Mariana Escolar

Primary Settlement Substrate of Scallop, Zygochlamys patagonica (King and Broderip, 1832) (Mollusca: Pectinidae) in Fishing Grounds in the Argentine Sea

Abstract The Patagonian scallop (Zygochlamys patagonica) fishery started in the Argentine Sea after exploratory cruises developed during 1995. Knowledge concerning the habitat requirements involved in the settlement processes of the target species was lacking. The main objectives of this study are to find Z. patagonica spat and to assess the characteristics and distribution of its primary settlement substrate (PSS). We observed under binocular microscope different invertebrate species (potential PSS) collected during 2006 from 125 sampling sites between 37° to 44°S and 83–133 m depth. Spat were found on the hydroid Symplectoscyphus subdichotomus (n = 215) and on adult Patagonian scallops (n = 51, attached to the encrusting sponge Iophon proximum, amphipod, and polychaete tubes in nearly half of the cases). To analyze possible interactions between the benthic assemblage and scallop spat throughout the study area, we performed a faunal analysis including the species considered potential PSS (hydroids and scallops) and potential predators. The analysis showed a unique cluster of species closely associated, with variable abundance of hydroids (higher in samples with spat), scallops, and predators. A particular study in MDQ Area (38°S) shows that the sites where spat was collected presented lower density of potential predators and had been scarcely fished in comparison with the other sites within the area. The availability of PSS should be monitored and areas with dense patches of dichotomous hydroids should be protected from trawling.

Invertebrate bycatch in Patagonian scallop fishing grounds: a study case with data obtained by the On Board Observers Program

Desde el inicio de la pesqueria de vieira patagonica, Zygochlamys patagonica, en el Mar Argentino, en 1996, el Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP) establecio un Programa de Observadores a Bordo (OBOP). Se analizaron las tendencias generales en la composicion de la captura incidental a partir de informacion provista por OBOP, de capturas y esfuerzo pesquero (219 viajes, 575 muestras), recolectada en cinco bancos de vieira entre 39o y 44oS, durante el periodo 1997-2002. Se encontraron grandes variaciones en la densidad promedio de la captura incidental y la presencia de ocho grupos taxonomicos durante el periodo estudiado. Echinodermata fue el taxon dominante en la mayoria de los bancos de vieira relevados. Se registraron aumentos en la densidad de equinodermos y gasteropodos, y escasos organismos sesiles en el banco SWSAO, sujeto a esfuerzo pesquero elevado y continuo. En el banco SWTB, menos explotado, se observaron organismos sesiles, cuya densidad disminuyo en el periodo estudiado, y no se registraron cambios en las densidades de equinodermos y gasteropodos. Estos dos ultimos grupos, en su mayoria carroneros y depredadores, se verian favorecidos por un aumento en la disponibilidad de alimento producto de la actividad pesquera (descarte y organismos danados). Contrariamente los organismos sesiles, sustrato de asentamiento potencial, disminuyeron en densidad en areas con intensa actividad pesquera. Tambien resaltamos la importancia de esta fuente de datos, que amplia la ventana espacio-temporal de la evaluacion anual y optimiza la produccion de bases de datos a mayor escala

Variability in epibiont colonization of shells of Fusitriton magellanicus (Gastropoda) on the Argentinean shelf

An inventory of the main epibiont organisms on living specimens, on empty shells and on pagurized shells of Fusitriton magellanicus collected in Zygochlamys patagonica fishing grounds off Argentina is provided here. Additionally, considering that the presence of the thick, hairy periostracum could be an inhibitor of boring and encrusting species, we analyse the presence of a periostracum in living F. magellanicus in relation to the presence of epibionts. More than 70% of all shells bore encrusting organisms (of at least 30 taxa) but only a small proportion of shells was heavily fouled, the majority of living, empty and pagurized shells being lightly or moderately fouled. Polychaetes were the most common epibiont group (present on more than 60% of shells) while sponges and ascidians were responsible for the majority of the heavily fouled living gastropods. In general, specimens had a moderate level of encrustation and, simultaneously, a low or medium coating of periostracum. Hairy gastropods (only 14% of the sampled specimens) had few or no epibionts. A relationship between the size of the shell and the level of encrustation was only found in living gastropods. Fusitriton magellanicus is the second species in importance (after the Patagonian scallop) for the provision of a hard settlement substrate in the shelf-break frontal area of the Argentine Sea.

Recently Settled Stages and Larval Developmental Mode of the Bivalves Zygochlamys patagonica and Hiatella meridionalis in the Argentine Sea

ABSTRACT In the current study we provide information to aid in the identification of bivalve larvae in plankton samples based on the descriptions of recently settled spat of Zygochlamys palagonica and Hiatella meridionalis, 2 conspicuous bivalves commonly distributed in the shelf-break frontal system of the Argentine Sea. The first species is of particular interest given that it has been commercially exploited since 1996, and the phase between gamete release and larval settlement was unknown. We provide empirical evidence of a planktotrophic development for the larvae of both species.

Spatial distribution, biomass and size structure of Ctenodiscus australis (Echinodermata: Asteroidea) in shelf-break areas, Argentine

Abstract Ctenodiscus australis is a common sea star in the Argentine Continental Shelf. Nevertheless, information about its population parameters is lacking. We investigated the spatial distribution, biomass and size structure of this sea star through a spatial and temporal scale in Patagonian scallop (Zygochlamys patagonica) fishing grounds associated with the shelf-break front in the Argentine Sea. The sea star C. australis was very common in the Patagonian scallop management units (MUs) analysed and reached 100% presence in most of them. The species biomass showed latitudinal differences with the highest values in northern MUs during the period 2002–2005, probably related to the organic content in sediments. The comparative study in two areas subjected to different fishing efforts in the same MU showed the highest biomass of this sea star in the area with low fishing effort. The size–frequency distribution of C. australis suggests a low or sporadic recruitment and slow growth. Differences in the median size were found between MUs but these cannot be attributed to fishing effort.

Latitudinal and bathymetric distribution patterns of ophiuroids (Echinodermata: Ophiuroidea) on scallop fishing grounds at the shelf-break frontal system, south-western Atlantic

mariana escolar, daniel rau’ l herna’ndez and claudia silvia bremec Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo 1, B7602HSA, Mar del Plata, Argentina, Instituto de Investigaciones Marinas y Costeras (IIMyC), Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Dean Funes 3250, Mar del Plata, Argentina