Mario Lasta

Feeding habits and prey selection by the skate Dipturus chilensis (Elasmobranchii: Rajidae) from the south-western Atlantic

The diet of Dipturus chilensis was composed mainly of the nototheniid fish Patagonotothen ramsayi , squid Illex argentinus , hake Merluccius hubbsi , serolid isopods, and crustaceans. Our results suggest that D. chilensis feeds selectively on some teleosts and rejects eel-like fishes. Total length of consumed P. ramsayi was significantly correlated with the skates mouth width.

Chapter 26 Argentina

Publisher Summary This chapter discusses the two species, Aequipecten tehuelchus (Tehuelche scallop) and Zygochlamys patagonica (Patagonic scallop), their fisheries, and experimental results that have significance in the future development of aquaculture. The fisheries supported by these two species are radically different from each other. The Tehuelche scallop is the target of small inshore fisheries in the gulfs of northern Patagonia, and involves dredging and commercial diving. In spite of the small volumes landed, these fisheries are of considerable significance for the local economies. The Patagonic scallop fishery is an industrial operation conducted by three or four factory trawlers that process the catch at sea. Catches in the order of 50,000 tons yr -1 now rank this species among the most important scallop fisheries in the World. The Tehuelche scallop is a simultaneous hermaphrodite and is iteroparous. The Tehuelche scallop may do quick and brief swimming movements as an escape response to the predators or other disturbances.

Annual shell growth increment formation in the deep water Patagonian scallop Zygochlamys patagonica

Abstract The Patagonian scallop Zygochlamys patagonica occurs on the SW Atlantic shelf of South America between 36°S to 55°S in beds at depths around 100 m. Stable oxygen and carbon isotope ratio analysis in scallops from four large beds (Uruguay, 36°17′S, Reclutas, 39°20′S, Tango B, 42°30′S, and Beagle, 55°10′S) in combination with condition indexes and oceanography date strongly suggest that shell growth increments in this species are formed annually. Most translucent growth bands coincide with low values of both δ13C and δ18O (i.e., they are formed at times of high remineralization activity and of higher water temperature). This pattern is consistent throughout the distributional range. Given the specific Argentinean shelf oceanography, higher temperatures at this depth occur during austral autumn—beginning winter in the region of Reclutas and Tango B but during summer–autumn at the northern and southern limit of the distributional range. Year-round investigations at Reclutas beds indicate that translucent shell growth bands coincide with a pause in somatic growth during austral winter, when energy investment is shifted from somatic growth to gonad development.

Variations in the Biological Characteristics of the Patagonian Scallop (Zygochlamys patagonica) Across the Argentine Shelf Break Front

ABSTRACT Oceanographic fronts and their associated physical processes create strong spatial patterns of food availability that may influence the metabolic processes of bivalves located within these areas. To investigate this prediction, we used mass-size relationships, condition indices, and carbon (C) and nitrogen (N) stable isotopes to evaluate how the biological characteristics of the Patagonian scallop (Zygochlamys patagonica) are influenced by the Shelf Break Front (SBF) and the surrounding chlorophyll a concentration (CSAT). Scallops from 2 transects across the front (38–39°S, 55–56°W, southwest Atlantic Ocean) were sampled with a nonselective dredge in October 2005. The results show that the SBF position, estimated from satellite-derived sea surface temperature, was more stable than the CSAT maximum concentrations. If muscle tissue is considered a better indicator of food shifts as previous studies indicate, scallops located far from the front have lower C isotopic signatures and C/N ratios than scallops located near the front. However, the lack of a shift in scallop organ conditions suggest that spatial differences in food supply are not strong enough during the time of year we sampled to impact scallop development, as may happen at a seasonal scale. Our results show that complicated interactions exist between oceanographic structures, food supply, and scallop life history characteristics.

Direct and Indirect Estimates of Natural Mortality for the Patagonian Scallop Zygochlamys patagonica

ABSTRACT The adequacy of empirical estimates of natural mortality (M) for the Patagonian scallop Zygochlamys patagonica (King & Broderip, 1832) is assessed against a direct estimate based on catch-at-ago data obtained from fishery research surveys and auxiliary information on fishing effort exerted by the commercial fleet. Based mostly on growth parameter information resulting from the von Bertalanffy equation, we obtained empirical estimates of M based on formulas commonly used in fisheries assessment and quantified variation in their estimates though parametric bootstrapping. The modal values of direct estimates of M was 0.38/y, with a 95% confidence interval in the range 0.09–0.77/y. Estimates obtained with empirical models were close to direct estimates. In particular, a model developed for invertebrate species (Arces model) was very close both in point values and variability. Our results suggest that for this species, the empirical estimates, which are easily obtainable and broadly used in many fisheries, can be reliably used when no other estimates are available. However, we contend that in other cases their use should be limited to species when the performances of empirical methods were compared with direct evaluations of M.