"In Situ" natural mortality of the tehuelche scallop, Aequipecten tehuelchus (d'Orb., 1846), from San José Gulf (Argentina)
N.F. Ciocco

Local variation in the rate of natural mortality “in situ” (as opposed to mortality related to stranding) of A.Tehuelchus from San José Gulf (Argentina) has been attributed to variations inthe condition of the individuals. One of the implications of this assumption is that the rate of natural mortality “in situ” (ISNMR) would be greatest in areas with low food availability (S-SE region) and smallest in areas of high primary productivity (N-W region). The objective of this study was to explore seasonal and interpopulational variations of the ISNMR in two sites, off the north and south coasts of the gulf. The ISNMR was estimated from the relative abundance of cluckers (empty shells held together by the ligament) and mean clucker “life”, calculated experimentally in natural environment. The ratio of cluckers to live scallops was observed periodically in the field between February, 1988, and April, 1989. Estimated mean clucker “life” was 57.2 days. Differences in mean ratios were not statistically significant among localities and/or sampling dates: 10.7% for the north coast (range: 4.1%- 16.0%), and 9.0% for the southcoast (range: 3.0%-19.0%). ISNMR varied temporally, being highest in March, 1988, in the south (M= 1.56 yr-1 and in December, 1988, in the north (M= 1.22 yr-1). ISNMR was highest in the area with highest productivity (N) in 3 of 4 paired monthly observations. These results suggest that condition due to foodavailability is not sufficient to explain interpopulational differences in ISNMR.

Keywords: Pectinidae, Aequipecten tehuelchus, natural mortality, cluckers, metapopulation,southwest Atlantic, Argentina.
Contents of this volume Sci. Mar. 60(4) : 461-468 Back PDF
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