Hábitats esenciales de condrictios (Chondrichthyes) costeros, y su relación con los procesos oceanográficos
The relationship between environmental variables (depth, temperature and salinity) and the abundance of sharks (Mustelus schmitti and Squatina guggenheim) and skates (Sympterygia bonapartii, Rioraja agassizi and Atlantoraja castelnaui) was analyzed in the Southwestern Atlantic coastal waters (between 34~'S and 42~'S at depths of less than 50 m from the coast line). Data were collected during research Cruises carried out by the National Institute of Fisheries Research and Development (INIDEP) during winter and late spring. Due to differences in the continental water discharges, salinity spatial distribution and in the environmental condition seasonality, data from the Río de la Plata and El Rincón were independently analyzed. Shark and skate species shows different relationships with the environmental variables, showing differences in the spatial distribution patterns and in the abundance seasonality between species. M. schmitti and S. guggenheim showed ontogenetic differences in the habitat use and in the abundance seasonality. Juveniles occupy shallow waters (< 25 m depth), defining nursery areas along the coast. Adults occupied deep waters (> 40 m depth) during no reproductive season (winter) and they migrate to shallow waters during the reproductive season (late spring). S. bonapartii, R. agassizi and A. castelnaui not showed ontogenetic differences in habitat use or in the abundance seasonality. Both study areas showed inter-annual variations in the temperature and salinity spatial distributions, which explains the abundance and spatial distribution variations of the coastal chondrichthyans. In these areas, zones with high environmental variability can be identified and associated to the edges of the oceanographic regimes (e.g. Punta Rasa, Punta Médanos, the coastal area among Montevideo and Punta del Este, coastal area among Monte Hermoso y Claromecó). The abundance and availability of M. schmitti, S. guggenheim, S. bonapartii, R. agassizi and A. castelnaui in the SW Atlantic coastal waters were affected by the seasonal and inter-annual variations in the geographical distribution of the environmental conditions. The viviparous chondrichthyans shows a strong seasonality in the habitat use, migrating from deep to shallow waters (M. schmitti, S. guggenheim). Habitat use seasonality in oviparous chondrichthyans studied here are not clearly defined being S. bonapartii the skate which showed higher abundance seasonality. Considering habitat use, the species that forms coastal aggregations as part of their reproductive migrations (M. schmitti, S. guggeheim and S. bonapartii) would be the most vulnerable to environmental variations and localized exploitation. Therefore, in the SW Atlantic coastal waters, the chondrichthyans which use specifics habitat for egg laying (S. bonapartti) or parturition (M. schmitti y S. guggenheim) would be more vulnerable in this regard than those which have no preference for specific habitats (R. agassizi y A. castelnaui). These findings represent an essential knowledge to these species and provide valuable information concerning the conservation programmes and management strategies of the chondrichthyan fishes.