Population biology and secondary production of the harvested clam T ivela mactroides ( B orn, 1778) ( B ivalvia, V eneridae) in S outheastern B razil

The population structure, growth and production of the trigonal clam T ivela mactroides were investigated by monthly sampling between J anuary 2003 and O ctober 2004 in two areas (southern and northern) of the intertidal and subtidal zones of Caraguatatuba Bay, S outheastern B razil. Intertidal sampling was carried out in each area along eight transects perpendicular to the shoreline. In the subtidal zone of both areas, one 50‐m dredging was performed along five sampling stations arranged on three transects perpendicular to the coast. The intertidal abundance of T . mactroides was higher in the southern (more dissipative conditions) than in the northern area. High abundances occurred in F ebruary– M arch 2004 in the south and in S eptember 2004 in the north. The size structure showed that younger individuals dominated in the sublittoral, indicating that recruitment occurs in this zone, followed by the migration of these individuals to the intertidal, where they complete their life cycle. Tivela mactroides showed continuous reproduction, with 26 cohorts detected in the study period. The lower estimates for the growth index (ϕ′ = 3.22), mortality rate (Z = 2.10 year −1 ) and turnover rate (P/B = 1.21 year −1 ), and conversely the longer life span (2.5 years) of T . mactroides in C araguatatuba B ay (24°S) compared with V enezuelan populations (10°N) suggests a latitudinal pattern of these life‐history traits. The high production of T . mactroides in C araguatatuba B ay was due to continuous recruitment and rapid and continuous growth, and demonstrates the importance of T . mactroides as a biological resource for many marine species and for the local residents.