Spatial pattern of distribution and reproductive strategy of vermiculate electric-rays Narcine vermiculatus

In the study, the authors evaluate the spatial distribution pattern of vermiculate electric-ray Narcine vermiculatus using geostatistical techniques to predict its spatial distribution and indicate its reproduction strategy. From January 2008 to December 2009, 3333 specimens of vermiculate electric-ray were caught. Total length (L_T ), sex, maturity stage, catch location and depth were recorded for each specimen. The L_T of vermiculate electric-ray ranged from 6.7-24.6 cm. The authors estimate an irregular spatial structure, with a high-density patch ( $$ 53 ind. ha^-1 ) located on the east coast, which concentrates 65.2% of the specimens. The high-density patch consists mainly of large juveniles (13.3-19.5 cm L_T ), sub-adults (14.0-19.8 cm L_T ) and young adults (14.7-21.3 cm L_T ). Data indicate that adults migrate to the high-density patch to reproduce. Males reached maturity at 14.5 cm L_T , whereas females reached maturity at 19.3 cm L_T . Vitellogenesis in female vermiculate electric-ray begins in June; ovulation, mating, fertilization and gestation in October and birth begins in February. This indicates an annual cycle with vitellogenesis and consecutive gestation, in females synchronized in reproduction. Fecundity was 1-8 ( $$ 4), and the sex ratio of embryos was 1:1. The birth occurred between February and April, with an average size at parturition of 6.3 cm L_T . Incidental capture of sub-adults and adults of N. vermiculatus by bottom trawls threatens the survival of this species.