ness or volume of tissue formed by accretionary 

 growth between successive growth lines." In fact, 

 Jones (1980:333) identified the layers as a "consist- 

 ently thin, dark gray, translucent increment" of pris- 

 matic microstructures which was "easily distin- 

 guished from" homogeneous and crossed micro- 

 structural layers. 



Assessment research on ages of ocean quahogs 

 requires accurate counts and measurements of 

 growth increments. Age observations are cus- 

 tomarily made of acetate peel images under optical 

 microscopes with transmitted light. An important 

 assessment requirement is that an annual increment 

 has a distinct beginning and end. The concept of a 

 growth line forming between successive growth 

 increments fulfills that requirement. 



Counts of supposed annual growth bands seen in 

 the shells of ocean quahogs by Thompson et al. 

 (1980a, b) resulted in slow growth rates and an 

 extreme longevity estimate of 150 yr. Slow growth 

 rate and suspiciously long life for a bivalve seemed to 

 invalidate the thesis of only a single growth line and 

 growth increment being formed annually. Supportive 

 evidence included finding similar bands in surf 

 clams; finding a low number of bands formed during 

 the onset of sexual maturity that were not explained 

 by less than an annual frequency; finding an expected 

 number of bands in small specimens of known age; 

 finding an expected number of bands formed 

 sequentially in samples taken frequently during 2 yr 

 that had only an annual periodicity; finding a line 

 deposited during the fall-winter, a period coinciding 

 with spawning; and finding ages determined by 

 radiometric analyses that were comparable with 

 band counting. The latter three types of investigation 

 have been expanded by Jones (1980) and Turekian et 

 al. (1982) with the same results. As part of the study, 

 I. Thompson (pers. comm.) marked and released 

 ocean quahogs in the natural environment, but none 

 was recovered. Direct and readily comprehended 

 observations of shell growth after marking were con- 

 sidered to be important additional evidence in sup- 

 port of the thesis of an annual periodicity of growth 

 line and growth increment deposition. 



In 1978, the National Marine Fisheries Service 

 marked large numbers of ocean quahogs for release 

 and recovery at a site 53 m deep and 48 km south- 

 southeast of Shinnecock Inlet, Long Island, N. Y., (lat. 



10 21'N,long.72 24'W). Detailsof this project have 

 been reported in Murawski et al. (1982). Periodicity 

 of growth line formation and shell accretion after 

 notching of recovered ocean quahogs and the micro- 

 structure of unmarked and marked shells are de- 

 scribed herein with photographic documentation. 



FISHERY BULLETIN: VOL. 82, NO. 1 



METHODS 



A commercial clam dredge vessel, the MV Diane 

 Maria, was chartered for the marking operation dur- 

 ing 25 July to 5 August 1978. The knife of the hy- 

 draulic dredge was 2.54 m wide, and the cage was 

 lined with 12.7 mm square-mesh hardware cloth to 

 retain small clams. Ocean quahogs for marking were 

 collected within 9 km of the planting site and released 

 during a 10-d period (ca. 17,000 on 26 July, 3,000 on 

 2 August, and 21,000 on 4 August 1978). Two 0.7 

 mm thick carborundum discs, spaced 2 mm apart 

 and mounted in the mandrel of an electric grinder, 

 produced distinctive parallel, shallow grooves from 

 the ventral margin up onto the valve surface (Ropes 

 and Merrill 1970). Four operators of grinders marked 

 about 1,600 clams/h. Groups (ca. 3,000-8,000) of 

 marked clams were released at loran-C coordinates 

 within a rectangular area of about 3 by 6 /as. 



Marked clam recoveries were made in conjunction 

 with annual clam resource surveys. During recovery 

 operations, a Northstar 6000 6 loran-C unit and Epsco 

 loran-C plotter aided in a systematic search of the plant- 

 ing site. Marked clam recoveries were highly variable. 

 On 20 and 2 1 August 1979 and about 387 d after the 

 marking operation, 43 hydraulic dredge tows at the 

 planting site captured 14,043 ocean quahogs and 74 

 (0.57c ) were marked; on 9 September 1980 and 773 d 

 after the marking operation, 1,899 ocean quahogs 

 were captured in 2 dredge tows and 249 (13.1%) were 

 marked. Some marked specimens were damaged, 

 but 67 recovered in 1979 and 200 recovered in 1980 

 were alive and had intact paired valves. 



Recaptured specimens were frozen to prevent 

 periostracum loss from drying and to facilitate open- 

 ing without shell damage. Microscopic examination 

 of 267 notched shells was made to assess the effects 

 of marking and to obtain growth measurements. 

 Shell measurements were made to the nearest 0.1 

 mm by calipers; growth after marking was measured 

 to the nearest 0.01 mm by an ocular micrometer in a 

 dissecting microscope. Acetate peels of all marked 

 ocean quahogs were prepared by the procedures de- 

 scribed by Ropes (198 2 7 ). Briefly, radial sect ions from 

 the umbo to ventral margin were produced on left 

 valves, oriented to include the broadest surface of the 

 single prominent tooth in the hinge. This exposed the 

 internal growth lines in the valve and hinge tooth for 

 later treatment. The paired notch marks in a valve 



''Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



'Ropes, J. W, 1982. Procedures for preparing acetate peels of 

 embedded valves of Arctica islandica foraging. U.S.Dep. Commer., 

 NOAA, NMFS, Woods Hole Lab., Doc. 82-18, 8 p. 



