Settlement of tehuelche scallop, Aequipecten tehuelchus D'Orb., larvae on artificial substrata in San Matı́as Gulf (Patagonia, Argentina)

Settlement of tehuelche scallop, Aequipecten tehuelchus (D'Orbigny), spat on several artificial substrata was monitored at three sites within the traditional fishing grounds of San Matias Gulf to determine which collector type and site optimize spat collection under natural environmental conditions. The experiments were conducted in the northern area of the gulf at El Sotano (40 degrees 57'S-65 degrees 06'W), El Fuerte (41 degrees 00'S-65 degrees 07'W) and Orengo (40 degrees 52'939"S-64 degrees 32'826"W). The first experiment, conducted from November 1996 to March 1997, tested two collector types: (I) shrub branches (50 g) included in two polyethylene onion bags (6 mm mesh size), and (II) Japanesse Netlon (120 g) inside polyethylene bags (2 mm mesh size). Type II collected significantly more spat than Type I (P < 0.05), with numbers of spat per collector ranging from 130 to 726 and 0 to 210, respectively. A second experiment was carried out from December 1998 to April 1999, with collectors of Netlon (Type II) and collectors made of three polyethylene onion bags (40 g each, 6 mm mesh) included in the external bag of the collector of Netlon (Type III). There were significant differences in the number of spat collected on different collectors and at different sites (P < 0.05) (235 to 1692 spat per Type II, and 125 to 556 spat per Type III, depending on sites). Differences in mean final size of spat collected at different sites suggest that larvae are originated from different sets of spawners. Type I collectors (Japanesse Netlon) were the best substrate for collecting tehuelche scallop spat in the natural environment. These collectors are re-usable and make a good material for commercial use.