does not apply for 1980 data, only one "ho holes" I station was found to contain one clam.
46 TABLE 7.1-2. RANGE OF PERCENT DIFFERENCES IN MEAN VALUES, COMPARING WORST CASE "NO-HOLES" METHOD SIMULATIONS WITH THE RANDOM SAMPLE MEAN ESTIMATE. RANGE OF PERCENTAGES OF UNDER (-) AND OVER (+) MINIMUM AND MAXIMUM DIFFERENCE (%) ESTIMATION BETWEEN WORST CASE AND RANDOM ESTIMATES FLAT 1 +9 to +24 109 to 124 FLAT 2 -33 to +15 67 to 115 FLAT 3 +16 to +66 116 to 166 FLAT 4 +. 0 110 FLAT 5 -17 to +45 83 to 145 I I I I I I I I
2 APPENDIX 7.2 SHELL SIZE DISTRIBUTION (NUMBER PER FT ) 0F YOUNG MYA ARENARIA COLLECTED FROM FIXED STATIONS IN SELECTED NORTHERN NEW ENGLAND ESTUARIES, 1976 THROUGH 1979. SEABROOK MYA ARENARIA STUDY, 1980. PLUM ISLAND SOUND MIDDLE GROUND SIZE 19 21 17 28 11 11 8 5 19 6 4 13 11 12 3 17 11 6 2 1 CLASS APR JUN AUG OCT FEB APR JUN AUG OCT JAN APR JUN AUG OCT APR JUL OCT APR JUL OCT (mm) 1976 1976 1976 1976 1977 1977 1977 1977 1977 1978 1978 1978 1978 1978 1979 1979 1979 1980 1980 1980 5 5 2 11 208 101 149 127 7 625 91 127 31 19 114 44 24 18 11 4 136 10 7 8 10 44 132 5 46 22 20 69 27 29 7 93 14 2 11 9 15 1 1 1 6 98 49 29 7 6 32 112 94 13 33 48 1 3 2 g 20 1 29 87 45 35 23 7 61 28 12 6 14 2 5 25 15 38 37 41 33 8 14 9 17 8 3 2 3 30 9 21 24 26 13 15 12 17 14 6 5 5 1 35 2 4 5 7 6 14 12 17 12 8 5 6 2 40 2 3 2 9 10 12 11 14 12 5 1 45 1 8 9 4 13 16 9 5 3
i 1 1 l i APPENDIX 7.2 (Continued) PLUM ISLAND SOUND LUFKIN'S FLAT j i SIZE 11 8 5 19 6 4 13 11 12 3 17 11 2 1 CLASS APR JUN AUG OCT JAN APR JUN AUG OCT APR JUL OCT JdL OCT 1977 1977 1977 1977 1978 1978 1978 1978 1978 1979 1979 1979 1980 1980 5 165 169 10 171 60 87 5 16 8 29 2 41 3 82 10 43 79 1 15 15 31 3 6 3 8 46 11 36 15 32 13 1 9 13 10 3 2 8 13 5 e 20 5 4 5 6 3 3 3 10 25 11 3 9 14 J 25 3 1 14 8 3 1 19 17 15 1 5 13 6 i 30 4 8 23 3 11 13 5 8 2 8 6 35 3 15 4 9 1 3 5 13 5 9 3 40 1 1 4 5 1 4 8 3 2 3 8 i 45 1 1 1 1 1 1 2 2 3 8 l l num ums uma uma amm amm ama man mum amm sus ama amm
W M M M M M M M M M M M M M M M M APPENDIX 7.2. (Continued) PLUM ISLAND SOUND EAGl.E HILL RIVER AT NUT SriOAL SIZE 11 8 5 10 6 4 13 11 12 3 17 11 6 2 1 CLASS APR JUN AUG OCT JAtl APR JUN AUG OCT APR JUL OCT APR JUL OCT (mm) 1977 1977 i977 1977 1978 1978 1978 1978 1978 1979-1979 1979 1980 1980 1980 5 142 23 68 912 199 182 50 97 80 292 17 534 67 4 136 10 28 58 12 36 27 143 13 10 59 10 8 2 4 15 11 110 28 4 2 38 55 74 10 57 4 4 6 i l 20 2 26 66 8 6 6 15 59 63 25 17 8 4 25 49 30 19 23 4 32 38 32 19 8 2 30 10 27 27 15 4 6 4 6 11 10 8 2 35 4 25 19 8 8 4 11 11 13 15 2 40 8* 6 11 10 11 15 23 13 17 15 4 2 45 2 4 4 8 8 23 8 6 6 8 6 I
APPENDIX 7.2. (Continued) HAMPT0M HARBOR FLAT #2 SIZE 12 21 18 16 21 11 14 7 1 17 4 5 3 14 9 5 11 9 3 1 2 Class MAR APR JUN AUG OCT JAN APR JUN AUG OCT JAN APR JUN AUG OCT APR JUL OCT APR JUL OCT (mm) 1976 1976 1976 1976 1976 1977 1977 1977 1977 1977 1978 1978 1978 1978 1978 1979 1979 1979 1980 1980 1980 5 160 '12 18 80 1284 612 691 593 219 118 78 157 42 24 106 97 93 103 79 36 105 10 1 2 1 10 104 119 58 29 38 43 5 9 40 10 7 30 1 15 39 89 87 69 8 77 29 10 17 3 4 37 20 2 4 15 21 3 64 61 39 12 9 3 7 o 25 2 46 51 29 17 20 2 3 30 18 20 22 21 10 1 9 1 35 2 5 8 12 11 8 11 3 40 2 1 4 12 14 5 9 5 45 2 12 2 2 6 M M M M M M M M M M M M
f M M M 2T0 2 6 2 6 4 7 6 4 5 C8 5 2 2 3 3 2 1 O9 1 M 1 L0 1 2 3 1 0 3 4 8 8 U8 2 1 1 2 2 3 1 1 J9 M 1 3R0 8 4 4 9 6 8 9 2 4 M P8 1 4 3 2 3 2 1 A9 1 1 9T9 4 6 6 0 7 9 2 7 4 C7 4 4 3 3 3 2 1 O9 1 1 M ) D 1 L9 0 1 2 4 3 5 3 7 5 N 1U7 3 4 6 6 4 2 1 U J9 1 RO 1 M OR BG RAE liLD 5R9 8 0 7 6 9 7 4 7 ND P7 G 8 7 8 5 1 1 M OI A9 2 TM 1 P( M A4 _H# T 5T8 9 7 5 0 0 1 5 A C7 2 3 4 4 6 2 L O9 5 1 1 1 F 1 M 4G8 0 7 6 5 6 6 3 1 1 U7 7 4 5 7 2 1 A9 1 1 M 9N8 0 5 6 6 5 1 U7 7 8 9 5 M J9 1 ) deun M i 5R8 2 6 4 8 5 t P7 8 0 9 6 n A9 2 3 3 o 1 C ( M 2 7 X I D 1 S f E ES)ZAm 5 0 5 0 5 0 5 0 5 P M P I L 1 1 2 2 3 3 4 4 A SC( M l l l i
APPENDIX 7.2. (Continued) OGUNQUIT BEACH FLAT I SIZE 20 22 20 29 14 12 9 9 21 17 3 14 10 11 4 18 12 7 CLASS APP. JUN AUG OCT JAN APR JUN AUG OCT JAN APR JUN AUG OCT APR JUL OCT APR JUL OCT (mm) 1976 1976 1976 1976 1977 1977 1977 1977 1977 1978 1978 1978 1978 1978 1979 1979 1979 1980 1980 1980 5 35 2 8 57 100 64 48 19 26 18 9 20 18 40 22 11 89 40 6 25 10 2 1 1 50 4 2 3 13 1 4 15 4 2 y, 15 5 33 2 1 1 4 12 1 11 1 3 20 66 12 6 10 1 9 2 2 1 1 1 25 8 6 11 5 5 4 4 1 2 1 1 30 4 4 10 10 5 3 2 5 2 <1 3 35 2 2 6 2 2 6 2 <1 <3 1 40 1 1 8 3 4 3 2 2 1 1 45 4 4 4 5 4 2 3 1 M M M M M M M M M M M M M M M M
W M M M M M M M M M M M M M M M APPENDIX 7.3. LENGTH-DENSITY DATA FROM THE NOVEMBER 1980 SURVEY. SEABROOK NY4 ARENARIA STUDY,1980. LENGTH DENSIJY % - AGE CUM LENGTH DENSIjY % - AGE CUM LENGTH DENSI{Y % - AGE CUM 2 (mm) (#/ft ) % - AGE (mm) (#/ft ) % - AGE (mm) (#/ft ) % - AGE 1 15.91 10.325 100.00 26 1.82 1.181 24.495 51 0.31 0.201 1.219 2 34.06 22.104 89.675 27 1.73 1.123 23.314 52 0.32 0.208 1.018 3 15.35 9.962 67.571 28 1.81 1.174 22.191 53 0.128 0.083 0.81G 4 6.27 4.070 57.609 29 2.10 1.363 21.017 54 0.114 0.074 0.727 l 5 3.77 2.446 53.539 30 2.97 1.927 19.654 55 0.26 0.169 0.653 6 1.56 1.012 51.093 31 2.10 1.363 17.727 56 0.140 0.091 0.484 7 1.05 0.681 50.081 32 2.34 1.518 16.364 57 0.075 0.049 0.393 8 1.34 0.870 49.400 33 1.46 0.947 14.946 SS 0.052 0.034 0.344 9 0.53 0.344 48.530 34 1.79 1.162 13.899 59 0.080 0.052 0.310 10 0.92 0.597 48.186 33 2.36 1.531 12.737 60 0.089 0.050 0.258 11 1.38 0.896 47.589 I 36 1.65 1.071 11.206 61 0.044 0.028 0.200 12 2.49 1.616 46.693 37 1.31 0.850 10.135 62 0.045 0.029 0.172 13 1.08 0.701 45.077 38 1.41 0.915 9.285 63 0.033 0.021 0.143 14 1.48 0.960 44.376 39 1.37 0.889 8.370 64 0.026 0.017 0.122 15 2.52 1.635 43.416 40 1.80 1.168 7.481 65 0.048 0.031 0.105 16 1.85 1.200 41.761 41 1.02 0.662 6.313 66 0.029 0.019 0.074 17 1.95 1.265 40.581 42 1.26 0.818 5.651 67 0.004 0.002 0.055 18 2.54 1.648 39.316 47 0.71 0.461 4.833 60 0.005 0.003 0.053 19 3.03 1.966 37.668 44 0.83 0.539 4.372 69 0.014 0.009 0.050 20 3.90 2.531 35.702 45 1.05 0.681 3.833 70 0.018 0.012 0.041 21 2.58 1.674 33.171 46 0.64 0.415 3.152 71 0.008 0.005 0.029 22 2.44 1.583 31.497 47 0.59 0.383 2.737 72 0.012 0.008 0.024 23 3.10 2.012 29.914 48 0.60 0.389 2.354 75 0.009 0.006 0.016 24 2.43 1.577 27.902 49 0.52 0.337 1.965 80 0.016 0.010 0.010 25 2.82 1.830 26.325 50 0.63 0.409 1.628 E 154.099
APPENDIX 7.3. LENGTH-DENSITY DATA FRCit T!!E NOVEMBER 1979 SURVEY. SEABROOK NYA ARENARTA STUDY,1980. LENGTH DENSITY %-AGE CUM LENGTH DENSITY %-AGE CUN LENGTH DENSITY %-AGE CUM 2 2 2 [nn] [#/ft 3 %-AGE [nm] [#/ft 3 %-AGE [imi] [#/ft 3 %-AGE 1 1 0.12 0.107 100.000 26 1.83 1.626 19.984 43 0.32 0.284 1.623 l l 2 4.11 3.651 99.893 27 2.08 1.048 19.358 44 0.22 0.195 1.339 l 3 4.69 4.166 96.243 28 1.99 1.768 16.510 45 0.27 0.240 1.143 4 5.16 4.584 92.077 29 1.70 1.510 14.743 46 0.14 0.124 0.903 5 5.28 4.690 87.493 30 2.28 2.025 13.232 47 0.14 0.124 0.779 6 4.81 4.273 82.803 31 1.55 1.377 11.20/ 48 0.116 0.103, 0.655 l 7 4.56 4.051 78.530 32 1.41 1.252 9.831 49 0.107 Q.095 0.552 l 8 2.31 2.052 74.480 33 1.19 1.057 8.578 50 0.192 0.171 0.457 9 2.52 2.238 72.428 34 1.03 9.915 7.521 51 0.061 0.054 0.286 10 2.81 2.496 70.189 35 1.22 1 083 6.606 52 0.041 0.036 0.232 m 11 3.75 3.331 67.693 36 0.81 0.720 5.522 53 0.034 0.030 0.195 6 12 5.16 4.584 64.362 37 0.75 0.666 4.803 54 0.023 0.020 0.165 13 3.64 3.233 59.779 38 0.81 0.720 4.137 55 0.025 0.022 0.145 14 5.04 4.477 56.545 39 0.59 0.524 3.417 56 0.040 0.036 0.123 15 4.22 3.749 52.068 40 0.67 0:595 2.893 57 0.005 0.004 0.087 16 4.34 3.855 48.320 41 0.35 0.311 2.298 58 0.014 0.012 0.083 17 3.75* 3.331 44.465 42 0.41 0.364 1.987 39 0.013 0.012 0.070 18 2.58 2.292 41.134 60 0.007 0.006 0.059 19 3.05 2.709 38.842 61 0.002 0.002 0.052 20 3.40 3.020 36.133 62 0.002 0.002 0.051 21 2.93 2.603 33.112 63 0. 0.0 0.049 22 4.22 3.749 30.510 64 0. 0.0 0.049 23 2.70 2.398 26.761 65 0.009 0.000 0.049 24 2.58 2.292 24.363 70 0.013 0.012 0.041 25 2.35 2.087 22.071 75 0.008 0.007 0.029 80 0.000 0.007 0.022 85 0.017 0.015 0.015 E 112.577 M M M M M M M M M M M M M M M M M
M M M M M M M M M M M M M APPNDIX 7.3. LENGTH-DENSITY DATA FROM THE NOVEMBER 1978 SURVEY. SEABROOK MA ARENARIA STUDY,1980. LENGTil DENSITY %-AGE CUM LENGTil DENSITY %-AGE CUM LENGTil DENSITY %-AGE CUM 2 2 2 [nm] [#/f t 1 %-AGE [imi] [#/ft ] %-AGE [ mil] [#/ft ] %-AGE 1 0.4s 0.211 100.000 26 1.19 0.559 3.185 43 0.02 0.009 0.073 2 4.30 2.056 99.789 '27 1.07 0.502 2.627 44 0.005 0.002 0.063 3 7. r> 3.469 97.732 28 0.66 0.310 2.124 45 0.005 0.002 0.061 4 11.47 5.385 94.233 29 0.74 0.347 1.815 46 0.002 0.001 0.059 5 9.20 4.319 88.878 30 0.74 0.347 1.467 47 0.005 0.002 0.058 6 9.51 4.465 84.559 31 0.38 0.178 1.120 48 0.02 0.009 0.655 7 10.41 4.887 80.094 32 0.41 0.192 0.941 49 0.007 0.003 0.046 8 10.56 4.958 75.207 33 0.30 0.141 0.749 50 0.002 0.001 0.043 9 10.11 4.746 70.249 34 0.23 0.108 0.608 51 0.002 0.001 0.042 10 11.92 5.596 65.503 35 0.30 0.141 0.500 52 0.007 0.003 0.041 11 11.32 5.314 59.907 36 0.15 0.070 0.359 53 0. 0.0 0.038 12 10.26 4.817 54.593 37 0.15 0.070 0.289 54 0. 0.0 0.038 vi 13 10.11 4.746 49.176 38 0.10 0.047 0.218 55 0.019 0.009 0.038 14 12.22 5.737 45.072 39 0.08 0.038 0.171 60 0.014 0.007 0.029 15 11.32 5.314 39.292 40 0.06 0.028 0.134 65 0.023 0.011 0.022 16 12.00 5.634 33.978 41 0.04 0.019 0.106 70 0.005 0.002 0.011 17 12.55 5.892 28.344 42 0.03 0.014 0.087 75 0.012 0.006 0.009 18 11.27 5.291 22.452 80 0.005 0.002 0.003 19 8.06 3.784 17.161 85 0.002 0.0009 0.0009 20 7.09 3.329 13.378 I 213.005 21 4.83 2.268 1-0.049 22 4.93 2.314 7.782 23 1.92 0.901 5.467 24 1.54 0.723 4.566 25 1.40 0.657 3.843
APPENDIX 7.4 TABLE A. SHELL SIZE DISTRIBUTION OF SOFT-SHELL CLAMS ON FLAT 1 FOR THE ANNUAL FALL SURVEYS, 1971-1980. SEABROOK ?/YA ARENARIA STUDY,1980. SIZE CLASS (mm) 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 5 19.00 74.00 30.00 2.50 55.00 1031.00 283.00 38.00 16.98 25.50 10 11.00 9.00 6.00 1.14 52.00 413.00 100.00 8.15 12.50 1 15 11.00 15.00 3.00 0.75 117.00 148.00 14.26 17.90 20 1.00 11.00 5.00 0.02 5.82 76.00 20.00 34.40 25 0.47 2.50 0.16 0.11 0.48 9.20 19.50 24.50 30 1.30 2.30 0.51 0.17 0.02 0.56 13.57 25.60 35 1.50 1.20 0.60 0.48 0.04 0.03 6.10 17.40 g 40 1.80 1.40 0.67 0.89 0,23 0.01 0.03 3.33 13.00 1 45 1.80 0.61 0.49 1.10 0.14 0.10 0.01 0.94 6.60 50 1.00 0.83 0.42 1.20 0.36 0.03 0.02 0.03 0.31 3.50 S5 0.64 1.60 0.30 0.82 0.25 0,04 0.03 0.03 0.06 0.68 60 0.36 0.33 0.29 0.42 0.28 0.23 0.02 0.03 0.03 0.15 65 0.08 0.19 0.18 0.31 0.14 0.13 0.01 0.04 0.08 70 0.03 0.19 0.11 0.10 0.11 0.06 0.04 0.01 75 0.03 0.08 0.05 0.10 0.03 0.03 0.02 0.02 0.03 80 0.02 .07 0.02 0.03 0.03 85 0.01 0.01 0.01 0.05 90 0.01 0.01 i
M M M M M M M M M M M M M M APPENDIX 7.4 (Continued) TABLE B. SiiELL SIZE DISTRIBUTION OF SOFTSilELL CLAMS ON FLAT #2, ANNUAL FALL SURVEYS 1971-1980. SEABROOK NYA ARENARIA STUDY,1980. SIZE i l CLASS 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 (nm) 5 37.00 116.00 114.00 9.10 351.00 83.00 11.00 32.44
- 33.00 10 35.00 26.00 8.00 2.90 10.56 0.60 15 11.00 2.40 2.60 10.56 0.15 20 9.00 0.91 10.00 1.94 2.26 0.15 25 0.89 0.11 0.67 0.50 2.61 1.04 0.33 i
30 0.44 0.44 0.80 0.22 1.58 1.03 0.47 l 35 0.67 0.50 0.66 0.30 0.29 0.88 0.79 m 40 1.20 0.83 0.61 0.40 0.15 0.90 0.96 l 45 1.60 0.27 0.39 0.65 0.04 0.35 1.02 50 1.10 0.22 0.36 0.75 0.02 0.06 0.21 1.28 1 55 0.89 0.33 0.33 0.32 0.02 0.02 0.10 0.80 60 0.94 0.27 0.08 0.34 0.07 0.02 0.03 0.05 0.37 65 0.44 0.22 0.14 0.15 0.02 0.03 0.31 70 0.33 0.11 0.11 0.19 0.09 0.04 0.28 75 0.11 0.08 0.06 0.04 0.02 0.02 0.05 80 C.06 0.06 0.06 0.06 0.07 0.02 0.02 l 85 0.06 0.06 0.02 0.02 90 0.11 0.02 0.04 0.06 95 0.06 0.06 100 0.04 0.02 0.02 l 105 l l 110 l
I 58 I APPENDIX 7.4 (Continued) TABLE C. SHELL SIZE DISTRIBUTION OF SOFT-SHELL CLAMS ON FLAT 3 FOR ANNUAL FALL SURVEYS, 1971-1980. SEABROOK MLi ARENARIA STUDY,1980. SIZE CLASS 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 (m) 5 35.00 28.00 6.00 0.63 1.14 556.00 67.00 38.00 10.18 55.60 10 29.00 4.70 1.00 4.10 3.40 1.10 15 5.20 4.00 3.40 3.00 20 4.80 2.00 1.13 3.71 25 0.17 0.42 1.00 0.05 3.74 0.18 0.02 30 0.92 0.25 1.00 0.14 0.85 0.14 0.05 35 0.67 0.17 0.38 0.12 0.02 0.10 0.27 0.14 0.06 40 1.50 0.33 0.62 0.11 0.02 0.29 0.08 45 1.40 0.42 0.50 0.30 0.02 0.04 0.14 0.19 50 1.30 0.17 0.29 0.11 0.03 0.02 0.02 0.07 0.10 [ 55 1.10 0.17 0.79 0.08 0.03 0.02 0.04 0.04 0.06 5 60 0.83 0.08 0.54 0.18 0.08 0.02 0.08 65 0.58 0.46 0.38 0.08 0.04 0.02 0.07 0.05 g 70 0.33 0.08 0.42 0.14 0.02 0.02 0.06 g 75 0.25 0.08 0.22 0.03 0.06 0.02 0.02 0.01 80 0.08 0.08 0.14 0.03 0.06 0.05 l 85 0.04 0.03 0.08 90 0.08 0.06 0.08 0.04 m .I I I I
59 APPENDIX 7.4 (Continued) TABLE D. SHELL SIZE DISTRIBUTION OF SOFT-SHELL CLAMS ON FLAT 4 FOR ANNUAL FALL SURVEYS, 1971-1980. SEABROOK NYA ARENARIA STUDY,1980. I SIZE CLASS 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 I (mm) 5 38.00 116.00 12.00 2.50 66.00 $30.00 117.00 113.00 49.13 58.20 10 11.00 31.00 1.00 1.80 13.20 183.00 91.00 38.34 7.90 15 7.00 20.00 3.00 115.00 48.00 49.13 9.60 20 4.00 18.00 2.00 0.64 20.40 45.10 30.75 14.40 25 2.80 1.10 0.52 0.05 0.01 0.62 12.38 16.77 12.40 30 3.50 3.00 1.40 0.26 0.01 0.02 8.29 13.46 10.20 35 4.60 2.80 0.62 0.58 0.01 0.01 3.19 8.98 8.70 I 40 4.00 1.70 0.46 0.96 0.16 0.85 4.98 7.60 45 2.60 2.00 0.35 0.92 0.16 0.09 0.02 2.21 4.50 50 1.30 1.00 0.38 0.80 0.18 0.03 0.85 3.10 I 55 1.10 0.79 0.14 0.50 0.21 0.13 0.01 0.27 1.06 60 0.25 0.21 0.08 0.29 0.12 0.07 0.58 65 0.17 0.04 0.14 0.21 0.14 0.01 0.01 0.02 0.16 70 0.12 0.08 0.06 0.03 0.04 0.01 0.03 I 75 0.02 0.01 0.01 80 0.04 0.01 0.01 85 0.01 0.01 0.01 I I I I I I
60 I APPENDIX 7.4 (Continued) TABLE E. SHELL SIZE DISTRIBUTION OF SOFT-SHELL CLAMS ON FLAT 5 FOR ANilUAL FALL SURVEYS, 1971-1980. SEABROOK MYA ARENARIA STUDY,1980. 1 SIZE CLASS 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 (mm) 5 67.00 136.00 22.00 2.40 7.50 546.00 92.00 44.00 11.03 67.90 E 10 38.00 94.00 1.00 2.80 8.30 4.80 2.55 0.19 g 15 12.00 16.00 7.50 20 3.00 6.00 5.30 4.80 25 0.06 0.55 0.10 0.75 2.28 0.05 30 0.11 0.89 0.31 2.17 0.31 0.17 35 0.33 0.61 0.14 0.01 0.01 1.41 0.73 0.33 40 0.44 1.00 0.28 0.07 0.41 0.33 0.56 45 0.44 0.77 0.12 0.10 0.22 ,0.67 50 0.94 0.94 0.10 0.02 0.04 0.12 0.50 55 0.39 0.51 0.12 0.01 0.03 0.47 g 60 0.28 0.50 0.12 0.36 5 65 0.11 0.05 0.08 0.01 0.07 70 0.11 0.05 0.04 0.01 l 75 0.05 0.01 0.01 0.01 80 0.06 0.01 0.01 l I I I I
M M M dM M M M M M M M M APPENDIX TABLE 7.5. 1980 GREEN CRAB CATCH STATISTICS. SEABROOK MYA ARENARIA STUDY, 1980. ^" DATE T0!AL NO. OF 10TAL NO. OF <3 3-3 1/2 3 1/2-4 4-4 1/2 4 1/2-fl 5-5 1/2 5 1/2-6 6-6 1/2 6 1/2-7 7-7 1/2 >7 1/2 C4RCIM'S MAEX4S CANCER SPP. MALES FEMALES 10 Jan IM IF IF IM IF 2 3 7 0 0 24 Jan 4 Apr 2F 5F 2F 2F 3F 11M 2M 22 14 49 IM IM 4M 3M 18 Apr IF IF 4F 9F(29) IF bF 6F 2F 59 32 70 IM 7M 14M 17M 14M bM 8 May IF(g) IF IF(g) IF 9M IF IM 31 5 25 IM IM 6M 12M IM 23 May IM IF 2M IF 4M IM 2M 14 2 68 4M 5 Jun 2F 2F 8F 12F ISP 2F IM 5 41 66 4M 20 Jun IM 2F(lg) 9F 12F(lg) 25F(49) 17F(Ig) 7F(29) IF(g) IM 23 73 67 SM 2M 2M 2M 3M 4M 3M 11 Jul 4F 7F 22F(lg) 30F 23F 15F 3F IF 8M 79 105 28 IM 4M 14.4 12M 16M 20M 14M 24 Jul IF 7F(Ig) ISP 28F ( 39) 19F ( 3g) 13F 6F IF 8M LM 82 99 57 p 2M IM 6M 17M 18M 15M IOM H 7 Aug 2F 7F 12F(lg) 9F 12F SF 4F IF 4M 3M $3 55 85 2M 2M 7M 2M 6M BM 14M SM 20 Aug 2M 2M 3r 14F 16F 9F 4F 2M IM 52 46 73 2M 4M BM 21M IOM 4 Sep IF 2F 9F 4F ar 4F 3F IF IM IM 51 32 58 5M 7M IOM 6M BM 3M 6M 4M 18 Sep 2F 6F 13F 8F 15F dF 1F 54 53 215 2M 7M 16M 9M lOM 'M 3M 3 Oct 2F BF flF 67F 80F 44F IdP IF 5H 241 67 IM IM TN 19M 15M 5M 2M 17 Oct IF SF '.1 F 145F 135F ll7F 3fsF 7F 2M 117 47) 19 6M SM 22M 36M 24M 13M 9M 7 Nov 2F llF 35F 97F LOOP 68F 19F 10F IF 1M 218 143 44 4M 3M 7M 30M 35M 58M 52M 21M 7M IM 21 Nov 2F (>F 31F 85F 126F lO4r 67F 32F 8F IF 355 462 HI 2M 32M 37M SIM 78M 86M SOM 12M 7M 12 Dec 2F I?F 22F 56F 20F IOP 6F 7M 2M IM 112 128 29 IM M 17M 26M 29M 32M 10M 30 Dec 0 0 6 1980 Totals SF 28F 127F(lg) 345F(2 ) 622F(7 ) 537F(89) 371F(lg) 157F(29) 28F(lg) 2F 17M 1407 223) 9 9 11M 17M 79M 121M 204M 302M 326M 208M 92M 44M Frequency (O 1.24 5.66 5.su 22.69 23.05 19.20 10.03 3.30 1.2a .47 g.44}}