Distribution and reproductive biology of the Electric ray Discopyge tschudii Heckel, 1846 in San Matías Gulf, Northern Patagonia, Argentina

Abstract

The Electric ray Discopyge tschudii is distributed in the Southwest Atlantic from southern Brazil to southern Argentina and in the Southeast Pacific from Peru to southern Chile. The main threat to this species is fishing. Discopyge tschudii is noncommercial and individuals caught are discarded on board. The present study analyzes the distribution and the morphological and reproductive characteristics of this ray in San Matías Gulf (SMG), Argentina. A total of 1087 individuals were analyzed. The species presented an aggregate distribution, with the main concentrations in the northern and eastern areas of SMG, at depths below 100 m. Males ranged from 9 to 43 cm and females from 11 to 38 cm. The species presented sexual dimorphism. Males were larger and heavier than females and also matured at larger sizes. Size at 50% of maturity was estimated at 30 cm for males and 21 cm for females. A total of 199 embryos were sampled and the proportion of sexes showed no significant differences from the expected 1:1. The number of embryos per female varied from 1 to 12. The most frequent values were 2 and 5. Length at birth was estimated at 82.17 ± 3.87 mm. Based on our findings, we hypothesize that the electric ray D. tschudii completes its reproductive cycle in SMG.

Growth and derived life‐history characteristics of the Brazilian electric ray Narcine brasiliensis

“…Within Torpediniformes, this form of sexual dimorphism is common with only one measured species, Discopyge tschudii Heckel 1846, exhibiting the opposite phenomenon with larger males than females (Estalles et al, 2011). These characteristics are concerning when considering this study's fishery-derived sample composed of over 40% more females than males.…”

“…Within the genera Narcine , N. brasiliensis is above the median (400 mm) (Carvalho et al ., 1999; Moreno et al ., 2010; Villavicencio‐Garayzar, 2000) for maximum observed length but smaller than Narcine bancroftii (Griffith & Smith 1834; 600 mm TL; females; Moreno et al ., 2010; Carlson et al ., 2016) and about half the size of N. entemedor (930 mm TL; females; Villavivencio‐Garayzar, 2000). The exponential rate of increase of the length‐weight relationship, b , was higher for females (3.2) and males (3.22) than that observed for other members of the order Torpediniformes, which with the exception of females of T. californica (3.02, Neer & Cailliet, 2001) and females of T. marmorata in Turkish waters (3.04, Duman & Başusta, 2013) had b less than 3 when measured (Villavivencio‐Garayzar, 2000; Consalvo et al ., 2007; Estalles et al ., 2011; El Kamel‐Moutalibi et al ., 2013; Cruz‐Aguero et al ., 2018) (Table 2).…”

“…Similar to many elasmobranchs, N. brasiliensis females were estimated to grow larger and slower, mature later and live longer than their male counterparts (Cailliet & Goldman, 2004; Cortés, 1998; Hamlett, 2005). Within Torpediniformes, this form of sexual dimorphism is common with only one measured species, Discopyge tschudii Heckel 1846, exhibiting the opposite phenomenon with larger males than females (Estalles et al ., 2011). These characteristics are concerning when considering this study's fishery‐derived sample composed of over 40% more females than males.…”

Crecimiento, madurez y mortalidad del pez gallo, Callorhinchus callorynchus, en el Golfo San Matías, Patagonia norte, Argentina

“…Por lo tanto, para el análisis de crecimiento se incluyeron las estructuras de tallas obtenidas en las campañas de investigación de recursos demersales realizadas en el GSM durante 2005, 2006y 2007. En estas muestras el rango de tallas fue mayor y estuvieron representados los ejemplares neonatos y de las primeras clases de edad (LCLS ~ entre 10-30 cm), dado que los lances de las campañas de investigación cubren las zonas de menor profundidad del golfo (Estalles et al 2011) que son descriptas como áreas de cría y reclutamiento de la especie y donde no pesca la flota comercial (Di Giácomo 1992).…”

“…Para esta pesquería, el pez gallo representa un recurso económico importante dado que históricamente es la segunda especie en toneladas desembarcadas y las capturas comerciales se registran durante todo el año (Di Giácomo & Perier 1991, Di Giácomo & Perier 2008 1 . A su vez, en esta región el pez gallo es la principal especie entre los peces cartilaginosos capturados por by-catch en cuanto a volumen de captura y frecuencia de ocurrencia en los viajes de pesca (Perier et al 2011). Conocer los parámetros de historia de vida de la especie permite realizar evaluaciones de stock y la implementación de medidas de conservación y manejo para la explotación sustentable.…”