Age and growth rate determinations for the Atlantic surf clam Spisula solidissima (Bivalvia: Mactracea), based on internal growth lines in shell cross-sections

Marked and recovered surf clams, Spisula solidissima Dillwyn, from Virginia (USA) deposited one internal growth line during a period of 11/2 years, probably in response to spawning during late summer. We have used these annual growth lines to make growth curves for two samples of New Jersey (USA) clams, one from inshore (1.8 km from shore, 15 m deep), the other from offshore (17.5 km from shore, 28 m deep) waters. The offshore and inshore clams grow at approximately the same rate until Age 3 years, after which time the growth rates differ, as does the ultimate lifespan; the offshore clams grow more rapidly and attain a greater age — up to 31 years. Comparison of our growth curves with other published curves revealed a close correspondence to a curve which was based on a study of growth over a 5-year period. Curves based on external growth lines probably underestimate growth rate in early life and overestimate it in later years.