Biological aspects of the velvet belly lantern shark, Etmopterus spinax (Linnaeus, 1758) off the Azores, North East Atlantic

The velvet belly lantern shark (Etmopterus spinax) forms a large component of the by-catch of the longline fishery off the Azores, but is discarded due to the lack of commercial value. The distribution and some biological aspects of Etmopterus spinax were investigated from longline surveys between 1995 and 2005 off the Azores. The highest catch rates were at depths between 500 and 650m (range 250-1200 m). The overall sex ratio was 1:2.26 (M:F), with the predominance of females in all depth strata. The total length range was 17.5-48.0 cm for females and 18.5-45.0 cm for males. This species is sexually dimorphic, with females growing to a larger size than males and attaining greater size at first maturity. During the sampled months all the maturity stages were observed. The immature females predominated but the increase proportion of expecting and post-natal females between April and July could indicate a breeding season. The variations of hepatosomatic index indicate that this species maintains a fine balance between the deposition of lipids by the liver and maturity development to increase the reproductive potential.