FISHERY BULLETIN: VOL. 80. NO. 1 



but claimed "the oldest clams were up to 18 years 

 and about 9 cm long. The bulk was in the 10-14 

 year group and 7-8.7 cm long." 



The external color of large ocean quahogs 

 (greater than about 60 mm shell length) is usu- 

 ally solid black; however, the periostracum of 

 small individuals is variable in color, grading 

 from pale yellow to deep brown (Loven 1929; 

 Hiltz 5 ). Concentric dark bands appearing in the 

 shell surface of small specimens have thus been 

 interpreted as annuli by several authors. 

 Although Loven did not present age-size rela- 

 tionships explicitly, he did note the presence of 

 external "annual rings" ("Jahresringe") and pre- 

 sented photographs of a size range of small ocean 

 quahogs, illustrating the relationship between 

 numbers of rings and shell lengths. Chandler 6 

 measured the maximum diameters of concentric 

 rings and derived growth relationships based on 

 eight specimens (96 total measurements, to milli- 

 meters). The largest number of such rings ap- 

 pearing on an individual ocean quahog was 21; 

 the corresponding shell length was 58.5 mm. 

 Caddy et al. 7 presented growth curves, based 

 on external markings, for small ocean quahogs 

 from the Northumberland Strait and Passama- 

 quoddy Bay. Average length at age was consis- 

 tently greater for the more southern area. 



Unpublished manuscripts by Chene 8 and Mea- 

 gher and Medcof 9 document efforts to more pre- 

 cisely establish ocean quahog growth rates. 

 Mark and recapture experiments were con- 

 ducted in Brandy Cove, New Brunswick. 

 Notched specimens (n = 14), averaging 57.4 mm 

 (shell length) when recaptured, grew an average 

 of 0.6 mm (shell height) between September 1970 



(Proceedings of the conference of Islandic Professional Engi- 

 neers. Fish. Res. Board Can., Biol. Stn., St. Andrews, N.B., 

 Trans. Bur., No. 1206.) 



5 Hiltz, L. M. 1977. The ocean clam (Arctica islandica). A 

 literature review. Fish. Mar. Serv. Tech. Branch, Halifax 

 N.S., Tech. Rep. 720, 177 p. 



6 Chandler, R. A. 1965. Ocean quahaug resources of 

 Southeastern Northumberland Strait. Fish. Res. Board. 

 Can., Manuscr. Rep. (Biol.) 828, 9 p. 



7 Caddy, J. F., R. A. Chandler, and D. G. Wildler. 1974. 

 Biology and commercial potential of several underexploited 

 molluscs and Crustacea on the Atlantic coast of Canada. Pre- 

 sented at Federal-Provincial committee meeting on Utiliza- 

 tion of Atlantic Resources, Montreal, Feb. 5-7 1974. Prepared 

 at Fisheries Research Board of Canada, St. Andrews Biologi- 

 cal Station, N.B. 



"Chene, P. L. 1970. Growth, PSP accumulation and other 

 features of ocean clams (Arctica islandica). Fish. Res. Board 

 Can., St. Andrews Biol. Stn., Orig. Manuscr. Rep. 1104, 34 p. 



s Meagher, J. J., and J. C. Medcof. 1972. Shell rings and 

 growth rate of ocean clams (Arctica islandica). Fish. Res. 

 Board Can., St. Andrews Biol. Stn., Orig. Manuscr. Rep. 1105, 

 26 p. 



and September 1971. Sequential observations of 

 eight small ocean quahogs (mean length 20.16 

 mm) was undertaken to assess growth rates and 

 seasonal changes in the color patterns of the peri- 

 ostracum. These individuals were held in cages 

 and grew an average 17% in length from 4 June 

 to 31 August 1971. Periostracum formed during 

 the interval was brown, contrasting with yellow 

 material formed before the study was begun. 

 However, this banding pattern may not have 

 been indicative of a normally occurring annual 

 event since "the caged clams were sensitive to 

 experimental treatments and produced distur- 

 bance rings each time they were air-exposed for 

 observation" (Meagher and Medcof footnote 

 9). 



Several recent studies have examined banding 

 patterns present in shell cross sections and have 

 attempted to validate the hypothesis of band for- 

 mation as an annual event. Jones (1980) noted 

 that marginal increments of shell deposition be- 

 yond the last band followed a seasonal progres- 

 sion; bands were formed once per year between 

 September and February. The most rapid pro- 

 duction of shell was from late spring to early 

 summer; annulus formation overlapped the 

 spawning period in mature individuals. Thomp- 

 son et al. (1980) presented size-frequency data of 

 small specimens from the Baltic Sea and inter- 

 preted external and cross-sectional banding in 

 these specimens as supporting evidence for an- 

 nual periodicity of band formation in larger 

 (older) specimens from the Middle Atlantic 

 Bight. Thompson et al. further stated that pre- 

 liminary results from radiochemical analysis of 

 shells corroborated age analysis based on shell 

 banding patterns. 



We initiated a project during summer 1978 to 

 assess in situ growth rates of ocean quahogs at a 

 deepwater site off Long Island, N.Y. Objectives 

 of the study were to obtain growth increment 

 data directly from mark-recapture, further eval- 

 uate the potential of banding patterns (both ex- 

 ternal and in shell cross section) as indicators of 

 age, and correlate growth measurements with a 

 10-yr time-series of length frequencies collected 

 in the vicinity of the marking site. Length- 

 weight relationships have been established for 

 the Middle Atlantic, based on a synoptic winter 

 survey (Murawski and Serchuk 1979); however, 

 no data have been published on seasonal varia- 

 tions. An additional objective of the project was 

 to compare winter and summer length-weight 

 relations at the marking site. 



22 



