MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANUICA 



length frequencies of the population as a whole, 

 and growth rates of marked individuals were 

 nearly equal between 1978-79 and 1979-80. 



Length-weight equations from February 1980 

 and August 1979 were parallel (Table 5); winter 

 samples were apparently heavier in drained 

 meat weight at a given shell length than 

 summer samples. However, the magnitude 

 of predicted differences in weight at length 

 was small (4-11% for 65-115 mm ocean quahogs). 

 Differences may be related to weight changes 

 associated with sexual development, or merely 

 a statistical artifact. Samples from winter and 

 summer were combined to predict average 

 weight for a given length during the year (Table 

 5). The resulting length-weight equation was 

 applied to computed lengths at age to derive 

 an age-weight relationship (Fig. 4). Initial 

 weight gains are proportionally greater than 

 concomitant length increases, but growth rates 

 are nearly identical at the oldest predicted ages. 

 Average annual increases in drained meat 

 weight are 18.1% at age 10, 1.6% at age 50, and 

 0.2% at age 100 (Fig. 4). 



Growth rates determined from the examina- 

 tion of concentric external banding patterns in- 

 dicate small ocean quahogs may grow faster off 

 Long Island than in the Northumberland Strait 

 and in Passamaquoddy Bay (Caddy et al. foot- 

 note 7). However, data are insufficient to con- 

 clude that a latitudinal cline in ocean quahog 

 growth exists. Factors influencing growth rates 

 in a particular area are speculative; however, 

 density dependence must be considered. Muraw- 

 ski and Serchuk (footnote 2) noted relative popu- 

 lation stability and poor recruitment for ocean 

 quahogs in the Middle Atlantic during 1965-77. 

 Stable population size, poor recruitment, and 

 slow growth are characteristic of populations 

 under density dependent regulation. Investiga- 

 tion of ocean quahog growth rates at various den- 

 sities may help to elucidate their interrelation- 

 ship and indicate the population consequences of 

 cropping high density areas. 



ACKNOWLEDGMENTS 



In particular we thank ships' personnel and 

 scientific parties aboard the various research 

 vessels during field sampling phases of the proj- 

 ect. Significant technical contributions were 

 made by Lt. Comdr. Ron Smolowitz, NOAA 

 Corps, and Dea Freid of the Northeast Fisheries 

 Center. The manuscript was critically reviewed 



by Brad Brown, Mike Sissenwine, Emma Hen- 

 derson, Mike Fogarty, and Rich Lutz. 



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33 



