Identification of factors affecting growth and survival of the tropical scallop Euvola (Pecten) ziczac in the Golfo de Cariaco, Venezuela

Abstract

We examined the effect of environmental variables on the growth and survival of the tropical scallop, Euvola ziczac (L.), in suspended culture at Turpialito in the Golfo de Cariaco, northeastern Venezuela. Four growth trials were run, three using 10-mm spat produced from hatchery spawnings in August 1992, which were grown at 8, 21 and 34 m in depth, and a fourth using 10-mm wild spat from spawning in April 1993, which were grown at 21 m in depth. Monthly measurements of somatic and reproductive growth were related to concurrent measures of numerous environmental factors, including fouling on the shells and pearl nets. Growth and survival varied markedly among treatments and the major factor explaining the differences appeared to be the negative effects of fouling (especially the effects of organisms colonizing the shells) and variations in when gonadal development began. Somatic growth was markedly greater in treatments where gonadal development was delayed. For the August 1992 cohort at 8 and 21 m in depth, low phytoplankton abundance and high temperatures, possibly coincident with physiological stress from spawning, probably caused decreased growth and survival in the period during and just after spawning. Phytoplankton abundance (number of cells and chlorophyll a concentration) was a good predictor of growth for the August 1992 cohort grown at 34 m and the April 1993 cohort at 21 m, the treatments in which the scallops attained the largest size. The growth of juveniles (prior to development of gonads) seemed to be little affected by temporal changes in environmental conditions in the Golfo do Cariaco. Suspended culture of E. ziczac is likely to be economically feasible during periods of low fouling, but not when fouling is intensive.